Time delay reserve pool calculation method based on dispersion orthogonal polarized light feedback VCSEL

Abstract

The invention discloses a time delay reserve pool calculation method based on dispersion orthogonal polarized light feedback VCSEL. An adopted time delay RC system comprises a tunable laser, a Mach-Zehnder modulator, a VCSEL, an optical isolator, an optical coupler, a polarization controller, a variable optical attenuator, a chirp fiber Bragg grating and a photoelectric detector. A signal of the input layer is modulated by a Mach-Zehnder modulator and then is injected into an X polarization component of the VCSEL of the reserve pool layer; emitted light of the VCSEL is divided into two paths after passing through the optical circulator, one path is reflected back to the VCSEL by the chirp fiber bragg grating after being subjected to cross-polarization rotation through the polarization controller, and a reserve pool layer of the time delay RC system is constructed; one path is transmitted to the output layer and is converted into an electric signal through a photoelectric detector. According to the method, the time delay characteristic can be further inhibited, so that generation of harmful resonance is further inhibited, and the method has stronger nonlinear characteristic and better calculation performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of reservoir computing systems, and particularly relates to a time delay reservoir computing method based on a dispersion orthogonal polarization light feedback VCSEL. BACKGROUND

[0002] RC is a new information processing method based on the further development of RNN, and is proposed to overcome the limitations of traditional neural network models. Although the early neural network model has good nonlinear mapping ability, FNN, for example, has a fixed hierarchical structure and information can only propagate in one direction, so it is difficult to effectively process complex tasks with time dependence. Therefore, RNN establishes a time sequence connection between the hidden layers of the network by introducing a loop structure to realize the memory and use of historical information. However, RNN is prone to problems such as gradient vanishing or explosion during training, and its parameter optimization process is complex. These problems make it very difficult to train long sequences, which limits its widespread application in practical applications. In this context, RC, as a simple and efficient information processing method, has emerged as the times require. The core idea is to fix and randomly initialize the weights of the loop network part in the traditional RNN, and only train the output layer, thereby simplifying the training process.

[0003] In recent years, the structure of RC is no longer limited to the spatial structure composed of multiple nonlinear nodes, but has developed into a time delay structure composed of a single nonlinear node and a delay feedback loop. The reservoir structure of the traditional RC is a spatial interconnection network of a large number of nonlinear physical nodes, so when implemented in physical hardware, it is necessary to control the state of a large number of nodes, the connection between nodes, and the collection of node outputs. This leads to the limitation of constructing large-scale RC networks with exponentially increasing number of nodes. The time delay RC system is composed of a nonlinear node with a time delay feedback loop, and the virtual nodes in the feedback loop replace a large number of nonlinear physical nodes in the traditional RC. Therefore, the hardware implementation of time delay RC is simpler, and therefore the time delay RC constructed by various nonlinear time delay systems is studied. In the time delay RC system, the total time delay feedback time is , and the same interval is along the feedback loop. N virtual nodes are set, i.e. The input layer of the time delay RC assigns corresponding input weight values to each virtual node. The time mask has a time span equal to , and is composed of random values uniformly distributed from -1 to 1. The reservoir layer of the time delay RC is composed of at least one nonlinear node and one feedback loop. In the output layer, the time interval The sampled output electrical signal is used as the virtual node state. Then, a relevant algorithm is used to train and optimize the output weights. Finally, the RC system output is obtained by linearly summing the virtual node states and the output weights.

[0004] With the expansion of delay-based RC applications and the diversification of requirements, designing RC systems with stronger computational performance remains a worthwhile challenge. Typically, the nonlinearity of nonlinear nodes in an RC system directly affects its computational performance; systems operating under higher nonlinear states often possess stronger computational capabilities. Currently... Under normal settings, a resonance can occur, weakening the nonlinearity of the nodes. The root cause of this resonance is the introduction of a time-delay feedback loop. The output of the reservoir carries certain time-delay characteristics, resulting in a weak periodicity in its impulse response. This periodicity matches the periodicity of the masked input signal. This resonance severely impairs the computational power of time-delay RC. Therefore, exploring how to suppress resonance to improve the performance of time-delay RC is of great significance.

[0005] Among existing optical delay RC schemes that enhance system computational performance by suppressing resonance, the closest to this invention is the delay RC technique based on orthogonally polarized feedback VCSELs. This scheme uses VCSELs as nonlinear nodes and utilizes the polarization dynamics characteristics of VCSELs to suppress, to some extent, the nonlinearity of the feedback VCSEL. and The resonance induced by matching enhances the nonlinearity of VCSELs and improves the computational performance of RC. The apparatus for this method is as follows: Figure 2 As shown.

[0006] Figure 2 The scheme shown mainly consists of a tunable laser, a Mach-Zehnder modulator, a VCSEL, an optical isolator, an optical coupler, a polarization controller, a variable optical attenuator, and a photodetector.

[0007] The implementation steps of the scheme are as follows: the input data is multiplied by the mask signal in the input layer to obtain the input signal, which is modulated by the Mach-Zehnder modulator. The modulated signal is injected into the X polarization component of the VCSEL. The light emitted from the VCSEL passes through the optical circulator, optical coupler, variable optical attenuator and polarization controller and is fed back to the VCSEL to form the reservoir pool layer of the time delay RC system. In the feedback process, the light emitted by the VCSEL is orthogonally polarized by the polarization controller, that is, the X polarization component of the light emitted by the VCSEL is fed back to the Y polarization component of the VCSEL, and the Y polarization component is fed back to the X polarization component. The output light signal of the VCSEL is sent to the output layer through the optical circulator and the optical coupler, and then converted into an output electrical signal by the photodetector. The RC output result can be obtained by equally time interval sampling and linearly weighting and summing the output electrical signal.

[0008] The existing technical solution is to use the polarization dynamics of the VCSEL to perform orthogonal polarization rotation operation on the light emitted by the VCSEL in the feedback loop, suppress the time delay characteristics of the output light, weaken the periodic characteristics of the reservoir pool impulse response, thereby weakening the harmful resonance caused by the matching between different periodic characteristics, and making the system obtain higher computing performance. However, in this scheme, the output light of the VCSEL is fed back twice, and in the first feedback, the polarization component is rotated to the orthogonal polarization direction, and in the second feedback, it is rotated to the original direction, resulting in strong time delay characteristics. That is, the upper limit of the time delay characteristics that can be achieved by this scheme is not high, and resonance cannot be completely avoided, and the computing performance of the RC system can be further improved.

[0009] Term explanation:

[0010] Feedforward neural network (FNN): a neural network model containing multiple hidden layers. Each neuron receives input from the previous layer of neurons, and the weighted sum is passed through a nonlinear activation function, and then the result is passed to the next layer of neurons.

[0011] Recurrent neural network (RNN): a neural network model for processing sequence data. The cyclic structure enables it to capture the time dependence in the data.

[0012] Reservoir computing (RC): a form of recurrent neural network. The internal weights are randomly fixed, the input data is converted into high-dimensional dynamics, only the output part of the network needs to be trained, and the time sequence information in the input sequence can be effectively captured.

[0013] Vertical Cavity Surface Emitting Laser (VCSEL): A special laser that can generate two mutually orthogonal polarization components, namely X-polarization component and Y-polarization component.

[0014] Orthogonal polarization optical feedback: The X-polarization component of the VCSEL output is fed back to the Y-polarization component, and the Y-polarization component is fed back to the X-polarization component.

[0015] Polarization dynamics: In VCSEL, it refers to the interaction and dynamic change between the two orthogonal polarization components.

[0016] Chirped Fiber Bragg Grating (CFBG): A fiber grating device with a non-uniform period structure.

[0017] Time delay feedback time: The time required for a signal to circulate one round in an optoelectronic feedback loop.

[0018] Time delay feature: The autocorrelation peak of the autocorrelation function of the time series of the laser output at the loop time delay. SUMMARY

[0019] To solve the above problems, the present application provides a time delay reservoir computing method based on dispersion orthogonal polarization optical feedback VCSEL.

[0020] The time delay RC system used in the time delay reservoir computing method based on dispersion orthogonal polarization optical feedback VCSEL includes an adjustable laser, a Mach-Zehnder modulator, a VCSEL, an optical isolator, an optical coupler, a polarization controller, a variable optical attenuator, a chirped fiber Bragg grating, and a photodetector.

[0021] In the input layer, the input data is multiplied by the mask signal to obtain the input signal, and the input signal is injected into the X-polarization component of the VCSEL in the reservoir layer after being modulated by the Mach-Zehnder modulator.

[0022] The emitted light of the VCSEL is divided into two paths after passing through the optical circulator, one path is reflected back to the VCSEL by the chirped fiber Bragg grating after being rotated by the polarization controller to complete orthogonal polarization rotation, thus constructing the reservoir layer of the time delay RC system; the other path is transmitted to the output layer and converted into an electrical signal by the photodetector, and the output electrical signal is sampled at equal time intervals and linearly weighted and summed to obtain the system output result.

[0023] Compared with the traditional time delay RC scheme based on orthogonal polarization optical feedback VCSEL, the dispersion effect of the chirped fiber Bragg grating is utilized in the time delay loop of the reservoir layer in the present application, which further suppresses the time delay feature, and the specific theoretical model rate equation is described as follows:

[0024]

[0025] where, and are the slow-varying complex electric field amplitudes of the X and Y polarization components, respectively, and are the total carrier number and the carrier number difference with opposite spin direction, respectively; is the field decay rate, is the linewidth enhancement factor; represents the decay rate, is the spin-flip rate, denotes the linear dichroism, represents the linear birefringence; is the normalized injection current; the third term in Eqs. (1) and (2) is the time-delayed feedback term, where represents the feedback strength, represents the feedback phase, and the impulse response of the chirped fiber Bragg grating is , represents the time-delayed feedback time of the feedback loop; and represent the angular frequencies of the X and Y polarization components, respectively, where , is the speed of light, is the central wavelength of the VCSEL; the last term in Eqs. (1) and (2) , represents the shot noise.

[0026] The fourth term in Eq. (1) describes the input layer, where the input data is multiplied by a mask signal to obtain a preprocessed input signal, which is modulated by a Mach-Zehnder modulator and injected into the X polarization component of the VCSEL, where is the injection strength of the external laser, is the injection light angular frequency, and since the input signal is injected into the X polarization component, the frequency detuning between the injection light and the laser is denoted by is the preprocessed input signal after mask modulation, where is the mask scaling factor, is the mask signal, is the input data after sample-and-hold; the mask signal is periodic over one delay loop time and constant over the virtual node interval ; the masked input signal can excite transient dynamics, and at the output layer, the output electrical signal is sampled at time intervals ​​ As a virtual node state Then, the ridge regression algorithm is used to train and optimize the output weights. Finally, during the testing process, the following was used: Obtain the output of the RC system.

[0027] The beneficial technical effects of this invention are as follows:

[0028] This invention, building upon the traditional time-delay RC system based on orthogonally polarized feedback VCSELs, utilizes the dispersion effect of CFBG to propose a time-delay RC calculation system based on dispersive orthogonally polarized feedback VCSELs. Compared to traditional schemes, this time-delay RC system can further suppress time-delay characteristics, thereby further suppressing the generation of harmful resonances, exhibiting stronger nonlinear characteristics and better computational performance. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the time delay RC of the VCSEL based on dispersive orthogonal polarization feedback in this invention.

[0030] Figure 2 This is a schematic diagram of the time delay RC based on orthogonally polarized light feedback VCSEL. Detailed Implementation

[0031] The present invention will be further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0032] This invention discloses a method for calculating the time delay reservoir based on a dispersive orthogonal polarization feedback VCSEL, employing a time delay RC system such as... Figure 1 As shown, the system includes a tunable laser, a Mach-Zehnder modulator, a VCSEL, an optical isolator, an optical coupler, a polarization controller, a variable optical attenuator, a chirped fiber Bragg grating, and a photodetector. The signal from the input layer is modulated by the Mach-Zehnder modulator and injected into the X-polarization component of the VCSEL in the reservoir layer. The emitted light from the VCSEL passes through the optical coupler; one path undergoes orthogonal polarization rotation and is reflected back to the VCSEL by the chirped fiber Bragg grating, while the other path is transmitted to the output layer and converted into an electrical signal by the photodetector.

[0033] This invention, based on the traditional time-delay RC system using orthogonal polarization feedback from VCSELs, further suppresses the time-delay characteristics by utilizing the dispersion effect of CFBGs, thereby further suppressing the generation of harmful resonances, enhancing the nonlinear characteristics of the system, and significantly improving the computational performance of RC. The specific implementation process is as follows: In the input layer, the input data is multiplied by a mask signal to obtain the input signal. The input signal is modulated by a Mach-Zehnder modulator and injected into the X-polarization component of the VCSEL in the reservoir layer. The emitted light from the VCSEL is split into two paths after passing through an optical circulator. One path undergoes orthogonal polarization rotation by a polarization controller and is reflected back to the VCSEL by a chirped fiber Bragg grating, constructing the reservoir layer of the time-delay RC system. The other path is transmitted to the output layer and converted into an electrical signal output by a photodetector. The output electrical signal is sampled at equal time intervals and then linearly weighted and summed to obtain the system output result.

[0034] Compared with the traditional time-delay RC scheme based on orthogonally polarized feedback VCSELs, this invention utilizes the dispersion effect of chirped fiber Bragg gratings in the time-delay loop of the reservoir layer to further suppress time-delay characteristics. Its specific theoretical model rate equation is described as follows:

[0035]

[0036] in, and The amplitudes of the slowly varying complex electric field, representing the X-polarization and Y-polarization components, are respectively. and These represent the difference between the total number of charge carriers and the numerical difference between charge carriers with opposite spin directions, respectively. For field attenuation rate, Linewidth enhancement factor; represent The attenuation rate, The spin-flip rate, Represents linear dichroism. Represents linear birefringence; It is the normalized injection current; the third term in equations (1) and (2) is the time-delay feedback term, where Represents the intensity of feedback. Representing the feedback phase, the impulse response of a chirped fiber Bragg grating is... , The feedback delay time represents the feedback loop. and These represent the angular frequencies of the X-polarization component and the Y-polarization component, respectively. , At the speed of light, The center wavelength of the VCSEL; the last term of equations (1) and (2) , , represents Langevin noise.

[0037] The fourth term of equation (1) describes the input layer, which multiplies the input data with a mask signal to obtain a pre-processed input signal, which is modulated by a Mach-Zehnder modulator and injected into the X-polarization component of the VCSEL, where is the injection strength of the external laser, is the injection optical angular frequency, since the input signal is injected into the X-polarization component, it is denoted by to indicate the frequency detuning between the injection light and the laser; is the pre-processed input signal after mask modulation, where is the mask scaling factor, is the mask signal, is the input data after sample-and-hold; the mask signal is periodic over one delay loop time and constant over the virtual node interval ; the masked input signal can excite transient dynamics, at the output layer, with a time interval to sample the output electrical signal as the virtual node state , then the ridge regression algorithm is used to train and optimize the output weights ; finally, in the test process, the RC system output is obtained using .

[0038] In the traditional time-delay RC system, there is a problem of resonance caused by the matching between different periodic characteristics, which damages the computing performance of the system. The existing scheme using the polarization dynamics of VCSEL suppresses this harmful resonance, but the upper limit of suppression is low, and there is still strong resonance affecting the computing performance of the system.

[0039] The present application simply adds a chirped fiber Bragg grating, a cheap passive optical device, in the feedback loop to reflect the light emitted by the laser. This modification further suppresses the time-delay characteristics on the basis of maintaining the simple structure of the traditional VCSEL-based time-delay RC, so as to further suppress the generation of resonance which damages the computing performance of the system, and significantly improves the computing performance of the RC system.

Claims

1. A time-delay reservoir computing method based on dispersion-orthogonal polarization light feedback VCSEL, characterized in that, The time-delay RC system includes an adjustable laser, a Mach-Zehnder modulator, a VCSEL, an optical isolator, an optical coupler, a polarization controller, a variable optical attenuator, a chirped fiber Bragg grating, and a photodetector; The input data is multiplied by a mask signal to obtain an input signal in the input layer, and the input signal is injected into the X polarization component of the VCSEL of the reservoir layer after being modulated by a Mach-Zehnder modulator; The emitted light of the VCSEL is divided into two paths after passing through an optical circulator, one path is reflected back to the VCSEL by a chirped fiber Bragg grating after being rotated by a polarization controller to complete orthogonal polarization, thereby constructing the reservoir layer of the time-delay RC system; the other path is transmitted to the output layer and converted into an electrical signal by a photodetector, and the output electrical signal is sampled at equal time intervals and linearly weighted and summed to obtain the system output result.

2. The time delay reservoir computing method based on the dispersion orthogonal polarization optical feedback VCSEL according to claim 1, wherein, In the time-delay loop of the reservoir layer, the dispersion effect of the chirped fiber Bragg grating is utilized to further suppress the time-delay characteristic, and the specific theoretical model rate equation is described as follows: ； where and are the slowly-varying complex electric field amplitudes of the X and Y polarization components, respectively, and are the total carrier number and the difference in carrier number with opposite spin direction, respectively; is the field decay rate, is the linewidth enhancement factor; represents the decay rate of is the spin-flip rate, denotes linear dichroism, represents linear birefringence; is the normalized injection current; the third term in Eqs. (1) and (2) is the time-delayed feedback term, where represents the feedback strength, represents the feedback phase, and the impulse response of the chirped fiber Bragg grating is , represents the time-delayed feedback time of the feedback loop; and represent the angular frequencies of the X and Y polarization components, respectively, where , is the speed of light, is the central wavelength of the VCSEL; the last term in Eqs. (1) and (2) , represents the shot noise; The fourth term of equation (1) describes the input layer, which multiplies the input data with the mask signal to obtain a preprocessed input signal. This preprocessed signal is then modulated by a Mach-Zehnder modulator and injected into the X-polarization component of the VCSEL. The injection intensity of the external laser. To determine the injected optical angular frequency, since the input signal is injected into the X-polarization component, we use... This indicates frequency detuning between the injected light and the laser; It is the preprocessed input signal after mask modulation, where This is the mask scaling factor. For mask signal, The input data is sampled and held; the mask signal is periodic over a delay loop time and at virtual node intervals. The above is constant; the input signal after masking. Transient dynamics can be excited in the output layer at time intervals. Sampled output electrical signal As a virtual node state Then, the ridge regression algorithm is used to train and optimize the output weights. Finally, during the testing process, the following was used: Obtain the output of the RC system.

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