Supermode Noise Suppression Research Articles

Harmonic active mode-locking optoelectronic oscillator with suppressed supermode noise based on pulse intensity feedback.

A harmonic active mode-locking optoelectronic oscillator (HAML-OEO) with pulse intensity feedback is proposed and experimentally demonstrated. It is capable of generating microwave pulses characterized by suppressed supermode noise, uniform intensity, and tunable repetition rates. Unlike traditional HAML-OEOs, active mode-locking and pulse intensity feedback are simultaneously achieved through the use of a dual-drive Mach-Zehnder modulator (DDMZM). By synchronously feeding back the generated microwave pulses to the DDMZM, each pulse undergoes a loss proportional to its intensity, facilitating pulse intensity equalization and supermode noise suppression. In the experiment, intensity-equalized microwave pulse trains with repetition rates of 499 kHz and 998 kHz are generated by the 5th- and 10th-order HAML-OEOs, respectively, with the measured supermode noise suppression ratios exceeding 40 dB.

Dual-band tunable microwave pulse signals generation based on a time domain mode locked optoelectronic oscillator

We propose and experimentally demonstrate a dual-band tunable microwave pulse signals generation method based on a time domain mode locked optoelectronic oscillator (TDML-OEO). The dual-band radio frequency (RF) combs are generated via injecting two single-tone signals and a low frequency signal. The two single-tone signals are injected to optimize the aimed center frequencies gain, while the low frequency signal is used to accomplish the multi-mode oscillation mode locking process. Furthermore, the dual-band RF combs with variable repetition rates of 3.69 MHz, 9.22 MHz, and 18.45 MHz are obtained with an over 72 dB ultra-high suppression of super mode noise as the TDML-OEO operates in the varied harmonic multiples mode locking state. Besides, by adjusting the amplitude and central frequency of the two injected local oscillator signals (LOs), a controllable output power and frequency tunability ranged from 11.1 GHz to 13.8 GHz are achieved for the generated dual-band RF combs. The proposed dual-band tunable microwave pulse generation method has great potential applications in multiband radars and electronic warfare.© 2023 Optica Publishing Group under the terms of the Optica Publishing Group Open Access Publishing Agreement.

A flexibly frequency switchable active mode-locking optoelectronic oscillator with supermode noise suppression

In this paper, we propose and experimentally demonstrate a flexibly frequency switchable active mode-locking optoelectronic oscillator (FSAML-OEO) in which a multi-passband microwave photonic filter (MPF) with two polarization-maintaining fibers (PMF) based Solc-Sagnac interferometer is used. Microwave frequency combs (MFCs) signals with four switchable central frequencies of 217 MHz, 453 MHz, 662 MHz and 1101 MHz are generated by controlling the polarization state of the Sagnac interferometer via rotating the polarization controller (PC). By cascading a dual-loop structure, MFCs signals with adjustable comb spacing of 1 MHz, 3 MHz, and 5 MHz are obtained with fundamental and harmonic FSAML-OEO, in which the supermode noise suppression ratios of the dominate modes and the super-modes are measured to be about 30 dB.

Tunable High-Purity Microwave Frequency Combs Generation Based on Active Mode-Locking OEO

A novel approach to generate tunable high-purity microwave frequency combs (MFCs) based on active mode-locking optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. In the proposed method, one cavity mode of the OEO is injection-locked by a local oscillator (LO) signal resulting in single-mode oscillation. Under the assistance of an additional radio frequency signal, the MFCs generation is realized by loss modulation the single-mode oscillation. A key significance of our scheme is that no tunable filter is needed in OEO cavity. By altering the frequency of the LO signal, the MFCs center frequency can be flexibly precisely tuned over a bandwidth of 1.6 GHz. Furthermore, the high suppression of the supermode noise is obtained due to the injection locking of the OEO decreasing the required loop gain. The experimental results show that the generated MFCs maintain a large supermode noise suppression ratio over the entire tuning range.

Rational number harmonic mode-locked dual-loop optoelectronic oscillator with low supermode noise and low intermodulation distortions

A rational number harmonic mode-locked dual-loop optoelectronic oscillator (RHML-DL-OEO) is proposed and experimentally demonstrated. In the proposed system, an external radio frequency (RF) signal and a feedback oscillating microwave signal drive two arms of a dual-drive Mach-Zehnder modulator (DMZM). Mode locking is realized by frequency detuning. The larger effective free spectrum range (FSR) and higher side-mode suppression result from the Vernier effect effectively suppress supermode noise and intermodulation distortions (IMDs). Experimental results demonstrate that the microwave frequency comb (MFC) signals with repetition frequencies of 901.8 kHz, 2.3046 MHz and 5.3106 MHz are generated by 9th-, 23rd- and 53rd-order rational number harmonic mode-locking, respectively. Compared with the rational number harmonic mode-locked optoelectronic oscillator based on single-loop structure, the supermode noise suppression ratios of the scheme we propose are improved by 30.5 dB, 27.6 dB and 20.3 dB, respectively. Furthermore, the performance of single sideband (SSB) phase noise is also investigated.

Timing jitter reduction of silicon hybrid harmonically mode-locked ring laser using an integrated sampled-grating DBR.

An integrated sampled-grating silicon hybrid mode-locked ring laser is proposed for 20-GHz super-mode noise suppression. The dynamics, phase noise, and timing jitter are investigated using a delay differential equation (DDE) model. The results show that the 20-GHz harmonic regime of the proposed structure is significantly increased when the sampled-grating structure is included. Additionally, a better selectivity of the optical modes by a sampled-grating distributed Bragg reflector (SGDBR) leads to more suppression of super-mode noise compared to the long-ring structures with a spectral filter which were previously reported. Compared to previous works, the phase noise is improved by approximately 6 dB and the timing jitter is decreased to less than a third.

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.

Supermode noise suppression with polarization-multiplexed dual-loop for active mode-locking optoelectronic oscillator.

The active mode-locking (AML) technique has been widely used in erbium-doped fiber lasers to generate picosecond pulse trains. Here we propose a novel active mode-locking dual-loop optoelectronic oscillator (AML-DL-OEO), which can generate microwave frequency comb (MFC) signals with adjustable comb spacings. Based on this scheme, the order of harmonic mode-locking is dramatically decreased for a certain AML driving frequency compared with a single-loop AML-OEO. Thus, the supermode noise caused by harmonic mode-locking can be efficiently suppressed. In addition, the sidemodes are well suppressed by the dual-loop architecture. An experiment is performed. MFC signals with different comb spacings are generated under fundamental or harmonic mode-locking states. AML-DL-OEO systems with different length differences between two loops are implemented to evaluate supermode noise suppression capability. The performance of the generated MFC signals is recorded and analyzed.

Mitigation of the supermode noise in a harmonically mode-locked ring fiber laser using optical injection.

We report on a new, to the best of our knowledge, technique enabling mitigation of the supermode noise (and timing jitter) in a soliton harmonically mode-locked (HML) fiber laser built on the nonlinear polarization evolution (NPE). An optical injection of an external continuous wave (CW) into the HML laser cavity results in an increase of the supermode noise suppression level (SSL) by a two-three order of magnitude for harmonics between 25th and 135th. The operation mechanism involves phase-locking between the injected light and soliton pulses and exhibits strong resonant dependence on the CW laser wavelength. Our findings offer important insights into the HML laser dynamics associated with an interaction between solitons and CW background in the laser cavity.

Super-mode noise suppression for coupled optoelectronic oscillator with optoelectronic hybrid filter

A novel scheme to implement the super-mode noise suppression for coupled optoelectronic oscillator (COEO) utilizing an optoelectronic hybrid filter (OEF) is proposed and experimentally demonstrated. The OEF is made up of a multi-mode optoelectronic oscillator, incorporated in the COEO loop to serve as a channelized RF filter, while the fiber laser in the COEO can be viewed as another channelized RF filter of high Q. The cascading of the two equivalent channelized RF filters can greatly improve the out-of-band rejection ratio of the combined filter and restrain the adjacent mismatched modes in the oscillating loop. In the experiment, a 9.955 GHz RF signal with the side mode suppression ratio of larger than 82.6 dB is obtained, and the super-mode noise spur at an offset frequency of 5.9 MHz is suppressed 15 dB to -145 dBc/Hz level compared with the conventional COEO.

Supermode noise suppression with mutual injection locking for coupled optoelectronic oscillator.

The coupled optoelectronic oscillator (COEO) is typically used to generate high frequency spectrally pure microwave signal with serious sidemodes noise. We propose and experimentally demonstrate a simple scheme for supermode suppression with mutual injection locking between the COEO (master oscillator with multi-modes oscillation) and the embedded free-running oscillator (slave oscillator with single-mode oscillation). The master and slave oscillators share the same electrical feedback path, which means that the mutually injection-locked COEO brings no additional hardware complexity. Owing to the mode matching and mutually injection locking effect, 9.999 GHz signal has been successfully obtained by the mutually injection-locked COEO with the phase noise about -117 dBc/Hz at 10 kHz offset frequency. Besides, the supermode noise can be significantly suppressed more than 50 dB to below -120 dBc.

Low pump threshold CVD graphene based passively harmonic mode‐locked fibre laser

A low pump threshold passively harmonic mode-locked fibre laser is demonstrated. The key component is a chemical vapour deposition grown graphene saturable absorber to enable higher order harmonic mode-locking (HML) of the fibre laser with good output noise characteristics. With a relatively low pump power of 100 mW, the fibre laser generates ∼1 ps soliton pulses at the 21st order of HML with 40 dB of super-mode noise suppression.

Gigahertz-repetition-rate Tm-doped fiber laser passively mode-locked by optoacoustic effects in nanobore photonic crystal fiber

We report a Tm-doped soliton fiber laser passively mode-locked by intense optoacoustic interactions in a short length of solid-core silica photonic crystal fiber (PCF) with a nanobore in core-center. A repetition rate of 1.446GHz pulse is achieved, corresponding to the 52nd harmonic of the 27.8MHz cavity round-trip frequency. Strong optoacoustic interactions in this PCF-based, Tm-doped fiber laser ensure stable and repeatable gigahertz-rate pulse train generation at 1.85μm wavelength, with a high supermode noise suppression ratio and low pulse timing jitter.

Wideband-tunable soliton fiber laser mode-locked at 1.88 GHz by optoacoustic interactions in solid-core PCF.

We report a wavelength-tunable soliton fiber laser stably mode-locked at 1.88 GHz (the 389th harmonic of the cavity round-trip frequency) by a light-driven acoustic resonance in the core of a photonic crystal fiber. Stable high-harmonic mode-locking could be maintained when the lasing wavelength was continuously tuned from 1532 to 1566 nm by means of an optical filter placed inside the laser cavity. We report on the experimental performance of the laser, including its power scalability, super-mode noise suppression ratio, long-term repetition rate stability, short-term pulse amplitude noise and timing jitter, optical comb structure and pulse-to-pulse phase fluctuations.

A special issue on Information Optoelectronics: Devices, Technologies and Applications

Information technology has entered a big-data era. The every-increasing data traffic has driven the rapid development of information optoelectronics, which is related to key devices, crucial technologies, and important applications for the generation, transmission, processing, and detection of optical data information. Recent progresses on devices, technologies and applications of information optoelectronics have led to reduced footprint, improved efficiency, enhanced flexibility and extended functionality generating, delivering/manipulating, and detecting optical data information. Lots of integrated photonic devices, such as silicon-, grapheneand plasmonassisted waveguides, lasers, modulators and detectors, speciality optical fiber, and coherent optical communications, have been widely reported, showing significant advances in devices, technologies and applications of information optoelectronics. It is believed that information optoelectronics will continue its rapid development towards integrated nanophotonic devices, more advanced technologies, flexible and multi-functional applications. It is our intention to draw great attention of the research community to those hot topics in devices, technologies and applications of information optoelectronics. In this “Special Issue on Information Optoelectronics: Devices, Technologies and Applications”, we present 8 review articles and 4 research articles focusing on relevant subjects by internationally active groups in the related fields. In the review articles, Dr. Sudharsanan Srinivasan at University of California, Santa Barbara reviewed recent results on hybrid silicon mode-locked lasers focusing on low phase noise optical pulse generation. Key results included demonstration of the longest (cavity length 9 cm) integrated on-chip mode locked laser, 14 dB reduction of Lorentzian noise on a 20 GHz radio-frequency (RF) signal, and greater than 55 dB optical supermode noise suppression using harmonically mode locked long cavity laser, 10 GHz passively mode locked laser with 15 kHz linewidth using on-chip all optical feedback stabilization. Dr. Ran Hao at Zhejiang University reviewed recent developments of graphene-based optical modulators, including material property, different integration schemes, single-layer graphene-based modulator, multi-layer and few-layer graphene-based modulators, corresponding figure-of-merits, wavelength/temperature tolerance, and graphene-based fiber-optic modulator. Dr. Lai Wang at Tsinghua University reviewed recent progresses on InGaN quantum dot (QD) light emitting diodes (LEDs), including the basic physics model of the strain relaxation in self-assembled InGaN QDs, the growth of InGaN QDs with a growth interruption method by metal organic vapor phase epitaxy, the optimization of GaN barrier growth in multilayer InGaN QDs, and the green, yellow-green and red InGaN QD LEDs. Dr. Xiaowei Guan and Dr. Daoxin Dai at Zhejiang University reviewed progresses on various hybrid plasmonic waveguides as well as ultrasmall functionality devices. Ultra-sharp bending of silicon hybrid nanoplasmonic waveguides, optical couplers/splitters, ultrasmall resonators, and polarization handing devices were discussed. Dr. Jian Wang at Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology reviewed recent progress on plasmon-assisted nanophotonic devices and their wide applications, including long-range hybrid plasmonic slot (LRHPS) waveguide, ultra-compact plasmonic microresonator with efficient thermo-optic tuning, high quality (Q) factor and small mode volume, compact active hybrid plasmonic ring resonator for deep-subwavelength lasing

Low phase noise hybrid silicon mode-locked lasers

In this paper, we review recent results on hybrid silicon mode-locked lasers with a focus on low phase noise optical pulse generation. Taking a high level design approach to lowering phase noise, we show the need for long on-chip optical delay lines for mode-locked lasers to reach and overcome material limits. Key results include demonstration of the longest (cavity length 9 cm) integrated on-chip mode locked laser, 14 dB reduction of Lorentzian noise on a 20 GHz radio-frequency (RF) signal, and greater than 55 dB optical supermode noise suppression using harmonically mode locked long cavity laser, 10 GHz passively mode locked laser with 15 kHz linewidth using on-chip all optical feedback stabilization.

Supermode noise suppression in an actively mode-locked fiber laser with pulse intensity feed-forward and a dual-drive MZM

The supermode noise in an actively mode-locked fiber laser is suppressed for the first time by a so-called pulse-intensity-feed-forward technique. In this novel scheme, the optical pulse is firstly converted into an electronic signal, and then fed forward to a dual-drive Mach–Zehnder modulator (MZM), where the optical pulse is modulated by the reversed intensity profile of itself. In a 12.5 m long actively mode-locked fiber ring laser experiment, the resulting power limiting shows a stable 10 GHz optical pulse train with a supermode-suppression ratio larger than 81 dB. The phase noise and pulse-to-pulse timing jitter are below −141 dBc Hz−1 at 10 MHz and 22.1 fs, respectively. Compared with the conventional fiber-nonlinearity-based power limiting schemes, our proposal is compact and stable.

A Comprehensive Study of Actively Mode-Locked Fiber Optical Parametric Oscillators for High-Speed Pulse Generation

We perform a comprehensive study on the implementation of active harmonic and rational harmonic mode-locking of a fiber optical parametric oscillator (FOPO). In particular, the effect of pump parameters and cavity designs on the characteristics of the generated pulses are analyzed. Two methods of frequency multiplication in FOPOs are discussed and compared and we show that we can generate optical pulses with very high-repetition-rate (up to 240 GHz) using rational harmonic mode-locking. We find that optical pulses with short duration can be obtained using pump pulses with small duty cycle, large pump power, and an intra-cavity optical filter with proper bandwidth. In addition, optical pulses with low root-mean-square timing jitter are achievable when no pump phase modulation is applied and hybrid gain of erbium-doped fiber amplifier and parametric amplifier is used. High supermode noise suppression ratio is achieved by taking advantage of the fast parametric gain and the combined effect of self-phase modulation and spectral filtering. We conclude that synchronous-pumping of an actively mode-locked FOPO offers many advantages in terms of reducing the cavity loss, increasing the modulation frequency, enabling rational harmonic mode-locking, and applications to all-optical clock recovery.

Asynchronous Harmonic Mode Locking in an All-Normal Dispersion Yb-Doped Fiber Laser

We present detailed experimental and theoretical results to demonstrate the possibility of asynchronous harmonic mode locking in an all-normal dispersion fiber laser. In contrast to asynchronous soliton mode-locking operation in the anomalous dispersion regime, more profound laser dynamics are found. The experimentally demonstrated 10-GHz asynchronous harmonic mode-locked Yb-doped fiber laser exhibits an excellent super-mode noise suppression ratio in the RF spectrum with picosecond output pulsewidth.

Sub-picosecond Graphene-based Harmonically Mode-Locked Fiber Laser With Repetition Rates up to 2.22 GHz

Passive harmonic-mode locking (PHML) of erbium-doped fiber laser with multilayer graphene is presented. The laser could operate at several harmonics (from 2nd to 21st) of the fundamental repetition frequency of the ring resonator (106 MHz). The highest achieved repetition rate was 2.22 GHz (which corresponds to the 21st harmonic) with 900 fs pulse duration and 50 dB of the supermode noise suppression. The saturable absorber was formed by multilayer graphene, mechanically exfoliated from pure graphite block through Scotch-tape and deposited on the fiber ferrule.