Tunable Optoelectronic Oscillator Research Articles

Frequency tunable optoelectronic oscillator with parity-time symmetry by using integrated components

Frequency tunable optoelectronic oscillator with parity-time symmetry by using integrated components

Design and simulation of a tunable parity-time symmetric optoelectronic oscillator utilizing integrated components

Non-Hermitian photonics, relaying on parity-time (PT) symmetry, have shown promise in achieving mode selection for optical or microwave single-mode oscillation. Typically, a PT-symmetric system is constructed using two coupled loops with identical geometry. This article utilizes the PT-symmetry property to select a single frequency mode in an optoelectronic oscillator (OEO). However, traditional OEO implementations often involve discrete components, limiting widespread adoption due to factors such as size, weight, power consumption, and cost. Our aim in this paper is to leverage integrated components within the OEO loop. The proposed structure incorporates an integrated micro-ring resonator (MRR) with a high-quality factor (Q-factor) that serves both as a modulator and a resonator. Additionally, we suggest employing an adjustable integrated power splitter utilizing a micro heater to balance the gain and loss of two mutually coupled OEO loops. In this configuration, two integrated photo detectors (PD) are also utilized. In this setup, the single-frequency mode can be easily identified by simultaneously utilizing the properties of PT-symmetry and an integrated high-Q-factor resonator, obviating the need for a narrowband microwave filter. By adjusting the center frequency of the microwave photonic filter (MPF), the frequency of the generated signal can be tuned over a wide range. For instance, setting the generated frequency of the microwave signal to 11.5 GHz results in a measured phase noise of − 76.5 dBc/Hz at a 10-kHz offset frequency, with a side mode suppression ratio (SMSR) of 40 dB.

Ka-band thin film lithium niobate photonic integrated optoelectronic oscillator

Photonics integration of an optoelectronic oscillator (OEO) on a chip is attractive for fabricating low cost, compact, low power consumption, and highly reliable microwave sources, which has been demonstrated recently in silicon on insulator (SOI) and indium phosphide (InP) platforms at X-band around 8 GHz. Here we demonstrate the first integration of OEOs on the thin film lithium niobate (TFLN) platform, which has the advantages of lower V π , no chirp, wider frequency range, and less sensitivity to temperature. We have successfully realized two different OEOs operating at Ka-band, with phase noises even lower than those of the X-band OEOs on SOI and InP platforms. One is a fixed frequency OEO at 30 GHz realized by integrating a Mach–Zehnder modulator (MZM) with an add-drop microring resonator (MRR), and the other is a tunable frequency OEO at 20–35 GHz realized by integrating a phase modulator (PM) with a notch MRR. Our work marks the first step of using TFLN to fabricate integrated OEOs with high frequency, small size, low cost, wide range tunability, and potentially low phase noise.

Single-loop tunable PT-symmetric optoelectronic oscillator based on a phase modulator.

In this paper, a single-loop tunable parity-time (PT) symmetric optoelectronic oscillator (OEO) based on a dual-mode optical phase modulator (PM) and a microwave photonic filter (MPF) has been proposed, analyzed, and designed. By adjusting the polarization angle θ between the input linearly polarized light and the z axis of the PM, the two-mode splitting ratio of the PM can be controlled, which results in a PT-symmetric structure based on a single physical loop. By adjusting the pump light wavelength, the center frequency of the stimulated Brillouin scattering (SBS)-based MPF can be tuned, which enables a fine tunable output frequency. The results reveal that, by adjusting the pump light wavelength with a step size of 0.0001nm, a frequency tuning accuracy of 12.5MHz can be obtained. Simultaneously, the OEO output frequency can be tuned from 0.9 to 22GHz, while the side-mode suppress ratio (SMSR) is 53dB, and the phase noise is -133.8d B c/H z at a frequency offset of 10kHz.

Theoretical and experimental study on stable oscillation of dual-frequency signals in an optoelectronic oscillator.

Due to the gain competition effect, it is hard to simultaneously maintain oscillation at two frequencies in an optoelectronic oscillator (OEO) loop. In this paper, a study of the gain competition effect in a dual-frequency OEO is theoretically and experimentally demonstrated. The steady-state conditions in the dual-frequency OEO are theoretically analyzed by deriving dynamic equations. A nonlinear time-varying model, as well as its calculation methods, is carried out to design and study the dynamic process of the dual-frequency OEO. Thanks to this model, the waveform, spectrum, and amplitude evaluation of generated signals, as well as the gain variation in the OEO loop, are numerically simulated. Based on the theoretical analysis and numerical simulation results, three schemes that can suppress the gain competition effect are proposed, and the one based on wavelength division multiplexing (WDM) technology is experimentally realized. The experimental results show that the novel independently tunable dual-frequency OEO, to the best of our knowledge, can generate two-tone RF signals in a range from 1.8 to 18.6 and 1.5 to 18.3GHz, respectively.

Polarization controlled dispersion tunable optoelectronic oscillator and frequency octupling without bandpass filter

Polarization controlled dispersion tunable optoelectronic oscillator and frequency octupling without bandpass filter

Finely Tunable Coupled Optoelectronic Oscillator Based on Injection Locking and Phase Locked Loop

Finely Tunable Coupled Optoelectronic Oscillator Based on Injection Locking and Phase Locked Loop

Optical Tunable Frequency-Doubling OEO Using a Chirped FBG Based on Orthogonally Polarized Double Sideband Modulation

We propose and experimentally demonstrate a tunable frequency-doubling optoelectronic oscillator (FD-OEO) based on a single-bandpass dispersion-induced microwave photonic filter (MPF) consisting of a Mach–Zehnder modulator (MZM), a linearly chirped fiber Bragg grating and polarization-multiplexed dual-loop. Thanks to the polarization dependence of the MZM, a special double sideband modulation is implemented where the optical carrier (OC) and subcarriers are orthogonally polarized. By simply tuning the PC in the OEO loop, the phase difference between the orthogonal polarization carrier and two sidebands can be controlled, and thus the center frequency of the fundamental OEO can be tuned. Furthermore, a PC and a polarizer are placed outside the OEO to achieve optical carrier suppression (OCS) modulation, which ensures that a frequency-tunable microwave signal at the second-harmonic frequency is generated. In the experiment, a fundamental frequency signal with tunable frequency from 3.6 to 6.85 GHz and FD-OEO with a tunable frequency range from 7.2 to 13.7 GHz are generated.

Hybrid-integrated wideband tunable optoelectronic oscillator.

As a photonic-based microwave signal generation method, the optoelectronic oscillator (OEO) has the potential of meeting the increasing demand of practical applications for high frequency, broadband tunability and ultra-low phase noise. However, conventional OEO systems implemented with discrete optoelectronic devices have a bulky size and low reliability, which extremely limits their practical applications. In this paper, a hybrid-integrated wideband tunable OEO with low phase noise is proposed and experimentally demonstrated. The proposed hybrid integrated OEO achieves a high integration level by first integrating a laser chip with a silicon photonic chip, and then connecting the silicon photonic chip with electronic chips through wire-bonding to microstrip lines. A compact fiber ring and an yttrium iron garnet filter are also adopted for high-Q factor and frequency tuning, respectively. The integrated OEO exhibits a low phase noise of -128.04 dBc/Hz @ 10 kHz for an oscillation frequency of 10 GHz. A wideband tuning range from 3 GHz to 18 GHz is also obtained, covering the entire C, X, and Ku bands. Our work demonstrates an effective way to achieve compact high-performance OEO based on hybrid integration, and has great potential in a wide range of applications such as modern radar, wireless communication, and electronic warfare systems.

Automatic Power Control for a Frequency Tunable Optoelectronic Oscillator

Automatic power control for a frequency tunable optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. The OEO is implemented by a tunable microwave photonic filter using a phase-shifted fiber Bragg grating (PS-FBG) for frequency-tuning. Taking advantage of the automatic power control (APC), the problem of large power fluctuation in the OEO output signal during the frequency tuning or interfered by the external disturbance can be significantly improved and the functionality of equalization is realized. By adjusting the DC reference voltage of the automatic power control circuit, the tuning of RF signal power is conveniently achieved. To the best of the authors’ knowledge, this is the first time that the output power regulation of OEO has been implemented. For verification, the low-cost OEO at 2–7 GHz is established. Experiment results show that the output power fluctuation of less than 3 dB and a phase noise of −113 dBc/Hz@10 kHz are achieved.

Tunable optoelectronic oscillator based on a high-Q microring resonator

This paper proposes a tunable optoelectronic oscillator (OEO) by using a silicon nitride high-Q microring resonator (MRR) with a Q value of 4.36 × 105. Inserting the high-Q MRR into a phase-modulated link, an 8–38 GHz tunable microwave photonic filter (MPF) is realized with a 3-dB bandwidth of ∼610 MHz. Based on the tunable MPF, a tunable OEO is established. The frequency range of the OEO is 14.60 to 25.65 GHz, and the measured phase noise of the 25.65-GHz oscillation signal is -88 dBc/Hz@10 kHz.

Stable and Widely Tunable Optoelectronic Oscillator Using a Cascade Microwave Photonic Filter

A widely tunable optoelectronic oscillator (OEO) with stable output based on a cascade microwave photonic filter (MPF) is proposed and demonstrated. The cascade MPF is implemented by a combination of a finite impulse response (FIR) filter based on shifted dispersion-induced power fading and an infinite impulse response (IIR) filter based on a double-parallel recirculating delay lines (DP-RDLs). Through adjusting the time delay difference between the upper and lower connecting arms of the dual-input Mach-Zehnder modulator within FIR filter, the center frequency of cascade MPF is changed and the oscillation frequency of the OEO can be tuned. The theoretical analysis and verified experiment of the proposed OEO is performed. Tunable oscillation signals from 6.1 to 11.98 GHz with an average step size of 490 MHz are generated. Due to the introduce of the IIR filter, the stable performance of the OEO is obtained, where the maximum frequency drift at 7.48 GHz is observed to be 1.817 kHz over 1 hour. The phase noise of the structure is also investigated

Tunable microwave frequency comb generation using a Si3N4-MDR based actively mode-locked OEO.

Microwave frequency combs (MFCs) have important applications in communication and sensing owing to their characteristics of large number of comb lines, wide frequency range, and high precision of comb spacing. In many applications, MFCs are required to emit signals with tunable center frequency and variable comb spacing to accommodate different operating frequency bands and accuracies. Here, we demonstrate a tunable MFC by injecting a low-frequency electrical signal into a tunable optoelectronic oscillator (OEO). Tuning of MFC's center frequency and comb spacing are realized, allowing a frequency tuning range from 1 to 22 GHz and 50 comb lines within a 5 MHz bandwidth obtained in the MFC generator. In addition, the introduction of the silicon nitride micro-disk resonator (Si3N4-MDR) in the system paves the way for the integration of MFC generator.

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.

Wideband Tunable Frequency Converter Based on an OEO Using a DP-QPSK Modulator

Flexibility and tunability are critical for frequency conversion in antenna, radar and modern communication systems. In this study we propose and experimentally demonstrate a wideband tunable frequency converter by using an optoelectronic oscillator (OEO) to generate high-purity local oscillator (LO) signal for flexible frequency conversion. In the proposed frequency converter, a dual-polarization quadrature phase shift-keying (DP-QPSK) modulator is utilized to receive the signal to be converted and also to form a tunable OEO based on a dispersion-induced microwave photonic filter. By adjusting the bias voltage of the DP-QPSK modulator, an LO signal with accurate adjustable frequency is generated by the OEO. The measured phase noise of generated LO signal can reach -110 dBc/Hz at 10 kHz offset. An experiment is performed to verify the feasibility of this proposed frequency converter. The 7.6-GHz radio frequency (RF) signal is freely converted to different intermediate frequency (IF) signals, respectively. Moreover, the proposed microwave photonic converter is applied into wireless transmission systems. A 1-Gb/s NRZ wireless signal centered at 6.5 GHz is down-converted to baseband successfully.

Parity-time symmetric tunable OEO based on dual-wavelength and cascaded PS-FBGs in a single-loop.

The ability to achieve low phase noise single-mode oscillation within an optoelectronic oscillator (OEO) is of fundamental importance. In the frequency-tunable OEO, the wide microwave photonic filter (MPF) bandwidth is detrimental to select single-mode among the large number of cavity modes, thus leading to low signal quality and spectral purity. Stable single-mode oscillation can be achieved in a large time delay OEO system by harnessing the mechanism from parity-time (PT) symmetry. Here, a PT-symmetric tunable OEO based on dual-wavelength and cascaded phase-shifted fiber gratings (PS-FBGs) in a single-loop is proposed and experimentally demonstrated. Combining the merits of wide frequency tuning of PS-FBG-based MPF and single mode selection completed by the PT-symmetric architecture of the OEO, where the gain and loss modes carried by dual-wavelengths to form two mutually coupled resonators in a single-loop, signals range from 1 GHz to 22 GHz with the low phase noise distributed in -122∼ -130 dBc/Hz at 10 kHz offset frequency are obtained in the experiment.

Stable and Tunable Optoelectronic Oscillator With External Stimulated Brillouin Beat Note Injection

Broadband and tunable microwave signals are widely used in modern communication systems and sensing systems. In this work, we demonstrate a stable and tunable optoelectronic oscillator (OEO) scheme based on external low-power beat note injection of the stimulated Brillouin signal and a phase modulation sideband of the original pump signal. The injection-locked system reduces the high-frequency disturbance induced by the beat note signal, and thus the power required only meets the OEO locking threshold requirement. In addition, the external stimulated Brillouin signal generator avoids the excessive length of the resonant cavity and guarantees the frequency stability, especially the mode stability in the OEO with a total path length of ~12 m. By varying the stimulated Brillouin signal frequency and selecting different pump modulation sidebands, a continuously tuned beat note is generated, and a beat note injected OEO with a maximum frequency up to 11.5 GHz is achieved, which is the intrinsic upper frequency limit of the devices used, even for an injection beat frequency power as low as -14 dBm ( ~ 40 μ W). Our work provides an important solution for the realization of widely tunable microwave systems.

Wideband tunable optoelectronic oscillator based on stimulated Brillouin scattering and a Mach-Zehnder interferometer.

We propose a novel optoelectronic oscillator (OEO) based on stimulated Brillouin scattering (SBS) and a Mach-Zehnder interferometer (MZI). The SBS and MZI form a microwave photonic filter (MPF), which completes the frequency selection of the OEO. The width of the MPF passband can be changed by adjusting the DC voltage of the MZI. When the gap between the passbands is aligned with the side mode, the side mode can be suppressed; in this way, a single-mode optoelectronic oscillator is achieved. Compared with the previous structure, the proposed structure is more stable and easier to integrate. A stable frequency signal at 9.4 GHz is obtained with a phase noise of -84.05dBc/Hz at 10 kHz, the side-mode-suppression ratio is 42 dB, and the frequency drift is below 50 kHz within 420 s. By adjusting the wavelength of the tunable laser source, a 280 MHz tuning range from 9.25 to 9.53 GHz is obtained. If an independent pump is introduced, a large tuning range is achieved from 9.4 to 24.9 GHz.

Photonic microwave synthesizer based on optically referenced sub-sampling phase-locked optoelectronic oscillator

Wideband and low phase noise microwave synthesizers are of critical significance for various applications. Phase-locked loop (PLL) based microwave synthesizers are widely used. Normally, the phase noise of the PLL based microwave synthesizer is limited by the phase noise of the reference, phase detector, frequency divider and voltage-controlled oscillator (VCO). It is challenging to achieve a pure electronic microwave synthesizer with wide frequency coverage and low phase noise, simultaneously. Here, we propose a photonic microwave synthesizer which incorporates an ultra-low phase noise fiber mode-locked laser (MLL) based reference and a wideband frequency tunable optoelectronic oscillator (OEO) based VCO in a hybrid optoelectronic sub-sampling PLL. The frequency of the OEO can be locked to the harmonics of the repetition-rate of the fiber MLL, which combines the distinct advantages of the low phase noise of MLL and the wideband frequency tuning of OEO. A sub-sampling phase detector formed by a balanced optical microwave phase detector (BOMPD) eliminates the use of RF frequency divider and maintains low residual phase noise. We attain an X- and Ku-band photonic microwave synthesizer with over an octave frequency coverage from 8 GHz to 18 GHz, frequency synthesis step of 60.74 MHz and phase noise of -80 dBc/Hz at 100 Hz offset and -100 dBc/Hz at 1 kHz offset for 10 GHz output. The characteristics of the optoelectronic sub-sampling phase detector, the phase-locking dynamics of the hybrid optoelectronic PLL, and the phase noise of the synthesized RF signals are both theoretically and experimentally investigated. The experimental results agree well with the theoretical models. Our approach is promising to achieve wideband and low phase noise microwave synthesis.

Tunable multi-frequency optoelectronic oscillator based on a microwave photonic filter and an electrical filter

We propose and experimentally demonstrate a multi-frequency optoelectronic oscillator (OEO) based on the phase-modulation to intensity-modulation conversion. A microwave photonic filter incorporating an optical fiber Bragg grating Fabry–Perot filter and an electrical yttrium iron garnet (YIG) filter in two branches are used to select the oscillation modes of the OEO. By adjusting the wavelength of laser source or the central frequency of YIG filter, two frequencies can be tuned independently within a wide range. The single sideband phase noises of the generated frequencies are measured experimentally. Moreover, the OEO shows potential ability to achieve more frequencies oscillation by multiplexing more optical and electrical filters.