Optical communication element and optical neural network

An optical communication element includes a plurality of slabs, an input port group, an output port group, a first waveguide group, and a second waveguide group. The plurality of slabs includes third waveguide. Each of the plurality of slabs include a predetermined number of first ports being arranged at an inlet the third waveguide at equal intervals in a lateral direction perpendicular to a light traveling direction, and input the optical signals, and a predetermined number of second ports being arranged at an outlet of the third waveguide at the equal intervals in the lateral direction so as to face the first ports, and output the optical signals. Each of the third waveguides are configured with a dimension that allows light intensity to be distributed at all traveling positions located in the lateral direction.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2020-21221, filed on Feb. 12, 2020, the entire contents of which are incorporated herein by reference.

FIELD

The embodiments discussed herein are related to an optical communication element and an optical neural network.

BACKGROUND

For example, there is known an optical neural network (NN) that implements the function of an NN processor, whose mainstream is a digital electronic integrated circuit, by a passive optical circuit or the like. In the optical NN, for example, since the inference is supposed to be completed in the traveling time during which the light travels, high throughput and low latency may be achieved until the inference is completed. Furthermore, in the optical NN, for example, consumed power when an optical signal travels in the passive optical circuit is not involved. Thus, in an optical communication element such as a unitary transformation element used to implement the optical NN, it is desired to miniaturize the entire element while increasing the upper limit of the number of ports that can be integrated in the circuit.

FIG.7is an explanatory diagram illustrating an example of a conventional optical NN200. The optical NN200illustrated inFIG.7includes an input port group201, an output port group202, and a unitary transformation element204in which a plurality of Mach-Zehnder (MZ) interference devices203are interconnected. The input port group201includes N input ports201A that input optical signals. The output port group202includes N output ports202A that output optical signals. The unitary transformation element204is configured by interconnecting the plurality of MZ interference devices203between the input port group201and the output port group202. The MZ interference device203includes two 2×2 fixed couplers211, a pair of waveguides212that connect the fixed couplers211to each other, and a phase shifter213that is provided for each one waveguide212A, which is one of the pair of waveguides212, and adjusts the phase amount of an optical signal that passes through one of the waveguides212.

When adjusting the phase amount of an optical signal that passes through one of the waveguides212, the MZ interference device203generates a phase difference between the optical signal that passes through the one waveguide212A and an optical signal that passes through the other of the waveguides212, which is referred to as the other waveguide212B. Then, the MZ interference device203adjusts the light intensity of output light according to the generated phase difference. As a result, by adjusting the light intensity of the output light of each MZ interference device203, the output light may be distributed at any ratio according to a change in the light intensity of the output light. For example, any vector-matrix operations in the optical NN200may be implemented using the plurality of interconnected MZ interference devices203.

Related techniques are disclosed in for example Japanese Laid-open Patent Publication Nos. 2018-200391, and No. 2019-101887.

SUMMARY

According to an aspect of the embodiments, an optical communication element includes a plurality of slabs; an input port group that includes a predetermined number of input ports that input optical signals; an output port group that includes the predetermined number of output ports that output the optical signals; a first waveguide group that includes first waveguides with phase shifters allocated between the input port group and the output port group and provided for each the predetermined number of input ports; and a second waveguide group that includes second waveguides with phase shifters allocated between the input port group and the output port group and provided for each the predetermined number of output ports. The plurality of slabs includes a first slab, a second slab, and a third slab, each of the plurality of slabs includes third waveguide, the third waveguide included in the first slab being connected between the input port group and the first waveguide group, the third waveguide included in the second slab being connected between t the first waveguide group and the second waveguide group, and the third waveguide included in the third slab being connected between the second waveguide group and the output port group. Each of the plurality of slabs include: a predetermined number of first ports that are arranged at an inlet the third waveguide at equal intervals in a lateral direction perpendicular to a light traveling direction, and input the optical signals, and a predetermined number of second ports that are arranged at an outlet of the third waveguide at the equal intervals in the lateral direction so as to face the first ports, and output the optical signals, and each of the third waveguides are configured with a dimension that allows light intensity to be distributed at all traveling positions located in the lateral direction.

DESCRIPTION OF EMBODIMENTS

In the related art, a horizontal width dimension Lm of the unitary transformation element204illustrated inFIG.7in a light traveling direction can be expressed by, for example, 2(N−1)×(Lc1+Lp1). N denotes the number of ports of the input ports201A, Lc1 denotes the horizontal width dimension of the 2×2 fixed coupler211in the light traveling direction, and Lp1 denotes the horizontal width dimension of the waveguide212with the phase shifter213in the light traveling direction. The horizontal width dimension Lm of the unitary transformation element204is given as, for example, Lm=(N−1)×1.2 mm when Lc1=100 μm and Lp1=500 μm are employed, and there is no choice but to lower the upper limit of the number N of integratable ports because the dimension is large. Moreover, since the number of phase shifters213arranged in the unitary transformation element204can be calculated by, for example, (N−1)×N, the number of phase shifters213to be controlled to implement any transformation is raised. As a result, the processing burden when controlling the phase shifters213to be controlled becomes larger.

This means that, in the conventional unitary transformation element204, as the number of input ports increases, the horizontal width dimension Lm becomes larger, and accordingly the mounting area of the integrated circuit becomes larger. Moreover, in the conventional unitary transformation element204, as the number of input ports increases, the number of the arranged phase shifters213to be controlled increases, and accordingly the processing burden when controlling the phase shifters213to be controlled becomes larger.

In one aspect, it is an object of the present embodiment to provide an optical communication element and an optical neural network for miniaturizing the entire element.

Hereinafter, the embodiments of the optical communication element and the like disclosed in the present application will be described in detail on the basis of the drawings. Note that the disclosed technology is not limited by each of the embodiments. Furthermore, each embodiment to be described below may also be combined as appropriate, without causing inconsistency.

Embodiments

FIG.1is a schematic cross-sectional perspective view illustrating an example of an optical communication element1of the present embodiment, andFIG.2is an explanatory diagram illustrating an example of the optical communication element1. The optical communication element1illustrated inFIG.1includes an input port group2, an output port group3, two waveguide groups4, and three slabs5. The input port group2includes a predetermined number N of input ports2A that input optical signals. The output port group3includes the predetermined number N of output ports3A that output optical signals.

The two waveguide groups4are, for example, a first waveguide group4A and a second waveguide group4B. The first waveguide group4A includes the predetermined number N of first waveguides41A connected between the input port group2and the output port group3and provided for each input port2A. Moreover, the second waveguide group4B includes the predetermined number N of second waveguides41B connected between the input port group2and the output port group3and provided for each output port3A. The first waveguide41A and the second waveguide41B are optical waveguides with phase shifters42. The phase shifter42changes the light intensity of output light by adjusting the phase amount. As a result, the output light may be distributed at any ratio according to the change in the light intensity of the output light. Note that the number of arranged phase shifters42used in the optical communication element1is, for example, 2N.

The first waveguide41A and the second waveguide41B each have a core that functions as an optical path, and a clad surrounding the core. Since the refractive index of the core and the refractive index of the clad are different from each other, the optical signal causes total reflection at a boundary surface between the core and the clad while traveling in a light traveling direction X1. The core is constituted by, for example, a high refractive index material, and the clad is constituted by, for example, a low refractive index material. Note that, in the first waveguide41A and the second waveguide41B illustrated inFIGS.1and2, the core portions are illustrated, but the illustration of the clad portions is omitted.

The slab5has a flat plate-shaped core and a flat plate-shaped clad, and is configured by surrounding the flat plate-shaped core whose cross-sectional shape extends in the light traveling direction X1, with the flat plate-shaped clad. Since the flat plate-shaped core is constituted by, for example, a high refractive index material, and the flat plate-shaped clad is constituted by, for example, a low refractive index material, light causes total reflection at a boundary surface between the flat plate-shaped core and the flat plate-shaped clad while traveling. Note that, in the slab5illustrated inFIGS.1and2, the flat plate-shaped core portions are illustrated, but the illustration of the flat plate-shaped clad portions is omitted.

The slab5includes a third waveguide51, the predetermined number N of first ports52, and a predetermined number N of second ports53. The predetermined number N of first ports52are arranged at an inlet of the third waveguide51at equal intervals p in a lateral direction X2 perpendicular to the light traveling direction X1. The first port52is a port that inputs an optical signal to the third waveguide51. The predetermined number N of second ports53are arranged at an outlet of the third waveguide51at the equal intervals p in the lateral direction X2 so as to face the first ports52. The second port53is a port that outputs an optical signal from the third waveguide51. The third waveguide51is a multi-mode waveguide having different propagation constants, in which optical signals in single-mode waveguides input from the first ports52interfere with each other, and the light intensity at respective traveling positions located in the lateral direction X2 changes according to the traveling of the optical signals. Moreover, the third waveguide51is configured with a dimension that allows the light intensity to be distributed at all the traveling positions located in the lateral direction X2 according to the traveling of the optical signals.

In the third waveguide51, the distance from a concentric axis of the first port52among the first ports52arranged in the lateral direction X2 to an inner wall51A of the third waveguide51located closest in the lateral direction X2 has the same dimension as the dimension of the interval p between the adjacent first ports52. In the third waveguide51, the distance from a concentric axis of the N-th first port52to an inner wall51B of the third waveguide51located closest in the lateral direction X2 has the same dimension as the dimension of the interval p between the adjacent first ports52.

The three slabs5are, for example, a first slab5A, a second slab5B and a third slab5C. The first slab5A includes the third waveguide51connected between the input ports2A in the input port group2and the first waveguides41A in the first waveguide group4A. The second slab5B includes the third waveguide51connected between the first waveguides41A in the first waveguide group4A and the second waveguides41B in the second waveguide group4B. The third slab5C also includes the third waveguide51connected between the second waveguides41B in the second waveguide group4B and the output ports3A in the output port group3.

A vertical width dimension W of the third waveguide51denotes the vertical width in the lateral direction X2 perpendicular to the light traveling direction X1, and has a dimension of a length capable of supporting a plurality-of-waveguide mode. Furthermore, a dimension L of the optical communication element1denotes the horizontal width of the optical communication element1in the light traveling direction X1. The dimension L of the optical communication element1can be expressed by, for example, 3Ls+2Lp. Ls denotes the horizontal width dimension of the third waveguide51of each slab5. Lp denotes the horizontal width dimension of the first waveguide group4A or the second waveguide group4B in the light traveling direction X1.

The horizontal width dimension Ls of the third waveguide51can be expressed by, for example, 2nH(N+1)p2/λ. Note that nH denotes the refractive index of the flat plate-shaped core in a high refractive index region, λ denotes the wavelength of the optical signal that passes through the flat plate-shaped core, N denotes the number of ports, and p denotes the arrangement interval between the adjacent first ports52. Therefore, the horizontal width dimension L of the optical communication element1can be expressed by 6nH(N+1)p2/λ+2Lp. For example, when nH=3, λ=1550 nm, and p=2 μm are employed, the horizontal width dimension L of the optical communication element1is given as (N+1)×46 μm+1 mm.

FIG.3is an explanatory diagram illustrating an example of distribution of light intensity in the third waveguide51for each traveling position located in the lateral direction X2 for each timing in the light traveling direction X1. In the third waveguide51, for example, the optical signals in single-mode waveguides input from the first ports52interfere with each other. The third waveguide51excites the waveguide mode in the lateral direction X2 according to the traveling of the optical signals by the mutual interference between the optical signals, and the interference effect of the plurality-of-waveguide mode having different propagation constants causes the light intensity at each traveling position located in the lateral direction X2 to change variously according to the traveling of the optical signals.

For example, when the predetermined number N of first port52is 10, and an optical signal is input from a port 1, the distribution of light intensity for each traveling position of ports 1 to 10 in the lateral direction X2 from the timing “1” to the timing “45” in the light traveling direction X1 is assumed. In the light intensity distribution at the timing “1” in the light traveling direction X1 at which the optical signal is input from the port 1, the distribution is such that the light intensity at the traveling position of the port 1 is 1.00 and the light intensity at the traveling positions of the ports 2 to 10 is 0.00.

In the light intensity distribution at the timing “2” in the light traveling direction X1, the distribution is such that the light intensity at the traveling positions of the ports 1 and 10 is 0.01, the light intensity at the traveling positions of the ports 2 and 9 is 0.05, and the light intensity at the traveling positions of the ports 3 and 8 is 0.10. Moreover, in the light intensity distribution, the light intensity at the traveling positions of the ports 4 and 7 is 0.15, and the light intensity at the traveling positions of the ports 5 and 6 is 0.18. This indicates that, in the light intensity distribution at the timing “2”, the light intensity is distributed at all the traveling positions of the ports 1 to 10 located in the lateral direction X2.

Then, in the light intensity distribution at the timing “12” in the light traveling direction X1, the light intensity at the traveling positions of the ports 1 and 10 is 0.50 and the light intensity at the traveling positions of the ports 2 to 9 is 0.00. This indicates that, in the light intensity distribution at the timing “12”, ½ of the whole light intensity is distributed at each of the traveling position of the port 1 and the traveling position of the port 10, which is a point of symmetry of the port 1.

Moreover, in the light intensity distribution at the timing “22” in the light traveling direction X1, the light intensity is distributed at all the traveling positions of the ports 1 to 10. Additionally, in the light intensity distribution at the timing “23” in the light traveling direction X1, the distribution is such that the light intensity at the traveling positions of the ports 1 and 9 is 0.00 and the light intensity at the traveling position of the port 10 is 1.00. This indicates that, in the light intensity distribution at the timing “22”, the distribution is such that the optical signal incident on the port 1 forms an image on the port 10, which is a point of symmetry of the port 1. Besides, in the light intensity distribution at the timing “24” in the light traveling direction X1, the light intensity is distributed at all the traveling positions of the ports 1 to 10.

Moreover, in the light intensity distribution at the timing “34” in the light traveling direction X1, ½ of the whole light intensity is distributed at each of the traveling position of the port 1 and the traveling position of the port 10, which is a point of symmetry of the port 1. In the light intensity distribution at the timing “44” in the light traveling direction X1, the light intensity is distributed at all the traveling positions of the ports 1 to 10. Then, in the light intensity distribution at the timing “45” in the light traveling direction X1, the light intensity at the traveling position of the port 1 is 1.00 and the light intensity at the traveling positions of the ports 2 to 10 is 0.00.

As illustrated inFIG.3, any timing at which the light intensity is distributed at all the traveling positions of the ports 1 to 10 located in the lateral direction X2 between the timing “1” and the timing “45” is supposed to occur at the timings of “2”, “22”, “24” and “54”. As a result, owing to the distribution of the light intensity at all the traveling positions located in the lateral direction X2, the degree of freedom of unitary transformation, for example, executed by the optical communication element1may be maximized.

The distance until the input light to the first first port52among the plurality of first ports52in the third waveguide51forms an image on the first second port53, which is the distance from the timing “1” to the timing “45”, is denoted as L1. Moreover, the distance until the input light to the first first port52forms an image on the tenth first port52, which is a point of symmetry with the first first port52, which is the distance from the timing “1” to the timing “23”, is denoted as L2. In this case, L2 approximates L1/2. Additionally, the distance until the light intensity of the input light to the first first port52is halved with respect to the tenth first port52, which is a point of symmetry with the first first port52, which is the distance from the timing “1” to the timing “12”, is denoted as L3. In this case, L3 approximates L2/2. The vertical width W of the third waveguide51/the port interval p approximates the number N of input ports.

In the third waveguide51, the light intensity is supposed to be distributed at all the traveling positions located in the lateral direction X2 at the timings “2”, “22”, “24” and “54” between the timing “1” and the timing “45” in the light traveling direction X1. Thus, among any timings at which the light intensity is distributed at all the traveling positions located in the lateral direction X2, the timing having a shortest distance from the timing “1” is a timing near L3(p/W), for example, the timing “2”. Accordingly, for the horizontal width dimension Ls of the third waveguide51, it is supposed to be sufficient to ensure the distance from the timing “1” to the timing “2”.

Therefore, the distance from the timing “1” to the timing “2” is enough for the horizontal width dimension Ls of the third waveguide51. This means that the horizontal width dimensions Ls of the third waveguide51of the first slab5A, the third waveguide51of the second slab5B, and the third waveguide51of the third slab5C are each the distance from the timing “1” to the timing “2”.

Therefore, the horizontal width dimension L of the optical communication element1is given as L=3Ls+2Lp=6nH(N+1)p2/λ+2Lp. At this time, when nH=3, λ=1550 nm, and p=2 μm are employed, L=(N+1)×46 μm+1 mm is given. Consequently, since the horizontal width dimension L of the optical communication element1can be made significantly short as compared with the conventional case, the present embodiment may contribute to the miniaturization of the optical communication element1.

Moreover, the number of arranged phase shifters42is given as 2N because one phase shifter42of the first waveguide41A and one phase shifter42of the second waveguide41B are involved for each of N ports, where N denotes the number of ports. Consequently, by significantly reducing the number of the phase shifter42arranged in the optical communication element1, not only the optical communication element1may be miniaturized but also the load expected for the control process for the phase shifters42may be mitigated.

FIG.4is an explanatory diagram illustrating an example of comparison results for the horizontal width dimension L of the optical communication element1between the present embodiment and prior art for each number N of input ports. The horizontal width dimension of an optical communication element of the prior art can be calculated by (N−1)×1.2 mm. On the other hand, the horizontal width dimension of the optical communication element1of the present embodiment can be calculated by (N+1)×46 μm+1 mm.

For example, when the number N of input ports is 10, the horizontal width dimension of the optical communication element of the prior art is 11 mm, whereas the horizontal width dimension L of the optical communication element1of the present embodiment is 1.5 mm. Therefore, the horizontal width dimension L of the optical communication element1of the present embodiment may be significantly shortened as compared with the horizontal width dimension of the optical communication element of the prior art. Furthermore, even when the number N of input ports is 20, the horizontal width dimension of the optical communication element of the prior art is 23 mm, whereas the horizontal width dimension L of the optical communication element1of the present embodiment is 2.0 mm. In addition, for example, when the number N of input ports is 50, the horizontal width dimension of the optical communication element of the prior art is 59 mm, whereas the horizontal width dimension L of the optical communication element1of the present embodiment is 3.3 mm. In addition, when the number N of input ports is 100, the horizontal width dimension of the optical communication element of the prior art is 120 mm, whereas the horizontal width dimension L of the optical communication element1of the present embodiment is 5.6 mm. Consequently, the horizontal width dimension L of the optical communication element1of the present embodiment may be significantly shortened as compared with the horizontal width dimension of the optical communication element of the prior art.

FIG.5is an explanatory diagram illustrating an example of comparison results between the present embodiment and the prior art in terms of the number of the phase shifters42arranged in the optical communication element1for each number N of input ports. The number of phase shifters arranged in the optical communication element of the prior art can be calculated by (N−1)×N. On the other hand, the number of the phase shifters42arranged in the optical communication element1of the present embodiment can be calculated by 2N.

For example, when the number N of input ports is 10, the number of phase shifters arranged in the optical communication element of the prior art is 90, whereas the number of the phase shifters42arranged in the optical communication element1of the present embodiment is 20. Therefore, the number of the phase shifters42arranged in the optical communication element1of the present embodiment may be significantly reduced as compared with the number of the phase shifters arranged in the optical communication element of the prior art. When the number of input ports is 20, the number of the phase shifters arranged in the optical communication element of the prior art is 380, whereas the number of the phase shifters42arranged in the optical communication element1of the present embodiment is 40. Furthermore, for example, when the number N of input ports is 50, the number of the phase shifters arranged in the optical communication element of the prior art is 2450, whereas the number of the phase shifters42arranged in the optical communication element1of the present embodiment is 100. When the number of input ports is 100, the number of the phase shifters arranged in the optical communication element of the prior art is 9900, whereas the number of the phase shifters42arranged in the optical communication element1of the present embodiment is 200. Consequently, the number of the phase shifters42arranged in the optical communication element1of the present embodiment may be suppressed significantly as compared with the number of the phase shifters arranged in the optical communication element of the prior art. As the number of the arranged phase shifters42is lowered, the processing load for the control of the phase shifters42becomes smaller.

The optical communication element1of the present embodiment includes the first waveguide group4A including the first waveguides41A with the phase shifters42connected between the input port group2and the output port group3and provided for each input port2A. Moreover, the optical communication element1includes the second waveguide group4B including the second waveguides41B with the phase shifters42connected between the input port group2and the output port group3and provided for each output port3A. The optical communication element1further includes the slab5including the third waveguide51connected between the input ports2A in the input port group2and the first waveguides41A in the first waveguide group4A. The optical communication element1further includes the slab5including the third waveguide51connected between the first waveguides41A in the first waveguide group4A and the second waveguides41B in the second waveguide group4B. The optical communication element1further includes the slab5including the third waveguide51connected between the second waveguides41B in the second waveguide group4B and the output ports3A in the output port group3. As a result, since the two phase shifters42are arranged for every waveguides41A and41B, the number of the phase shifters42mounted on the optical communication element1is lowered, such that the phase shifters42may be easily controlled.

The slab5of the optical communication element1includes the predetermined number N of the first ports52that are arranged at an inlet of the third waveguide51at equal intervals in the lateral direction X2 perpendicular to the light traveling direction X1 and input optical signals to the third waveguide51. In addition, the slab5includes the predetermined number N of the second ports53that are arranged at an outlet of the third waveguide51at equal intervals in the lateral direction X2 so as to face the first ports52and output optical signals from the third waveguide51. Moreover, the third waveguide51is a multi-mode waveguide having different propagation constants, in which optical signals in single-mode waveguides input from the first ports52interfere with each other, and the light intensity at respective traveling positions located in the lateral direction X2 changes according to the traveling of the optical signals. Additionally, the third waveguide51is configured with a dimension that allows the light intensity to be distributed at all the traveling positions located in the lateral direction X2. As a result, the horizontal width dimension Ls of the third waveguide51of the slab5may be shortened, such that the horizontal width dimension L of the optical communication element1may be made shorter even if the number N of input ports increases. Therefore, the optical communication element1can be miniaturized as compared with the prior art.

The third waveguide51is configured such that the horizontal width dimension Ls of the third waveguide51coincides with the shortest distance in the light traveling direction X1 from the timing “1” to any timing “2”, “22”, “24”, and “44” at which the light intensity is distributed at all the traveling positions located in the lateral direction X2. As a result, the horizontal width dimension Ls of the third waveguide51is shortened, such that the optical communication element1may be miniaturized.

The horizontal width dimension Ls of the third waveguide51has a dimension obtained by L3×(p/W). As a result, the horizontal width dimension Ls of the third waveguide51is shortened, such that the optical communication element1may be miniaturized.

In the third waveguide51, the distance from a concentric axis of the first first port52among the first ports52arranged in the lateral direction X2 to the inner wall51A of the third waveguide51located closest in the lateral direction X2 has the same dimension as the dimension of the interval p between the adjacent first ports52. Moreover, in the third waveguide51, the distance from a concentric axis of the N-th first port52to the inner wall51B of the third waveguide51located closest in the lateral direction X2 has the same dimension as the dimension of the interval p between the adjacent first ports52. As a result, in the third waveguide51, the light intensity at respective traveling positions located in the lateral direction X2 changes according to the traveling of the optical signals, and the light intensity is allowed to be distributed at all the traveling positions located in the lateral direction X2.

The horizontal width dimension Ls of the third waveguide51has a dimension obtained by 2nH(N+1)p2/λ (where nH: the refractive index in a high refractive index region, A: the wavelength of light to be used, N: the number of ports, p: the arrangement interval between the adjacent first ports52). As a result, the horizontal width dimension Ls of the third waveguide51is shortened, such that the horizontal width dimension L of the entire optical communication element1may be made shorter even if the number N of input ports increases. The optical communication element1may be miniaturized.

The optical communication element1of the present embodiment may be adopted as a unitary transformation element in an optical neural network, and an embodiment of this case will be described below.FIG.6is an explanatory diagram illustrating an example of an optical neural network100that adopts unitary transformation elements formed by the optical communication element1of the present embodiment. Any neuron operation in the optical neural network100can be expressed by a matrix operation of unitary matrix×diagonal matrix×unitary matrix. An ordinary real matrix M can be decomposed as M=USV*. U denotes the m×m unitary matrix, S denotes the m×n diagonal matrix with a non-negative real number diagonally, and V* denotes the complex conjugate of the n×n unitary matrix V. The optical neural network100illustrated inFIG.6includes a first unitary transformation element1A (1) that carries out matrix operations using the matrix V, a plurality of optical amplifiers6that carry out matrix multiplication using the matrix S, and a second unitary transformation element1B (1) that carries out matrix operations using the matrix U. The first unitary transformation element1A receives inputs of a predetermined number N of optical signals, and transforms the predetermined number N of optical signals into the m×m unitary matrix. The first unitary transformation element1A outputs the predetermined number N of optical signals after unitary transformation.

The optical amplifiers6are optical amplifiers provided for each of the predetermined number N of optical signals. The optical amplifiers6attenuate the light intensity of the predetermined number N of optical signals after unitary transformation output from the first unitary transformation element1A. The second unitary transformation element1B receives inputs of the optical signals attenuated by the respective optical amplifiers6, and unitarily transforms the attenuated optical signals. The second unitary transformation element1B outputs the optical signals after unitary transformation.

Since the optical neural network100illustrated inFIG.6has a configuration in which the optical amplifiers6are inserted between the first unitary transformation element1A and the second unitary transformation element1B, any matrix operation, which is neuron operation, may be implemented.

Note that, in the present embodiment, the horizontal width dimension Ls of the third waveguide51is exemplified as the distance from the timing “1” to the timing “2”; however, the timing is not limited to the timing “2” and any timing is sufficient as long as the light intensity is distributed at all the traveling positions located in the lateral direction X2. As illustrated inFIG.3, for example, the timings “22”, “24” and “54” may be employed and may be selected as appropriate.

Furthermore, each of the constituent elements of the units illustrated in the drawings is not necessarily physically configured as illustrated in the drawings. For example, specific forms of separation and integration of the respective units are not limited to the illustrated forms, and all or some of the units may be functionally or physically separated and integrated in any units according to various loads, use situations, and the like.

Moreover, all or some of various processing functions executed in the respective devices may be executed by a central processing unit (CPU) (or a microcomputer such as a micro processing unit (MPU) and a micro controller unit (MCU)). Furthermore, all or some of the various processing functions may of course be executed by a program analyzed and executed by a CPU (or a microcomputer such as an MPU and an MCU) or hardware using wired logic.