A new photonic scheme for various waveforms generation has been proposed and demonstrated. In the scheme, two cascaded single-drive LiNbO₃ Mach-Zehnder modulators serve as pulse shaper and the polarization-dependent character of the modulators is fully exploited and utilized. By arranging the polarization states of the incident light, two different spectra are achieved on two orthogonal polarization components respectively. Finally, the desired waveforms can be obtained by superimposing the photocurrents of the two orthogonal signals on a photodetector. The detailed theoretical analyses and simulations are given. In the experiment, square-shaped waveform, triangular waveform and sawtooth (or reversed-sawtooth) waveform are obtained successfully. Furthermore, an approach to smoothing the sawtooth waveform with fewer harmonics is suggested and verified.

We propose a new injection-locked optoelectronic oscillator (OEO) which is locked by a low frequency RF signal and without adding high speed devices. From a low frequency modulated optical carrier, the injection-locking effect in a Fabry-Pérot laser diode is able to generate and selectively amplify one high order harmonic component, which is subsequently injected into a single-loop OEO to lock one of the oscillation modes. This process can improve the injected signal quality and simultaneously implement a single-mode OEO with precise oscillation frequency. In the experiment demonstration, a 20-GHz single-mode OEO locked by a 1-GHz RF signal is obtained. The measured side-mode suppression ratio is 65 dB and the phase noise at 1-kHz frequency offset is -94.7 dBc/Hz.

Flat optical frequency comb (OFC) can be generated by using single phase modulator (PM), where combined harmonics are applied to drive the PM. However, the number of comb lines and flatness of OFC are limited under this scheme. In this work, we use cascaded PMs with combined harmonics to generate flat OFC. The optimized phases and modulation indices in terms of amplitudes for each harmonic are obtained by solving optimization problem to minimize the fluctuation of OFC with a certain number of comb lines. Both simulation and experiment are carried out to evaluate the feasibility of the proposed scheme. Regarding the case of combined fundamental tone, third harmonic, and fifth harmonic, a 15-line OFC is generated with the flatness of 0.29 dB and 0.65 dB observed in simulation and experiment, respectively. Other feasible solutions to flat OFC with combined harmonics are also investigated.

An all-optical microwave oscillator is proposed and experimentally demonstrated. Based on a pure photonic feedback loop, this system can generate a photonic microwave signal without optical–electrical–optical conversion or any electrical microwave devices. A semiconductor optical amplifier implements the functions of microwave envelope detection and feedback modulation. Meanwhile, Brillouin-selective sideband amplification is employed to lock oscillation frequency. In experiment, a good quality microwave signal with a frequency of 10.8 GHz is obtained. The tunability is also demonstrated by adjusting the Brillouin pump wavelength.

We propose a simple and cost-effective multifrequency optoelectronic oscillator (OEO) which is able to simultaneously generate two or more independent microwave signals by adding parallel filtering branches in the feedback loop. In the experimental demonstration, two signals with frequencies of 20 and 9 GHz are successfully generated. Compared with a conventional OEO, the generated signals have no additional noise and do not interfere with each other. The side-mode suppression by the optical dual-loop configuration is effective for both channels. The measured side-mode suppression ratios are larger than 65 dB, and the phase noises at a 10-kHz frequency offset are −108 and −113 dBc/Hz for 20 and 9-GHz signals, respectively.

Under the conventional scheme to generate an optical frequency comb (OFC) using an electro-optic modulator (EOM), the frequency interval of the OFC is determined via the frequency of the fundamental tone of the radio frequency (RF) driving signals. In this work, we use two harmonics without the fundamental tone to drive two EOMs, where the frequency interval of the generated flat OFC is the frequency of the fundamental tone. The orders of the two harmonics are coprime. Specifically, one harmonic drives the first branch of the dual-parallel Mach–Zehnder modulator (DPMZM) only, and the other harmonic drives the phase modulator (PM). The flatness of the OFC is achieved by adjusting the amplitude and phase of the RF driving harmonics as well as the bias of the EOM. Both a simulation and an experiment were carried out to verify the effectiveness of the proposed scheme. When the second harmonic drives the DPMZM and the third harmonic drives the PM, an 11-comb line OFC is generated, where the flatness of the OFC was 0.63 dB and 0.65 dB under the simulation and experiment, respectively. When the third harmonic drives the DPMZM and the second harmonic drives the PM, a 13-comb line OFC is generated, where the flatness of the OFC was 0.62 dB and 0.95 dB under the simulation and experiment, respectively. We also investigate the performance of the generated OFC when one harmonic drives two branches of the DPMZM and the other harmonic drives the PM. The comparison of the OFCs’ performance demonstrates the effectiveness of the proposed scheme.