An approach to generating periodic spiking and spiking cluster in a broadband nonlinear opto-electronic oscillator (OEO) is proposed and demonstrated. Through injecting a long-duration square-wave pulse train with a repetition frequency equal to an integral multiple of the free spectral range into the OEO with a high net gain, controllable spiking and spiking cluster oscillation can be achieved when the dual-drive Mach-Zehnder modulator (DDMZM) in the OEO is biased far away from its quadrature point. The proposed scheme is verified by both numerical simulation and experiment. The results indicate that, when the DDMZM in the OEO cavity is biased near its minimum transmission point, positive spiking train with nanosecond-level pulse width is excited by the rising edge of the injected square-wave pulse train. Through further enhancing the injection strength, uniformly-spaced positive spiking fills the high-level voltage duration of each injected square-wave pulse. Hence, spiking cluster oscillation is achieved. Benefiting from its controllability, this approach can be applied in ultra-wideband (UWB) communications, electronic countermeasures, spiking coding and high-speed neuromorphic computing.

We propose and demonstrate an approach to generating wide-range tunable coherent dual-frequency microwave signals with high side-mode suppression ratios (SMSRs), ultra-low phase noise and high stability, based on a dual-passband optoelectronic oscillator (OEO). The narrowband passband with a relatively high gain is used to generate the initial oscillation at a fixed frequency. Through injecting a single-tone signal into the OEO cavity via a microwave mixer, frequency-tunable oscillation in the other broadband passband with a relatively low gain is initiated through frequency mixing injection locking. Then, the two oscillation signals are phase-locked through frequency mixing mutual injection locking. In addition, a dual-loop configuration with the assistance of balanced photodetection is utilized to suppress the side modes and improve the phase noise performance, which also enhances the stability of the generated signal. In the experiment, coherent dual-frequency microwave signals with a fixed frequency at 20.0056 GHz and a tunable frequency in the range of 13.9705 GHz to 18.0075 GHz are generated, where the frequency tuning step is 625.6 kHz. The power fluctuation during frequency tuning is smaller than 1.5 dB, and the SMSRs are larger than 77 dB. In addition, the Allan deviation and the phase noise are in the order of 10–11@1 s and better than –138 dBc/Hz@10 kHz, respectively.

Optoelectronic oscillators (OEOs), which have attracted extensive studies in the past decades, are high quality-factor optoelectronic feedback loops for generating various ultra-pure microwave signals. In essence, OEOs are also dissipative nonlinear systems with multiple timescale characteristics and abundant nonlinearities, which open the possibilities for exploring localized dissipative solitary waves. In this paper, we demonstrate a new-class temporal dissipative soliton, i.e., dissipative microwave photonic soliton molecule (DMPSM), in a dual-bandpass OEO. Both the numerical simulation and experiment are conducted to reveal the physical mechanism of DMPSM generation and to evaluate the characteristics of the generated DMPSM sequences. Unlike optical soliton molecules in mode-locked lasers, the formation of DMPSMs arises from the combined action of multiple timescale coupling, nonlinear bistability, and time-delayed feedback in the OEO cavity, where the soliton interval and number in a DMPSM can be well-controlled through varying the multiple timescale variables in the OEO cavity, and the repetition frequency of the DMPSMs can be tuned through changing that of the initially injected perturbation signal. Meanwhile, the generated DMPSM sequence performs with high stability and excellent coherence, which shows enormous application potentials in pulse radar detection, dense microwave comb generation, and neuromorphology.

A new non-uniform photonic sampling (NPS) strategy and its special signal reconstruction algorithm are proposed to achieve digital acquisition of broadband periodic signals at a low sampling rate. Compared with the existing schemes, the NPS strategy can largely reduce the sampling number to acquire identical signal information as that obtained by using its equivalent high-speed uniform photonic sampling, which is beneficial for reducing the sampling time and the data volume of the NPS-based analog-to-digital converter (ADC). In addition, the calculation time of the proposed algorithm is millions of times lower than that of the digital alias-free signal processing (DASP) algorithm used before, which benefits from the fast Fourier transform calculation of a one-dimensional data array instead of a two-dimensional data array calculation in the DASP algorithm. A simulation is performed to validate the feasibility of the proposed scheme. In the simulation, a single-channel NPS-based ADC with an average sampling rate of 1 GSa/s is demonstrated by using the proposed NPS strategy and signal reconstruction algorithm. The results indicate the reconstructed signal information for a single-tone microwave signal at 9.9 GHz and a linear frequency modulation signal in the frequency range of 1 GHz to 9 GHz are identical to those obtained by using its equivalent high-speed uniform photonic sampling-based ADC with a sampling rate of 20 GSa/s.

An approach to generating coherent dual-band chirped microwave signals with programmable chirp shapes is proposed and demonstrated based on a single phase-modulated optical loop and a heterodyne structure. The driving signals applied to the electrooptic phase modulator (PM) are composed of a customized low-frequency waveform and a high-frequency single-tone microwave signal. Consequently, a coherent dual-band chirped optical signal is generated from the phase-modulated optical fiber loop. Therefore, the low-frequency waveform defines the chirp shape of the generated dual-band chirped optical signal, and the high-frequency single-tone microwave signal determines the frequency interval between the two bands. Through heterodyne beating the output dual-band chirped optical signal with an external continuous-wave (CW) laser, coherent dual-band chirped microwave signals with customized chirp shapes can be generated, where the frequency intervals between the two bands, the center frequencies, and the bandwidths of the two bands are reconfigurable. In the experiment, coherent dual-band chirped microwave signals with customized chirp shapes, variable frequency intervals between the two bands, tunable center frequencies, and definable bandwidths are generated. This scheme provides a path to generate coherent broadband chirped microwave signals for cutting-edge multiband radar systems.

A delay-matched self-feedback injection-locked optoelectronic oscillator (SIL-OEO) is proposed to realize wideband tunable microwave signal generation, which are featured with ultra-low phase noise and low spurs. In the OEO cavity, two cascaded electro-optic Mach-Zehnder modulators (MZMs) are used to form two loops with an identical time delay. Thereinto, one loop serves as the oscillation path, and the other acts as the self-feedback injection locking path. Benefited from the delay-matched self-feedback injection locking effect, the gain of the dominant oscillation mode far exceeds that of the unwanted side modes, largely suppressing the spurs in the generated microwave signal. In addition, the usage of self-feedback injection locking avoids the requirement of an external precisely-tunable microwave source and the phase noise degradation due to external injection in the high-frequency range, which facilitates freely wideband frequency tuning by using a tunable bandpass filter. In a proof-of-concept experiment, tunable microwave signals from 2.99931 GHz to 20.0013 GHz are generated. The side-mode suppression ratios (SMSRs) reach beyond 65.3 dB within the whole frequency tuning range, and the phase noise is superior over –120 dBc/Hz@1 kHz and –142 dBc/Hz@10 kHz. Moreover, the power fluctuation during frequency tuning is smaller than 3.2 dB.