Abstract
An optoelectronic oscillator (OEO) is a microwave photonic system that produces microwave signals with ultralow phase noise using a high-quality-factor optical energy storage element. This type of oscillator is desired in various practical applications, such as communication links, signal processing, radar, metrology, radio astronomy, and reference clock distribution. Recently, new mode control and selection methods based on Fourier domain mode-locking and parity-time symmetry have been proposed and experimentally demonstrated in OEOs, which overcomes the long-existing mode building time and mode selection problems in a traditional OEO. Due to these mode control and selection methods, continuously chirped microwave waveforms can be generated directly from the OEO cavity and single-mode operation can be achieved without the need of ultranarrowband filters, which are not possible in a traditional OEO. Integrated OEOs with a compact size and low power consumption have also been demonstrated, which are key steps toward a new generation of compact and versatile OEOs for demanding applications. We review recent progress in the field of OEOs, with particular attention to new mode control and selection methods, as well as chip-scale integration of OEOs.
Highlights
An oscillator is a resonant device that produces a periodic oscillating signal without any input
A singlemode operation is achieved in a parity-time (PT) symmetric optoelectronic oscillator (OEO),[21,22,110,111,112,113,114] due to the mode selection based on PT symmetry using two feedback loops, with one having a gain and another having a loss of the same magnitude
A coupled PT-symmetric structure using two identical feedback loops, with one having a gain and the other having a loss of the same magnitude, has been widely investigated as a powerful tool for cavity mode selection both in photonic[130,131,132,133,134,135] and electronic[136] cavities
Summary
An oscillator is a resonant device that produces a periodic oscillating signal without any input. Using a seeded single frequency OEO, the generation of linearly chirped, phase-coded, triangular, and even arbitrary microwave waveforms has been demonstrated.[19,72,73,74] In addition to signal generation, signal processing[10,75,76,77] such as clock recovery and format conversion has been demonstrated using OEOs. a large number of applications of OEOs to sensing, measurement, and detection have been developed[15,16,18,78,79,80,81,82,83,84,85,86,87,88,89,90,91] to measure signals or specific parameters such as strain, temperature, refractive index, transverse load, distance, length change, position as well as RF/optical signals.
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