JP4043788B2 - Multilayer optical filter thickness design apparatus, program, multilayer optical filter thickness design method, optical amplifier, and wavelength division multiplexing optical transmission system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present inventionMultilayer optical filter thickness design apparatus, program, multilayer optical filter thickness design method, optical amplifier, and wavelength division multiplexing optical transmission system used for optical communicationAbout.
[0002]
[Prior art]
With the advent of the broadband era, there is a need for further increases in data transmission volume, and there is a great expectation for WDM (Wavelength Division Multiplexing) communication systems that multiplex and transmit optical signals of different wavelengths. ing.
[0003]
  As one of key devices in this WDM communication system, an optical amplifier such as an EDFA (Erbium Doped Fiber Amplifier) that can amplify the multiplexed optical signal without performing photoelectric conversion has been developed.
[0004]
  By the way, in the WDM transmission system, if there is a level deviation in the transmitted signal light of each wavelength, the optical signal may deteriorate and the transmission distance and transmission band may be reduced. Therefore, when using an optical amplifier such as an EDFA, it is required to flatten (equalize) the gain characteristics in the transmission wavelength band at the output.
[0005]
  In this respect, the gain characteristic in 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 equalization filter (GFF; Gain) having a light transmission loss characteristic that is opposite to the gain characteristic of the optical amplifier in the transmission wavelength band. The gain characteristics of the optical amplifier are equalized by combining a flattening filter with the optical amplifier (see FIG. 21).
[0006]
  As this GFF, a fiber grating, an etalon filter, a multilayer filter, or the like is used. For an optical amplifier for mass production, a multilayer optical filter (hereinafter also referred to as a multilayer filter) excellent in mass productivity is used. .
[0007]
  In this specification, “multilayer” is used to mean a plurality of layers.
[0008]
  FIG. 22 is a graph showing a design target (target) loss characteristic (GFF specification: ◇) of the multilayer filter described above, a loss characteristic (solid line) based on the design value of the multilayer filter, and a loss deviation (□) of both. is there. The flatness (Flatness), which is a measure of loss deviation, is a value obtained by subtracting the minimum deviation from the maximum deviation.
[0009]
  As shown in FIG. 22, the multilayer filter has a target loss characteristic (GFF required loss) that is opposite to the gain characteristic of the optical amplifier in the transmission wavelength band (for example, 1530 nm to 1565 nm) of the corresponding optical amplifier in the preceding stage. Characteristic), and the design value of GFF is designed / manufactured by bringing it close to the above-mentioned GFF required loss characteristic.
[0010]
[Problems to be solved by the invention]
By the way, in an optical amplifier, there may be a request to output pumping light for optical amplification through the GFF or a request to output the pumping light after blocking it.
[0011]
  In this regard, it is considered to transmit / block (transmit and / or block) the pump light using a conventional GFF.
[0012]
  However, the wavelength band of pump light for optical amplification (for example, around 1450 nm in the case of the pump light wavelength band of EDFA) is different from the transmission wavelength band (1530 nm to 1565 nm) of the normal optical amplifier described above. For this reason, a GFF having a transmission loss characteristic {(designed by a solid line (no PP [Pump Pass]) in FIG. 22) designed simply by targeting the GFF required loss characteristic is in the wavelength band corresponding to the transmission loss characteristic. , It does not have the property of transmitting / blocking the pump light.
[0013]
  For example, as shown in FIG. 22, sufficient transmission characteristics (for example, -1 dB or more) are not obtained in the wavelength band (near 1450 nm) of the pump light for optical amplification.
[0014]
  Therefore, the pump light transmission / blocking request for the multilayer filter (GFF) having the gain equalization function cannot be satisfied.
[0015]
  The present invention has been made in view of the above circumstances, and is a multilayer filter having both a gain equalization function and a pump light transmission / cutoff function.Multilayer optical filter thickness design apparatus, program, multilayer optical filter thickness design method, optical amplifier, wavelength division multiplexing optical transmission systemThe purpose is to provide.
[0016]
[Means for Solving the Problems]
According to a first aspect of the invention,A film thickness designing apparatus for designing an optical film thickness of a multilayer optical filter formed by laminating a plurality of optical films, wherein a predetermined wavelength characteristic in a preset wavelength band for gain equalization is expressed by the optical characteristics of each optical film. Means for calculating a first error between a theoretical value representing the film thickness as a parameter and a target wavelength characteristic value in the corresponding gain equalizing wavelength band; and in a pumping light wavelength band other than the gain equalizing wavelength band Means for calculating a second error between the theoretical value representing the wavelength characteristic as a parameter of the optical film thickness of each optical film and the target wavelength characteristic value in the corresponding excitation light wavelength band, and the calculated first and first Means for designing the optical film thickness of each of the optical films using a fitting having a predetermined optical film thickness as an initial value so that the error of 2 is reduced.ing.
[0017]
  According to a second aspect of the invention,A film thickness design apparatus for designing an optical film thickness of each optical layer in a multilayer optical filter formed by laminating a plurality of optical films, and having wavelength characteristics in a predetermined wavelength band other than a preset excitation light wavelength band Means for calculating 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 in the excitation light wavelength band When the transmittance corresponding to the characteristic value is smaller than the minimum necessary transmittance 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 Means for calculating a second error between wavelength characteristic values in the corresponding excitation light wavelength band, and Means for designing the optical film thickness of each of the optical films using a fitting having a predetermined optical film thickness as an initial value so that the first and second errors are reduced.ing.
[0018]
  According to a third aspect of the invention,When the transmittance corresponding to the target wavelength characteristic value in the pumping light wavelength band is greater than the minimum necessary transmittance in the pumping light wavelength band, the design means sets the wavelength characteristics in the pumping light wavelength band to the respective wavelength characteristics. Means for setting 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 excitation light wavelength band to zeroing.
[0019]
  According to a fourth aspect of the present invention, there is provided a film thickness designing apparatus for designing an optical film thickness of each optical layer in a multilayer optical filter formed by laminating a plurality of optical films, wherein a preset excitation light wavelength is provided. Means for calculating a first error between a theoretical value representing a wavelength characteristic in a predetermined wavelength band other than the band as a parameter and an 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 excitation light wavelength band is larger than the maximum transmittance allowed in the excitation light wavelength band,The theoretical value representing the wavelength characteristics in the excitation light wavelength band as a parameter of the optical film thickness of each optical film and the corresponding excitation light wavelength bandGoalThe means for calculating the second error between the wavelength characteristic values, and the optical film thickness of each optical film, the predetermined optical film thickness being an initial value so that the calculated first and second errors are reduced, respectively. And designing means for designing using the fitting.
[0020]
  According to a fifth aspect of the present invention, the design means includes the excitation light wavelength band.GoalThe transmittance corresponding to the wavelength characteristic value isMaximum allowedWhen the transmittance is smaller than the transmittance, the wavelength characteristic in the excitation light wavelength band is a theoretical value representing the optical film thickness of each optical film as a parameter and the corresponding excitation light wavelength band.GoalSecond error between wavelength characteristics0 andMeans to do.
[0021]
  According to the sixth aspect of the present invention, the optical film thickness of each optical layer in the multilayer optical filter formed by laminating a plurality of optical films is designed.Computer-executable program forBecauseComputerPresetPredetermined in the wavelength band for gain equalizationMeans for calculating a first error between a theoretical value expressing the wavelength characteristic as a parameter of the optical film thickness of each optical film and a target wavelength characteristic value in a corresponding gain equalization wavelength band;Other than the wavelength band for gain equalizationMeans for calculating a second error between a theoretical value representing the wavelength characteristic in the pumping light 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; Means for designing the optical film thickness of each optical film using a fitting having a predetermined optical film thickness as an initial value so that the first and second errors are reduced.Is functioning as.
[0022]
  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, the computer comprising: Preset excitation light wavelength bandOther thanPredeterminedIn the wavelength bandMeans for calculating a first error between a theoretical value representing a wavelength characteristic as a parameter of an optical film thickness of each optical film and a target wavelength characteristic value in a corresponding predetermined wavelength band; and the excitation light wavelength bandGoal inwavelengthWhen the transmittance corresponding to the characteristic value is smaller than the minimum necessary transmittance in the excitation light wavelength band,Wavelength characteristics in the excitation light wavelength bandSaidMeans for calculating the optical thickness of each optical film as a parameter and means for calculating a second error between the corresponding wavelength characteristic values in the excitation light wavelength band, and the calculated first and second errors are reduced respectively. As described above, the optical film thickness of each optical film is made to function as a means for designing using a fitting having a predetermined optical film thickness as an initial value.ing.
[0023]
  According to an eighth aspect of the present invention,The design means includes a target wavelength in the excitation light wavelength band. When the transmittance corresponding to the characteristic value is larger than the minimum necessary transmittance in the excitation light wavelength band, the theoretical value representing the wavelength characteristic in the excitation light wavelength band as a parameter of the optical film thickness of each optical film, and Means are provided for setting the second error between the target wavelength characteristic values in the corresponding excitation light wavelength band to zero..
[0024]
  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,
  The computer calculates a wavelength characteristic in a predetermined wavelength band other than a preset excitation light wavelength band 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 predetermined wavelength band. Means for calculating the first error of
  When the transmittance corresponding to the target wavelength characteristic in the excitation light wavelength band is larger than the maximum transmittance allowed in the excitation light wavelength band, the wavelength characteristic in the excitation light wavelength band is changed to the optical property of each optical film. Means for calculating a second error between a theoretical value representing the film thickness as a parameter and a target wavelength characteristic value in a corresponding excitation light wavelength band;
  The optical film thickness of each optical film is caused to function as a means for designing using a fitting with a predetermined optical film thickness as an initial value so that the calculated first and second errors are reduced.
[0025]
  According to a tenth aspect of the present invention,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 design means sets the wavelength characteristics in the pumping light wavelength band to the respective wavelength characteristics. Means for setting second error between theoretical value representing optical film thickness of optical film as parameter and target wavelength characteristic in corresponding excitation light wavelength band to zeroIt has.
[0026]
  According to an eleventh aspect of the present invention,A film thickness design method for designing an optical film thickness of each optical layer in a multilayer optical filter formed by laminating a plurality of optical films, wherein predetermined wavelength characteristics in a preset wavelength band for gain equalization are Calculating a first error between a theoretical value representing the optical film thickness of the optical film as a parameter and a target wavelength characteristic value in a corresponding gain equalization wavelength band; and excitation other than the gain equalization wavelength band Calculating a second error between a theoretical value representing the wavelength characteristic in the optical wavelength band as a parameter of the optical film thickness of each optical film and a target wavelength characteristic value in the corresponding excitation light wavelength band; and Designing the optical film thickness of each optical film using a fitting with a predetermined optical film thickness as an initial value so that the first and second errors are reduced, respectively.I have.
[0027]
  According to a twelfth aspect of the present invention, there is provided a film thickness design method for designing an optical film thickness of each optical layer in a multilayer optical filter formed by laminating a plurality of optical films,
  A first characteristic value between a theoretical value representing a wavelength characteristic in a predetermined wavelength band other than a preset excitation light wavelength band as a parameter of an optical film thickness of each optical film and a target wavelength characteristic value in the corresponding predetermined wavelength band. Calculating the error of
  When the transmittance corresponding to the target wavelength characteristic value in the excitation light wavelength band is smaller than the minimum necessary transmittance in the excitation light wavelength band,Wavelength characteristics in the pumping light wavelength band are theoretical values representing the optical film thickness of each optical film as a parameter, and in the corresponding pumping light wavelength band.Between target wavelength characteristicsA step of calculating the second error, and fitting with the optical film thickness of each optical film as an initial value so that the calculated first and second errors are reduced. Using and designing steps.
[0028]
  According to a thirteenth aspect of the present invention,In the design step, when the transmittance corresponding to the target wavelength characteristic value in the excitation light wavelength band is larger than the minimum necessary transmittance in the excitation light wavelength band, the wavelength characteristics in the excitation light wavelength band The optical film thickness of the optical film is a parameter. The second error between the theoretical value expressed as data and the target wavelength characteristic value in the corresponding excitation light wavelength band is set to zero.
[0029]
  According to a fourteenth aspect of the present invention, there is provided a film thickness design method for designing an optical film thickness of each optical layer in a multilayer optical filter formed by laminating a plurality of optical films,
  A first characteristic value between a theoretical value representing a wavelength characteristic in a predetermined wavelength band other than a preset excitation light wavelength band as a parameter of an optical film thickness of each optical film and a target wavelength characteristic value in the corresponding predetermined wavelength band. And calculating a target error in the excitation light wavelength band.Wavelength characteristicsWhen the transmittance corresponding to is larger than the maximum transmittance allowed in the excitation light wavelength band, the wavelength characteristic in the excitation light wavelength band and the theoretical value representing the optical film thickness of each optical film as a parameter and the corresponding The step of calculating the second error between the target wavelength characteristic values in the excitation light wavelength band, and the optical film thickness of each of the optical films is set to a predetermined value so that the calculated first and second errors are reduced. And a step of designing using fitting with an optical film thickness as an initial value.
[0030]
  According to the fifteenth aspect of the present invention, in the design step, when the transmittance corresponding to the target wavelength characteristic value in the excitation light wavelength band is smaller than the maximum transmittance allowed in the excitation light wavelength band, A step of setting a second error between a theoretical value representing the wavelength characteristic in the excitation light wavelength band as a parameter and an optical film thickness of each optical film and a target wavelength characteristic in the corresponding excitation light wavelength band is zero.
[0031]
  According to a sixteenth aspect of the present invention, a rare earth element-doped fiber provided on an optical transmission line for amplifying signal light, comprising a fiber doped with a rare earth element;
  An excitation light source for generating excitation light for exciting the rare earth element-doped fiber; and provided on the optical transmission line, the excitation light generated by the excitation light source is combined with the signal light, and the excitation light is combined with the rare earth element. A multiplexer that emits light to the element-doped fiber, and a multilayer optical filter provided on the upstream side or the downstream side of the rare earth element-doped fiber on the optical transmission line, and the multilayer optical filter includes the above film It is formed by a thickness design device or designed and formed by the above-described film thickness design method.
[0032]
  According to a seventeenth aspect of the present invention, there is provided a wavelength division multiplexing optical transmission system that transmits a plurality of signal lights having different wavelengths, and an optical transmitter that transmits the plurality of signal lights to an optical transmission line; 17. The optical amplifier according to claim 16, wherein a plurality of signal lights transmitted from the optical transmitter and transmitted through the optical transmission path are collectively amplified, and the optical transmission path is amplified through the optical amplifier. And an optical receiver for receiving a plurality of signal lights transmitted through the optical receiver.
0033]
DETAILED DESCRIPTION OF THE INVENTION
  (First embodiment)
  FIG. 1 is a diagram showing a multilayer filter 1 according to the first embodiment of the present invention.
0034]
  As shown in FIG. 1, a multilayer filter 1 includes a 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. ). Of the plurality of thin film layers 3a1 to 3aN, the refractive index of the film material of the thin film layer of the odd-numbered layers (first layer 3a1, third layer 3a3,..., Second N-1 layer,. And the refractive index of the film material of the thin film layers of the even layers (second layer 3a2, fourth layer 3a4,..., Second N layer,...) From the substrate 2 side are different from each other.
0035]
  Each thin film layer constituting the plurality of thin film layers 3, that is, the optical film thickness that is the product of the physical film thicknesses d1 to dN and the refractive indexes n1 to nN of the first layer 3a1 to the Nth layer 3an is a film described later. Each thin film layer is accurately designed based on the thickness design process.
0036]
  FIG. 2 is a diagram showing a hardware configuration of the film thickness design apparatus 10 for designing the optical film thickness of each of the thin film layers 3a1 to 3aN of the multilayer filter 1 shown in FIG.
0037]
  As shown in FIG. 2, the film thickness design apparatus 10 is a computer system, and an input unit 11 that can be inputted by a designer to input information, a computer 12 connected to the input unit 11, and a computer 12 A memory 13 as a storage medium that is connected so as to be communicable and prestores a program P for executing a film thickness design process to be described later, and an external input / output interface 14 that performs an interface process related to external input / output I have. As the storage medium, various storage media such as a semiconductor memory and a magnetic memory are applicable.
0038]
  The memory 13 also includes a theoretical data file 20 including theoretical data representing theoretical values of light transmittance at continuous wavelengths of the N-layer multilayer filter 1, and a target light transmission loss value (target) required as GFF. Value) and 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) in a pump light transmission wavelength band (for example, 1460 nm to 1495 nm). ing.
0039]
  Hereinafter, the theoretical formula data stored in the theoretical formula data file 20 will be described.
0040]
  The theoretical expression of the light transmittance of the N-layer multilayer filter 1 with the optical film thickness of each of the layers 3a1 to 3aN as a parameter assumes that the incident angle is perpendicular to the film surface of the multilayer filter 1, and the following formula (1 ) And the following equations (2) to (5).
[0041]
[Expression 1]
[0042]
[Expression 2]
[0043]
[Equation 3]
[0044]
[Expression 4]
[0045]
[Equation 5]
[0046]
  Here, τ in equation (1) is expressed by equation (2), and parameter m shown in equation (2)₁₁, M₁₂, M_{twenty one}, M_{twenty two}Are the elements of the characteristic matrix M in all N layers given by Equation (3), and M_j(J is an integer that increases by 1 from 1 to N in order, such as 1, 2,...), And the characteristic matrix M of the j-th layer_jIs given by equation (4). G shown in Formula (4)_jIs represented by the formula (5), and n_jIs the complex refractive index of the jth layer, d_jIs the physical film thickness of the jth layer.
0047]
  Further, the wavelength for obtaining the transmittance is substituted for λ in the equation (5), and n₀, N_sAre respectively the complex refractive index of the medium and the complex refractive index of the filter substrate 2 at the wavelength λ. In the formula (1), τ^*Is a conjugate complex number of τ, and i in the equations (3) and (4) is an imaginary unit.
0048]
  Therefore, by using these formulas (1) to (5), the optical transmittance value at the continuous wavelength of the multilayer filter 1 of the N layers is used with the value of the optical film thickness of the jth layer as a parameter. If a value 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).
0049]
  That is, the theoretical formula data file 21 stores a theoretical formula representing the light transmission loss value (insertion loss value) IL as the theoretical formula data DA.
0050]
  Next, the overall operation of this embodiment will be described.
0051]
  In manufacturing the multilayer filter 1, first, the optical film thickness of each layer 3a1 to 3an of the multilayer filter 1 is designed (step S1).
0052]
  That is, the designer inputs the target transmission loss value (data) IL (λi) to the computer 12 via the input unit 11 of the film thickness design apparatus 10. The target transmission loss value (data) IL (λi) represents the target transmission loss characteristic of the pump light and the target transmission loss characteristic of the GFF, respectively. 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 nm), each discontinuous wavelength λi (i is an integer that increases from 1 to N in order, i = 1, 2, 3, .., N-1 and N) are the specification loss values for the pump light transmission and the GFF.
0053]
  Furthermore, the designer pumps the cutoff band 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 the film thickness parameter) a. A value that does not overlap the light transmission wavelength band (1460 nm to 1495 nm) is input (step S1).
0054]
  The computer 12 operates according to the program P, and receives the input target transmission loss characteristic value IL (λi) and the film thickness parameter a (initial value). Then, the computer 12 stores the film thickness parameter a in the memory 13 and stores the target transmission loss characteristic value IL (λi) in the target transmission loss value data file 21 (step S11).
0055]
  FIG. 5 is a graph showing a target transmission loss characteristic (target transmission characteristic) T1 of the pump light in the characteristic wavelength band, a target transmission loss characteristic T2 of the GFF, and a transmission loss profile PR (a) corresponding to the initial value of the optical film thickness. It is.
0056]
  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 a band exceeding 1570 nm and an edge portion on the short wavelength side of the cutoff band. Is set to the initial value of the transmission loss characteristic of the GFF portion, it can be seen that the cutoff band does not overlap the pump light transmission wavelength band (1460 nm to 1495 nm).
0057]
  Next, the computer 12 sets the variable n to 0 (step S12), increments the variable n by 1 (step S13), and sets the wavelength parameter λn in the characteristic wavelength band to λi. Since n = 1 at this time, λn = λ1 (step S14).
0058]
  Next, the computer 21 reads the theoretical formula data stored in the theoretical formula data file 21 of the memory 42 and inputs the film thickness parameter a (initial value) to the read theoretical formula data DA. Then, the computer 21 obtains the insertion loss value IL (λn, a) of the multilayer film 3 using the film thickness parameter a and the wavelength λn as variables. Subsequently, the computer 21 calculates the square error E between the insertion loss value IL (λn, a) of the multilayer film 3 and the target transmission loss value IL (λn) of the entire multilayer film 3 at the corresponding wavelength λn._n(A):
[0059]
[Formula 6]
[0060]
  And the square error E of the obtained multilayer film 3 as a whole_n(A) is stored in the memory 13 (step S15).
0061]
  Next, the computer 12 determines whether or not n> N (step S16). Now, since n = 1, the determination in step S16 is NO, and the computer 12 returns to step S13, increments n by 1, and executes the processes in and after step S13.
0062]
  That is, the computer 12 repeatedly executes the processes of steps S13 to S16 described above until n> N, that is, until the process of step S15 based on the wavelength parameter λn = λN is completed.
0063]
  As a result, the target transmission loss value IL (λn) at the wavelength λn corresponding to the theoretical light transmission loss value IL (λn, a) in the entire characteristic wavelength band with the film thickness parameter a (initial value) in each of the layers 3a1 to 3N. Square error E_n(A) is obtained for each wavelength.
0064]
  When n> N, the process of step S16 is YES, and the computer 12 determines the square error E of the entire multilayer film 3 in the obtained entire characteristic wavelength band._nThe addition average value (square average error, square error average value) of (a) is calculated according to the following equation (7), and the calculated mean square error in the wavelength parameter a is stored in the memory 13 (step S17).
0065]
[Expression 7]
0066]
  Next, based on the square average error in the calculated wavelength parameter a, the computer 12 converges the value of the square average error or determines the current optical film thickness values a (1) to a (N). Loss deviation (flatness) between the transmission loss value IL (λ1 to λN, a (1) to a (N)) of the entire multilayer film 3 used and the corresponding target transmission loss value IL (λ1 to λN) is a constant value. It is determined whether or not (for example, 1 dB) or less (step S18).
0067]
  As a result of the determination in step S18, NO (when the mean square error value is non-convergent and the loss deviation exceeds a certain value), the computer 12 determines the film thickness of at least one of the optical film layers 3a1 to 3aN. The parameter a is changed (step S19), the process returns to step S12, and the fitting process of steps S12 to S19 is repeated and executed until the result of determination in step S18 becomes YES.
0068]
  That is, the computer 12 corresponds to the transmission loss values IL (λ1 to λN, a (1) to a (N)) of the entire multilayer film 3 using the current optical film thickness values a (1) to a (N). The fitting process in steps S12 to S19 is repeated until the film thickness parameter a of the optical film layers 3a1 to 3aN is changed for each layer until the target transmission loss value IL (λ1 to λN) is sufficiently close. When the error value converges, or the transmission loss values IL (λ1 to λN, a (1) to a (a) of the entire multilayer film 3 using the current optical film thickness values a (1) to a (N). N)) and the corresponding transmission loss value IL (λ1 to λN) corresponding to the loss deviation become a certain value or less (step S18 → YES), the process is terminated.
0069]
  In the fitting process, in this embodiment, the cutoff band of the transmission loss profile PR (a) corresponding to the initial value of the optical film thickness does not overlap with the pump light transmission wavelength band (1460 nm to 1495 nm). Fitting can be performed well for the wavelength band.
0070]
  For example, as in the normal GFF design, a center wavelength is set at the center of the wavelength band (1529 nm to 1561 nm) for the transmission loss characteristics of the GFF, and the transmission loss profile PR (b corresponding to the initial value of the optical film thickness is set. ) Is set to the initial value of the target transmission loss characteristic T2 in the edge part on the long wavelength side of the cut-off band, it is possible to perform good fitting in the optical transmission loss characteristic part of the GFF.
0071]
  However, in the initial value setting similar to that of the normal GFF, the cutoff band overlaps with the pump light transmission wavelength band (1460 nm to 1495 nm) as shown in FIG. It becomes difficult.
0072]
  Therefore, as an initial value of each optical film thickness described in this embodiment, by using a value whose cutoff band does not overlap with the pump light transmission wavelength band (1460 nm to 1495 nm), in addition to the light transmission loss characteristic portion of GFF Good fitting can also be performed in the pump light transmission wavelength band.
0073]
  When the film thickness parameters a (1) to a (N) for each layer are optimized in this way, the computer 12 causes the optimized film thickness parameters a (1) to a (N) for each layer to be optimized. That is, the optical film thickness values a (1) to a (N) optimally set (designed) for the layers 3a1 to 3aN of the multilayer filter 1 are stored in the memory 13.
0074]
  When the optical film thickness values a (1) to a (N) are optimally set for the respective layers 3a1 to 3aN in this way, the optimally designed optical film thickness values a (1) to a ( The film forming process is executed while controlling the film thickness using N) (step S2).
0075]
  In this film forming process, a film forming material is deposited on the substrate 2 by vapor deposition or sputtering. At this time, the thin film being formed is irradiated with monitoring light, and the transmitted light is monitored, for example, so that the optical film thickness of the thin film being formed matches the optimally designed optical film thickness. Thickness controlled. This film formation process (film thickness control process) is executed by a film formation apparatus including a computer based on each of the optimized optical film thickness values a (1) to a (N).
0076]
  As described above, according to the present embodiment, the initial value of each optical film thickness is determined so that the cutoff band of the transmission loss characteristic based on the initial value does not overlap with the pump light transmission wavelength band (1460 nm to 1495 nm). The short wavelength side edge portion of the cutoff band is set to the initial value of the transmission loss characteristic of the GFF portion. For this reason, the optical film thickness of each thin film layer 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 multi-functional multilayer filter 1 having both the target transmission loss characteristic T1 of the pump light and the target transmission loss characteristic T2 of GFF can be provided.
0077]
  In this embodiment, by increasing the optical film thickness of each layer and narrowing the cutoff bandwidth of the transmission loss characteristic based on the initial value, the initial value a1 is set to the initial value as shown in FIG. The cutoff band of the transmission loss characteristic PR (a1) based on the value a1 does not overlap the pump light transmission wavelength band (1460 nm to 1495 nm), and the central wavelength of the transmission loss characteristic is the wavelength band for the transmission loss characteristic of the GFF ( It is also possible to set it at the center of 1529 nm to 1561 nm.
0078]
  (Second Embodiment)
  It is a figure which shows the hardware constitutions of 10 A of film thickness design apparatuses of this embodiment.
0079]
  In the present embodiment, a program PA for executing the film thickness design process and a film thickness design process (see FIG. 9) executed by the computer 12 based on the program PA are different from the configuration of the first embodiment.
0080]
  Further, the memory 13A of the present embodiment includes a maximum insertion loss IL allowed in the pump light transmission wavelength band (1460 nm to 1495 nm)._maxIs the minimum transmittance data T converted to transmittance_minIs stored in advance.
0081]
  Since the other points are the same as those of the first embodiment, the description thereof is omitted.
0082]
  In the present embodiment, when executing the film thickness design process, the computer 12 operates according to the program PA, and performs the processes of steps S11 to S14 as in the first embodiment.
0083]
  Next, the computer 12 determines whether or not the parameter wavelength λn is the pump light transmission wavelength band (step S20).
0084]
  As a result of this determination, that is, while the parameter wavelength λn is not in the pump light transmission wavelength band, the processing of Step S12 to Step S14, Step S20, and Step S15 to Step S16 is repeatedly performed as in the first embodiment. . As a result, the wavelength λ corresponding to the insertion loss value IL (λn, a) of the entire multilayer film 3 is obtained._nMean square error E with the target transmission loss value IL (λn) of the entire multilayer film 3 at_n(A) is stored in the memory 13.
0085]
  On the other hand, when the increment of n is repeated and the parameter wavelength λn is included in the pump light transmission wavelength band 1460 nm to 1495 nm, the determination in step S20 is YES, and the computer 12 sets the target transmission loss value IL (λn). The target transmittance T (λn) converted into the transmittance is the minimum transmittance data T stored in the allowable minimum transmittance data file 25._minIt is determined whether or not the above is true (step S21).
0086]
  As a result of the determination in step S21, NO, that is, the target transmittance T (λn) is the minimum transmittance data T stored in the allowable minimum transmittance data file 25._minIf not, the process proceeds to step S15, and the square error E between the insertion loss value IL (λn, a) of the multilayer film 3 and the target transmission loss value IL (λn) is obtained by the above-described processing._n(A) is calculated and stored in the memory 13.
0087]
  On the other hand, as a result of the determination in step S21, that is, the target transmittance T (λn) is the minimum transmittance data T stored in the allowable minimum transmittance data file 25._minIn the above case, the square error E of this part_n(A) is set to 0 (step S22).
0088]
  Next, the computer 12 proceeds to the process of step S16, and until n> N, the above-described steps S13, S14, S20, S15 to S16 (when the wavelength parameter λn is other than the pump light transmission wavelength band), step S13 S14, S20 to S21, and S15 to S16 (the wavelength parameter λn is within the pump light transmission wavelength band and the target transmittance T (λn) is the minimum transmittance data T_minSteps S13 to S14 and S20 to S22 (the wavelength parameter λn is within the pump light transmission wavelength band and the target transmittance T (λn) is the minimum transmittance data T)_min) Is repeated.
0089]
  Thereafter, as in the first embodiment, when n> N, the process of step S16 is YES, and the computer 12 calculates the square error E of the entire multilayer film 3 in the obtained entire characteristic wavelength band._nThe addition average value (square average error, square error average value) of (a) is calculated and stored in the memory 13 (step S17).
0090]
  Next, based on the square average error in the calculated wavelength parameter a, the computer 12 converges the value of the square average error or determines the current optical film thickness values a (1) to a (N). Loss deviation (flatness) between the transmission loss value IL (λ1 to λN, a (1) to a (N)) of the entire multilayer film 3 used and the corresponding target transmission loss value IL (λ1 to λN) is a constant value. It is determined whether or not (for example, 1 dB) or less (step S18).
0091]
  As a result of the determination in step S18, NO (when the mean square error value is non-convergent and the loss deviation exceeds a certain value), the computer 12 determines the film thickness of at least one of the optical film layers 3a1 to 3aN. The parameter a is changed (step S19), the process returns to step S12, and the processes of steps S12 to S19 and S20 to S22 are repeated until the determination result of step S18 is YES.
0092]
  That is, the computer 12 corresponds to the transmission loss values IL (λ1 to λN, a (1) to a (N)) of the entire multilayer film 3 using the current optical film thickness values a (1) to a (N). The fitting process in steps S12 to S19 is repeated until the film thickness parameter a of the optical film layers 3a1 to 3aN is changed for each layer until the target transmission loss value IL (λ1 to λN) is sufficiently close. When the error value converges, or the transmission loss values IL (λ1 to λN, a (1) to a (a) of the entire multilayer film 3 using the current optical film thickness values a (1) to a (N). N)) and the corresponding transmission loss value IL (λ1 to λN) corresponding to the loss deviation become a certain value or less (step S18 → YES), the process is terminated.
0093]
  At this time, in this embodiment, the target transmittance T (λn) is the minimum transmittance data T within the pump light transmission wavelength band._minIs exceeded, the mean square error between the insertion loss value IL (λN, a) of the entire multilayer film 3 and the target transmission loss value IL (λN) is forcibly set to 0, and the deviation (ripple) of this portion is forced. ) Is allowed. And the ripple in this pump light transmission wavelength band is permitted, and the fitting characteristic of other light transmission loss bands (for example, the light transmission loss band of strict GFF) is improved.
0094]
  That is, the film thickness design apparatus 10A of the present embodiment is particularly effective when the specifications for the flatness of the light transmission loss characteristics of the GFF portion are strict.
0095]
  In order to verify the effect of the present embodiment, the present inventors used the multilayer filter 1 according to the specifications shown in Table 1 below as the multilayer film design apparatus 10 of the first embodiment and the second multilayer film design. Each device 10A was actually designed, and the design results are shown in FIGS. 10 (a) and 10 (b) and FIGS. 11 (a) and 11 (b), respectively.
0096]
  10 (a) and 10 (b) and FIGS. 11 (a) and 11 (b) differ in the total number N of multilayer films (multilayer film filter 1A → N in FIGS. 10 (a) and 10 (b)). = 46; multilayer filter 1B → N = 26 in FIGS. 11 (a) and 11 (b).
0097]
[Table 1]
[0098]
  FIG. 10A shows a design target (target) loss characteristic of the multilayer filter 1A obtained by the film thickness design based on the film thickness design apparatus 10 of the first embodiment (a target in the GFF target and the pump light transmission wavelength band: ◇), loss characteristics (solid line) based on the design value of the multilayer filter 1A, and loss deviation (□) between the target value and the design value. The target in the pump light transmission wavelength band was set to 0 dB.
0099]
  As shown in FIG. 10A, in the film thickness design of the first embodiment, the flatness of the GFF portion was 0.24 dB, and the required flatness of the GFF portion: 0.2 dB or less could not be satisfied. As described above, this is considered to be an influence of fitting in the pump light transmission wavelength band.
[0100]
  On the other hand, FIG. 10B shows a design target (target) loss characteristic (GFF target in the pump light transmission wavelength band) of the multilayer filter 1B obtained by the film thickness design based on the film thickness design apparatus 10A of the second embodiment. 3 is a graph showing loss characteristics (solid line) based on design values of the multilayer filter 1B and 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. Maximum insertion loss IL_max(Minimum transmittance data T_min) Was set to 0.6 dB.
[0101]
  As shown in FIG. 10B, 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 has the minimum transmittance data T._minSince the square error between the target value and the design value in the case of having a transmittance exceeding 1 is set to 0, a ripple corresponding to that is generated. However, the specification of this ripple part sufficiently satisfies the above specification because the allowable range is as large as 0.8 dBpp or less between the maximum value and the minimum value {between pp (peak to peak)}. Further, the flatness of the GFF portion was 0.19 dB, and the required flatness of the GFF portion: 0.2 dB or less could be satisfied.
[0102]
  Similarly, FIG. 11A shows a design target loss characteristic (GFF target, target in the pump light transmission wavelength band) of the multilayer filter 1B obtained by the film thickness design based on the film thickness design apparatus 10 of the first embodiment: ◇) is a graph showing loss characteristics (solid line) based on the design value of the multilayer filter 1B and loss deviation (□) between the target value and the design value. The target in the pump light transmission wavelength band was set to 0 dB.
[0103]
  As shown in FIG. 11A, in the film thickness design of the first embodiment, the flatness of the GFF portion is 0.265.dB, and the required flatness of the GFF portion: 0.2 dB or less could not be satisfied. This is also considered to be the influence of fitting in the pump light transmission wavelength band.
[0104]
  On the other hand, FIG. 11B shows a design target loss characteristic (GFF target, target in the pump light transmission wavelength band) of the multilayer filter 1B obtained by the film thickness design based on the film thickness design apparatus 10A of the second embodiment: ), And a loss characteristic (solid line) based on the 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. Maximum insertion loss IL_max(Minimum transmittance data T_min) Was set to 0.6 dB.
[0105]
  Similarly to FIG. 10B, FIG. 11B also shows a loss characteristic (solid line) based on the design value in the pump light transmission wavelength band in the film thickness design of the second embodiment. Has occurred. However, since the specification of the 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 portion was 0.20 dB, and the required flatness of the GFF portion: 0.2 dB or less could be satisfied.
[0106]
  And according to the film thickness design based on the film thickness design apparatus 1A of the present embodiment, the allowable maximum insertion loss IL in the pump light transmission wavelength band_max(Minimum transmittance data T_min) Setting is increased (minimum transmittance data T_minThe degree of freedom of film thickness fitting increases and the flatness characteristic can be improved. If the ripple in the transmission band is allowed up to about 1 dB, the value of Fitness becomes 0.18 dB, and flatness characteristics equivalent to the normal design GFF not considering pump light transmission can be obtained (see FIG. 12).
[0107]
  In the first and second embodiments, the transmission wavelength band of the transmitted pump light is 1450 nm to 1495 nm. However, the present invention is not limited to this, and the pump light transmission wavelength band is not limited to this. It is also possible to design to transmit pump light in a wavelength band, for example, 980 nm band.
[0108]
  FIG. 13A shows design values of a multilayer filter having predetermined light transmission characteristics with respect to the pump light wavelength band of 980 nm band and predetermined light transmission loss characteristics in the GFF portion (1529 nm to 1561 nm) (second embodiment). It is a graph which shows the loss characteristic (solid line) based on the film thickness design of this. FIG. 13B is an enlarged graph showing the light transmission characteristics of the portion shown as (b) in FIG. 13A, that is, the 980 nm band. 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).
[0109]
  As shown in FIGS. 13A to 13C, even if the pump light transmission band is different, a multilayer filter having both the pump light transmission function and the gain loss transmission loss function can be designed. . In the first and second embodiments, a multilayer filter having a pump light transmission function and a GFF function for transmitting pump light in a predetermined pump light transmission wavelength band is designed. However, the present invention is limited to this. Instead, it is also possible to design a multilayer filter having both a pump light blocking function and a GFF function for blocking pump light in a predetermined pump light blocking wavelength band by the same design method as in the first and second embodiments. is there.
[0110]
  In particular, in the second embodiment, in place of or in addition to the allowable minimum transmittance data file 25 in the memory 13A, a pump light cut-off wavelength band (cut-off wavelength band having a central wavelength of 1480 nm; for example, 1460 nm ˜1520 nm) minimum insertion loss IL allowed_minIs the maximum transmittance data T converted to transmittance_maxThe allowable maximum transmittance data file 25 'including
[0111]
  At this time, in the process of step S21 in the film thickness design process shown in FIG. 9, the computer 12 uses the target transmission loss value IL (λn) converted to the transmittance so that the target transmittance T (λn) is the allowable maximum transmittance. Maximum transmittance data T stored in the data file 25 '_maxIt is determined whether the following is true (step S21 ′).
[0112]
  As a result of the determination in step S21 ′, NO, that is, the target transmittance T (λn) is the maximum transmittance T._maxIf not, the process proceeds to step S15, and the square error E between the insertion loss value IL (λn, a) of the entire multilayer film 3 and the target transmission loss value IL (λn) is obtained by the above-described process._n(A) is calculated and stored in the memory 13.
[0113]
  On the other hand, as a result of the determination in step S21 ′, that is, the target transmittance T (λn) is the maximum transmittance data T._maxIn the following cases, this part of the square error E_n(A) is set to 0 (step S22).
[0114]
  That is, according to this modification, the target transmittance T (λn) is the maximum transmittance data T within the pump light cutoff wavelength band._maxIn the following cases, the square error E between the insertion loss value IL (λn, a) of the entire multilayer film 3 and the target transmission loss value IL (λn)_nThe fitting characteristic is enhanced by forcibly setting (a) to 0.
[0115]
  As a result, for example, as shown in FIG. 14, it is possible to provide a multilayer filter having both a pump light blocking function and a GFF function that can cope with a case where the specification for the flatness of the light transmission loss characteristic of the GFF portion is severe. Can do.
[0116]
  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 modifications thereof will be described with reference to the drawings.
[0117]
  FIG. 15 is a diagram showing a schematic configuration of the forward pumping type optical amplifier 100. As shown in FIG.
[0118]
  As shown in FIG. 15, the optical amplifier 100 is connected to an optical fiber 107a to which signal light is input, and is composed of a fiber doped with (added to) a rare earth element such as erbium (Er). The EDF 101 is connected in cascade to the first EDF 101, and is arranged between the first EDF 101 and the second EDF 102, and the second EDF 102 made of a rare earth element, for example, an erbium (Er) -doped fiber. The multilayer filter 1 and the GFF 103 based on the first multilayer filter 1 according to the present invention are provided, and the second EDF 102 and the GFF 103 are connected to the optical fiber 107b.
[0119]
  In the above-described embodiments of the optical amplifier, an optical amplifier including an EDF doped with erbium as a dopant as an amplification medium has been described. However, the present invention is not limited to this. An optical amplifier having a similar pumping configuration is applicable. For example, Tellurite, Fluoride, Silica, etc. can be applied to the host glass of the fiber as the amplification medium, and thulium, praseodymium, yttrium, terbium, etc. can be applied in addition to erbium. It is.
[0120]
  The optical amplifier 100 also includes a pumping light source 104 that emits pumping light (pump light) for EDF pumping, and pumping light emitted from the pumping light source 104 from the signal light input end side of the first EDF 101 to the first. And a multiplexer 105 that supplies the EDF 101 and the second EDF 102.
[0121]
  Furthermore, in the optical amplifier 100, the isolator 108 can be disposed in at least one of the signal light input side optical fiber 107a and the signal light output side optical fiber 107b as necessary. In FIG. 100, a configuration is shown in which isolators 108 are provided in both the optical fiber 107a and the optical fiber 107b.
[0122]
  FIG. 16 is a diagram illustrating a schematic configuration of the backward pumping type optical amplifier 110.
[0123]
  The difference from the forward pumping type optical amplifier 100 shown in FIG. 15 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 disposed on the signal light output side of the second EDF 102 and a pumping light source 114 that emits pumping light for EDF excitation. Thus, the excitation light emitted from the excitation light source 114 is supplied from the signal light output end side of the second EDF 102 to the second EDF 102 and the first EDF 101.
[0124]
  FIG. 17 is a diagram showing a schematic configuration of a bidirectional pumping type optical amplifier 120.
[0125]
  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 includes a pumping light source 104 that emits pumping light for EDF pumping, and pumping light emitted from the pumping light source 104 from the signal light input end side of the first EDF 101 to the first. The first multiplexer 105 a that supplies the EDF 101 and the second EDF 102, the excitation light source 114 that emits the excitation light for EDA excitation, and the excitation light emitted from the excitation light source 114 as the signal light of the second EDF 102 And a second multiplexer 105b that supplies the second EDF 102 and the first EDF 101 from the output end side.
[0126]
  As shown in FIGS. 15 to 17, in the optical amplifiers 100, 110, and 120 including the GFF 103 based on the multilayer filters 1, 1 </ b> A described in the first and second embodiments and the modifications thereof according to the present invention, The characteristics shown in FIGS. 18 and 19 were obtained.
[0127]
  FIG. 18 is a graph showing the correlation between gain and wavelength (wavelength characteristic of gain) in the bidirectionally pumped optical amplifier 120 shown in FIG. In FIG. 18, ◯ indicates the wavelength characteristic of the gain (with a Pump Pass) in the optical amplifier 120 including the GFF 103 according to the present invention, and Δ indicates the wavelength characteristic (Pump) of the gain in the optical amplifier not including the GFF 103 according to the present invention. No Pass).
[0128]
  As can be seen from FIG. 18, the gain value of the optical amplifier can be improved by about 0.5 to 0.7 dB by arranging the GFF 103 according to the present invention in the optical amplifier.
[0129]
  FIG. 19 is a graph showing the correlation between NF (Noise Figure) and wavelength in the bidirectional pumping optical amplifier shown in FIG. In FIG. 19, ◯ indicates the wavelength characteristic of NF (with a Pump Pass) in the optical amplifier 120 including the GFF 103 according to the present invention, and Δ indicates the wavelength characteristic (Pump) of the NF in the optical amplifier not including the GFF 103 according to the present invention. No Pass).
[0130]
  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 arranging the GFF 103 according to the present invention for the optical amplifier.
[0131]
  18 and 19 show the gain wavelength characteristic and the NF wavelength characteristic of the bidirectional pumping optical amplifier 120 shown in FIG. 17, respectively. However, the forward pumping optical amplifier 100 shown in FIG. Also in the backward pumping optical amplifier 110 shown in FIG. 5, since the wavelength characteristics substantially the same as those of the bidirectional pumping optical amplifier 120 are obtained, illustration and description are omitted.
[0132]
  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 in the optical amplifier and the wavelength characteristic of NF are improved. be able to.
[0133]
  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.
[0134]
  FIG. 20 is a block diagram showing a schematic configuration of the wavelength division multiplexing optical transmission system 200.
[0135]
  As shown in FIG. 20, the wavelength division multiplexing optical transmission system 200 includes an optical transmitter T for transmitting a wavelength division multiplexed signal light, in which a plurality of signal lights having different wavelengths are multiplexed, to an optical transmission line P, and the optical transmission. The optical receiver R that receives the wavelength multiplexed signal light transmitted through the path P, and the function as a repeater interposed between the optical transmitter T and the optical receiver R, are connected in series. And a plurality of optical amplifiers 100 connected to each other. That is, the optical amplifier 100 has a function of collectively amplifying wavelength multiplexed signal light transmitted through the optical transmission line P.
[0136]
  Note that the optical amplifier is not limited to the forward pumping optical amplifier 100 shown in FIG. 15, and the backward pumping optical amplifier 110 and the bidirectional pumping optical amplifier 120 shown in FIG. 16 may be used. Is natural. Any one of the forward pumping optical amplifier 100, the backward pumping optical amplifier 110, and the bidirectional pumping optical amplifier 120 can be freely selected and arranged arbitrarily.
[0137]
  According to the wavelength division multiplexing optical transmission system 200 shown in FIG. 20, the wavelength division multiplexed signal light transmitted from the optical transmitter T is sequentially amplified through each optical amplifier 100 provided with the GFF 103 (see FIG. 15). It is transmitted to the optical receiver R. At this time, in each optical amplifier 100, gain equalization and NF suppression for the wavelength multiplexed signal light are performed by the GFF 103, so that the wavelength multiplexed signal light having a high optical SN ratio in which the levels of the respective wavelengths are uniform is transmitted to the optical transmitter. Transmission from T to the optical receiver R becomes possible. As mentioned above, although this invention was demonstrated using embodiment, this invention is not limited to the said embodiment. That is, various modifications or improvements can be added to the above-described embodiment within the scope based on the technical idea of the present invention.
【The invention's effect】
  As described above, according to the present inventionMultilayer optical filter thickness design device, program, multilayer optical filter thickness design method, etc.According to the above, the optical film thickness of each thin film layer of the multilayer filter has a predetermined wavelength characteristic for each wavelength within a preset gain equalization wavelength band, and other than the gain equalization wavelength band. Provided is a multilayer optical filter having both predetermined wavelength characteristics in the gain equalization wavelength band and predetermined wavelength characteristics in the excitation light wavelength band because it is designed to have predetermined wavelength characteristics in the excitation light wavelength band. be able to.
[0138]
  Therefore, it is possible to meet the demand for excitation light transmission / blocking for a multilayer optical filter such as GFF having a gain equalization function, and the practicality of the multilayer optical filter can be greatly enhanced.
[0139]
  In addition, by combining a multilayer optical filter having sufficient wavelength characteristics corresponding to the pumping light transmission / cutoff requirement with an optical amplifier, the output characteristics of the optical amplifier can be set to a lower loss / higher output than before. . As a result, it is possible to provide an optical amplifier having amplification characteristics with high output efficiency.
[0140]
  Furthermore, by combining the above-described optical amplifier with an optical transceiver to form a system, the power consumption of the entire system can be reduced.
[0141]
[Brief description of the 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 design apparatus for designing an optical film thickness of each thin film layer of the multilayer filter shown in FIG. 1;
FIG. 3 is a flowchart showing an example of a multilayer filter manufacturing process in the first embodiment of the present invention.
FIG. 4 is a schematic flowchart showing an example of a film thickness design process in 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 the initial value of the optical film thickness in the 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 the initial value of the 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 the initial value of the optical film thickness in the 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 design apparatus for designing an optical film thickness of each thin film layer of a multilayer filter according to a second embodiment of the present invention.
FIG. 9 is a schematic flowchart showing an example of a film thickness design process in the second embodiment of the present invention.
10A is a graph showing a design target loss characteristic of the multilayer filter according to the first embodiment, a loss characteristic based on the design value of the multilayer filter, and a loss deviation between the target value and the design value, respectively. FIG. FIG. 7B is a graph showing a design target loss characteristic of the multilayer filter according to the second embodiment, a loss characteristic based on the design value of the multilayer filter, and a loss deviation between the target value and the design value.
FIG. 11A is a graph showing a design target loss characteristic of the multilayer filter according to the first embodiment, a loss characteristic based on the design value of the multilayer filter, and a loss deviation between the target value and the design value; FIG. 7B is a graph showing a design target loss characteristic of the multilayer filter according to the second embodiment, a loss characteristic based on the design value of the multilayer filter, and a loss deviation between the target value and the design value.
FIG. 12 is a graph showing a design target loss characteristic of a multilayer filter according to the second embodiment, a loss characteristic based on a design value of the multilayer filter, and a loss deviation between the target value and the design value.
FIG. 13A is a multilayer diagram having predetermined light transmission characteristics with respect to a pump light wavelength band of 980 nm band and predetermined light transmission loss characteristics in the GFF portion according to a modification of the second embodiment of the present invention. FIG. 13B is a graph showing the loss characteristics based on the design value of the membrane filter, FIG. 13B is a graph showing an enlarged portion shown as (b) in FIG. 13A, and FIG. ) Is an enlarged graph showing a portion indicated as).
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 is a diagram showing a schematic configuration of a forward-pumped optical amplifier including GFF based on a multilayer filter according to the present invention.
FIG. 16 is a diagram showing a schematic configuration of a backward pumping type optical amplifier including GFF based on a multilayer filter according to the present invention.
FIG. 17 is a diagram showing a schematic configuration of a bidirectionally pumped optical amplifier including GFF based on a multilayer filter according to the present invention.
18 is a graph showing the correlation between gain and wavelength in the bidirectional pumping optical amplifier shown in FIG.
19 is a graph showing the correlation between NF (Noise Figure) and wavelength in the bidirectional pumping 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 of FIG. 15 (FIGS. 16 and 17).
FIG. 21 is a diagram for explaining a gain equalization function of a 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 Substrate
3 Multilayer film
3a1-3aN thin film layer
10, 10A film thickness design equipment
11 Input section
12 Computer
13, 13A memory
14 External I / O interface
20 Theoretical data file
21 Target transmission loss data file
25 Allowable minimum transmittance data file
100 Forward-pumped 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 Bidirectionally pumped optical amplifier
200 wavelength division multiplexing transmission system
P, PA program
T optical transmitter
R optical receiver

Claims (17)

A film thickness design apparatus for designing an optical film thickness of a multilayer optical filter formed by laminating a plurality of optical films,
A predetermined wavelength characteristic in a preset gain equalization wavelength band is a first value 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 gain equalization wavelength band. Means for calculating the error of
Wavelength characteristics in the pumping light wavelength band other than the gain equalizing wavelength band are expressed as second values between theoretical values representing the optical film thickness of each optical film as a parameter and target wavelength characteristic values in the corresponding pumping light wavelength band. Means for calculating the error;
Means for designing the optical film thickness of each of the optical films using a fitting having a predetermined optical film thickness as an initial value so that the calculated first and second errors are reduced, respectively. A multilayer optical filter film thickness design apparatus. A film thickness design apparatus for designing an optical film thickness of each optical layer in a multilayer optical filter formed by laminating a plurality of optical films,
A first characteristic value between a theoretical value representing a wavelength characteristic in a predetermined wavelength band other than a preset excitation light wavelength band as a parameter of an optical film thickness of each optical film and a target wavelength characteristic value in the corresponding predetermined wavelength band. Means for calculating the error of
When the transmittance corresponding to the target wavelength characteristic value in the excitation light wavelength band is smaller than the minimum necessary transmittance in the excitation light wavelength band, the wavelength characteristic in the excitation light wavelength band Means for calculating a second error between a theoretical value representing the optical film thickness as a parameter and a wavelength characteristic value in a corresponding excitation light wavelength band;
Means for designing the optical film thickness of each of the optical films using a fitting having a predetermined optical film thickness as an initial value so that the calculated first and second errors are reduced, respectively. A multilayer optical filter film thickness design apparatus. When the transmittance corresponding to the target wavelength characteristic value in the pumping light wavelength band is greater than the minimum necessary transmittance in the pumping light wavelength band, the design means sets the wavelength characteristics in the pumping light wavelength band to the respective wavelength characteristics. The multilayer film according to claim 2, further comprising means for setting a second error between a theoretical value representing the optical film thickness of the optical film as a parameter and a target wavelength characteristic value in a corresponding excitation light wavelength band to zero. Optical filter thickness design device. A film thickness design apparatus for designing an optical film thickness of each optical layer in a multilayer optical filter formed by laminating a plurality of optical films,
A first characteristic value between a theoretical value representing a wavelength characteristic in a predetermined wavelength band other than a preset excitation light wavelength band as a parameter of an optical film thickness of each optical film and a target wavelength characteristic value in the corresponding predetermined wavelength band. Means for calculating the error of
When the transmittance corresponding to the target wavelength characteristic in the excitation light wavelength band is larger than the maximum transmittance allowed in the excitation light wavelength band, the wavelength characteristic in the excitation light wavelength band is changed to the optical property of each optical film. Means for calculating a second error between a theoretical value representing the film thickness as a parameter and a target wavelength characteristic value in a corresponding excitation light wavelength band;
Design means for designing the optical film thickness of each of the optical films using a fitting having a predetermined optical film thickness as an initial value so that the calculated first and second errors are reduced, respectively. An apparatus for designing a film thickness of a multilayer optical filter. 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 design means sets the wavelength characteristics in the pumping light wavelength band to the respective wavelength characteristics. The multilayer optical system according to claim 4 , further comprising means for setting a second error between a theoretical value representing the optical film thickness of the optical film as a parameter and a target wavelength characteristic in a corresponding excitation light wavelength band to zero. Filter film thickness design device. 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 calculates a predetermined wavelength characteristic in a preset wavelength band for gain equalization 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 wavelength band for gain equalization. Means for calculating the first error of
Wavelength characteristics in the pumping light wavelength band other than the gain equalizing wavelength band are expressed as second values between theoretical values representing the optical film thickness of each optical film as a parameter and target wavelength characteristic values in the corresponding pumping light wavelength band. Means for calculating the error;
The optical film thickness of each of the optical films is made to function as means for designing using a fitting having a predetermined optical film thickness as an initial value so that the calculated first and second errors are reduced. Program. 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 calculates a wavelength characteristic in a predetermined wavelength band other than a preset excitation light wavelength band 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 predetermined wavelength band. Means for calculating the first error of
When the transmittance corresponding to the target wavelength characteristic value in the excitation light wavelength band is smaller than the minimum necessary transmittance in the excitation light wavelength band, the wavelength characteristic in the excitation light wavelength band Means for calculating a second error between a theoretical value representing the optical film thickness as a parameter and a wavelength characteristic value in a corresponding excitation light wavelength band;
The optical film thickness of each of the optical films is made to function as means for designing using a fitting having a predetermined optical film thickness as an initial value so that the calculated first and second errors are reduced. Program. When the transmittance corresponding to the target wavelength characteristic value in the pumping light wavelength band is greater than the minimum necessary transmittance in the pumping light wavelength band, the design means sets the wavelength characteristics in the pumping light wavelength band to the respective wavelength characteristics. The program according to claim 7, further comprising means for setting a second error between a theoretical value representing the optical film thickness of the optical film as a parameter and a target wavelength characteristic value in a corresponding excitation light wavelength band to zero. 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 calculates a wavelength characteristic in a predetermined wavelength band other than a preset excitation light wavelength band 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 predetermined wavelength band. Means for calculating the first error of
When the transmittance corresponding to the target wavelength characteristic in the excitation light wavelength band is larger than the maximum transmittance allowed in the excitation light wavelength band, the wavelength characteristic in the excitation light wavelength band is changed to the optical property of each optical film. Means for calculating a second error between a theoretical value representing the film thickness as a parameter and a target wavelength characteristic value in a corresponding excitation light wavelength band;
The optical film thickness of each of the optical films is made to function as means for designing using a fitting having a predetermined optical film thickness as an initial value so that the calculated first and second errors are reduced. Program. 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 design means sets the wavelength characteristics in the pumping light wavelength band to the respective wavelength characteristics. The program according to claim 9, further comprising means for setting a second error between a theoretical value representing the optical film thickness of the optical film as a parameter and a target wavelength characteristic in a corresponding excitation light wavelength band to zero. A film thickness design method for designing an optical film thickness of each optical layer in a multilayer optical filter formed by laminating a plurality of optical films,
A predetermined wavelength characteristic in a preset gain equalization wavelength band is a first value 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 gain equalization wavelength band. Calculating the error of
Wavelength characteristics in the pumping light wavelength band other than the gain equalizing wavelength band are expressed as second values between theoretical values representing the optical film thickness of each optical film as a parameter and target wavelength characteristic values in the corresponding pumping light wavelength band. Calculating an error;
Designing the optical film thickness of each of the optical films using a fitting having a predetermined optical film thickness as an initial value so that the calculated first and second errors are reduced. A method for designing a film thickness of a multilayer optical filter. A film thickness design method for designing an optical film thickness of each optical layer in a multilayer optical filter formed by laminating a plurality of optical films,
A first characteristic value between a theoretical value representing a wavelength characteristic in a predetermined wavelength band other than a preset excitation light wavelength band as a parameter of an optical film thickness of each optical film and a target wavelength characteristic value in the corresponding predetermined wavelength band. Calculating the error of
When the transmittance corresponding to the target wavelength characteristic value in the excitation light wavelength band is smaller than the minimum necessary transmittance in the excitation light wavelength band, the wavelength characteristic in the excitation light wavelength band Calculating a second error between a theoretical value representing the optical film thickness as a parameter and a target wavelength characteristic in a corresponding excitation light wavelength band;
Designing the optical film thickness of each of the optical films using a fitting having a predetermined optical film thickness as an initial value so that the calculated first and second errors are reduced. A method for designing a film thickness of a multilayer optical filter. In the design step, when the transmittance corresponding to the target wavelength characteristic value in the excitation light wavelength band is larger than the minimum necessary transmittance in the excitation light wavelength band, the wavelength characteristics in the excitation light wavelength band The multilayer film according to claim 12, further comprising a step of setting a second error between a theoretical value representing an optical film thickness of the optical film as a parameter and a target wavelength characteristic value in a corresponding excitation light wavelength band to zero. Optical filter thickness design method. A film thickness design method for designing an optical film thickness of each optical layer in a multilayer optical filter formed by laminating a plurality of optical films,
A first characteristic value between a theoretical value representing a wavelength characteristic in a predetermined wavelength band other than a preset excitation light wavelength band as a parameter of an optical film thickness of each optical film and a target wavelength characteristic value in the corresponding predetermined wavelength band. Calculating the error of
When the transmittance corresponding to the target wavelength characteristic in the excitation light wavelength band is larger than the maximum transmittance allowed in the excitation light wavelength band, the wavelength characteristic in the excitation light wavelength band is changed to the optical property of each optical film. Calculating a second error between a theoretical value representing the film thickness as a parameter and a target wavelength characteristic value in a corresponding excitation light wavelength band;
Designing the optical film thickness of each of the optical films using a fitting having a predetermined optical film thickness as an initial value so that the calculated first and second errors are reduced. A method for designing a film thickness of a multilayer optical filter. In the design step, when the transmittance corresponding to the target wavelength characteristic value in the excitation light wavelength band is smaller than the maximum transmittance allowed in the excitation light wavelength band, the wavelength characteristics in the excitation light wavelength band are each 15. The multilayer optical system according to claim 14, further comprising a step of setting a second error between a theoretical value representing the optical film thickness of the optical film as a parameter and a target wavelength characteristic in a corresponding excitation light wavelength band to zero. Filter thickness design method.
A rare earth element-doped fiber provided on an optical transmission line for amplifying signal light, having a fiber doped with a rare earth element;
An excitation light source for generating excitation light for exciting the rare earth element-doped fiber;
Provided on the optical transmission line, and combines the pump light generated by the pump light source with the signal light. A multiplexer for emitting the excitation light to the rare earth element-doped fiber;
A multilayer optical filter provided on the upstream side or the downstream side of the rare earth element-doped fiber on the optical transmission line;
With
The multilayer optical filter is formed by the film thickness design apparatus according to any one of claims 1 to 5, or designed by the film thickness design method according to any one of claims 11 to 15. Is formed
An optical amplifier characterized by that. A wavelength division multiplexing optical transmission system for transmitting a plurality of signal lights having different wavelengths,
  An optical transmitter for transmitting the plurality of signal lights to an optical transmission line;
  The optical amplifier according to claim 16, wherein a plurality of signal lights transmitted from the optical transmitter and transmitted through the optical transmission path are collectively amplified,
  An optical receiver for receiving a plurality of signal lights amplified through the optical amplifier and transmitted through the optical transmission line;
  A wavelength division multiplexing optical transmission system comprising: