Optoelectronic oscillators (OEOs) have emerged as indispensable tools for generating low-phase-noise microwave and millimeter-wave signals, which are critical for a variety of high-performance applications. These include radar systems, satellite links, electronic warfare, and advanced instrumentation. The ability of OEOs to produce signals with exceptionally low phase noise makes them ideal for scenarios demanding high signal purity and stability. In radar systems, low-phase-noise signals enhance target detection accuracy and resolution, while, in communication networks, such signals enable higher data throughput and improved signal integrity over extended distances. Furthermore, OEOs play a pivotal role in precision instrumentation, where even minor noise can compromise the performance of sensitive equipment. This review examines the progress in OEO technology, transitioning from classical designs relying on long optical fiber delay lines to modern integrated systems that leverage photonic integration for compact, efficient, and tunable solutions. Key advancements, including classical setups, hybrid designs, and integrated configurations, are discussed, with a focus on their performance improvements in phase noise, side-mode suppression ratio (SMSR), and frequency tunability. A 20-GHz oscillation with an SMSR as high as 70 dB has been achieved using a classical dual-loop configuration. A 9.867-GHz frequency with a phase noise of −142.5 dBc/Hz @ 10 kHz offset has also been generated in a parity–time-symmetric OEO. Additionally, integrated OEOs based on silicon photonic microring resonators have achieved an ultra-wideband tunable frequency from 3 GHz to 42.5 GHz, with phase noise as low as −93 dBc/Hz at a 10 kHz offset. The challenges in achieving fully integrated OEOs, particularly concerning the stability and phase noise at higher frequencies, are also explored. This paper provides a comprehensive overview of the state of the art in OEO technology, highlighting future directions and potential applications.

The performance of a free-space optical (FSO) communication system is limited by light intensity fluctuations induced by atmospheric turbulence. To improve the system performance, one effective way is to use forward error correction (FEC). Pulse position modulation (PPM) is a power- efficient modulation scheme employed in FSO systems. So this paper evaluates the performance improvement of an FSO system with M-ary PPM due to FEC in atmospheric turbulence. The FEC scheme are based on Reed-Solomon (RS) codes, and the results show that FEC can decrease the required average signal light intensity for a high bit rate FSO system to keep a BER below 10"9, and that with the FEC scheme, the system is tolerant of the noise resulted from the background light stronger than the desired signal light. Furthermore, we also found that FEC can remarkably increase the system tolerance for intensity fluctuations caused by atmospheric turbulence.

A scheme for parametric optical frequency comb (OFC) generation using an electroabsorption modulated laser (EML) based optoelectronic oscillator is proposed and experimentally demonstrated. A phase modulator is cascaded with EML in the oscillating loop. In addition, the phase modulated laser is used as pump seeds for the parametric frequency mixer. In the mixer, a 100-m single-mode fiber is employed to compress the pump pulses, and the parametric process is stimulated in a 200-m-high nonlinear fiber (HNLF) with flat normal dispersion. In our experiments, a 10-GHz radio frequency signal with a side-mode suppression radio of 47 dB and a single-sideband phase noise of -109.89 dBc/Hz at 10 kHz offset is obtained. When the pump power injected into HNLF is 28 dBm, a 10-tone parametric OFC with a 5-dB power variation and spacing equal to the oscillation frequency is generated.