Microwave photonic approaches for the generation of microwave signals have attracted substantial attention in recent years, thanks to the significant advantages brought by photonics technology, such as high frequency, large bandwidth, and immunity to electromagnetic interference. An optoelectronic oscillator (OEO) is a paradigmatic microwave photonic oscillator that produces microwave signals with ultra-low phase noise, thanks to the high-quality-factor of the OEO cavity that is achieved with the help of optical energy storage elements, such as low-loss optical fiber or a high-quality-factor optical resonator. Different OEO architectures have been proposed to generate spectrally pure single-frequency microwave signals with ultra-low phase noise. Multiple oscillation mode control methods have been proposed in recent years to obtain different kinds of microwave signals. With the rapid development of photonic integration technologies, prototypes of integrated OEOs have been demonstrated with compact size and low power consumption. Moreover, OEOs have also been used for sensing, computing, and signal processing. This Tutorial aims to provide a comprehensive introduction to the developments of OEOs. We first discuss the basic principle and the key phase noise property of OEOs and then focus on its developments in spectrally pure low phase noise signal generation and mode control methods, its chip-scale integration, and its applications in various fields.

We present a reconfigurable microwave frequency measurement technique with adjustable measurement range and resolution. The key novelty of the technique is the employment of stimulated Brillouin scattering, which results in a tunable amplitude comparison function, leading to an adjustable measurement range and resolution. The proposed technique is switchable between a wideband tunable narrow measurement range ($\sim 2\mathrm{GHz}$) with high resolution ($\pm 0.05\mathrm{GHz}$) and a fixed wide measurement range (12 GHz) with moderate resolution ($\pm 0.25\mathrm{GHz}$).

The optoelectronic oscillator (OEO) has attracted a great deal of attention in recent years as a high-performance microwave source. Thanks to the high quality-factor (Q-factor) provided by the optical delay line, the OEO can generate spectrally pure microwave signals with ultralow phase noise. Various approaches for realization of OEO architectures for the generation of single-frequency microwave signals have been demonstrated in the past two decades. Seeded by the microwave signal generated by OEO, the generation of complex microwave waveforms has been demonstrated, which can be used in applications such as radar and communication systems. OEO has also been demonstrated to perform other specific functionalities in different applications, including optical pulses and frequency comb generation, optical sensing, low-power microwave signal detection, and optical signal processing. This paper reviews the developments of OEO over the past two decades. An integrated OEO with monolithically integrated photonic parts and radio frequency subsections is reported as a promising example toward the monolithic integration of OEO. Key features of OEO and prospects for future development of the integration of OEO are also described.

This paper presents a review and discussion of the directly modulated semiconductor lasers and their applications to optical communications and microwave photonics. A detailed and comprehensive demonstration of directly modulated semiconductor lasers from development history to specific techniques on measurement, analysis, and packaging is provided for the first time to the best of our knowledge. A few typical applications based on directly modulated lasers are also illustrated, such as optical fiber communications, free-space optical communications and microwave photonics. Future directions of research are also highlighted.

We propose and demonstrate a tunable Fourier domain mode locked optoelectronic oscillator (FDML OEO) using a frequency scanning microwave photonics filter (MPF) based on stimulated Brillouin scattering (SBS). Fourier domain mode locking operation is achieved by synchronizing the tuning period of the SBS-based MPF to the cavity round-trip time of OEO. As a result, thousands of longitudinal modes are stimulated simultaneously in the OEO cavity. Linearly chirped microwave waveforms with a chirp rate up to 0.84 GHz/μs and a time bandwidth product as high as 22,446 are generated in the experiment. The proposed approach provides an important solution for chirped microwave waveforms generation which is widely used in modern radar and communication systems, and has the potential to be integrated on a chip.

We report a photonic scheme to generate background-free frequency-doubled binary phase-coded microwave pulses. The key component is a dual-polarization dual-parallel Mach–Zehnder modulator that is used to realize phase modulation and carrier-suppressed double second-order sideband modulation at two orthogonal polarization states, respectively. The $\pi$ phase jump of the frequency-doubled phase-coded microwave pulse is dependent on the polarity of the coding signal rather than its amplitude. Besides, the generated microwave pulses are free from the baseband-modulated signals, because the optical power launched to a photodetector (PD) keeps constant all the time. Since no electrical or optical filters are involved, the photonic generator can ensure a broad operation bandwidth and wide tunability. Our scheme is theoretically analyzed and experimentally verified. The 4 Gb/s at 16 GHz and 7 Gb/s at 28 GHz background-free frequency-doubled phase-coded microwave pulses have been successfully generated.