Optoelectronic Oscillator Research Articles

Injection Locking of Optoelectronic Oscillators With Large Delay

The optoelectronic oscillator is a delay line oscillator that leverages optical fibre technology to realize the large delay required for low phase noise systems. Spurious sidemodes are an artefact of the delay line oscillator, yet treatments of injection locking of optoelectronic oscillators have relied on the application of classical injection locking theory valid only for single mode oscillators. The large delay contributed by the optical fibre delay line is accounted for by the classical theory only in part through the quality factor Q that captures the round-trip group delay in a neighborhood of the oscillation frequency. This paper presents a new formulation of time delay oscillators subject to injection that describes all the essential features of their dynamics and phase noise. The common assumptions of a single mode oscillator and weak injection are removed. This is important to correctly predict the lock-in range, the suppression of sidemodes and the phase noise spectrum. The findings of the analysis are validated by experimental measurements provided by an optoelectronic oscillator under injection by an external source.

Self-Forced Oscillation in Heterogeneously Integrated Multi-Mode Laser

High-stability optoelectronic oscillators (OEOs) are attained using self-forced oscillation techniques using long optical delays. Free-running InP-based multi-mode laser (MML) diodes with free-spectral range (FSR) of 11.7 GHz is stabilized using self-electrical injection-locked (SEIL) and dual self-phase-locked loop (DSPLL) (SEILDPLL) approach; phase noise of the free-running OEO of −52.8 dBc/Hz at 10-kHz offset was improved by 36 dB experimentally. Self-forced stabilization of MML-based OEO results in timing jitter of 0.9 ps, a factor of 33 times reduction in the free-running performance. A fully integrated solution using Si-photonics (SiP) is more environmentally stable and amenable to a reduced large volume manufacturing. A heterogeneously integrated MML combined with self-forced function is designed on an approximately 91-cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> SiP chip using 325- and 975-ns time delays.

Dissipative microwave photonic solitons in spontaneous frequency-hopping optoelectronic oscillators

Dissipative solitons relying on the double balance between nonlinear and linear effects as well as cavity loss and gain have attracted increasing attention in recent years, since they give rise to novel operating states of various dissipative nonlinear systems. An optoelectronic oscillator (OEO) is a dissipative nonlinear microwave photonic system with a high quality factor that has been widely investigated for generating ultra-low noise single-frequency microwave signals. Here, we report a novel operating state of an OEO related to dissipative solitons, i.e., spontaneous frequency hopping related to the formation of dissipative microwave photonic solitons. In this operating state, dissipative microwave photonic solitons occur due to the double balance between nonlinear gain saturation and linear filtering as well as cavity loss and gain in the OEO cavity, creating spontaneous frequency-hopping microwave signals. The generation of wideband tunable frequency-hopping microwave signals with a fast frequency-hopping speed up to tens of nanoseconds is observed in the experiment, together with the corresponding soliton sequences. This work reveals a novel mechanism between the interaction of nonlinear and linear effects in an OEO cavity, extends the suitability and potential applications of solitons, and paves the way for a new class of soliton microwave photonic systems for the generation, processing, and control of microwave and RF signals.

Controlling birhythmicity in a new Dual Loop Optoelectronic Oscillator with an injection locked van der Pol oscillator

In the present literature, an attempt has been made to understand the birhythmic behaviour of a modified time delayed Dual Loop Optoelectronic Oscillator (DLOEO). To this end, an analytical solution of periodic oscillation is obtained using weakly nonlinear analysis. Two coexisting periodic oscillations are identified, considering shorter loop delay as a control parameter. Subsequently, to control the birhythmicity, a self-feedback mechanism is applied that incorporates the variable to be controlled and its canonical conjugate. Our study reveals that with proper control of the feedback strength, birhythmicity can be removed and monorhythmicity can be induced in the oscillator.

Efficient sensings of temperature, refractive index, and distance measurement using the cubic-nonlinear optoelectronic oscillators

In this work, we use the cubic-nonlinear optoelectronic oscillator (CNOEO) in three different configurations to successfully perform the sensings of temperature, refractive index, and distance measurement with high precision. From our results, the use of the CNOEO through the variation of the values of the cubic-nonlinear parameter increases the sensitivity of the different sensings and the measurement carried out compared to the results obtained with the standard OEO which is a particular CNOEO featuring a cubic-nonlinear parameter equal to zero.

Enhanced performance of a reservoir computing system based on a dual-loop optoelectronic oscillator.

Time-delayed reservoir computing (RC) is a brain inspired paradigm for processing temporal information, with simplification in the network's architecture using virtual nodes embedded in a temporal delay line. In this work, a novel, to the best of our knowledge, RC system based on a dual-loop optoelectronic oscillator is proposed to enhance the prediction and classification. The hardware is compact and easy to implement, and only a section of fiber compared to the traditional optoelectronic oscillator reservoir is added to conform the dual-loop scheme. Compared with the traditional reservoir, a remarkable performance of the proposed RC system is demonstrated by simulation on three well-known tasks, namely the nonlinear auto regressive moving average (NARMA10) task, signal waveform recognized task, and handwritten numeral recognition. The parameter optimization in the NARMA10 task is presented with influenced factors. The novel RC system finally obtains a normalized mean square error at 0.0493±0.007 in NARMA10 task, 6.172×10-6 in signal waveform recognized task, and a word error rate at 9% in handwritten numeral recognition with suitable parameters.

Chip-Scaled Ka-Band Photonic Linearly Chirped Microwave Waveform Generator

Synthetic aperture radar (SAR) systems employ a Linearly Chirped Microwave Waveform Generator (LCMWG) with large time–bandwidth product (TBWP), to provide a wide range resolution. Photonics has now been recognized as a disruptive approach to achieve high performance at bandwidth of few tens of gigahertz, with light and compact architectures, due to the typical photonics benefits, such as electromagnetic interference immunity, small power consumption, small footprint, and high immunity to vibration/shock and radiation. In this article, we report on the photonic generation of a high-frequency LCMW, with a large TBWP (102–103), using a chip-scaled architecture, based on a frequency-tunable optoelectronic oscillator (OEO) and a recirculating phase modulation loop (RPML). A new configuration of the OEO employing an ultrahigh Q-factor resonator has been conceived to allow the oscillator working in Ka band at 40 GHz or even more, with very low phase noise. Key building block of the RPML is a phase modulator driven by an engineered parabolic split waveform. The ultra-large pulse compression rate (PCR) &amp;gt;&amp;gt; 102, together with large signal purity, was also obtained, making the proposed architecture particularly suitable for SAR systems with large range resolution demand, such as Earth surveillance and monitoring.

High-gain narrowband radio frequency signal amplifier based on a dual-loop optoelectronic oscillator.

A novel photonic-assisted method for radio frequency (RF) signal amplification with high-gain and narrowband based on a dual-loop optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. In the proposed system, the low-power RF signal is injected into a dual-loop OEO which is below the threshold oscillation state. And the maximum gain is obtained when the frequency of the RF signal matches with the potential oscillation mode of the dual-loop OEO. The approach provides an average gain greater than 22 dB for the RF signal which matches with oscillation mode. After amplification, the signal-to-noise ratio (SNR) turns out to be 40 dB. Furthermore, the 3 dB bandwidth of the suggested system can be narrower than 1.2 kHz which can effectively remove the out-of-band noise and spurious effects. Meanwhile, the performance of sensitivity and phase noise are also investigated.

A parity-time-symmetric optoelectronic oscillator with polarization multiplexed channels

In this manuscript, we experimentally demonstrate a parity-time-symmetric optoelectronic oscillator (OEO) with polarization multiplexed channels. We obtained a microwave single-mode oscillation at 9.5 GHz with phase noise values of −116.2 and −122.3 dBc Hz−1 at 10 kHz offset frequencies, and side mode suppression values below −68 and −75 dBc Hz−1, by utilizing a 1 km long and 5 km long single mode fiber delay lines, respectively. Our experimental results suggest that parity-time-symmetric OEOs with polarization multiplexed channels are simple and cost-efficient alternatives to their more complex counterparts.

Improved Next-Generation Radio Access Networks Using a Centralized Opto-Electronic Oscillator

Next-generation 5G and 6G radio access networks (RANs) require millimetre-wave (mm-W) oscillators to generate extremely low phase-noise signals for the frequency up-conversion and down-conversion in radio units (RUs). The opto-electronic oscillator (OEO) is an outstanding candidate for generating a high-purity mm-W signal in a centralized radio access network (C-RAN) where the distributed base-stations are dislocated from the digital units (DUs) and there are only RUs on the remote side. In this paper we propose placing an OEO in the central-office, while distributing its signal from there to multiple RU base-stations through the mobile front-haul network using a radio-over-fibre (RoF) transmission approach. This new approach was used in experiments that proved the smaller degradation of the phase noise compared to a degradation of 6 dB for the well-known frequency-doubling electrical oscillator in the RU. In addition, we present the signal-strength degradation due to fibre dispersion in mm-W signal distribution, as well as the challenges in long-term stability and multimode operation. We propose solutions to overcome these drawbacks and make our new approach useful for a centralized carrier signal distribution in next-generation RANs.

Self-Injection-Locked Optoelectronic Oscillator Based on Frequency Conversion Filtering

The multi-mode noise is an important issue for the optoelectronic oscillator (OEO) in generating a spectrally pure microwave. Especially in oscillators with low phase noise, increasing the cavity length to improve the phase noise performance will make the mode interval smaller, which is more likely to cause multi-mode noise. Here, we proposed a low phase noise and high side-mode suppression ratio self-injection-locked OEO based on frequency conversion filtering. We theoretically and experimentally studied the influence of the phase noise of the external microwave source on the proposed OEO and, as a comparison, the conventional injection-locked OEO. The results show that, compared with the traditional injection-locked OEO, the proposed OEO is less sensitive to the phase noise of the external microwave source. Under the same experimental conditions, the proposed OEO achieved the same side-mode suppression ratio and the phase noise is reduced by 30 dB at 10 kHz offset from the 10-GHz carrier compared with the conventional injection-locked OEO.

Microwave-photonics iterative nonlinear gain model for optoelectronic oscillators.

The nonlinear dynamic behavior of optoelectronic oscillators (OEOs), which is important for the OEO based applications, is investigated in detail by a Microwave-photonics Iterative Nonlinear Gain (MING) model in this paper. We connect the oscillating processes with the trajectories of an iterated map based on a determined nonlinear mapping relation referred to as open-loop input to output amplitude mapping relation (IOAM). The results show that the envelope dynamic is determined by the slope of IOAM at a special point called fixed point. Linear features dominate the loop if the slope is relatively large, and the nonlinear features emerge and become increasingly significant with the decreasing of the slope. Linear features of homogeneity and monotonicity are gradually lost. Furthermore, OEO is even unstable when the slope is less than a general threshold value of -1. The behavior of OEO loops with the different slope values are discussed by simulations and are experimentally confirmed. Moreover, the proposed model also applies to the OEO with an externally injected microwave signal, the bifurcation phenomena caused by injected signal are experimentally evidenced.

Flat Self-Oscillating Parametric Optical Frequency Comb Based on a Dual-Mode Microcavity Laser

A highly coherent and flat optical frequency comb (OFC) based on an optoelectronic oscillator (OEO) is presented using a dual-mode microcavity laser. In this scheme, the microcavity laser is applied as a light source and a photonic microwave filter simultaneously. The dual-mode is phase-locked in the self-injection OEO configuration. Meanwhile, a 10-tones OFC with a frequency spacing of 28.8 GHz is generated without an external microwave source. The generated OFC is further broadened through a parametric frequency mixer by the dispersion compensation and nonlinear expansion technique. Forty-three optical tones with a 5-dB power variation spanning over 10 nm are obtained.

O-Band Frequency-Tunable (10–22 GHz) Ultra-Low Timing-Jitter (&lt;12-fs) Regenerative Mode-Locked Laser

A frequency-tunable and low-timing-jitter O-band regenerative mode-locked laser (RMLL) using an optoelectronic oscillation configuration and electric-controlled yttrium iron garnet (YIG) bandpass filter is proposed and demonstrated. In this scheme, an O-band semiconductor optical amplifier (SOA) is used as the gain medium of the RMLL to realize a dispersion-management-free operation during frequency tuning. With a polarization-maintaining fiber loop of 300 m, we produced a robust frequency-tunable RMLL with a pulse width below 16 ps, phase noises below −123 dBc/Hz at a 10-kHz frequency offset from the carrier frequency, and timing jitter less than 12 fs (integrated in 1-kHz to 1-MHz range) in a frequency tuning range between 10 GHz and 22 GHz.

Harmonically mode-locked optoelectronic oscillator with ultra-low supermode noise

A harmonically mode-locked optoelectronic oscillator (OEO) based on a dual-loop architecture is proposed to generate a microwave pulse train with ultra-low supermode noise. Through using a dual-loop architecture, the unwanted longitudinal modes can be weakened by the “Vernier effect” at the early stage of the oscillation, which is beneficial for suppressing the supermode noise originating from phase locking among the unwanted modes in a harmonically mode-locked OEO. The proposed scheme is numerically and experimentally demonstrated. In the experiment, microwave pulse trains with repetition rates of 179 kHz and 186 kHz are generated through 2nd- and 5th-order harmonic mode locking, where the supermode noise suppression ratios are measured to be beyond 60 dB and 55 dB, respectively. The effective suppression of supermode noise can greatly improve the output power stability and the correlation between different pulses. Under 2nd-order harmonic mode locking, the output power drifts of the single-loop and the dual-loop architectures are measured to be 38.13 dB and 0.97 dB, respectively.

Polarization-insensitive coupled optoelectronic oscillator with low spurious tones and phase noise

A coupled optoelectronic oscillator (COEO) based on σ-shaped fiber ring structure and intra-cavity semiconductor optical amplifier (SOA) is proposed and experimentally demonstrated. The σ-shaped fiber ring structure is skillfully utilized in COEO to eliminate the harmful influence of polarization disturbance. The SOA is embedded for super-mode suppression due to the fast gain saturation effect. The eximious phase noise performance of COEO could be maintained by operating the SOA at the unitary gain regime. The stable operation of COEO is guaranteed by the immunity to polarization fluctuation and the greatly suppressed spurious-mode competition. As a result, a 10-GHz signal is generated featuring high spectral purity and ultra-low spurious tones as soon as the system is power-on, and can hold steady even if the polarization changes dramatically. The single sideband phase noise of the proposed COEO is about -133 dBc/Hz at 10-kHz offset frequency, and the spurious suppression ratio reaches more than 95 dB, which is 60-dB superior than the conventional COEO.

Enhancement of Optical Chaos Generator using Double Delayed Feedback

Chaotic lasers are widely used in secure communication, optical detection and other applications due to their noise-like randomness, excellent anti-jamming and other advantages. This research looks into the chaotic laser's performance at a low cost. The performance related to a semiconductor laser with double delayed feedback is observed and its characteristics are determined in experimental research utilizing OptiSystem simulator. The chaotic laser output is fed back to the Mach-Zehnder modulator (MZM) to make the original system. The gain coefficient changes dynamically, and a second time delay is introduced into the system. The feedback time and feedback strength of the improved chaotic system are studied under varying input bias current, frequency and modulation beak current. Bifurcation diagram results show that the chaotic laser output by the optoelectronic oscillator (OEO) is more complex and has lower delay characteristics. This method does not increase too much Under the premise of system cost, more complex chaotic signals can be generated, and the signal delay characteristics can be reduced, which is conducive to improving the security of the communication system.

Dynamics of optoelectronic oscillators with band-pass filter and laser nonlinearities: theory and experiment

Dynamics of optoelectronic oscillators with band-pass filter and laser nonlinearities: theory and experiment

Widely tunable frequency-doubling optoelectronic oscillator using a polarization modulator and a phase-shifted fiber Bragg grating

A frequency-doubling optoelectronic oscillator with wideband frequency tunability implemented using a polarization modulator (PolM) and a phase-shifted fiber Bragg grating (PS-FBG) is proposed and experimentally demonstrated. In the proposed structure, the output from the PolM is divided into two branches by an optical coupler. In the lower branch, an optoelectronic feedback loop is formed in which a tunable microwave photonic filter (MPF) is constructed by the joint operation of the PolM, the PS-FBG, a tunable laser source (TLS), a polarization controller (PC), and a polarizer, the MPF serves as an oscillation mode selector that its central frequency is a function of the frequency difference between the TLS and the notch of the PS-FBG. In the upper branch, an equivalent Mach–Zehnder modulator (MZM) is performed by the joint use of the PolM, a second PC, and a second polarizer, the second PC is adjusted to let the bias point of the MZM located at the minimum transmission point (MITP), which generates an optical signal with two sidebands at the ±first orders. By beating the two sidebands at a second photodetector (PD), a frequency-doubled microwave signal is generated. By simply adjusting the wavelength of the TLS, the central frequency of the MPF is shifted, and the fundamental oscillation and its frequency-doubled signals can be tuned. The detailed theoretical study is achieved, and a verified experiment is established. A fundamental oscillation signal with a frequency tuning range from 9.39 to 15.4 GHz is generated in the OEO loop, which is multiplied to generate a tunable frequency-doubled signal. Their overall performances are also investigated.

Microresonator Dissipative Kerr Solitons Synchronized to an Optoelectronic Oscillator

Using phase-modulation-induced potential gradient whose period is synchronized to a microwave optoelectronic oscillator, dissipative Kerr solitons generated in a crystalline optical microresonator are trapped by the soliton tweezing effect, exhibiting a stabilized soliton repetition rate. In the meantime, side-mode suppression of the microwave signal is enabled by the photodetection of the soliton train. Substantiated both experimentally and theoretically, the hybrid system produces a drift-reduced microcomb and a spectrum-purified optoelectronic oscillator simultaneously, yielding a low-cost toolkit for microwave and optical metrology.