Time-delayed optoelectronic oscillators are at the center of a large body of scientific literature. The complex behavior of these nonlinear oscillators has been thoroughly explored both theoretically and experimentally, leading to a better understanding of their dynamical properties. Beyond fundamental research, these systems have also inspired a wide and diverse set of applications, such as optical chaos communications, pseudorandom number generation, optoelectronic machine learning based on reservoir computing, ultrapure microwave generation, optical pulse-train synthesis, and sensing. The aim of this review is to provide a comprehensive survey of this field, to outline the latest achievements, and discuss the main challenges ahead.

Optoelectronic oscillators with time-delayed feedback

An ultrawideband (UWB) radar system for remote ranging based onmicrowave-photonic chaotic signal generation and fiber-optic distribution is proposedand demonstrated experimentally. In this system, an optical-feedback semiconductorlaser with optical injection in the central office generates photonic UWB chaos as probingsignal, and two single-mode fibers transport the optical signal to the remote antennamonitoring terminal and return the corresponding echoed signal back to the centraloffice. In the remote antenna terminal, the photonic signal is transformed into microwavechaos by a fast photodetector and then launched to target by a transmitting antenna,and the echoed signal received by another antenna is converted into optical domain bymodulating a laser diode. The target ranging is achieved at the central office by correlat-ing the echoed signal with the reference signal. We experimentally realize a detectionrange of 8 m, for a free-space target, after 24-km remote distance, and achieve a rang-ing resolution of 3 cm for single target and 8 cm for double targets. In another fiber linkbranch with 15-km fiber transmission, we obtained the 2-cm ranging resolution for asingle target.Index Terms: Chaos, remote radar, semiconductor lasers.

Remote Radar Based on Chaos Generation and Radio Over Fiber

A distributed multiple-input multiple-output chaotic radar based on wavelength-division multiplexing technology (WDM) is proposed and demonstrated. The wideband quasi-orthogonal chaotic signals generated by different optoelectronic oscillators (OEOs) are emitted by separated antennas to gain spatial diversity against the fluctuation of a target’s radar cross section and enhance the detection capability. The received signals collected by the receive antennas and the reference signals from the OEOs are delivered to the central station for joint processing by exploiting WDM technology. The centralized signal processing avoids precise time synchronization of the distributed system and greatly simplifies the remote units, which improves the localization accuracy of the entire system. A proof-of-concept experiment for two-dimensional localization of a metal target is demonstrated. The maximum position error is less than 6.5 cm.

Distributed MIMO chaotic radar based on wavelength-division multiplexing technology.

A photonics-based wideband distributed coherent aperture radar (DCAR) system is proposed and experimentally demonstrated. In the proposed system, the central controlling system and several spatially dispersed remote transceivers are connected by the optical fiber-based time synchronization network. In the central controlling system, the optical-carried orthogonal/coherent linear frequency modulated waveforms (LFMWs) are generated by a reconfigurable multi-channel optical arbitrary waveform generator (RMOAWG), and the signal processing for the echo waves is also implemented there. While in the remote transceivers, only the optical/RF and RF/optical conversions are carried out. Benefitting from the use of photonics-based methods, bandwidths of the generated radar signals can be large, improving the detection resolution of the system. Due to the centralized signal generation and processing, the remote transceivers can be simplified, reducing the system complexity. Moreover, the fiber-based distribution ensures low loss, good transportability, and great flexibility. Experimentally, a two-unit DCAR system operating in X-band with a bandwidth of 3 GHz is presented. When full coherence is achieved, signal-to-noise ratio (SNR) gains of 8.3 dB and 8.33 dB are obtained over a single radar for radar 1 and radar 2, respectively. Results are in good agreement with theoretical prediction. Theoretically, with such SNR gain, the range detection precision can be improved to about 2.6 times that of a single radar.

Photonics-based wideband distributed coherent aperture radar system.

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.

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Tutorial on optoelectronic oscillators

A fiber-distributed Ultra-wideband (UWB) noise radar was achieved, which consists of a chaotic UWB noise source based on optoelectronic oscillator (OEO), a fiber-distributed transmission link, a colorless base station (BS), and a cross-correlation processing module Due to a polarization modulation based microwave photonic filter and an electrical UWB pass-band filter embedded in the feedback loop of the OEO, the power spectrum of chaotic UWB signal could be shaped and notch-filtered to avoid the spectrum-overlay-induced interference to the narrow band signals Meanwhile, the wavelength-reusing could be implemented in the BS by means of the distributed polarization modulation-to-intensity modulation conversion The experimental comparison for range finding was carried out as the chaotic UWB signal was notch-filtered at 52 GHz and 78 GHz or not Measured results indicate that space resolution with cm-level could be realized after 3-km fiber transmission thanks to the excellent self-correlation property of the UWB noise signal provided by the OEO The performance deterioration of the radar raised by the energy loss of the notch-filtered noise signal was negligible

Li Wei

Papers

Fiber-distributed Ultra-wideband noise radar with steerable power spectrum and colorless base station.