We propose a novel image-like channelization method that utilizes a convolutional recurrent neural network (CRNN) for channel synthesis to reduce the bandwidth requirements of the electrical hardware. In this study, the spectrum of a 30-GBaud QPSK signal is spectrally sliced and received by four low-speed coherent receivers based on a conventional coherent optical communication system. After the recovery of the trained CRNN, the average error vector magnitude (EVM) of the 30-GBaud baseband signal is improved from over 60% by uncorrected channel synthesis to around 15%.
We propose and demonstrate a high-resolution and high-sensitivity tunable liquid refractive index (RI) sensor interrogated using a microwave photonic filter (MPF) with two taps implemented based on optical polarization orthogonality. In the structure, a fiber laser with its wavelength determined by a microfiber Bragg grating (mFBG) is employed as a light source. A chirped fiber Bragg grating (CFBG) is incorporated in one tap, and an optical tunable delay line (TDL) is included in the other tap. The sensing information is encoded in the laser wavelength caused by the RI change, which will cause a change in the time delay difference between the two taps due to the wavelength-dependent group delay of the CFBG, which would result in a change in the MPF frequency response. By monitoring the spectral response, the sensing information is detected. The spectral response of the MPF is tuned by controlling the length of the TDL, which would lead to a change in the sensor sensitivity. An experiment is performed. The results show, for three TDL time delays of 300 ps, 400 ps and 500 ps, the liquid RI sensitivities are 50.621 GHz/ RIU, 37.293 GHz/RIU and 26.015 GHz/RIU, respectively, and the corresponding resolutions are 8.0253×10-5 RIU, 1.0893×10-4 RIU and 1.5616×10-4 RIU.
An optoelectronic oscillator (OEO) that combines injection locking and parity-time (PT) symmetry is proposed and demonstrated to generate microwave signals with low phase noise and a high side-mode suppression ratio. In the experiment, a microwave signal at 10 GHz with a phase noise as low as -117.5 dBc/Hz at an offset frequency of 10 kHz is generated. An ultra-high side-mode suppression ratio of 86.33 dB is achieved.
We propose a novel approach to the generation of optical arbitrary waveforms with an ultra-high sampling rate in the photonic temporal synthetic dimension based on a dual-loop fiber-optic system assisted by low-speed electronics. The generation of optical waveforms with a sampling rate of 182 GSa/s is simulated.
Microwave signal with high frequency and low phase noise is generated based on a parity-time (PT) symmetric optoelectronic oscillator (OEO). The PT-symmetric OEO based on normal and reversed traveling-wave modulation is formed by normal and reversed modulation in a travelling-wave intensity modulator (IM) using the radio-fiber (RF) input and termination ports. Gain and loss balance can be realized to achieve PT symmetry thanks to the different modulation efficiencies for microwave signals applied via different RF ports. The operation of the proposed OEO has been experimentally verified. A microwave signal is generated at 10 GHz with a phase noise of -110.7 dBc/Hz at an offset frequency of 10 kHz and a sideband suppression ratio of 46.46 dB. The approach has potential applications in high-quality microwave signal generation and simplify the structure of PT-symmetric OEO system.
Conventional parity-time (PT) symmetric systems consist of two physically separated resonators to form one-dimensional spatial potential symmetry, with the gain and loss modes localized in respective resonators. We show that PT-symmetry can be implemented between subspaces in non-spatial parameter spaces, in which the gain and loss modes can perfectly overlay spatially but are distinguishable in the designated parameter space. Such optical parameter spaces can be implemented by optical wavelength, wavevector and polarization, etc. The resultant spatial singularity enables the possibility in implementing PT-symmetric systems with increased structural simplicity, integration density and long-term stability. In this talk, PT-symmetric optoelectronic oscillators (OEOs) are implemented in the parameter space of optical wavelength and wavevector; a PT-symmetric laser is implemented in the parameter space of optical polarization. All systems are shown to operate with stable single-mode oscillation and with low structural complexity. We believe that PTsymmetric system in non-spatial parameter spaces can find great applications in optical instrumentation due to its capability for low phase noise signal generation.
A high speed TFBG-SPR sensing demodulation system based on microwave photonics interrogation is proposed theoretically. The wavelength shifting of the SPR envelope in optical domain is converted to the microwave pulse shifting in time domain. The RI resolution is improved by one order of magnitude compared with wavelength demodulation, and the sensing speed is as high as 40 KHz.
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