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

With the rapid development of the modern communication systems, radar and wireless services, microwave signal with high-frequency, high-spectral-purity and frequency tunability as well as microwave generator with light weight, compact size, power-efficient and low cost are increasingly demanded. Integrated microwave photonics (IMWP) is regarded as a prospective way to meet these demands by hybridizing the microwave circuits and the photonics circuits on chip. In this article, we propose and experimentally demonstrate an integrated optoelectronic oscillator (IOEO). All of the devices needed in the optoelectronic oscillation loop circuit are monolithically integrated on chip within size of 5×6cm2. By tuning the injection current to 44 mA, the output frequency of the proposed IOEO is located at 7.30 GHz with phase noise value of −91 dBc/Hz@1MHz. When the injection current is increased to 65 mA, the output frequency can be changed to 8.87 GHz with phase noise value of −92 dBc/Hz@1MHz. Both of the oscillation frequency can be slightly tuned within 20 MHz around the center oscillation frequency by tuning the injection current. The method about improving the performance of IOEO is carefully discussed at the end of in this article.

Integrated optoelectronic oscillator.

A ten-user truly asynchronous gigabit coherent-optical-code-division-multiple-access (OCDMA) transmission was experimentally demonstrated without using any timing coordination. The enabling technologies are a record-length 511-chip superstructured-fiber-Bragg-grating (SSFBG) en/decoder and a supercontinuum (SC)-based optical-thresholding technique to significantly suppress the signal interference beat noise as well as the multiple-access-interference (MAI) noise.

Ten-user truly asynchronous gigabit OCDMA transmission experiment with a 511-chip SSFBG En/Decoder

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.

Toward Monolithic Integration of OEOs: From Systems to Chips

A frequency tunable short optical pulse generation scheme based on a self-starting optoelectronic oscillator (OEO) with an optically injected semiconductor laser is proposed and investigated The generation of optical pulses with a repetition rate coarsely tuned from 65 to 15 GHz are demonstrated Phase noise of the electrical clock signal from the OEO is below −101 dBc/Hz at 10 kHz within the whole tuning range, which leads to a very small timing jitter of the generated optical pulses Assisted by optical pulse compression technique in the OEO, the full-width-at half-maximum of the generated optical pulses is narrower than 20 ps

Optical Pulse Generation by an Optoelectronic Oscillator With Optically Injected Semiconductor Laser

A novel scheme to realize a low-cost and wideband frequency tunable optoelectronic oscillator based on a directly modulated distributed feedback (DFB) semiconductor laser is proposed and experimentally demonstrated. In the proposed scheme, neither an external modulator nor an electrical filter is used, and no more than 25 dB of the electrical loop gain is required due to the high modulation efficiency of the relaxation oscillation frequency of the DFB laser. Microwave signals with frequency coarsely tuned from 3.77 to 8.75 GHz are generated by changing the bias current and operation temperature of the DFB laser. The single sideband phase noise of the generated 6.97 GHz microwave signal is measured to be −103.6  dBc/Hz at 10 kHz offset.

Low-cost and wideband frequency tunable optoelectronic oscillator based on a directly modulated distributed feedback semiconductor laser.

A novel approach to realizing single sideband (SSB) modulation with optical carrier to sideband ratio (OCSR) of 0 dB, which is optimum for maximizing the transmission performance of a radio-over-fiber system, is proposed and experimentally demonstrated based on a strong optical injection-locked distributed feedback (DFB) laser. Tunable OCSR with optimum value of 0 dB is achieved by tuning the injection ratio and the detuning frequency precisely. A simulation is carried out to confirm the optimum OCSR. Gain properties of the DFB laser under strong optical injection are also measured for the first time to our knowledge. Doubled frequency of the LO signal is obtained without any filter. The generated optical SSB signal of 20 GHz is transmitted over 60-km single-mode fiber experimentally; results show it is almost not affected by the fiber chromatic dispersion.

A Novel Approach to Realizing SSB Modulation With Optimum Optical Carrier to Sideband Ratio

Optical code-division multiple-access (OCDMA) technology is attractive for optical broadband access network. It is very interesting to use the super-structure fiber-Bragg-grating-based en/decoders to construct a wavelength-division-multiplexing (WDM)-compatible OCDMA system. Based on the equivalent phase-shift technique, we have proposed a subsampled-Bragg-grating (S-SBG)-based en/decoder. Based on the proposed method, only a single uniform phase mask can be used to accommodate different WDM channels with relevant central wavelengths and spectrum width. Using the S-SBG-based en/decoder, we can make different WDM channels have similar as well as better encoding efficiency and correlation performance. S-SBG-based en/decoders with 127 chips for two different wavelength channels are fabricated and measured. The experiments indicate the advantages revealed by the theoretical simulation.

Novel Encoder/Decoder Using Subsampled Bragg Grating for a WDM-Compatible OCDMA System

A novel method of utilizing optical source with relatively-narrow spectrum is proposed for coherent temporal-phase optical code-division multiple-access (OCDMA) system based on equivalent phase shift super-structure fiber Bragg grating (EPS-SFBG). Simulation and experiment show that better decoding performance will be achieved by making the source's relatively-narrow spectrum cover half-side of encoding spectrum. Meanwhile, we can obtain more tolerance of wavelength deviation between the encoder and decoder and less inter-symbol-interference (ISI) and corresponding inter-symbol beat noise (BN) comparing with traditional matching method. The improvements will make low-cost optical source with relatively-narrow spectrum fit for OCDMA system and accordingly accelerate the OCDMA's practical application. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2688–2691, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24711

A novel method of utilizing practical optical source with relatively‐narrow spectrum for OCDMA

A sample fiber Bragg grating (SFBG) with Gaussian apodization profile is designed and optimized for the narrowband wavelength filter, and the relevant conclusions provide a guide for the further filter fabrication. With the grating length limited, a narrowband (5 GHz) grating filter used in the radio over fiber (ROF) system is fabricated, which has insertion loss of 3.463 dB, sideband suppression of 24.21dB, 3 dB bandwidth of 40 pm, and 20 dB bandwidth of 106.3 pm.

Lin Lu

Papers

Low-cost and wideband frequency tunable optoelectronic oscillator based on a directly modulated distributed feedback semiconductor laser.

A Novel Approach to Realizing SSB Modulation With Optimum Optical Carrier to Sideband Ratio

Novel Encoder/Decoder Using Subsampled Bragg Grating for a WDM-Compatible OCDMA System

A novel method of utilizing practical optical source with relatively‐narrow spectrum for OCDMA

Optimization design and realization of Gaussian apodized sample gratings for narrowband wavelength selectivity filters