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Reservoir computing (RC) is a simplified recurrent neural network, can be implemented by using a nonlinear system with delay feedback, called as delay-based RC. Various nonlinear nodes and feedback loop structures are proposed. Most works are based on the dynamical responses in intensity of the nonlinear systems. There are also a photoelectric RC system based on wavelength dynamics and an all-optical RC based on the phase dynamics of a semiconductor laser with optical feedback, as well as so-called polarization dynamics of a vertical cavity surface emitting laser (VCSEL). However, these VCSEL-RCs actually are based on the intensity dynamics of two mutually orthogonal polarization modes, or polarization-resolved intensity dynamics. The RC based on rich dynamical responses in polarization has not yet been seen. A semiconductor optical amplifier (SOA) fiber ring laser can produce rich dynamical states in polarization, is used in optical chaotic secure communication and distributed optical fiber sensing. To further expand the application of polarization dynamics of the SOA fiber ring laser and open up a new direction for the research of optical RC neural network, an all-optical RC system based on polarization dynamics of the ring laser is proposed. The ring laser is used as the reservoir, and the SOA as the nonlinear node. After the input signal is masked according to a synchronization scheme, it is injected into the reservoir by intensity modulation for a continuous wave generated by a super-luminescent light emitting diode (SLED). The dynamical response in polarization of the ring laser is detected by a polarizer and a photodetector. The influences of the SOA operation current, output power of the SLED and attenuation of a variable optical attenuator (VOA) in the fiber loop on the polarization dynamic characteristic, mainly refers to the output degree of polarization, of the laser are analyzed experimentally. The fading memory abilities and nonlinear responses of the RC system based on the polarization dynamic response and intensity dynamic response are compared in experiment. The influences of output power of the SLED and attenuation of the VOA on fading memory ability, consistency and separation of the RC system based on the two kinds of dynamic responses are investigated experimentally. Thus the range of the VOA attenuation is determined. The network performance of the polarization dynamics RC system is evaluated by processing the Santa Fe time series prediction task and the multi-waveform recognition task. The prediction error can be as low as 0.0058 for the time series prediction task, and the accuracy can be as high as 100% for the recognition task under the appropriate system parameters and only 30 virtual nodes. The experimental results show that the polarization dynamics RC system has good prediction performance and classification ability, which are comparable to the existing intensity dynamics RC system based on the ring laser. The system can be expected to process two tasks in parallel when the polarization dynamics and intensity dynamics are used at the same time.
Reservoir computing (RC) is a simplified recurrent neural network, can be implemented by using a nonlinear system with delay feedback, called as delay-based RC. Various nonlinear nodes and feedback loop structures are proposed. Most works are based on the dynamical responses in intensity of the nonlinear systems. There are also a photoelectric RC system based on wavelength dynamics and an all-optical RC based on the phase dynamics of a semiconductor laser with optical feedback, as well as so-called polarization dynamics of a vertical cavity surface emitting laser (VCSEL). However, these VCSEL-RCs actually are based on the intensity dynamics of two mutually orthogonal polarization modes, or polarization-resolved intensity dynamics. The RC based on rich dynamical responses in polarization has not yet been seen. A semiconductor optical amplifier (SOA) fiber ring laser can produce rich dynamical states in polarization, is used in optical chaotic secure communication and distributed optical fiber sensing. To further expand the application of polarization dynamics of the SOA fiber ring laser and open up a new direction for the research of optical RC neural network, an all-optical RC system based on polarization dynamics of the ring laser is proposed. The ring laser is used as the reservoir, and the SOA as the nonlinear node. After the input signal is masked according to a synchronization scheme, it is injected into the reservoir by intensity modulation for a continuous wave generated by a super-luminescent light emitting diode (SLED). The dynamical response in polarization of the ring laser is detected by a polarizer and a photodetector. The influences of the SOA operation current, output power of the SLED and attenuation of a variable optical attenuator (VOA) in the fiber loop on the polarization dynamic characteristic, mainly refers to the output degree of polarization, of the laser are analyzed experimentally. The fading memory abilities and nonlinear responses of the RC system based on the polarization dynamic response and intensity dynamic response are compared in experiment. The influences of output power of the SLED and attenuation of the VOA on fading memory ability, consistency and separation of the RC system based on the two kinds of dynamic responses are investigated experimentally. Thus the range of the VOA attenuation is determined. The network performance of the polarization dynamics RC system is evaluated by processing the Santa Fe time series prediction task and the multi-waveform recognition task. The prediction error can be as low as 0.0058 for the time series prediction task, and the accuracy can be as high as 100% for the recognition task under the appropriate system parameters and only 30 virtual nodes. The experimental results show that the polarization dynamics RC system has good prediction performance and classification ability, which are comparable to the existing intensity dynamics RC system based on the ring laser. The system can be expected to process two tasks in parallel when the polarization dynamics and intensity dynamics are used at the same time.
The laser probe method is one of the main techniques for capturing ultrafast dynamic processes and has extensive applications in fields such as plasma physics, photochemistry, and biomedical science. In this paper, a time-wavelength encoding optical probe generation scheme is proposed, which uses cascaded frequency doubling crystals with different phasematching angles and independent delay lines to achieve time-wavelength encoding. This method offers single-shot high spatiotemporal resolution, high frame rate, a wide range of adjustable time windows. The temporal resolution of the optical probe depends on the pulse width of the second harmonic, which can be adjusted by changing the phase-matching angle of the frequency doubling crystal. The time window of the optical probe is only related to the change in the delay line, which can be adjusted by changing the length of the delay line. Therefore, the time resolution and time window of the optical probe are independent of each other. An optical probe generation system was constructed with 247 fs temporal resolution, 4 μm spatial resolution, 4.05 THz maximal frame rate, and an adjustable time window from sub-picosecond to 3 ns. The threedimensional spatiotemporal evolution process of plasma filaments was captured within a single shot using the optical probe. The experimental results showed that the ionization front of the plasma propagated forward at a velocity of (2.963 ± 0.024) × 10<sup>8</sup> <i>m</i>/<i>s</i>,which was consistent with the theoretical prediction. This demonstrated the feasibility of using the probe for capturing ultrafast events. In the discussion, we analyzed that the key parameters of the optical probe can reach a maximum frame rate of 35.7 THz, a maximum time resolution of 28 fs, and a time window range that can be adjusted from hundreds of femtoseconds to tens of nanoseconds. Finally, the optimal design parameters of the optical probe are given for different application scenarios. The optical probe generation scheme has good scalability and versatility, and can be combined with any wavelength decoding device, diffraction imaging, holographic imaging, tomography scanning, and other technologies. The high spatiotemporal resolution of the optical probe and the independent adjustability of its parameters provide a feasible solution for single-shot high spatiotemporal resolution captures of ultrafast dynamic processes at multiple time scales.
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