JP7822333B2 - Reservoir Computing Device - Google Patents

Description

This disclosure relates to reservoir computing technology.

A recurrent neural network (RNN) consists of an input layer, a recurrent layer (reservoir layer), and an output layer. Generally, when an RNN is trained, the weights (coefficients) of the input layer, recurrent layer, and output layer are updated. Reservoir computing is a type of RNN that only updates the weights of the output layer during training, and does not update the weights of the input layer or recurrent layer. In reservoir computing, the weights of the input layer and recurrent layer are set to fixed values that are randomly generated, for example. Instead of only updating the weights of the output layer, reservoir computing increases the number of neurons in the recurrent layer.

Reservoir computing's recurrent layer (reservoir layer) implemented in hardware is called "physical reservoir computing." Non-patent documents 1 to 3 disclose physical reservoir computing. In physical reservoir computing, to represent the random weights of the reservoir layer, a masking process is performed on the input data and then input to the reservoir layer. Non-patent documents 1 and 2 implement the masking process in the digital domain. On the other hand, non-patent document 3 discloses a configuration in which the masking process is implemented in the optical domain. By implementing the masking process in the optical domain, it is possible to perform the masking process faster than when implemented in the digital domain.

Appeltant, L. , etc. al. , Constructing optimized binary masks for reservoir computing with delay systems. Sci Rep 4, 3629, 2014 Quentin Vinkier, et. al. , "High-performance photonic reservoir computer based on a coherently driven passive cavity", Optica 2, 438-446, 2015 Nakajima, M. , etc. al. , "Scalable reservoir computing on coherent linear photonic processor"Commun Phys4, 20, 2021

However, Non-Patent Document 3 requires an ultrafast light source, such as an ultrashort optical pulse light source, making the configuration complex.

This disclosure provides a technology that performs masking in the optical domain without using an ultrashort optical pulse light source.

According to one aspect of the present disclosure, a reservoir computing device includes a generating means for generating multiple carrier lights; a modulating means for generating modulated light by modulating light including the multiple carrier lights with a composite signal obtained by combining an input signal and a sinusoidal signal; a dispersive medium; an optical element that optically realizes a reservoir layer and is disposed downstream of the dispersive medium; and a processing means for processing output light output from the optical element when the modulating means inputs the modulated light into the dispersive medium. The processing means includes a receiving means for coherently receiving the output light and converting it into an electrical signal, and a compensating means for compensating an output signal corresponding to the input signal, which is included in the electrical signal, based on a pilot signal that corresponds to the sinusoidal signal and is included in the electrical signal.

According to this disclosure, masking can be performed in the optical domain without using an ultrashort optical pulse light source.

FIG. 1 is a block diagram of a reservoir computing device, according to one embodiment. 4 is an illustration of internal signals of a reservoir computing device, according to one embodiment. FIG. 2 is a block diagram of a processing unit according to one embodiment. FIG. 2 is a block diagram of a processing unit according to one embodiment.

The following embodiments are described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the claimed invention, and not all combinations of features described in the embodiments are necessarily essential to the invention. Two or more of the features described in the embodiments may be combined in any desired manner. Furthermore, the same reference numbers are used for identical or similar components, and duplicate descriptions will be omitted.

Figure 1 is a diagram illustrating the configuration of a reservoir computing device according to this embodiment. The multi-wavelength light source 1 generates and outputs continuous light (carrier light) at multiple different frequencies. Figure 2(A) shows the frequency components of the light output by the multi-wavelength light source 1. In Figure 2(A), reference numeral 90 denotes a carrier light. Each carrier light 90 may be generated individually by an independent light source included in the multi-wavelength light source 1. Alternatively, some of the multiple carrier lights 90 may be generated in a phase-synchronized state by a single light source. The frequency spacing of the multiple carrier lights 90 may be, for example, on the order of terahertz (THz). For example, if all of the multiple carrier lights 90 satisfy the mode-locking condition, the time waveform of the light including the multiple carrier lights will be an ultrashort pulse. However, as described above, in this embodiment, it is not necessary to satisfy the mode-locking condition. The multiple carrier lights 90 generated by the multi-wavelength light source 1 are input to the modulator 2.

An input signal indicating data to be input to the reservoir computing device is input to the synthesis unit 6. The oscillator 7 generates a sine wave signal of a predetermined frequency and outputs it to the synthesis unit 6. The frequency of the sine wave signal is outside the band of the input signal. The synthesis unit 6 outputs a synthesized signal, which is the combination of the input signal and the sine wave signal, to the modulator 2.

The modulator 2 collectively modulates multiple carrier lights 90 from the multi-wavelength light source 1 with a composite signal. Figure 2(B) shows the frequency components of the modulated light output by the modulator 2. Reference numeral 80 denotes a component corresponding to the input signal (input signal component 80), and reference numeral 81 denotes a component corresponding to the sine wave signal (sine wave signal component 81). A set 82 of input signal components 80 and sine wave signal components 81 is generated for each carrier light 90. In other words, the modulated light includes sets 82 of input signal components 80 and sine wave signal components 81 corresponding to each of the multiple carrier lights 90.

The output light from the modulator 2 is input to the dispersive medium 3. The dispersive medium 3 applies dispersion according to the frequency to the modulated light from the modulator 2. As a result, each component of the modulated light is masked according to the dispersion applied by the dispersive medium 3. In this embodiment, multiple carrier lights 90 with wide frequency intervals are used, so high-speed masking is performed in the dispersive medium 3. A reservoir section 4 is provided downstream of the dispersive medium 3. The reservoir section 4 includes an optical circuit (optical component) that optically realizes a reservoir layer. As an example, the reservoir section 4 has a delay loop configuration. Processing corresponding to the connections between neurons is performed in the reservoir section 4. The modulated light input to the dispersive medium 3 passes through the dispersive medium 3 and the reservoir section 4 and is input to the processing section 5 as output light.

Figure 3 is a configuration diagram of the processing unit 5. The coherent receiver 51 of the processing unit 5 has a local light source, and coherently receives the output light from the reservoir unit 4 to generate an electrical signal, which is then output to the compensation unit 52. The electrical signal includes an output signal component corresponding to the input signal component 80 in Figure 2(B) and a set of pilot signal components corresponding to the sinusoidal signal component 81. The set of output signal components and pilot signal components each correspond to the carrier light 90.

In this embodiment, the multiple carrier lights 90 are not mode-locked, and therefore have relative phase noise, etc. Therefore, the output light passing through the dispersive medium 3 also fluctuates depending on the phase noise, etc. This corresponds to the masking process in the dispersive medium 3 changing over time. Because the masking process needs to remain constant over time, it is necessary to compensate for the effects of phase noise, etc. to keep the masking process constant. Furthermore, the local light source of the compensation unit 52 also contains phase noise, etc. In other words, the output signal component is affected not only by the phase noise, etc. of the carrier light 90, but also by the phase noise, etc. of the local light source. Therefore, the compensation unit 52 compensates the output signal component based on the pilot signal component to compensate for the effects of phase noise, etc. contained in the output signal component. Specifically, the compensation unit 52 multiplies the complex conjugate component of the pilot signal component by the corresponding output signal component, i.e., the output signal component corresponding to the same carrier light 90. This makes it possible to compensate for the effects of phase noise, etc. contained in the output signal component. Each output signal component compensated by the compensation unit 52 is also compensated for changes in the masking process over time.

For example, if some of the multiple first carrier lights 90 are generated to satisfy the mode-locking condition, the output signal components corresponding to each of the multiple first carrier lights can be collectively compensated based on the pilot signal component corresponding to one of the multiple first carrier lights.

Each output signal component compensated by the compensation unit 52 is input to the post-processing unit 53. The post-processing unit 53 performs processing on each output signal component according to the application of the reservoir computing device.

The processing unit 5 can also be configured as shown in Figure 4. The frequency separation unit 54 in Figure 4 separates the output light from the reservoir unit 4 into first to third output lights according to the frequency band. The number of separations is not limited to three and can be any value equal to or greater than two. The first to third output lights each contain one or more sets of output signal components and pilot signal components. The frequency separation unit 54 outputs the first output light to the first path, the second output light to the second path, and the third output light to the third path. A coherent receiver 51 and a compensation unit 52 are provided in each of the first to third paths. By separating the output light from the reservoir unit 4 according to the frequency band, the bandwidth to be processed by the compensation unit 52 can be narrowed.

As described above, according to this embodiment, masking processing can be performed in the optical domain without using an ultrashort optical pulse light source.

The above configuration makes it possible to perform masking in the optical domain without using an ultrashort optical pulse light source. This will therefore contribute to Goal 9 of the United Nations' Sustainable Development Goals (SDGs), which states, "Build resilient infrastructure, promote sustainable industrialization and foster innovation."

1: Multi-wavelength light source, 2: Modulator, 3: Dispersive medium, 4: Reservoir section, 5: Processing section, 51: Coherent receiver, 52: Compensation section

Claims (3)

generating means for generating a plurality of carrier lights;
a modulation means for generating modulated light by modulating the light including the plurality of carrier lights with a combined signal obtained by combining an input signal and a sinusoidal signal;
a dispersive medium;
an optical element that optically embodies a reservoir layer, disposed downstream of the dispersive medium;
a processing unit that processes output light output from the optical element by inputting the modulated light into the dispersive medium by the modulation unit;
Equipped with
The processing means
a receiving means for coherently receiving the output light and converting it into an electrical signal;
a compensation means for compensating an output signal corresponding to the input signal included in the electrical signal based on a pilot signal corresponding to the sinusoidal signal included in the electrical signal;
1. A reservoir computing device comprising: the processing means further includes frequency separation means for separating the output light into a plurality of output lights according to frequency bands;
The reservoir computing device of claim 1 , wherein the receiving means and the compensating means are provided for each of the plurality of output lights. The reservoir computing device of claim 1, wherein the compensation means compensates the output signal corresponding to the first carrier light included in the electrical signal based on the pilot signal corresponding to the first carrier light among the plurality of carrier lights included in the electrical signal.