JP2784374B2 - Optical add / drop circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of branching and extracting an optical signal of a predetermined optical frequency from an optical signal multiplexed in an optical frequency division multiplexing transmission system and having the same optical frequency as the extracted optical frequency. The present invention relates to an optical add / drop circuit for newly inserting and multiplexing an optical signal.

[0002]

2. Description of the Related Art A conventional optical add / drop circuit includes an optical demultiplexer for demultiplexing an optical signal of each optical frequency from an optical frequency multiplexed optical signal, and a single optical waveguide for transmitting a plurality of optical signals having different optical frequencies. An optical multiplexer that multiplexes with a wave path is combined, and an optical signal of a predetermined optical frequency is dropped and inserted between them. In addition,
Since the optical demultiplexer and the optical multiplexer are reversible in principle, two optical components having the same configuration are realized.

Here, a configuration example of a conventional arrayed waveguide type optical multiplexer / demultiplexer used as an optical multiplexer / demultiplexer will be described with reference to FIGS. In the following description, first, a case where an arrayed waveguide type optical multiplexer / demultiplexer is used as an optical demultiplexer will be described. For details of the optical multiplexer / demultiplexer shown here, refer to the literature (C. Dragone et al., IEEE
E Photonics Technology Letters, vol.3, No.10,1991, p
p.896-899).

In FIG. 5, an arrayed waveguide type optical multiplexer / demultiplexer comprises an N × M star coupler 51 and an M × N star coupler 5.
2 and M single-mode waveguide arrays 53 that sequentially couple both star couplers with an optical path length difference of ΔL. Here, when used as an optical demultiplexer, N ×
N star single mode waveguides 5 in M star coupler 51
4 as an input port and an M × N star coupler 52
Are coupled to N output single-mode waveguides 55 to form output ports. The N × M star coupler 51 is connected to N input single-mode waveguides 54 via a slab waveguide 56.
And M single-mode waveguide arrays 53. The M × N star coupler 52 includes a slab waveguide 57
, The M single-mode waveguide array 53 and the N output single-mode waveguides 55 are coupled to each other. Further, the input port numbers of the N × M star coupler 51 are set to i = 1, 2,...
.., N in order from the bottom.

FIG. 6 is an enlarged view of a slab waveguide 56 constituting the N × M star coupler 51. In the M × N star coupler 52, the left and right sides may be reversed. In the figure, the distance between the waveguides of the N input single-mode waveguides 54 is ΔX, the distance between the waveguides of the M single-mode waveguide arrays 53 is d, and the diameter of the Rowland circle formed by both waveguide end faces. (Propagation distance in the slab waveguide 56) is L ₀ , the coordinate axis in the propagation direction of the optical signal is z, and the coordinate axis in the direction perpendicular to the z-axis direction on the waveguide end face of the M single-mode waveguide array 53. X ₁ , and a coordinate axis perpendicular to the z-axis direction on the end face of the N input single-mode waveguides 54 is x ₂ .

Here, an optical frequency interval Δf is input from the waveguide having the input port number i = 1 to the N × M star coupler 51.
When an optical frequency multiplexed signal having optical frequencies f ₁ , f ₂ ,..., F _N is input, the slab waveguide 5
6 will spread the light intensity distribution in portions to x ₂ axis direction in the process of propagating. Therefore, by optimally designing the propagation distance L ₀ , M single-mode waveguide arrays 5
At the input terminal of _No. 3 (on the x1 coordinate axis), the light can be coupled to each of the M waveguides with substantially uniform light intensity distribution without depending on each optical frequency of the optical frequency multiplexed signal.

Next, M single-mode waveguide arrays 53
Each optical frequency multiplexed signal coupled to the optical waveguide propagates through each waveguide. However, since each waveguide has an optical path length difference of ΔL, it is output from an adjacent waveguide at its output end. A phase difference Δθ occurs between the optical frequency multiplexed signals.
This phase difference Δθ is represented by β, where the propagation constant of the optical signal is β, the effective refractive index of the waveguide is n _c , the center frequency of the optical signal is f ₀ , and the speed of light in a vacuum is C.

[0008]

(Equation 1)

Can be represented by As described above, it can be seen that the phase difference Δθ differs depending not only on the optical path length difference ΔL of each waveguide but also on each optical signal frequency subjected to optical frequency multiplexing. Each optical signal given a different phase delay by the M single-mode waveguide arrays 53 is emitted from its output end to the slab waveguide 57 of the M × N star coupler 52. Each optical signal is gradually widened in the process of propagating through the slab waveguide 57 and the light intensity distribution in portions x ₁ coordinate axis direction, but interferes with the optical signal at this time the same optical frequency emitted from the other waveguide. The result of this interference, the input end of the output single-mode waveguide 55 of the N in (x ₂ coordinate axes), so that the points strong point light intensity and weak appear. This light intensity distribution I (x ₂ , z)

[0010]

(Equation 2)

It can be expressed as Further, the position of the point where the light intensity becomes strong differs depending on the optical frequency of each optical signal. That is, similar to the action of diffraction by the diffraction grating,
The optical frequency multiplexed signal emitted from the M single-mode waveguide arrays 53 has different diffraction angles depending on the optical frequency of the signal. At this time, the displacement dx ₂ at the position where the optical signals emitted from the M single-mode waveguide arrays 53 are diffracted is determined by the effective refractive index of the slab waveguide 57.
n _s , the diffraction order is m, and when the propagation distance L ₀ is sufficiently large with respect to the optical frequency change df ₀ of the optical signal,

[0012]

(Equation 3)

It can be expressed as Also, the diffraction order m
Is approximately

[0014]

(Equation 4)

It can be expressed as Therefore, (3) as given by equation, the position on the x ₂ coordinate axis is diffracted in accordance with the optical frequency having the respective optical signal changes, x of the output single-mode waveguide 55 of the N ₂ If the position on the coordinate axis is appropriately set, the optical signal of each optical frequency can be separated and extracted from the M × N star coupler 52 to each of the N output single-mode waveguides 55.

That is, when an optical frequency multiplexed signal having optical frequencies f ₁ , f ₂ ,..., F _N with an optical frequency interval Δf is input from the waveguide having the input port number i = 1, the output port number j = 1, 2,..., N, the optical frequency f ₁ ,
The optical signals of f ₂ ,..., f _N can be demultiplexed and output. The resolution of an optical demultiplexer having such a configuration is approximately

[0017]

(Equation 5)

## EQU1 ## Here, Δf ₀ is a pass bandwidth when expressed in full width at half maximum. Moreover, such an optical component is a point on the x ₂ coordinate axis transmittance is maximum in the filter, periodically appearing in the higher order diffraction satisfies place. When the optical frequency intervals corresponding to the spacing of a point on the diffraction satisfying x ₂ coordinate axes of the high-order referred to as FSR (Free-Spectral-Range) , it is approximately

[0019]

(Equation 6)

## EQU1 ## Therefore, if the value of FSR obtained from equation (6) is made equal to (N−1) × Δf, for example, the optical frequencies f ₁ , f ₂ ,. , if entered by the optical frequency division multiplexed signal having a f _N, the output port number j = 1, 2, ..., N
Each waveguide of the optical frequency _{f 2, f 3, ...,} f N, the optical signal of f ₁ can be output respectively demultiplexed to. That is,
The input port number for inputting the optical frequency multiplexed signal is i = 1,
2,..., N, the output port number j = 1
The waveguide optical frequency f _1, f _2, ..., the optical signal of f _N are output in order. Alternatively, it can be said that the output port number for demultiplexing the optical signal of the optical frequency f ₁ is j = 1, N, N- 1, moves to ... and order. Table 1 shows the relationship between the input port number i and the optical signal frequency of the output port number j.

[0021]

[Table 1]

[0022] Generally, an input port number i optical frequency division multiplexed signal is input, while the optical signals of the optical frequency f _a is the output port number j to be demultiplexed, a = (i + j- 1) MOD ( N) The relationship of (7) holds. Here, the MOD function is (x ₁ ) MOD (x ₂ ) = x ₁ −int (x ₁ / x ₂ ) x ₂ (8) Note that int (x) is a function for converting x to an integer by truncating the decimal part of x. When a = 0, a = N
Replace with

FIG. 7 is a diagram showing transmittance characteristics of a conventional arrayed waveguide type optical demultiplexer. In the figure, the solid line shows the transmittance characteristic of the output single-mode waveguide 55 in the j = N waveguide, and the dotted line shows the transmission single-mode waveguide 55 of j = N.
9 shows transmittance characteristics of an N-1 waveguide. Note that d =
3 [mu] m, a characteristic in the case of _{N = M = 11, n c} -n s = 0.0035, the insertion loss 3 dB, the resolution (channel wavelength spacing) 1.5
nm and FSR = 16.5 nm.

Since the optical demultiplexer and the optical multiplexer are reversible, the N input single-mode waveguides 5 shown in FIG.
4 for output, N output single-mode waveguides 55 for input, and waveguides of j = 1, 2,..., N as input ports, and optical frequencies f ₁ and f ₂ , respectively. ,…,
When an optical signal of f _N (optical frequency interval Δf) is input to the M × N star coupler 52, i = 1 from the N × M star coupler 51
An optical frequency multiplexed signal multiplexed into the waveguide can be taken out. To change the position of the waveguide from which the multiplexed optical frequency multiplexed signal is extracted, the input optical frequency
It may be changed according to the formula or table. As described above, the configuration shown in FIG. 5 can also be used as an N × N optical multiplexer.

A conventional optical add / drop circuit combines such an optical demultiplexer and an optical multiplexer, and demultiplexes each optical frequency with the optical demultiplexer, and outputs an optical signal of a predetermined optical frequency. And an optical signal of the same optical frequency as the extracted optical frequency is input from a predetermined port of the optical multiplexer and multiplexed with an optical signal of another optical frequency, thereby realizing an optical add / drop function. ing.

[0026]

As described above, in the conventional optical add / drop circuit, it is necessary to separately provide an optical demultiplexer used as an optical add / drop circuit and an optical multiplexer used as an optical add circuit. In order to function as two optical add / drop circuits, it was necessary to make the characteristics of the optical demultiplexer and the optical multiplexer identical.

An object of the present invention is to provide an optical add / drop circuit that can be realized by one optical circuit by utilizing the reversibility of an optical demultiplexer and an optical multiplexer.

[0028]

According to a first aspect of the present invention, there is provided a 2N × M star coupler (N is an integer of 1 or more, M is an integer of 2 or more) having a slab waveguide, and an M × 2N star coupler. Are connected by an M single-mode waveguide array having a predetermined optical path length difference, and one of a set of adjacent ports among N sets of adjacent ports of a 2N × M star coupler is set as an input port, and Optical frequency with optical frequency interval Δf at input port
_{f 1, f 2, ...,} f x (x is 1 or more N an integer) when entering the optical frequency division multiplexed signal having a sequential light frequency interval port of the 2N ports M × 2N star coupler f ₁ ,
f _2, ..., a configuration for demultiplexing the optical signal of f _x, to the port adjacent the septum port of M × 2N star coupler, as well as folded binding except given set, adjacent the given set The port is a branch terminal and an insertion terminal for dropping / inserting an optical signal of a predetermined optical frequency corresponding to the input port of the optical frequency multiplexed signal, and the other of a pair of adjacent ports of the 2N × M star coupler is used for the optical frequency multiplexed signal. It is characterized as an output port.

According to a second aspect of the present invention, a predetermined distance is set between a 2N × M star coupler having a slab waveguide (N is an integer of 1 or more, M is an integer of 2 or more) and an M × 2N star coupler. Coupled by M single-mode waveguide arrays having optical path length differences, one of N consecutive ports of a 2N × M star coupler is used as an input port, and the input port has an optical frequency f with an optical frequency interval Δf. _When an optical frequency multiplexed signal having ₁ , f ₂ ,..., F _x (x is an integer of 1 or more and N or less) is inputted, M ×
2N Star N ports sequentially optical frequency f ₁ successive coupler, f _2, ..., a configuration for demultiplexing the optical signal of f _x, M × 2
From the N consecutive ports of the N-star coupler to the remaining N ports, the optical frequency of the demultiplexed optical signal except for a predetermined port pair is folded back and coupled in the same order or cyclically. In addition, a predetermined port pair is a branch terminal and an insertion terminal for dropping / inserting an optical signal of a predetermined optical frequency corresponding to an input port of an optical frequency multiplexed signal, and the remaining consecutive N ports of the 2N × M star coupler Of which corresponds to the input port and return path
One of them is an output port of an optical frequency multiplexed signal.

[0030]

According to the present invention, there is provided a 2N × M star coupler having a slab waveguide, an M × 2N star coupler,
An optical demultiplexer and an optical multiplexer are constituted by M single-mode waveguide arrays having a predetermined optical path length difference coupling therebetween. In other words, the optical frequency f ₁ to one input port of 2N × M star coupler, f _2, ..., when you enter the optical frequency division multiplexed signal having the f _x, the M × 2N star coupler 2N
The optical frequencies f ₁ , f ₂ ,...
The optical signal of f _x constituting the demultiplexed output light demultiplexer. Also,
Each optical signal demultiplexed and output by the M × 2N star coupler is folded back and coupled to an adjacent port, and an optical frequency multiplexed signal in which each optical frequency is multiplexed to an adjacent port of the input port of the 2N × M star coupler is output. Configure the container. As described above, the optical demultiplexer and the optical multiplexer are configured by one optical circuit using the reversibility.

Here, a part of the return coupling path in the M × 2N star coupler is cut off, the split optical signal is taken out to the branch terminal, and the optical signal of the same optical frequency is input from the insertion terminal to the return port. An optical add / drop circuit is realized by one optical circuit.

According to a second aspect of the present invention, there is provided a 2N × M star coupler having a slab waveguide, an M × 2N star coupler, and M single-mode waveguides having a predetermined optical path length difference coupling therebetween. The array forms an optical demultiplexer and an optical multiplexer. In other words, the optical frequency f ₁ to one input port of 2N × M star coupler, f _2, ..., when you enter the optical frequency division multiplexed signal having the f _x, the N ports of consecutive M × 2N star coupler sequential light frequencies f _1, f _2, ..., constitute an optical demultiplexer for demultiplexing outputs an optical signal of f _x. Also, M ×
The optical frequency of the demultiplexed optical signal is coupled back to the other N ports of the 2N star coupler such that the optical frequencies of the demultiplexed optical signals are arranged in the same order or cyclically, and the input port of the 2N × M star coupler and the M × 2N star are coupled. An optical multiplexer for outputting an optical frequency multiplexed signal obtained by multiplexing the respective optical frequencies is formed at the output port of the 2N × M star coupler corresponding to the return input port of the coupler. Thus, by utilizing reversibility, 1
An optical demultiplexer and an optical multiplexer are composed of two optical circuits.

Here, a part of the return coupling path in the M × 2N star coupler is cut off, the split optical signal is taken out to the branch terminal, and the optical signal of the same optical frequency is input from the insertion terminal to the return port. An optical add / drop circuit is realized by one optical circuit.

[0034]

FIG. 1 is a diagram showing a basic configuration of an optical add / drop circuit according to the first aspect of the present invention. In the figure, an optical add / drop circuit is a 2N × having a slab waveguide with a propagation distance L _0.
The M star coupler 11 and the M × 2N star coupler 12 are sequentially coupled by M single mode waveguide arrays 13 having an optical path length difference of ΔL, and further coupled to the 2N × M star coupler 11. One set of adjacent 2N input / output single mode waveguides 14 is set as an input / output port, and N is set except for the k-th (k = 1 to N integer) of the adjacent port set of the M × 2N star coupler 12. -1 folded single mode waveguide 1
It is folded back at 5.

Here, assuming that the port numbers of the 2N × M star coupler 11 are i = 1, 2,..., 2N in this order from the top, in this embodiment, the input port is i = 2n−1 (n = 1 to 1).
N), and the corresponding output port is i = 2n. That is, i = 1, 3,..., 2N−1
, The corresponding output ports are i = 2, 4,..., 2N, respectively.

When the port numbers of the M × 2N star coupler 12 are j = 1, 2,..., 2N in order from the bottom,
The ports of j = 2n and j = 2n-1 are connected back.
That is, j = 2, 4,..., 2N and j = 1, 3,.
The N-1 ports are respectively coupled back. However,
A single mode waveguide 16 for branching an optical signal of a predetermined optical frequency is connected to a port of j = 2k, and a single mode waveguide 17 for inserting an optical signal of a predetermined optical frequency to a port of j = 2k-1. Connect.

In such a configuration, for example, an optical frequency multiplexed signal having optical frequencies f ₁ , f ₂ ,..., F _N with an optical frequency interval Δf is supplied to a port number i = 1 to 2N × M star coupler 11. When input, the light of the optical frequencies f ₁ , f ₂ ,..., F _k ,..., F _{N is obtained} from the port numbers j = 2, 4,. Set the variance shown in equation (3) so that the signal is split and output. Here, f ₁ , f ₂ ,..., F _N are numbers assigned to identify optical frequencies, and do not indicate the magnitude relations. For example, in the case of FIG. 1, f _N <... <
f ₂ <f ₁ .

At this time, the optical signals of the optical frequencies f ₁ , f ₂ ,..., F _N output to the M × 2N star coupler 12 at the port numbers j = 2, 4,. .., 2N-1 are again input to the port numbers j = 1, 3,..., 2N−1 of the M × 2N star coupler 12 via the single mode waveguide 15. That is, the relationship between the return input port number j of the optical signal demultiplexed and output by the M × 2N star coupler 12 and the frequency of the return optical signal is as shown in FIG.
By performing such a return, the optical frequency from the waveguide of port number i = 2 of the 2N × M star coupler 11 is changed.
An optical frequency multiplexed signal obtained by multiplexing optical signals of f ₁ , f ₂ ,..., f _N (optical frequency interval Δf) can be extracted.

Here, j = 2 of the M × 2N star coupler 12
The optical signal of the optical frequency f _k which is branched and output from the 2k port to the single mode waveguide 16 is taken out without folding, and instead the optical signal of the same optical frequency f _k is passed through the single mode waveguide 17. , J = 2k of the M × 2N star coupler 12
An optical add / drop circuit can be constituted by one optical circuit by inputting to the port of -1. Note that k is 1 to
An arbitrary integer of N may be used, and two or more kinds of values may be taken to have a plurality of branch / insert terminals.

The position of the output port changes according to the position of the input port of the optical frequency multiplexed signal having the optical frequencies f ₁ , f ₂ ,..., F _N with the optical frequency interval Δf input to the 2N × M star coupler 11. At this time, the optical frequency that is demultiplexed and output from the j = 2k return output port of the M × 2N star coupler 12 to the single mode waveguide 16 is also switched. Table 2 shows the relationship between the combination of the input / output port number i and the optical signal frequency of the folded output / input port number j.

[0041]

[Table 2]

Generally, 2N for inputting an optical frequency multiplex signal
× M which splits an input port number i of the M star coupler 11 and an optical signal of an optical frequency f _a (a is any one of 1 to N)
Between the return output port number j of the 2N star coupler 12,

[0043]

(Equation 7)

The following relationship is established. However, when a> N, a → a−N. In the configuration shown in FIG.
The input port of the 2N × M star coupler 11 is set to i = 2n while the folded connection of the M × 2N star coupler 12 is kept as it is.
If (n = 1 to N), the corresponding output port is i = 2n-1. That is, the same is true even if the input / output ports are reversed. However, in that case, in the example described above, j = 2k-1 (k =
(An integer from 1 to N) is a branch port, and j = 2k is an insertion port. Table 3 shows part of the relationship between the combination of the input / output port number i and the optical signal frequency of the folded output / input port number j.

[0045]

[Table 3]

In the structure shown in FIG. 1, 2N × M
When the input port of the star coupler 11 is i = 2n, j = 2n + 1 and j = 2 of the M × 2N star coupler 12
When n ports are coupled back, the corresponding output port is i = 2n + 1. In that case, in the example described above, j = 2k−1 of the M × 2N star coupler 12 is a branch port, and j = 2k−2 is an insertion port.
However, when i, j, k = 2N + 1, i, j, k = 1
And The combination of this input / output port number i,
Table 4 shows part of the relationship between the folded output / input port number j and the optical signal frequency.

[0047]

[Table 4]

FIG. 2 is a diagram showing a basic configuration of an optical add / drop circuit according to the second aspect of the present invention. In the figure, an optical add-drop circuit, 2N with slab waveguide propagation distance L ₀
The × M star coupler 11 and the M × 2N star coupler 12 are sequentially coupled by M single-mode waveguide arrays 13 having an optical path difference of ΔL, and further coupled to the 2N × M star coupler 11. A predetermined set of 2N input / output single-mode waveguides 14 is used as an input / output port, and k sets (k = 1 to N) of predetermined ports of the M × 2N star coupler 12 are excluded. Then, the coupling is performed by Nk folding single-mode waveguides 15.

Here, when the port numbers of the 2N × M star coupler 11 are set to i = 1, 2,..., 2N in this order from the top, in this embodiment, the input ports are set to i = n (n = 1 to N). Integer) and the corresponding output port is i = N + n. That is, when the input port is any of i = 1, 2,..., N, the corresponding output port is i = N +
1, N + 2,..., 2N.

When the port numbers of the M × 2N star coupler 12 are j = 1, 2,..., 2N in order from the bottom,
The ports of j = N + n and j = n are connected back. That is, j = 2N, 2N-1,..., N + 1 and j = N, N-
The ports of 1,..., 1 are respectively connected back. However, a single mode waveguide 16 for branching an optical signal of a predetermined optical frequency is connected to a port of j = N + k (k = 1 to an integer of N), and an optical signal of a predetermined optical frequency is connected to a port of j = k. Is connected.

In such a configuration, for example, an optical frequency multiplexed signal having optical frequencies f ₁ , f ₂ ,..., F _N at an optical frequency interval Δf is supplied to the port number i = 1 to 2N × M star coupler 11. When input, the port numbers j = N + 1,..., N + k,.
From −1 and 2N, the optical frequencies f ₁ ,..., F _k ,.
Optical signal of _N-1, f _N sets the dispersion value indicated by way (3) is demultiplexed output.

At this time, the optical signals of the optical frequencies f ₁ ,..., F _N−1 , f _{N that} are demultiplexed and output to the port numbers j = N + 1,..., 2N−1, 2N of the M × 2N star coupler 12 ., N−1, N are again input to the port numbers j = 1,..., N−1, N of the M × 2N star coupler 12 via the single mode waveguide 15 for return. That is, the return input port number j of the optical signal demultiplexed and output by the M × 2N star coupler 12, and
The relationship with the return optical signal frequency is as shown in FIG. By performing such folding, 2N
An optical frequency multiplexed signal obtained by multiplexing optical signals of optical frequencies f ₁ , f ₂ ,..., F _N (optical frequency interval Δf) can be extracted from the waveguide of port number i = N + 1 of × M star coupler 11.

Here, j of the M × 2N star coupler 12 is j =
Optical signal of the optical frequency f _k from port N + k is output single-mode waveguide 16 demultiplexed retrieves it is without folded, the optical signal having the same optical frequency f _k instead via a single mode waveguide 17 , M × 2N star coupler 12, a single optical circuit can constitute an optical add / drop circuit. Note that k may be an arbitrary integer from 1 to N, and two or more values may be taken to have a plurality of branch / insert terminals.

The position of the output port changes according to the position of the input port of the optical frequency multiplexed signal having the optical frequencies f ₁ , f ₂ ,..., F _N with the optical frequency interval Δf input to the 2N × M star coupler 11. At this time, the optical frequency that is demultiplexed and output to the single mode waveguide 16 from the folded output port of j = N + k of the M × 2N star coupler 12 is also switched.
Table 5 shows the relationship between the combination of the input / output port number i and the optical signal frequency of the folded output / input port number j.
Shown in

[0055]

[Table 5]

In the configuration shown in FIG. 2, M × 2N
2N ×
The input port of the M star coupler 11 is set to i = N + n (n = 1
整数 N), the corresponding output port is i
= N. That is, the same is true even if the input / output ports are reversed. However, in that case, in the example described above, M × 2N
J = k (k = 1 to N) of the star coupler 12 is a branch port, and j = N + k is an insertion port. The combination of this input / output port number i and the return output /
Table 6 shows part of the relationship between the input port number j and the optical signal frequency.
Shown in

[0057]

[Table 6]

In the configuration shown in FIG. 2, M × 2N
By changing the combination of the folded output-input port of the star coupler 12, i = optical frequency f ₁ of the optical frequency interval Δf input to one input port, f _2, ..., the optical frequency division multiplexed signal having a f _N i = N + 1. For example, i = N or i =
When outputting to the 2N port, the relationship between the folded output port and the folded input port in the M × 2N star coupler 12 is as shown in Table 7. Other combinations of input / output ports are also possible by changing the combination of the folded output / input ports in the M × 2N star coupler 12.

[0059]

[Table 7]

As shown in Tables 2 and 5, 2N
× M optical frequency f ₁ of the optical frequency spacing Δf to be input to the star coupler 11, f _2, ..., when switching the position of the input ports of the optical frequency division multiplexed signal having a f _N, j of M × 2N star coupler 12 = 2k or j = N + k, the optical frequency of the optical signal branched and output to the single mode waveguide 16 from the folded output port is also switched. Therefore, by selecting the input port, the optical frequency of the optical signal to be dropped and added can be selected.

An embodiment of a tunable optical add / drop circuit capable of switching the frequency of an optical signal to be added / dropped by using the basic structure of the optical add / drop circuit according to the first aspect of the present invention shown in FIG. An example configuration will be described.

FIG. 3 is a block diagram showing the configuration of the first embodiment of the tunable optical add / drop circuit. In the figure, the optical frequency of the optical frequency interval Δf input from the input terminal 31
The optical frequency multiplexed signal having f ₁ , f ₂ ,..., f _N is passed through a 1 × N switch 30 linked to two channels, and the i = 1, 3,. Input to any input port. Also, an optical frequency multiplexed signal obtained by multiplexing optical signals of optical frequencies f ₁ , f ₂ ,..., F _N output from any one of i = 2, 4,. Is a 1 × N switch 3 linked to two channels
0 is output to the output terminal 32.

Note that j = 2 of the M × 2N star coupler 12
The optical frequency f _a of the optical signal branched and output from the k-fold output port to the single mode waveguide 16 is the optical frequency f ₁ ,
It can be obtained by equation (9) according to the input port number i for inputting the optical frequency multiplexed signal having f ₂ ,..., f _N.
That is, by providing the 1 × N switch 30 linked to the two channels in the optical add / drop circuit, the optical frequency to be dropped / added can be controlled according to the switch operation, and the tunable type can be achieved.

FIG. 4 is a block diagram showing a second embodiment of the tunable optical add / drop circuit. In the figure, the optical frequency of the optical frequency interval Δf input from the input terminal 31
The optical frequency multiplexed signal having f ₁ , f ₂ ,..., f _N is 1 × 2 ^p
Through a switch (p is a positive integer, 2 ^p ≧ N) 40a,
.., 2N−1 of the 2N × M star coupler 11
Is input to any of the input ports. Also, an optical frequency multiplexed signal obtained by multiplexing optical signals of optical frequencies f ₁ , f ₂ ,..., F _N output from any one of i = 2, 4,. Is the 1 × 2 ^p switch 4
0b is output to the output terminal 32.

This 1 × 2^pSwitches 40a and 40b are the same
Mach-Zehnder 1 × 2 optical switch for each stage
Itch 41₁₁, 41_{twenty one}~ 41_{twenty two}, 41₃₁~ 41₃₄,…,
41 _p1~ 41_pqAre connected in a p-stage cascade (q is
1 or more 2^p-1Integer below). Each Mach-Zehnder type 1 × 2
Optical switch 41₁₁~ 41_pqIs applied to the heater electrode.
Current value I₁₁~ I_pqThe switch operates according to.

FIG. 4B shows a configuration example of one Mach-Zehnder type 1 × 2 optical switch 41. MZ 1 × 2 optical switch 41, 3 dB coupler 44 ₁ in a single-mode waveguide 43 on the waveguide substrate 42, 44 ₂ is formed, the heater electrode 45 to one single-mode waveguides in between
Are arranged. By changing the current I applied to the heater electrode 45, the output terminal or the output terminal is selected by changing the phase state of the optical signal input from the input terminal. By connecting such a Mach-Zehnder 1 × 2 optical switch 41 in multiple stages as shown in FIG.
The 2 × ^p switches 40a and 40b can be configured to realize the same function as the 2-channel linked 1 × N switch 30 shown in the first embodiment.

Also in this embodiment, since the optical add / drop circuit is provided with the 1 × 2 ^p switches 40a and 40b, the optical frequency to be dropped / added can be controlled in accordance with the operation of the switch, and the tunable type can be controlled. It can be. Further, in this embodiment, since all the components can be constituted by optical waveguides, a small, inexpensive, and more stable circuit can be realized.

In the first and second embodiments, when the input / output ports of the 2N × M star coupler 11 are reversed as shown in Table 3, the 1 × N switch 30 or 1 × 2 ^p The switches 40a and 40b and the 2N × M star coupler 11 are connected by exchanging input and output. Also, as shown in Table 4, when the coupling pattern of the folded single mode waveguide 15 of the M × 2N star coupler 12 is changed, the input / output terminals 31 and 32 and 2
The connection pattern with the input / output port of the N × M star coupler 11 is appropriately set. The same applies to the case where the present invention is applied to the optical add / drop circuit of the second aspect.

[0069]

As described above, according to the present invention, by forming an optical demultiplexer and an optical multiplexer using a folded waveguide, a part of the folded waveguide is used for adding and dropping an optical signal. The optical add / drop circuit described above can be realized by one optical circuit. Therefore, the entire optical add / drop circuit according to the present invention can be constituted by an optical waveguide, and can be made into one chip, and a small, inexpensive, and stable circuit can be realized.

Also, since the optical signal frequency to be dropped / added corresponds to the input port for inputting the optical frequency multiplexed signal, a configuration capable of switching the input port position is employed, so that the tunable optical drop / insertion can be easily performed. A circuit can be realized. Note that the position of the output port for outputting the optical frequency multiplexed signal is determined according to the configuration conditions and the input port position corresponding to each of the first and second aspects of the present invention.

[Brief description of the drawings]

FIG. 1 is a diagram showing a basic configuration of an optical add / drop circuit according to the first embodiment;

FIG. 2 is a diagram showing a basic configuration of an optical add / drop circuit of the invention according to claim 2;

FIG. 3 is a block diagram showing a configuration of a first embodiment of a tunable optical add / drop circuit.

FIG. 4 is a block diagram showing the configuration of a second embodiment of a tunable optical add / drop circuit.

FIG. 5 is a diagram showing a configuration example of a conventional arrayed waveguide optical multiplexer / demultiplexer.

FIG. 6 is an enlarged view of a slab waveguide 56 constituting the N × M star coupler 51.

FIG. 7 is a diagram showing transmittance characteristics of a conventional arrayed waveguide optical demultiplexer.

[Explanation of symbols]

Reference Signs List 11 2N × M star coupler 12 M × 2N star coupler 13 Single mode waveguide array 14 Single mode waveguide for input / output 15 Single mode waveguide for folding 30 1 × N switch 31 Input terminal 32 Output terminal 40a, 40b 1 × 2 ^p switch 41 Mach-Zehnder 1 × 2 optical switch 42 waveguide substrate 43 single mode waveguide 44 3 dB coupler 45 heater electrode 51 N × M star coupler 52 M × N star coupler 53 single mode waveguide array 54 input Single-mode waveguide 55 for output Single-mode waveguide for output 56, 57 Slab waveguide

Claims (2)

(57) [Claims] 1. A 2N × M star coupler having a slab waveguide (N is an integer of 1 or more; M is an integer of 2 or more);
It is coupled to a 2N star coupler by M single-mode waveguide arrays having a predetermined optical path length difference, and one of N sets of adjacent ports of the 2N × M star coupler is connected.
And a set of one of the adjacent ports and the input port, the optical frequency f ₁ of the optical frequency spacing Δf to the input _{port, f 2, ..., f x} (x is an integer 1 or more N) enter the optical frequency division multiplexed signal having a when, the M × 2N Stars ₁ sequential light frequency f in septum port of the 2N ports of the coupler, f _2, ..., a configuration for demultiplexing the optical signal of f _x, of the M × 2N star coupler The remote port is coupled back to the adjacent port except for a predetermined set, and the predetermined set of adjacent ports is used to split an optical signal of a predetermined optical frequency corresponding to the input port of the optical frequency multiplexed signal. An optical add / drop circuit comprising: a branch terminal to be inserted; and an insert terminal, wherein the other of a pair of adjacent ports of the 2N × M star coupler is an output port of the optical frequency multiplexed signal. 2. A 2N × M star coupler having a slab waveguide (N is an integer of 1 or more; M is an integer of 2 or more);
It is coupled to the 2N star coupler by an M single-mode waveguide array having a predetermined optical path length difference, and one of the N consecutive ports of the 2N × M star coupler
One as an input port, and the optical frequency interval Δ
When an optical frequency multiplexed signal having optical frequencies f ₁ , f ₂ ,..., f _x (x is an integer of 1 or more and N or less) of f is inputted, N consecutive ports of the M × 2N star coupler are sequential light frequencies f _1, f _2, ..., a configuration for demultiplexing the optical signal of f _x, to the M × 2N from N ports successive star coupler remaining N ports, a predetermined port While the optical frequencies of the optical signals demultiplexed except for the pair are folded back and coupled so as to be arranged in the same order or cyclically, a predetermined port pair is connected to an optical port of a predetermined optical frequency corresponding to the input port of the optical frequency multiplexed signal. A branch terminal and an insertion terminal for branching / inserting a signal are used. Of the remaining N consecutive ports of the 2N × M star coupler, one corresponding to the input port and the return path is used for the optical frequency multiplexed signal. Output port An optical add / drop circuit.