JP2003207617A - Multi-layered optical filter and method and apparatus for designing film thickness thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multi-layered film filter which has both a gain equalizing function and an exciting light transmitting/cutting-off function. <P>SOLUTION: The multi-layered optical filter 1 has optical films 3a<SB>1</SB>to 3aN laminated. The optical film thicknesses of the optical films 3a<SB>1</SB>to 3aN are designed by using fittings based upon a specified optical film thickness as an initial value so that 1st errors between logical values representing previously set wavelength characteristics in a wavelength band for gain equalization by using the optical film thicknesses of the optical films 3a<SB>1</SB>to 3aN as parameters and a corresponding target wavelength characteristic value in the wavelength band for gain equalization and 2nd errors between logical values rep resenting wavelength characteristics of an exciting light wavelength band other than the wavelength band for gain equalization by using the optical film thicknesees of the optical films 3a<SB>1</SB>to 3aN as parameters and a corresponding target wavelength characteristic value in a corresponding exciting light wavelength range becomes small respectively. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer optical filter used for optical communication, and a film thickness designing method and apparatus thereof.

[0002]

2. Description of the Related Art With the advent of the broadband era, it is required to further increase the amount of data transmission. At present, WDM (Wave) that multiplexes and transmits optical signals of different wavelengths is transmitted.
There are great expectations for lengthDivision Multiplexing (wavelength division multiplexing) communication systems.

One of the key devices in this WDM communication system is an EDFA (Erbium Doped Fiber Ampli) capable of collectively amplifying the multiplexed optical signal without performing photoelectric conversion.
optical amplifiers such as fier) have been developed.

By the way, in the WDM transmission system, if a level deviation occurs in the signal light of each wavelength to be transmitted, the optical signal may be deteriorated and the transmission distance and the transmission band may be reduced. Therefore, when using an optical amplifier such as an EDFA, it is required to flatten (equalize) the gain characteristic in the transmission wavelength band at the output thereof.

In this respect, the gain characteristic of the optical amplifier has wavelength dependence in the transmission wavelength band. Therefore, in order to flatten the gain characteristic having the wavelength dependency (gain wavelength dependency), a gain equalizing filter (GFF; Gain) having a light transmission loss characteristic contradictory to the gain characteristic of the optical amplifier in the transmission wavelength band. By combining a flattening filter) with an optical amplifier, the gain characteristics of the optical amplifier are equalized (see FIG. 21).

As the GFF, a fiber grating, an etalon filter, a multilayer film filter or the like is used, but for an optical amplifier for mass production, a multilayer film optical filter (hereinafter also referred to as a multilayer film filter) having excellent mass productivity is used. Is used.

In this specification, the term "multilayer" means
It is used to mean multiple layers.

FIG. 22 shows the design target (target) loss characteristic (GFF specification: ◇) of the above-mentioned multilayer filter, the loss characteristic (solid line) based on the design value of the multilayer filter, and the loss deviation (□) between them. It is a graph shown. The flatness (Flatness), which is a measure of the loss deviation, is a value obtained by subtracting the minimum deviation from the maximum deviation.

As shown in FIG. 22, the multilayer filter has
In the transmission wavelength band (for example, 1530 nm to 1565 nm) of the corresponding optical amplifier in the preceding stage, the transmission loss characteristic contradictory to the gain characteristic of the optical amplifier is targeted loss characteristic (G
FF required loss characteristic), and the design value of GFF is the above GFF.
Designed / manufactured by approaching the required loss characteristics.

[Problems to be Solved by the Invention]

By the way, in the optical amplifier, there is a case where the pumping light (pump light) for optical amplification is required to pass through the GFF and output, or the pump light is blocked and output.

In this respect, it has been considered to transmit / block (transmit and / or block) the pump light using the conventional GFF.

However, the wavelength band of the pump light for optical amplification (for example, in the case of the pump light wavelength band of the EDFA, 1
(Around 450 nm) is different from the transmission wavelength band (1530 nm to 1565 nm) of the above-described normal optical amplifier. Therefore, the transmission loss characteristic {(solid line (PP
GPF having [Pump Pass] -less design)} does not have the property of transmitting / blocking pump light in the wavelength band corresponding to its transmission loss property.

For example, as shown in FIG. 22, in the wavelength band of pump light for optical amplification (around 1450 nm),
Sufficient transmission characteristics (for example, -1 dB or more) are not obtained.

Therefore, it was not possible to meet the pump light transmission / blocking requirement for the multilayer filter (GFF) having a gain equalizing function.

The present invention has been made in view of the above circumstances, and provides a multilayer filter having both a gain equalizing function and a pump light transmitting / blocking function, a method and an apparatus for designing a film thickness of the multilayer filter. Is its purpose.

[0016]

According to a first aspect of the present invention, there is provided a multilayer optical filter in which a plurality of optical films are laminated, wherein the optical film thickness of each optical film is preset. It is designed to have a predetermined wavelength characteristic in the gain equalization wavelength band and have a predetermined wavelength characteristic in the pumping light wavelength band other than the gain equalization wavelength band.

According to a second aspect of the present invention, there is provided a multilayer optical filter comprising a plurality of optical films laminated, wherein the wavelength characteristics in a predetermined wavelength band other than the preset excitation light wavelength band are set forth above. Corresponding to a theoretical value representing the optical film thickness of each optical film as a parameter and a first error between a target wavelength specifying value in a corresponding predetermined wavelength band, and a target wavelength characteristic value in the excitation light wavelength band. When the transmittance is smaller than the minimum required transmittance in the excitation light wavelength band, a theoretical value representing the wavelength characteristic in the excitation light wavelength band using the optical film thickness of each optical film as a parameter and the corresponding excitation light wavelength. By using fitting with the optical film thickness of each of the optical films as an initial value, a second error between wavelength characteristic values in the band is reduced. It has a total of.

According to a third aspect of the present invention, there is provided a multilayer optical filter comprising a plurality of optical films laminated, wherein the wavelength characteristic in a predetermined wavelength band other than a preset excitation light wavelength band is It corresponds to a first error between a theoretical value representing the optical film thickness of each optical film as a parameter and a target wavelength characteristic value in a corresponding predetermined wavelength band, and a target wavelength characteristic value in the excitation light wavelength band. When the transmittance is larger than the maximum transmittance allowed in the excitation light wavelength band, the theoretical value representing the wavelength characteristic in the excitation light wavelength band using the optical film thickness of each optical film as a parameter and the corresponding excitation light wavelength. In order to reduce the second error between the target wavelength characteristic values in the band, the optical film thickness of each optical film is set to an initial value of a predetermined optical film thickness. It has designed stomach.

According to a fourth aspect of the present invention, there is provided a film thickness designing device for designing an optical film thickness of a multilayer optical filter comprising a plurality of optical films laminated, which is for preset gain equalization. Means for calculating a first error between a theoretical value representing a predetermined wavelength characteristic in the wavelength band using the optical film thickness of each optical film as a parameter and a target wavelength characteristic value in the corresponding gain equalizing wavelength band, A second value between a theoretical value representing the wavelength characteristic in the pumping light wavelength band other than the gain equalizing wavelength band using the optical film thickness of each optical film as a parameter and a target wavelength characteristic value in the corresponding pumping light wavelength band.
Of the optical film thickness of each of the optical films is designed so that the calculated first error and the second error can be reduced by using fitting with an initial value of a predetermined optical film thickness. And means for doing so.

According to a fifth aspect of the present invention, there is provided a film thickness designing device for designing an optical film thickness of each optical layer in a multilayer optical filter formed by laminating a plurality of optical films, which is preset. A first error between a theoretical value representing the wavelength characteristic in a predetermined wavelength band other than the excitation light wavelength band using the optical film thickness of each optical film as a parameter and a target wavelength characteristic value in the corresponding predetermined wavelength band is calculated. And a transmittance corresponding to a target wavelength characteristic value in the pumping light wavelength band is smaller than a minimum required transmittance in the pumping light wavelength band, the wavelength characteristic in the pumping light wavelength band is Means for calculating a second error between the theoretical value representing the optical film thickness of each optical film as a parameter and the wavelength characteristic value in the corresponding excitation light wavelength band, and the calculated first and second values. As the difference is decreased, respectively, the optical thickness of each optical film, and a means designed using fitting to an initial value a predetermined optical film thickness.

According to a sixth aspect of the present invention, there is provided a film thickness designing device for designing an optical film thickness of each optical layer in a multilayer optical filter formed by laminating a plurality of optical films, which is preset. A first error between a theoretical value representing the wavelength characteristic in a predetermined wavelength band other than the excitation light wavelength band using the optical film thickness of each optical film as a parameter and a target wavelength characteristic value in the corresponding predetermined wavelength band is calculated. And a transmittance corresponding to a target wavelength characteristic in the pumping light wavelength band is larger than the maximum transmittance allowed in the pumping light wavelength band, the wavelength characteristic in the pumping light wavelength band Means for calculating a second error between the theoretical value representing the optical film thickness of the optical film as a parameter and the target wavelength characteristic value in the corresponding pumping light wavelength band, and the calculated first and first errors. So that the error in the decrease, respectively, the optical thickness of each optical film, and a design means for designing with a fitting to an initial value a predetermined optical film thickness.

According to a seventh aspect of the present invention, there is provided a computer-executable program for designing an optical film thickness of each optical layer in a multilayer optical filter formed by laminating a plurality of optical films, Between a theoretical value that represents a predetermined wavelength characteristic in a preset wavelength band for gain equalization using the optical film thickness of each optical film as a parameter and a target wavelength characteristic value in the corresponding wavelength band for gain equalization, Means for calculating the first error of, and a theoretical value representing the wavelength characteristic in the pumping light wavelength band other than the gain equalizing wavelength band with the optical film thickness of each optical film as a parameter and the corresponding pumping light wavelength band. A means for calculating the second error between the target wavelength characteristic values, and an optical film thickness of each of the optical films so that the calculated first and second errors are reduced respectively. To function as a means of designing with fitting to an initial value a predetermined optical film thickness.

According to an eighth aspect of the present invention, there is provided a computer-executable program for designing an optical film thickness of each optical layer in a multilayer optical filter formed by laminating a plurality of optical films, Between the theoretical value representing the wavelength characteristic in a predetermined wavelength band other than the preset excitation light wavelength band as a parameter using the optical film thickness of each optical film and the target wavelength characteristic value in the corresponding predetermined wavelength band, Means for calculating a first error of the pumping light wavelength band, and the pumping light having a transmittance corresponding to a target wavelength characteristic value in the pumping light wavelength band is smaller than a minimum required transmittance in the pumping light wavelength band. A second error between the theoretical value representing the wavelength characteristic in the wavelength band using the optical film thickness of each optical film as a parameter and the wavelength characteristic value in the corresponding excitation light wavelength band. As a means for calculating and a means for designing the optical film thickness of each of the optical films by using fitting with an initial value of a predetermined optical film thickness so that the calculated first and second errors are reduced respectively. Make it work.

According to a ninth aspect of the present invention, there is provided a computer-executable program for designing an optical film thickness of each optical layer in a multilayer optical filter formed by laminating a plurality of optical films, Between the theoretical value representing the wavelength characteristic in a predetermined wavelength band other than the preset excitation light wavelength band as a parameter using the optical film thickness of each optical film and the target wavelength characteristic value in the corresponding predetermined wavelength band, Means for calculating a first error of the pumping light and the pumping light having a transmittance corresponding to a target wavelength characteristic value in the pumping light wavelength band is larger than a maximum transmittance allowed in the pumping light wavelength band. A second value between the theoretical value representing the wavelength characteristic in the wavelength band using the optical film thickness of each optical film as a parameter and the target wavelength characteristic value in the corresponding excitation light wavelength band. A means for calculating an error and an optical film thickness of each of the optical films are designed by using fitting with an initial value of a predetermined optical film thickness so that the calculated first and second errors are reduced respectively. Make it function as a means.

According to the tenth aspect of the present invention, there is provided a rare earth element-doped fiber, the rare earth element-doped fiber for amplifying the signal light, and the excitation light for exciting the rare earth element-doped fiber. A pumping light source for generating, a pumping light generated by the pumping light source is multiplexed with the signal light, a multiplexer for outputting the pumping light to the rare earth element-doped fiber, and from the multiplexer. The excitation light emitting side and the signal light downstream side are arranged.
And a multilayer filter as described above.

According to an eleventh aspect of the present invention, there is provided a wavelength division multiplexing optical transmission system for transmitting a plurality of signal lights having mutually different wavelengths, the optical signal transmitting the plurality of signal lights to an optical transmission line. The optical amplifier according to claim 19, which amplifies a plurality of signal lights transmitted from the optical transmitter and transmitted via the optical transmission line, and the optical amplifier amplified via the optical amplifier. And an optical receiver for receiving a plurality of signal lights transmitted via the transmission path.

According to a twelfth aspect of the present invention, there is provided a film thickness designing method for designing an optical film thickness of each optical layer in a multilayer optical filter formed by laminating a plurality of optical films, which is set in advance. A first error between a theoretical value representing a predetermined wavelength characteristic in the gain equalizing wavelength band using the optical film thickness of each optical film as a parameter and a target wavelength characteristic value in the corresponding gain equalizing wavelength band is calculated. Between the theoretical wavelength value in the pumping light wavelength band other than the gain equalization wavelength band and the target wavelength characteristic value in the corresponding pumping light wavelength band. Calculating a second error of
And a step of designing the optical film thickness of each of the optical films by using fitting with an initial value of a predetermined optical film thickness so that the calculated first and second errors are reduced.

According to a thirteenth aspect of the present invention, there is provided a film thickness designing method for designing an optical film thickness of each optical layer in a multilayer optical filter formed by laminating a plurality of optical films, which is set in advance. A first error between a theoretical value representing the wavelength characteristic in a predetermined wavelength band other than the excitation light wavelength band using the optical film thickness of each optical film as a parameter and a target wavelength characteristic value in the corresponding predetermined wavelength band is calculated. Step, when the transmittance corresponding to the target wavelength characteristic value in the pumping light wavelength band is smaller than the minimum required transmittance in the pumping light wavelength band, the wavelength characteristics in the pumping light wavelength band Calculating a second error between the theoretical value representing the optical film thickness of each optical film as a parameter and the wavelength characteristic value in the corresponding excitation light wavelength band,
And a step of designing the optical film thickness of each of the optical films by using fitting with an initial value of a predetermined optical film thickness so that the calculated first and second errors are reduced.

According to a fourteenth aspect of the present invention, there is provided a film thickness designing method for designing an optical film thickness of each optical layer in a multilayer optical filter formed by laminating a plurality of optical films, which is set in advance. A first error between a theoretical value representing the wavelength characteristic in a predetermined wavelength band other than the excitation light wavelength band using the optical film thickness of each optical film as a parameter and a target wavelength characteristic value in the corresponding predetermined wavelength band is calculated. Step, when the transmittance corresponding to the target wavelength characteristic value in the pumping light wavelength band is larger than the maximum transmittance allowed in the pumping light wavelength band, the wavelength characteristic in the pumping light wavelength band A step of calculating a second error between the theoretical value representing the optical film thickness of each optical film as a parameter and the target wavelength characteristic in the corresponding pumping light wavelength band; And as the second error decreases, respectively, the optical thickness of each optical film, and a step of designing with fitting to an initial value a predetermined optical film thickness.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIG. 1 is a diagram showing a multilayer filter 1 according to a first embodiment of the present invention.

As shown in FIG. 1, the multilayer filter 1 has
The substrate 2 and a plurality of thin film layers 3 (first layer 3a1 to Nth layer 3aN) formed and laminated on the substrate 2 by a method such as vapor deposition or sputtering are provided. Of the plurality of thin film layers 3a1 to 3aN, odd layers (first layer 3a1, third layer 3a3, ..., 2N-1 layer, ...
The refractive index of the film material of the thin film layer of () and the even layers (the second layer 3a2, the fourth layer 3a4, ..., The second N layer, ...
The refractive index of the film material of the thin film layer of *) is different from each other.

The optical film thickness, which is the product of the physical film thicknesses d1 to dN and the refractive indices n1 to nN of the thin film layers constituting the plurality of thin film layers 3, that is, the first layer 3a1 to the Nth layer 3an, is: Each thin film layer is accurately designed based on the film thickness designing process described later.

FIG. 2 is a diagram showing a hardware configuration of a film thickness designing device 10 for designing the optical film thickness of each thin film layer 3a1-3aN of the multilayer film filter 1 shown in FIG.

As shown in FIG. 2, the film thickness designing apparatus 10 is a computer system, and an input section 11 which a designer can operate to input information, a computer 12 connected to the input section 11, and a computer 12 connected to the input section 11. A memory 13 that is communicatively connected to the computer 12 and that stores a program P for executing a film thickness designing process to be described later in advance, and an external input / output interface that performs an interface process regarding input / output with the outside. 14 and.
As the storage medium, various storage media such as a semiconductor memory and a magnetic memory can be applied.

Further, the memory 13 includes a theoretical formula data file 20 containing theoretical formula data representing the theoretical value of the light transmittance at successive wavelengths of the N layer multilayer film filter 1, and the GFF.
Target light transmission loss value (target value) and pump light transmission wavelength band (for example, 1460 nm to 1)
A target transmission loss value data file 21 for storing a target light transmission loss value (transmittance; for example, a transmittance of −1 dB or more) at 495 nm).

The theoretical formula data stored in the theoretical formula data file 20 will be described below.

The theoretical formula for the light transmittance of the N-layer multilayer filter 1 with the optical film thickness of each of the layers 3a1-3aN as a parameter is given below assuming that the incident angle is perpendicular to the film surface of the multilayer filter 1. Equation of energy transmittance shown in Equation (1),
And the following equations (2) to (5).

[Equation 1]

[Equation 2]

[Equation 3]

[Equation 4]

[Equation 5] Here, τ in the equation (1) is represented by the equation (2), and the parameters m ₁₁ , m ₁₂ , m ₂₁ , m ₂₂ shown in the equation (2) are given.
Is each element of the characteristic matrix M in all N layers given by the equation (3), and M _j (j is an integer increasing from 1 by 1 in order such as 1, 2, ...) The characteristic matrix M _j of the j-th layer given by the total product is given by Expression (4).
G _j shown in Expression (4) is represented by Expression (5), n _j is the complex refractive index of the j-th layer, and d _j is the physical film thickness of the j-th layer.

Further, the wavelength for obtaining the transmittance is substituted for λ in the equation (5), and n ₀ and n _s are the complex refractive index of the medium and the complex refractive index of the filter substrate 2 at the wavelength λ, respectively. Further, in Expression (1), τ ^* is a conjugate complex number of τ, and i in Expressions (3) and (4) is an imaginary unit.

Therefore, by using these equations (1) to (5), the light transmission at the continuous wavelength of the continuous multilayer filter 1 of N layers is performed with the value of the optical film thickness of the j-th layer as a parameter. If the theoretical value of the rate is obtained and this light transmittance is converted into a light transmission loss value (insertion loss value), the light transmission loss value can be expressed using the optical film thickness and wavelength as variables (parameters).

That is, the theoretical formula data file 21 stores a theoretical formula representing the light transmission loss value (insertion loss value) IL as theoretical formula data DA.

Next, the overall operation of this embodiment will be described.

In manufacturing the multilayer filter 1, first, the optical film thickness of each layer 3a1-3an of the multilayer filter 1 is designed (step S1).

That is, the designer inputs the target transmission loss value (data) IL via the input unit 11 of the film thickness designing apparatus 10.
Input (λ _i ) to the computer 12. The target transmission loss value (data) IL (λ _i ) represents the target transmission loss characteristic of the pump light and the target transmission loss characteristic of the GFF, and the target characteristic wavelength band of the pump light (for example, 1460 nm to 1495 nm) and the target characteristic wavelength band of GFF (for example, 1530 nm to 1560 n).
m) each wavelength λ _i (i
Is an integer sequentially increasing from 1 to N by 1 and i =
1, 2, 3, ..., N-1, N) for the pump light transmission and GFF.

Furthermore, the designer sets the cutoff in the transmission loss profile within the characteristic wavelength band corresponding to the initial value (film thickness) as the initial value of the optical film thickness parameter (hereinafter referred to as film thickness parameter) a. A value that does not overlap the pump light transmission wavelength band (1460 nm to 1495 nm) is input (step S1).

The computer 12 operates according to the program P, and the inputted target transmission loss characteristic value IL (λ _i )
And a film thickness parameter a (initial value). Then, the computer 12 stores the film thickness parameter a in the memory 1
3, and the target transmission loss characteristic value IL (λ _i ) is stored in the target transmission loss value data file 21 (step S1).
1).

FIG. 5 shows a target transmission loss characteristic (target transmission characteristic) T1 of pump light in the characteristic wavelength band, a target transmission loss characteristic T2 of GFF, and a transmission loss profile PR (a) corresponding to the initial value of the optical film thickness. It is a graph which shows each.

That is, as shown in FIG. 5, the transmission loss profile PR (a) corresponding to the initial value a of the optical film thickness.
Has a center wavelength in the band exceeding 1570 nm, and the edge part on the short wavelength side of the stop band is set to the initial value of the transmission loss characteristic of the GFF part, so that the stop band is the pump light transmission wavelength band ( (1460 nm to 1495 nm)
You can see that they do not overlap.

Next, the computer 12 sets the variable n to 0.
(Step S12), the variable n is incremented by 1 (step S13), and the wavelength parameter λ _n within the characteristic wavelength band is set to λ _i . Since n = 1 at this time, λ _n = λ ₁ (step S14).

Next, the computer 21 has a memory 42.
The theoretical formula data stored in the theoretical formula data file 21 is read, and the film thickness parameter a (initial value) is input to the read theoretical formula data DA. Then, the computer 21 obtains the insertion loss value IL (λ _n , a) of the multilayer film 3 with the film thickness parameter a and the wavelength λ _n as variables. Subsequently, computer 21 square error E _n of the insertion loss value IL of the multilayer film 3 (lambda _n, a) with a corresponding multi-layer film 3 across the target transmission loss value IL of a wavelength λ _n (λ _n) (A):

[Equation 6] And the obtained squared error E _n (a) of the entire multilayer film 3 is stored in the memory 13 (step S15).

Next, the computer 12 determines whether or not n> N (step S16). Since n = 1 now, the determination in step S16 is NO, the computer 12 returns to step S13, increments n by 1, and executes the processing of step S13 and thereafter.

That is, the computer 12 repeatedly executes the above-described processing of steps S13 to S16 until n> N, that is, until the processing of step S15 based on the wavelength parameter λ _n = λ _N is completed.

As a result, the target transmission loss value at the wavelength λ _n corresponding to the theoretical value IL (λ _n , a) of the light transmission loss in the entire characteristic wavelength band with the film thickness parameter a (initial value) in each of the layers 3a1 to 3aN. The squared error E _n (a) from IL (λ _n ) is obtained for each wavelength.

When n> N, the above step S
The process of 16 is YES, and the computer 12 causes the computer 12 to calculate the squared error E _{n of the} entire multilayer film 3 in the entire characteristic wavelength band.
(A) arithmetic mean value (square mean error, square error mean value)
Is calculated according to the following equation (7), and the root mean square error in the calculated wavelength parameter a is stored in the memory 13 (step S17).

[0054]

[Equation 7]

Next, based on the calculated root mean square error in the wavelength parameter a, the computer 12 has converged the value of the root mean square error, or the present optical film thickness values a (1) to a ( N), the loss deviation between the transmission loss value IL (λ _{1 to} λ _N , a (1) to a (N)) of the entire multilayer film 3 and the corresponding target transmission loss value IL (λ _{1 to} λ _N ). It is determined whether (flatness) has become a fixed value (for example, 1 dB) or less (step S18).

As a result of the judgment in step S18, NO (2
If the value of the root-mean-square error is non-converging and the loss deviation exceeds a certain value), the computer 12 causes the optical film layers 3a1-3a to
The film thickness parameter a of at least one layer of N is changed (step S19), the process returns to step S12, and the fitting process of steps S12 to S19 is repeated until the result of the determination of step S18 is YES. Run.

That is, the computer 12 causes the transmission loss values IL (λ _{1 to} λ _N , a (1) to a () of the entire multilayer film 3 using the current optical film thickness values a (1) to a (N). N)) is sufficiently close to the corresponding target transmission loss value IL (λ _{1 to} λ _N ), the fitting process of steps S12 to S19 is performed, and the film thickness parameter a of the optical film layers 3a1 to 3aN is changed layer by layer. When the value of the root mean square error converges, the current optical film thickness values a (1) to a (a)
The transmission loss value IL (λ ₁ ~
If the loss deviation between λ _N , a (1) to a (N)) and the corresponding target transmission loss value IL (λ _{1 to} λ _N ) is below a certain value (step S18 → YES), the process is executed. finish.

In the above fitting process, in the present embodiment, the stop band of the transmission loss profile PR (a) corresponding to the initial value of the optical film thickness does not overlap the pump light transmission wavelength band (1460 nm to 1495 nm). Good fitting can be performed even in the pump light transmission wavelength band.

For example, as in the case of designing a normal GFF,
Wavelength band for transmission loss characteristics of GFF (1529 nm to 1
561 nm) and the center wavelength is set to the center, and the transmission loss profile PR (b) corresponding to the initial value of the optical film thickness is set to the initial value of the target transmission loss characteristic T2 at the edge portion on the long wavelength side of the stop band. If so, good fitting can be performed in the light transmission loss characteristic portion of the GFF.

However, in the same initial value setting as that of the normal GFF, as shown in FIG. 6, the stop band overlaps the pump light transmission wavelength band (1460 nm to 1495 nm), so that in the pump light transmission wavelength band portion. Fitting becomes difficult.

Therefore, as the initial value of each optical film thickness described in the present embodiment, a value whose stop band does not overlap with the pump light transmission wavelength band (1460 nm to 1495 nm) is used, so that the light transmission loss characteristic portion of the GFF is obtained. In addition, good fitting can be performed in the pump light transmission wavelength band.

In this way, the film thickness parameter a for each layer
When (1) to a (N) are optimized, the computer 12
Is an optimized film thickness parameter a (1) to a for each layer.
(N), that is, each layer 3a1-3 of the multilayer filter 1
Each optical film thickness value a that is optimally set (designed) for aN
(1) to a (N) are stored in the memory 13.

When the optical film thickness values a (1) to a (N) are optimally set for the respective layers 3a1 to 3aN in this manner, the optimum designed optical film thickness values a (1) are obtained. ~ A
The film forming process is executed while controlling the film thickness using (N) (step S2).

In this film forming process, the film forming material is vapor-deposited on the substrate 2 by vapor deposition or sputtering.
At this time, the thin film during film formation is irradiated with monitoring light, and the transmitted light is monitored, for example, so that the optical film thickness of the thin film during film formation matches the optimally designed optical film thickness. Thickness controlled. This film formation process (film thickness control process)
Is each of the optimized optical film thickness values a (1) to a (N)
It is executed by a film forming apparatus including a computer based on.

As described above, according to this embodiment,
The cutoff band of the transmission loss characteristic based on the initial value of each optical film thickness is the pump light transmission wavelength band (1460 nm-
(1495 nm) and the short wavelength side edge portion of the stop band thereof is set to the initial value of the transmission loss characteristic of the GFF portion. Therefore, the optical film thickness of each of the thin film layers 3a1 to 3aN of the multilayer filter 1 can be fitted with the target transmission loss characteristic T1 of pump light and the target transmission loss characteristic T2 of GFF as targets. Therefore, the target transmission loss characteristic T1 of the pump light is
It is possible to provide the multi-functional multilayer filter 1 that also has the target transmission loss characteristic T2 of GFF.

In this embodiment, by increasing the optical film thickness of each layer and narrowing the cutoff band width of the transmission loss characteristic based on the initial value, the initial value a1 is changed as shown in FIG. , The transmission loss characteristic PR based on the initial value a1
The stop band of (a1) is the pump light transmission wavelength band (1460
It is also possible to set the center wavelength of the above transmission loss characteristics at the center of the wavelength band (1529 nm to 1561 nm) for the transmission loss characteristics of GFF.

(Second Embodiment) It is a diagram showing a hardware configuration of a film thickness designing apparatus 10A of the present embodiment.

In this embodiment, a program PA for executing the film thickness designing process and the program PA
The film thickness designing process (see FIG. 9) executed by the computer 12 based on the above is different from that of the first embodiment.

In the memory 13A of this embodiment, the maximum insertion loss IL _max allowed in the pump light transmission wavelength band (1460 nm to 1495 nm) includes the minimum transmittance data T _min converted into the transmittance. The transmittance data file 25 is stored in advance.

Since the other points are the same as those of the first embodiment, the description thereof will be omitted.

In this embodiment, when executing the film thickness designing process, the computer 12 operates in accordance with the program PA, and steps S11 to S are performed as in the first embodiment.
14 processing is performed.

Next, the computer 12 determines whether or not the parameter wavelength λ _n is in the pump light transmission wavelength band (step S20).

As a result of this determination NO, that is, while the parameter wavelength λ _n is not in the pump light transmission wavelength band, as in the first embodiment, steps S12 to S14, step S20, and steps S15 to S are performed.
The processing of 16 is repeated. As a result, the root mean square error E _n (a between the insertion loss value IL (λ _n , a) of the entire multilayer film 3 and the target transmission loss value IL (λ _n ) of the entire multilayer film 3 at the corresponding wavelength λ _n. ) Is stored in the memory 13.

On the other hand, the increment of n is repeated,
The parameter wavelength λ _n is the pump light transmission wavelength band 1460 _n
m to 1495 nm, in step S20.
Is YES, the computer 12 converts the target transmission loss value IL (λ _n ) into the target transmittance T.
It is determined whether (λ _n ) is greater than or equal to the minimum transmittance data T _min stored in the allowable minimum transmittance data file 25 (step S21).

As a result of the determination in step S21, NO,
That is, the target transmittance T (λ_n) Is the minimum allowable transmittance
Data T stored in the data file 25_minTo
If it does not exceed, the process proceeds to step S15.
Then, the insertion loss value IL (λ
_n, A) and the target transmission loss value IL (λ_n) And the squared error E _n
(A) is calculated and stored in the memory 13.

On the other hand, as a result of the judgment in step S21, YE
S, that is, the target transmittance T (λ _n ) is the minimum transmittance data T stored in the allowable minimum transmittance data file 25.
If it is more than _{min, the} square error E _n (a) of this part is set to 0.
Is set (step S22).

Next, the computer 12 causes the step S
The process proceeds to step S16, and steps S13, S14, S20, and S15 to S16 (when the wavelength parameter λ _n is outside the pump light transmission wavelength band), steps S13 to S14, and S20 to S21 until n> N. And S15-
S16 (when the wavelength parameter λ _n is within the pump light transmission wavelength band and the target transmittance T (λ _n ) does not exceed the minimum transmittance data T _min ) and steps S13 to S14 and S
20 to S22 (where the wavelength parameter λ _n is the pump light transmission wavelength band, the target transmittance T (λ _n ) is the minimum transmittance data T _min
If it exceeds the value), repeat.

Thereafter, as in the first embodiment, if n> N, the processing in step S16 becomes YES, and the computer 12 causes the square error E _n (of the entire multilayer film 3 in the obtained entire characteristic wavelength band to be E _n ( The arithmetic mean value (square mean error, square error mean value) of a) is calculated and stored in the memory 13 (step S17).

Next, based on the calculated root mean square error in the wavelength parameter a, the computer 12 converges the value of the root mean square error, or the present optical film thickness values a (1) to a ( N), the loss deviation between the transmission loss value IL (λ _{1 to} λ _N , a (1) to a (N)) of the entire multilayer film 3 and the corresponding target transmission loss value IL (λ _{1 to} λ _N ). It is determined whether (flatness) has become a fixed value (for example, 1 dB) or less (step S18).

As a result of the judgment in step S18, NO (2
If the value of the root-mean-square error is non-converging and the loss deviation exceeds a certain value), the computer 12 causes the optical film layers 3a1-3a to
The film thickness parameter a of at least one layer of N is changed (step S19), the process returns to step S12, the processes of steps S12 to S19 and S20 to S22 are performed, and the determination result of step S18 is YES. Repeat until and execute.

That is, the computer 12 uses the present optical film thickness values a (1) to a (N) to obtain the transmission loss values IL (λ _{1 to} λ _N , a (1) to a ( N)) is sufficiently close to the corresponding target transmission loss value IL (λ _{1 to} λ _N ), the fitting process of steps S12 to S19 is performed, and the film thickness parameter a of the optical film layers 3a1 to 3aN is changed layer by layer. When the value of the root mean square error converges, the current optical film thickness values a (1) to a (a)
The transmission loss value IL (λ ₁ ~
If the loss deviation between λ _N , a (1) to a (N)) and the corresponding target transmission loss value IL (λ _{1 to} λ _N ) is below a certain value (step S18 → YES), the process is executed. finish.

At this time, in this embodiment, when the target transmittance T (λ _n ) exceeds the minimum transmittance data T _min within the pump light transmission wavelength band, the insertion loss value IL of the entire multilayer film 3 is obtained. (Λ _n , a) and the target transmission loss value IL (λ _n )
The root mean square error between and is forced to 0, and the deviation (ripple) in this portion is allowed. Then, the ripples within the pump light transmission wavelength band are allowed, and the fitting characteristics of other light transmission loss bands (for example, the light transmission loss band of GFF, which has a severe demand) are enhanced.

That is, the film thickness designing apparatus 10 of the present embodiment.
A is the flatness (Flatnes) of the light transmission loss characteristic of the GFF part.
This is especially effective when the specifications for s) are strict.

In order to verify the effect of the present embodiment, the inventors of the present invention installed the multilayer film filter 1 according to the specifications shown in Table 1 below in the multilayer film designing apparatus 10 and the second embodiment of the first embodiment.
Each of the multilayer film design apparatuses 10A of FIG.
Shown as (a) and (b) respectively.

10 (a) and 10 (b) and FIG.
10A and 10B, the total number N of multilayer films is different (the multilayer filter 1A of FIGS. 10A and 10B).
→ N = 46; the multilayer filter 1B of FIGS. 11A and 11B → N = 26).

[0086]

[Table 1] FIG. 10A is a design target (target) loss characteristic of the multilayer filter 1A obtained by the film thickness design based on the film thickness designing apparatus 10 of the first embodiment (the GFF target and the target in the pump light transmission wavelength band: 6] is a graph showing a loss characteristic (solid line) based on the design value of the multilayer filter 1A and a loss deviation (□) between the target value and the design value. The target in the pump light transmission wavelength band was set to 0 dB.

As shown in FIG. 10A, in the film thickness design of the first embodiment, the flatness of the GFF part was 0.24 dB, and the required flatness of the GFF part: 0.2 dB or less could not be satisfied. This is considered to be the influence of fitting in the pump light transmission wavelength band, as described above.

On the other hand, FIG. 10B shows a design target (target) loss characteristic (G) of the multilayer filter 1B obtained by the film thickness design based on the film thickness designing apparatus 10A of the second embodiment.
3 is a graph showing an FF target, a target in a pump light transmission wavelength band: ⋄), a loss characteristic (solid line) based on a design value of the multilayer filter 1B, and a loss deviation (□) between the target value and the design value. The target in the pump light transmission wavelength band is set to -0.6 dB. Further, the maximum insertion loss IL _max (minimum transmittance data T _min ) was set to 0.6 dB.

As shown in FIG. 10B, in the film thickness design of the second embodiment, the minimum transmittance data T is shown in the loss characteristic (solid line) based on the design value in the pump light transmission wavelength band.
_{Since the} squared error between the target value and the design value when the transmittance exceeds _min is set to 0, the ripple is generated accordingly. However, the specification of this ripple portion has a large allowable range of 0.8 dBpp or less between the maximum value and the minimum value {between peaks (peak to peak)}, and thus sufficiently satisfies the above specifications. In addition, the GFF part
Flatness becomes 0.19 dB, and the required Flatness of GFF part:
We were able to satisfy 0.2 dB or less.

Similarly, FIG. 11A shows the design target loss characteristics (GFF target, pump light transmission wavelength band) of the multilayer filter 1B obtained by the film thickness design based on the film thickness designing apparatus 10 of the first embodiment. Target in: ◇),
Loss characteristics based on design values of multilayer filter 1B (solid line)
3 is a graph showing a loss deviation (□) between a target value and a design value. The target in the pump light transmission wavelength band was set to 0 dB.

As shown in FIG. 11A, in the film thickness design of the first embodiment, the flatness of the GFF portion was 0.265B, and the required flatness of the GFF portion: 0.2 dB or less could not be satisfied. This is also considered to be the effect of fitting in the pump light transmission wavelength band.

On the other hand, FIG. 11B shows the design target loss characteristics (in the GFF target and pump light transmission wavelength band) of the multilayer filter 1B obtained by the film thickness design based on the film thickness designing apparatus 10A of the second embodiment. Target: ◇),
Loss characteristics based on design values of multilayer filter 1B (solid line)
3 is a graph showing a loss deviation (□) between a target value and a design value. The target in the pump light transmission wavelength band is set to -0.6 dB. Further, the maximum insertion loss IL _max (minimum transmittance data T _min ) was set to 0.6 dB.

Similar to FIG. 10B, in FIG. 11B, in the film thickness design of the second embodiment, the loss characteristic (solid line) based on the design value in the pump light transmission wavelength band shows the corresponding wavelength transmission. There is ripple in the band. However, since the specification of this ripple portion has a large allowable range of 0.8 dBpp or less, the above specification is sufficiently satisfied. Further, the Flatness of the GFF part was 0.20 dB, and it was possible to satisfy the required Flatness of the GFF part: 0.2 dB or less.

According to the film thickness design based on the film thickness designing apparatus 1A of this embodiment, the maximum allowable insertion loss IL _max (minimum transmittance data T _min ) in the pump light transmission wavelength band is obtained.
As the setting of (1) is increased (the setting of the minimum transmittance data T _min is decreased), the degree of freedom of the film thickness fitting is increased, and the Flatness characteristic can be improved. If the ripple in the transmission band is allowed up to about 1 dB, the Fitness value is 0.1
8dB, GF of normal design without considering pump light transmission
Flatness characteristics equivalent to F can be obtained (see FIG. 12).

In the first and second embodiments, the transmission wavelength band of the pump light to be transmitted is set to 1450n.
However, the present invention is not limited to this, and it is also possible to design the pump light transmission wavelength band so as to transmit pump light in another wavelength band, for example, the 980 nm band.

FIG. 13A shows design values (first value) of a multilayer filter having a predetermined light transmission characteristic for the pump light wavelength band of 980 nm and a predetermined light transmission loss characteristic in the GFF portion (1529 nm to 1561 nm). It is a graph which shows the loss characteristic (solid line) based on the film thickness design of 2 embodiment. It should be noted that FIG.
3A is a graph showing an enlarged part of FIG. 3A as (b), that is, the light transmission characteristics around the 980 nm band. In addition, FIG. 13C is a graph showing an enlarged transmission loss characteristic in the portion shown as (c) in FIG. 13A, that is, the GFF portion (1529 nm to 1561 nm).

As shown in FIGS. 13 (a) to 13 (c), a multilayer film filter having a pump light transmission function and a transmission loss function for gain equalization is designed even if the pump light transmission bands are different. be able to. Further, in the first and second embodiments, a pump light transmission function of transmitting pump light in a predetermined pump light transmission wavelength band and G
Although the multilayer filter having the FF function is designed, the present invention is not limited to this, and the pump light is cut off in a predetermined pump light cutoff wavelength band by the same design method as in the first and second embodiments. It is also possible to design a multilayer filter having both a pump light blocking function and a GFF function.

In particular, in the second embodiment, the pump light cutoff wavelength band (1480) is added to the memory 13A instead of or in addition to the allowable minimum transmittance data file 25.
A cut-off wavelength band having a center wavelength of nm (for example, 1460 nm to 1520 nm), the allowable maximum transmittance data file 25 including the maximum transmittance data T _max obtained by converting the minimum insertion loss IL _min allowed into the transmittance.
Remember ´.

At this time, the computer 12 operates as shown in FIG.
In the process of step S21 in the film thickness designing process shown in, the target transmittance T (λ _n ) obtained by converting the target transmission loss value IL (λ _n ) into the transmittance is stored in the maximum allowable transmittance data file 25 ′. It is determined whether or not it is equal to or less than the maximum transmittance data T _max (step S21 ′).

If the result of the determination in step S21 'is NO, that is, if the target transmittance T (λ _n ) is not less than or equal to the maximum transmittance T _max , the process proceeds to step S15 and the above-described process is performed. Therefore, the insertion loss value IL (λ _n , a) of the entire multilayer film 3 and the target transmission loss value IL (λ _n ) are 2
The multiplication error E _n (a) is calculated and stored in the memory 13.

On the other hand, as a result of the judgment in step S21 ', YE
If S, that is, the target transmittance T (λ _n ) is less than or equal to the maximum transmittance data T _max , the squared error E of this portion is obtained.
_n (a) is set to 0 (step S22).

That is, according to this modification, when the target transmittance T (λ _n ) is equal to or less than the maximum transmittance data T _{max in} the pump light cutoff wavelength band, the insertion loss value IL of the entire multilayer film 3 is reduced. (Λ _n , a) and the target transmission loss value IL (λ _n )
The squared error E _n (a) between and is forcibly set to 0 to improve the fitting characteristic.

As a result, for example, as shown in FIG.
It is possible to provide a multilayer filter having both a pump light blocking function and a GFF function, which can be applied even when the specifications regarding the flatness (Flatness) of the light transmission loss characteristic of the GFF portion are strict.

Next, an embodiment of an optical amplifier including a GFF based on the multilayer filters 1 and 1A described in the first and second embodiments and their modifications will be described with reference to the drawings.

FIG. 15 is a diagram showing a schematic configuration of the forward-pumping type optical amplifier 100.

As shown in FIG. 15, the optical amplifier 100 is
The first EDF is connected to the optical fiber 107a to which the signal light is input, and is composed of a fiber doped (doped) with a rare earth element such as erbium (Er).
101 and a second EDF 102 that is cascade-connected to the first EDF 101 and is composed of a rare earth element, for example, erbium (Er) -doped fiber, and is arranged between the first EDF 101 and the second EDF 102. GF based on the multilayer filter 1, 1A according to the present invention
F103 and a second EDF 102 and G
The FF 103 is connected to the optical fiber 107b.

In the embodiment of the optical amplifier described above,
EDF doped with erbium as a dopant
Although the optical amplifier including is used as an amplification medium, the present invention is not limited to this. An optical amplifier having a similar pump configuration is applicable. For example, as a medium for amplification, Tellurite is added to the host glass of the fiber.
, Fluoride, Silica, etc. are applicable, and
In addition to erbium, thulium, praseodymium, ytterbium, terbium, etc. can be used as the dopant.

Further, the optical amplifier 100 pumps the pumping light (pump light) for pumping the EDF, and the pumping light emitted from the pumping light source 104 to the first EDF 1.
The multiplexer 105 supplies the first EDF 101 and the second EDF 102 from the signal light input end side of 01.

Further, in the optical amplifier 100, at least one of the signal light input side optical fiber 107a and the signal light output side optical fiber 107b is connected to the optical amplifier 100, if necessary.
It is also possible to provide the isolator 108. Note that FIG. 100 shows a configuration in which the isolator 108 is provided in both the optical fiber 107a and the optical fiber 107b.

FIG. 16 is a diagram showing a schematic configuration of the backward pumping type optical amplifier 110.

Forward pump optical amplifier 10 shown in FIG.
The difference from 0 is that pumping light is supplied from the signal light output side of the second EDF 102. That is, the backward pumping optical amplifier 110 includes a multiplexer 105 arranged on the signal light output side of the second EDF 102 and a pumping light source 114 that emits pumping light for EDF pumping. The excitation light emitted from the excitation light source 114 by the second ED
The signal light is output from the F102 to the second EDF 102 and the first EDF 101.

FIG. 17 shows a bidirectional pumping type optical amplifier 120.
It is a figure which shows schematic structure of.

As shown in FIG. 17, the bidirectional pumping optical amplifier 120 has a configuration in which the forward pumping optical amplifier 100 shown in FIG. 15 and the backward pumping optical amplifier 110 shown in FIG. 16 are combined. . That is, the bidirectional pumping optical amplifier 120 is a pumping light source 1 that emits pumping light for EDF pumping.
04 and the pumping light emitted from this pumping light source 104 from the signal light input end side of the first EDF 101 to the first EDF 1
01 and the second multiplexer 105a to be supplied to the second EDF 102, the excitation light source 114 for emitting the excitation light for EDA excitation, and the excitation light emitted from this excitation light source 114 for the signal light of the second EDF 102. The second EDF from the output end side
102 and a second multiplexer 105b that supplies the first EDF 101.

As shown in FIGS. 15 to 17, the optical amplifiers 100, 110 and 120 including the GFF 103 based on the multilayer filters 1 and 1A described in the first and second embodiments of the present invention and the modifications thereof. In FIG.
And the characteristics shown in FIG. 19 were obtained.

FIG. 18 is a graph showing the correlation between gain and wavelength (gain wavelength characteristic) in the bidirectionally pumped optical amplifier 120 shown in FIG. In FIG. 18, ● represents
The wavelength characteristic of gain (with Pump Pass) in the optical amplifier 120 including the GFF 103 according to the present invention is shown, and Δ is
9 shows the wavelength characteristics of gain (without Pump Pass) in the optical amplifier not including the GFF 103 according to the present invention.

As can be seen from FIG. 18, by disposing the GFF 103 according to the present invention in the optical amplifier, the gain value of the optical amplifier can be improved by about 0.5 to 0.7 dB.

FIG. 19 is a graph showing the correlation between NF (Noise Figure) and wavelength in the bidirectionally pumped optical amplifier shown in FIG. In FIG. 19, ● indicates the NF wavelength characteristic (with Pump Pass) in the optical amplifier 120 including the GFF 103 according to the present invention, and Δ indicates the NF wavelength characteristic (Pump Pass) in the optical amplifier that does not include the GFF 103 according to the present invention. No Pass) is shown.

As can be seen from FIG. 19, the NF value of the optical amplifier can be reduced by about 0.03 to 0.04 dB by disposing the GFF 103 according to the present invention in the optical amplifier.

18 and 19, the gain wavelength characteristic and the NF wavelength characteristic of the bidirectional pumping optical amplifier 120 shown in FIG. 17 are shown, but the forward pumping optical amplifier 100 shown in FIG. 15 is shown. Also, the backward pumping optical amplifier 110 shown in FIG. 16 can obtain substantially the same wavelength characteristics as the bidirectional pumping optical amplifier 120, and therefore the illustration and description thereof are omitted.

As described above, by arranging the GFF based on the multilayer filters 1 and 1A according to the present invention in the optical amplifier, in addition to the effect of the GFF itself, the gain and NF wavelength characteristics in the optical amplifier are respectively reduced. Can be improved.

Next, an embodiment of a wavelength division multiplexing optical transmission system including the optical amplifier of FIG. 15 (FIGS. 16 and 17) will be described with reference to FIG.

FIG. 20 shows the wavelength division multiplexing optical transmission system 2 described above.
It is a block diagram which shows schematic structure of 00.

As shown in FIG. 20, the wavelength division multiplexing optical transmission system 200 includes an optical transmitter T for transmitting a wavelength division multiplexing signal light in which a plurality of signal lights having different wavelengths are multiplexed to an optical transmission line P, The optical receiver R receives the wavelength-multiplexed signal light transmitted through the optical transmission line P, and has a function as a repeater interposed between the optical transmitter T and the optical receiver R. , A plurality of optical amplifiers 10 connected in series to each other
It has 0 and. That is, the optical amplifier 100 is
It has a function of collectively amplifying the wavelength division multiplexed signal light transmitted through the optical transmission line P.

The optical amplifier is not limited to the forward pump type optical amplifier 100 shown in FIG. 15, but the backward pump type optical amplifier 110 and the bidirectional pump type optical amplifier 120 shown in FIG. Of course it is good. Freely select any one of the forward pumping optical amplifier 100, the backward pumping optical amplifier 110 and the bidirectional pumping optical amplifier 120,
It can be arranged arbitrarily.

The wavelength division multiplexing optical transmission system 20 shown in FIG.
According to 0, the wavelength-multiplexed signal light transmitted from the optical transmitter T is transmitted to the optical receiver R while being sequentially amplified via each optical amplifier 100 including the above-mentioned GFF 103 (see FIG. 15). At this time, in each optical amplifier 100, the gain equalization and the NF suppression for the WDM signal light are GFF1.
03, so the light S with the same level of each wavelength
The wavelength division multiplexed signal light having a high N ratio is transmitted from the optical transmitter T to the optical receiver R.
Can be transmitted to. Although the present invention has been described above using the embodiment, the present invention is not limited to the above embodiment. That is, it is possible to add various changes or improvements to the above embodiment within the scope based on the technical idea of the present invention.

As described above, according to the multilayer optical filter of the present invention, and the film thickness setting method and device thereof, the optical film thickness of each thin film layer of the multilayer filter is set to a predetermined gain. It has a predetermined wavelength characteristic for each wavelength in the equalization wavelength band, and since it is designed to have a predetermined wavelength characteristic in the pumping light wavelength band other than the gain equalization wavelength band, the gain, etc. It is possible to provide a multilayer optical filter having both a predetermined wavelength characteristic in a chemical wavelength band and a predetermined wavelength characteristic in an excitation light wavelength band.

Therefore, it is possible to meet the demand for excitation light transmission / blocking for a multilayer optical filter such as GFF having a gain equalizing function, and it is possible to greatly enhance the practicality of the multilayer optical filter.

By combining a multilayer optical filter having a sufficient wavelength characteristic corresponding to the pumping light transmission / cutoff requirement with an optical amplifier, the output characteristic of the optical amplifier can be set to a lower loss / higher output than before. be able to. As a result, it becomes possible to provide an optical amplifier having an amplification characteristic with high output efficiency.

Furthermore, by combining the above-mentioned optical amplifier with an optical transmitter / receiver to form a system, it is possible to reduce the power consumption of the entire system.

[0129]

[Brief description of drawings]

FIG. 1 is a diagram showing a multilayer filter according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a hardware configuration of a film thickness designing device for designing an optical film thickness of each thin film layer of the multilayer film filter shown in FIG.

FIG. 3 is a flowchart showing an example of a multilayer filter manufacturing process according to the first embodiment of the present invention.

FIG. 4 is a schematic flowchart showing an example of a film thickness designing process according to the first embodiment of the present invention.

FIG. 5 is a graph showing a target transmission loss characteristic of pump light, a target transmission loss characteristic of GFF, and a transmission loss profile corresponding to an initial value of an optical film thickness in a characteristic wavelength band according to the first embodiment of the present invention. .

FIG. 6 is a graph showing a target transmission loss characteristic of pump light in a characteristic wavelength band, a target transmission loss characteristic of GFF, and a transmission loss profile corresponding to an initial value of an optical film thickness.

FIG. 7 is a graph showing a target transmission loss characteristic of pump light, a target transmission loss characteristic of GFF, and a transmission loss profile corresponding to an initial value of an optical film thickness in a characteristic wavelength band according to the first embodiment of the present invention. .

FIG. 8 is a diagram showing a hardware configuration of a film thickness designing device for designing an optical film thickness of each thin film layer of the multilayer film filter according to the second embodiment of the present invention.

FIG. 9 is a schematic flowchart showing an example of a film thickness designing process according to the second embodiment of the present invention.

10A is a graph showing the design target loss characteristic of the multilayer filter according to the first embodiment, the loss characteristic based on the design value of the multilayer filter, and the loss deviation between the target value and the design value, FIG. b) is a graph showing the design target loss characteristic of the multilayer filter according to the second embodiment, the loss characteristic based on the design value of the multilayer filter, and the loss deviation between the target value and the design value.

FIG. 11A is a graph showing the design target loss characteristic of the multilayer filter according to the first embodiment, the loss characteristic based on the design value of the multilayer filter, and the loss deviation between the target value and the design value, respectively. b) is a graph showing the design target loss characteristic of the multilayer filter according to the second embodiment, the loss characteristic based on the design value of the multilayer filter, and the loss deviation between the target value and the design value.

FIG. 12 is a graph showing the design target loss characteristic of the multilayer filter according to the second embodiment, the loss characteristic based on the design value of the multilayer filter, and the loss deviation between the target value and the design value.

FIG. 13A is a multilayer having a predetermined light transmission characteristic with respect to a pump light wavelength band of 980 nm band and a predetermined light transmission loss characteristic in a GFF portion according to a modification of the second embodiment of the present invention. A graph showing a loss characteristic based on a design value of the membrane filter, (b) is an enlarged graph showing a portion shown as (b) in FIG. 13 (a),
FIG. 13C is an enlarged graph showing the portion shown in FIG.

FIG. 14 is a graph showing a design target loss characteristic and a loss characteristic based on a design value of a multilayer filter having both a pump light blocking function and a GFF function according to a modification of the second embodiment of the present invention.

FIG. 15: GF based on a multilayer filter according to the present invention
The figure which shows schematic structure of the forward pumping type optical amplifier containing F.

FIG. 16: GF based on a multilayer filter according to the present invention
The figure which shows schematic structure of the backward pumping type optical amplifier containing F.

FIG. 17: GF based on a multilayer filter according to the present invention
The figure which shows schematic structure of the bidirectional pumping type optical amplifier containing F.

18 is a graph showing the correlation between gain and wavelength in the bidirectionally pumped optical amplifier shown in FIG.

19 is a graph showing a correlation between NF (Noise Figure) and wavelength in the bidirectionally pumped optical amplifier shown in FIG.

20 is a block diagram showing a schematic configuration of a wavelength division multiplexing optical transmission system including the optical amplifier shown in FIG. 15 (FIGS. 16 and 17).

FIG. 21 is a diagram for explaining the gain equalization function of the gain equalization filter.

FIG. 22 is a graph showing a design target loss characteristic of a multilayer filter, a loss characteristic based on a design value of the multilayer filter, and a loss deviation between the two.

[Explanation of symbols]

1 Multilayer filter 2 substrates 3 multilayer film 3a1-3aN thin film layer 10, 10A film thickness design device 11 Input section 12 computers 13, 13A memory 14 External I / O interface 20 theoretical formula data file 21 Target transmission loss value data file 25 Allowable minimum transmittance data file 100 Forward pump optical amplifier 101 First EDF 102 Second EDF 103 GFF 104, 114 Excitation light source 105, 105a, 105b multiplexer 107a, 107b Optical fiber 108 Isolator 110 Back-pumped optical amplifier 120 Bi-directional pump type optical amplifier 200 WDM system P, PA program T optical transmitter R optical receiver

Claims (25)

[Claims] 1. A multilayer optical filter comprising a plurality of optical films laminated, wherein the optical film thickness of each optical film has a predetermined wavelength characteristic within a preset wavelength band for gain equalization. In addition, the multilayer optical filter is designed to have a predetermined wavelength characteristic in a pumping light wavelength band other than the gain equalization wavelength band. 2. A first value between a theoretical value representing the wavelength characteristic in the wavelength band for gain equalization using the optical film thickness of each optical film as a parameter and a target wavelength characteristic value in the corresponding wavelength band for gain equalization. And a theoretical value representing the wavelength characteristic in the pumping light wavelength band with the optical film thickness of each optical film as a parameter, and a second error between the target wavelength characteristic value in the corresponding pumping light wavelength band. 2. The multilayer optical filter according to claim 1, wherein the optical film thickness of each optical film is designed to be small by using fitting with an initial value of a predetermined optical film thickness. 3. The initial value of the optical film thickness of each optical film in the fitting is designed so that the cutoff wavelength band in the wavelength characteristic profile does not overlap with the excitation light wavelength band. The multilayer optical filter described. 4. The initial value of the optical film thickness of each of the optical films in the fitting is designed so that the edge portion on the short wavelength side of the cutoff wavelength band in the wavelength characteristic profile overlaps the wavelength band for gain equalization. The multilayer optical filter according to claim 3, wherein 5. A multilayer optical filter comprising a plurality of optical films laminated, wherein a wavelength characteristic in a predetermined wavelength band other than a preset excitation light wavelength band is determined by a parameter of an optical film thickness of each optical film. In the pumping light wavelength band, the first error between the theoretical value and the target wavelength specifying value in the corresponding predetermined wavelength band and the transmittance corresponding to the target wavelength characteristic value in the pumping light wavelength band are A second value between the theoretical value representing the wavelength characteristic in the pumping light wavelength band with the optical film thickness of each optical film as a parameter and the wavelength characteristic value in the corresponding pumping light wavelength band when the transmittance is smaller than the minimum required transmittance. The optical film thickness of each optical film is designed by using fitting with an initial value of a predetermined optical film thickness so that the error of Film optical filter. 6. When the transmittance corresponding to the target wavelength characteristic value in the pumping light wavelength band is higher than the minimum required transmittance in the pumping light wavelength band, the wavelength characteristic in the pumping light wavelength band 6. The multilayer optical filter according to claim 5, wherein the second error between the theoretical value representing the optical film thickness of the optical film as a parameter and the target wavelength characteristic value in the corresponding pumping light wavelength band is set to zero. 7. A multilayer optical filter comprising a plurality of optical films laminated, wherein wavelength characteristics in a predetermined wavelength band other than a preset excitation light wavelength band are parameters of the optical film thickness of each optical film. The first error between the theoretical value expressed as and the target wavelength characteristic value in the corresponding predetermined wavelength band, and the transmittance corresponding to the target wavelength characteristic value in the pumping light wavelength band are in the pumping light wavelength band. When it is larger than the maximum permissible transmittance, the wavelength characteristic in the pumping light wavelength band is a theoretical value representing the optical film thickness of each optical film as a parameter and a target wavelength characteristic value in the corresponding pumping light wavelength band. So that the error of 2 and
A multilayer optical filter, wherein the optical film thickness of each optical film is designed by using fitting with a predetermined optical film thickness as an initial value. 8. When the transmittance corresponding to the target wavelength characteristic value in the pumping light wavelength band is smaller than the maximum transmittance allowed in the pumping light wavelength band, the wavelength characteristics in the pumping light wavelength band are set to the respective ones. 8. The multilayer optical filter according to claim 7, wherein the second error between the theoretical value representing the optical film thickness of the optical film as a parameter and the target wavelength characteristic in the corresponding pumping light wavelength band is set to zero. 9. A film thickness designing device for designing an optical film thickness of a multilayer optical filter comprising a plurality of optical films laminated, wherein a predetermined wavelength characteristic in a preset wavelength band for gain equalization is set. Means for calculating a first error between the theoretical value representing the optical film thickness of each optical film as a parameter and the target wavelength characteristic value in the corresponding gain equalization wavelength band, and means other than the gain equalization wavelength band Means for calculating a wavelength characteristic in the excitation light wavelength band, a second error between a theoretical value representing the optical film thickness of each optical film as a parameter and a target wavelength characteristic value in the corresponding excitation light wavelength band, And a means for designing the optical film thickness of each of the optical films by using fitting with an initial value of a predetermined optical film thickness so that the first and second errors become smaller. Device for designing film thickness of multilayer optical filter. 10. A film thickness designing device for designing an optical film thickness of each optical layer in a multilayer optical filter formed by laminating a plurality of optical films, the device having a predetermined wavelength other than a preset excitation light wavelength band. Means for calculating a first error between a theoretical value representing the wavelength characteristic in the band using the optical film thickness of each optical film as a parameter and a target wavelength characteristic value in the corresponding predetermined wavelength band; and the pumping light wavelength band. In the case where the transmittance corresponding to the target wavelength characteristic value in is smaller than the minimum required transmittance in the excitation light wavelength band, the wavelength characteristics in the excitation light wavelength band are parameterized by the optical film thickness of each optical film. Means for calculating the second error between the theoretical value expressed as and the wavelength characteristic value in the corresponding pumping light wavelength band, and the calculated first and second errors are reduced respectively. As described above, the film thickness designing apparatus for a multilayer optical filter, comprising: means for designing the optical film thickness of each optical film by using fitting having a predetermined optical film thickness as an initial value. 11. The design means, in the case where the transmittance corresponding to the target wavelength characteristic value in the pumping light wavelength band is higher than the minimum required transmittance in the pumping light wavelength band, in the pumping light wavelength band. A means for setting a second error between a theoretical value representing the wavelength characteristic using the optical film thickness of each optical film as a parameter and a target wavelength characteristic value in the corresponding pumping light wavelength band to be 0. 1
0. A film thickness designing apparatus for a multilayer optical filter according to 0. 12. A film thickness designing device for designing an optical film thickness of each optical layer in a multilayer optical filter formed by laminating a plurality of optical films, the device having a predetermined wavelength other than a preset excitation light wavelength band. Means for calculating a first error between a theoretical value representing the wavelength characteristic in the band using the optical film thickness of each optical film as a parameter and a target wavelength characteristic value in the corresponding predetermined wavelength band; and the pumping light wavelength band. When the transmittance corresponding to the target wavelength characteristic in is larger than the maximum transmittance allowed in the excitation light wavelength band, the wavelength characteristic in the excitation light wavelength band is set with the optical film thickness of each optical film as a parameter. Means for calculating a second error between the theoretical value represented and the target wavelength characteristic value in the corresponding pumping light wavelength band, and the calculated first and second errors are small. As described above, the optical film thickness designing device for designing the optical film thickness of each optical film by using fitting having a predetermined optical film thickness as an initial value. . 13. The design means, in the pumping light wavelength band, when the transmittance corresponding to the target wavelength characteristic value in the pumping light wavelength band is smaller than the maximum transmittance allowed in the pumping light wavelength band. 2. A means for setting a second error between the theoretical value representing the wavelength characteristic using the optical film thickness of each optical film as a parameter and the target wavelength characteristic in the corresponding pumping light wavelength band to be 0.
2. A film thickness designing apparatus for a multilayer optical filter according to 2. 14. A computer-executable program for designing an optical film thickness of each optical layer in a multilayer optical filter formed by laminating a plurality of optical films, the computer comprising a preset gain and the like. Means for calculating a first error between a theoretical value representing a predetermined wavelength characteristic in the wavelength band for equalization using the optical film thickness of each optical film as a parameter and a target wavelength characteristic value in the corresponding wavelength band for gain equalization. And a theoretical value representing the wavelength characteristic in the pumping light wavelength band other than the gain equalizing wavelength band as the optical film thickness of each optical film and a target wavelength characteristic value in the corresponding pumping light wavelength band. 2 means for calculating an error, and an optical film thickness of each of the optical films is set to an initial value of a predetermined optical film thickness so that the calculated first and second errors become smaller. A program characterized by causing it to function as a means for designing using fitting. 15. A computer-executable program for designing an optical film thickness of each optical layer in a multilayer optical filter comprising a plurality of optical films laminated, wherein the computer sets a preset excitation light. A means for calculating a first error between a theoretical value representing the wavelength characteristic in a predetermined wavelength band other than the wavelength band using the optical film thickness of each optical film as a parameter and a target wavelength characteristic value in the corresponding predetermined wavelength band. When the transmittance corresponding to the target wavelength characteristic value in the pumping light wavelength band is smaller than the minimum required transmittance in the pumping light wavelength band, the wavelength characteristic in the pumping light wavelength band is set to each of the optical values. Means for calculating a second error between the theoretical value representing the optical film thickness of the film as a parameter and the wavelength characteristic value in the corresponding pumping light wavelength band; The optical film thickness of each of the optical films is made to function as a means for designing using a fitting having an initial value of a predetermined optical film thickness so that the respective first and second errors are reduced. Program to do. 16. The pumping light wavelength band in the pumping light wavelength band when the transmittance corresponding to the target wavelength characteristic value in the pumping light wavelength band is higher than the minimum required transmittance in the pumping light wavelength band. A means for setting a second error between a theoretical value representing the wavelength characteristic using the optical film thickness of each optical film as a parameter and a target wavelength characteristic value in the corresponding pumping light wavelength band to be 0. 1
The program described in 5. 17. A computer-executable program for designing an optical film thickness of each optical layer in a multilayer optical filter comprising a plurality of optical films laminated, the computer comprising: A means for calculating a first error between a theoretical value representing the wavelength characteristic in a predetermined wavelength band other than the wavelength band using the optical film thickness of each optical film as a parameter and a target wavelength characteristic value in the corresponding predetermined wavelength band. When the transmittance corresponding to the target wavelength characteristic in the pumping light wavelength band is larger than the maximum transmittance allowed in the pumping light wavelength band, the wavelength characteristics in the pumping light wavelength band are set to the respective optical films. A means for calculating a second error between the theoretical value representing the optical film thickness of as a parameter and the target wavelength characteristic value in the corresponding pumping light wavelength band; It is characterized in that it functions as a means for designing the optical film thickness of each of the optical films by using a fitting whose initial value is a predetermined optical film thickness so that the first and second errors that have been produced are reduced. And the program. 18. The design means, in the pumping light wavelength band, when the transmittance corresponding to the target wavelength characteristic value in the pumping light wavelength band is smaller than the maximum transmittance allowed in the pumping light wavelength band. 2. A means for setting a second error between the theoretical value representing the wavelength characteristic using the optical film thickness of each optical film as a parameter and the target wavelength characteristic in the corresponding pumping light wavelength band to be 0.
7. The program described in 7. 19. A rare-earth-element-doped fiber for amplifying signal light, a pumping light source for generating pumping light for pumping the rare-earth-element-doped fiber, and the pumping. A multiplexer that combines the excitation light generated by a light source with the signal light and emits the excitation light to the rare earth element-doped fiber, and a pumping light emission side from the multiplexer and the signal light downstream. An optical amplifier comprising the multilayer film filter according to claim 1 disposed on the side. 20. A wavelength division multiplexing optical transmission system for transmitting a plurality of signal lights having mutually different wavelengths, the optical transmitter transmitting the plurality of signal lights to an optical transmission line, and the optical transmitter. 20. An optical amplifier according to claim 19, which collectively amplifies a plurality of signal lights transmitted and transmitted via the optical transmission line, and a plurality of optical amplifiers amplified via the optical amplifier and transmitted via the optical transmission line. And a light receiver for receiving the signal light of the wavelength division multiplexing optical transmission system. 21. A film thickness designing method for designing an optical film thickness of each optical layer in a multilayer optical filter formed by laminating a plurality of optical films, the method comprising: Calculating a first error between a theoretical value representing the wavelength characteristic with the optical film thickness of each of the optical films as a parameter and a target wavelength characteristic value in the corresponding gain equalizing wavelength band; A step of calculating a second error between a theoretical value representing the wavelength characteristic in the pumping light wavelength band other than the wavelength band using the optical film thickness of each optical film as a parameter and a target wavelength characteristic value in the corresponding pumping light wavelength band. And designing the optical film thickness of each optical film by using fitting with an initial value of a predetermined optical film thickness so that the calculated first and second errors are reduced respectively. A method of designing a film thickness of a multilayer optical filter, comprising: 22. A film thickness designing method for designing an optical film thickness of each optical layer in a multilayer optical filter formed by laminating a plurality of optical films, the method having a predetermined wavelength other than a preset excitation light wavelength band. Calculating a first error between a theoretical value representing the wavelength characteristic in the band using the optical film thickness of each optical film as a parameter and a target wavelength characteristic value in the corresponding predetermined wavelength band; and the pumping light wavelength band. In the case where the transmittance corresponding to the target wavelength characteristic value in is smaller than the minimum required transmittance in the excitation light wavelength band, the wavelength characteristics in the excitation light wavelength band are parameterized by the optical film thickness of each optical film. And a step of calculating a second error between the target wavelength characteristics in the corresponding pump light wavelength band and the calculated first and second errors, respectively. And a step of designing the optical film thickness of each of the optical films so that the optical film thickness becomes smaller, using a fitting having a predetermined optical film thickness as an initial value. . 23. In the designing step, when the transmittance corresponding to the target wavelength characteristic value in the pumping light wavelength band is higher than the minimum required transmittance in the pumping light wavelength band, the designing step in the pumping light wavelength band is performed. 7. A step of setting the second error between the theoretical value representing the wavelength characteristic using the optical film thickness of each optical film as a parameter and the target wavelength characteristic value in the corresponding pumping light wavelength band to 0. 22. A method for designing a film thickness of a multilayer optical filter according to 22. 24. A film thickness designing method for designing an optical film thickness of each optical layer in a multilayer optical filter formed by laminating a plurality of optical films, the predetermined wavelength other than a preset excitation light wavelength band. Calculating a first error between a theoretical value representing the wavelength characteristic in the band using the optical film thickness of each optical film as a parameter and a target wavelength characteristic value in the corresponding predetermined wavelength band; and the pumping light wavelength band. When the transmittance corresponding to the target wavelength characteristic in is larger than the maximum transmittance allowed in the excitation light wavelength band, the wavelength characteristic in the excitation light wavelength band is set with the optical film thickness of each optical film as a parameter. Calculating a second error between the theoretical value represented and the target wavelength characteristic value in the corresponding pumping light wavelength band; and calculating the first and second errors respectively. And a step of designing the optical film thickness of each of the optical films by using fitting having a predetermined optical film thickness as an initial value so as to be smaller. Method. 25. In the designing step, when the transmittance corresponding to the target wavelength characteristic value in the pumping light wavelength band is smaller than the maximum transmittance allowed in the pumping light wavelength band, the designing step in the pumping light wavelength band is performed. 25. The step of setting the second error between the theoretical value representing the wavelength characteristic using the optical film thickness of each of the optical films as a parameter and the target wavelength characteristic in the corresponding pumping light wavelength band to 0, 25. A method for designing a film thickness of the multilayer optical filter described.