Microwave Photonics Research Articles

Reconfigurable Free Form Silicon Photonics by Phase Change Waveguides

AbstractThe rapid reprogramming of photonic integrated circuits (PICs) offers transformative potential for photonic technologies. Traditional programmable photonic devices, relying on thermo‐optic or electro‐optic effects, face limitations like large size and high energy consumption. Chalcogenide phase‐change materials (CPCMs) have gained attention for enabling energy‐efficient, non‐volatile optical manipulation on‐chip, crucial for in‐memory optical computing. Sb₂S₃ emerges as a promising alternative to conventional CPCMs, providing low loss and reversibility. This work introduces a CMOS‐compatible reconfigurable waveguide platform using Sb₂S₃ thin film on silicon‐on‐insulator (SOI). Laser direct writing enables the creation of complete channel waveguides in a single step, with the flexibility to erase and rewrite segments for rapid design adjustments. The platform demonstrates stable waveguide erasure using a cost‐effective laser engraver and low‐loss coupling between SOI and the phase‐change material‐on‐silicon (PCMoS) waveguide. By combining an economical fabrication process with a robust device architecture, this integration scheme offers a versatile solution for applications such as optical interconnects, neuromorphic and quantum computing, and microwave photonics.

Optoelectronic oscillator system with low phase noise based on a microwave multiplexor: evaluation of construction possibilities

The paper is dedicated to the current issue of microwave photonics: the development of optoelectronic oscillators for ultra-high frequency signals. The interest in creating such oscillators is largely driven by the possibility of obtaining signals with low levels of phase noise. The use of multiplexers as fi lters in optoelectronic oscillators opens up new possibilities in building optoelectronic systems for generating ultra-high frequency signals at different frequencies. This implementation of the optoelectronic generator allows for discrete regulation of the frequency of the generated signal, or generating the signal simultaneously at multiple specifi ed frequencies. In the investigated system, phase noises were measured: less than 100 dBc/Hz at 1 kHz offset from the carrier frequency and less than 130 dBc/Hz at 10 kHz offset from the carrier frequency. The obtained results confirm the potential use of multiplexers as bandpass filters, which is important for the development and optimization of optoelectronic oscillators

Silicon Nitride Spot-Size Converter with Coupling Loss < 1.5 dB for Both Polarizations at 1W Optical Input

Microwave photonics (MWP) applications often require a high optical input power (>100 mW) to achieve an optimal signal-to-noise ratio (SNR). However, conventional silicon spot-size converters (SSCs) are susceptible to high optical power due to the two-photon absorption (TPA) effect. To overcome this, we introduce a silicon nitride (SiN) SSC fabricated on a silicon-on-insulator (SOI) substrate. When coupled to a tapered fiber with a 4.5 μm mode field diameter (MFD), the device exhibits low coupling losses of <0.9 dB for TE modes and <1.4 dB for TM modes at relatively low optical input power. Even at a 1W input power, the additional loss is minimal, at approximately 0.1 dB. The versatility of the SSC is further demonstrated by its ability to efficiently couple to fibers with MFDs of 2.5 μm and 6.5 μm, maintaining coupling losses below 1.5 dB for both polarizations over the entire C-band. This adaptability to different mode diameters makes the SiN SSC a promising candidate for future electro-optic chiplets that integrate heterogeneous materials such as III-V for gain and lithium niobate for modulation with the SiN-on-SOI for all other functions using advanced packaging techniques.

Advances in Soliton Crystal Microcombs

Soliton crystal microcombs, as a new type of Kerr frequency comb, offer advantages such as higher energy conversion efficiency and a simpler generation mechanism compared to those of traditional soliton microcombs. They have a wide range of applications in fields like microwave photonics, ultra-high-speed optical communication, and photonic neural networks. In this review, we discuss the recent developments regarding soliton crystal microcombs and analyze the advantages and disadvantages of generating soliton crystal microcombs utilizing different mechanisms. First, we briefly introduce the numerical model of optical frequency combs. Then, we introduce the generation schemes for soliton crystal microcombs based on various mechanisms, such as utilizing an avoided mode crossing, harmonic modulation, bi-chromatic pumping, and the use of saturable absorbers. Finally, we discuss the progress of research on soliton crystal microcombs in the fields of microwave photonics, optical communication, and photonic neural networks. We also discuss the challenges and perspectives regarding soliton crystal microcombs.

Integrated Optical Tunable Delay Line and Microwave Photonic Beamforming Chip: A Review

AbstractThe microwave photonic (MWP) beamforming chip is a crucial component for achieving the miniaturization of optically controlled phased array radar systems. It addresses the unwanted ‘beam squint’ effect of traditional electronic antenna arrays in processing wideband RF signals through optical tunable delay lines (OTDLs), which has garnered significant attention and research efforts in recent years. This review provides a comprehensive overview of the latest research progress on the classification, working principle, calibration and delay measurement methods, driving and control technologies, and system function verifications of OTDL and MWP beamforming chips. Also, discussions about the challenges that need to be addressed and the future development trends for this technology are given.

Ultra-Compact, Fully Packaged Broadband Thin-Film Lithium Niobate Modulator for Microwave Photonics

Ultra-Compact, Fully Packaged Broadband Thin-Film Lithium Niobate Modulator for Microwave Photonics

Recent Development of Fourier Domain Mode-Locked Laser

Since the advent of Fourier Domain Mode-Locked (FDML) lasers, they have demonstrated outstanding performance in several fields. They achieve high-speed, narrow-linewidth laser output with the new mode-locking mechanism, which has been intensively researched in the past decades. Compared with conventional wavelength-scanning light sources, FDML lasers have successfully increased the scanning rate of frequency-sweeping lasers from kHz to MHz. They are widely used in optical coherence tomography, spectral analysis, microscopy, and microwave photonics. With the deepening research on FDML lasers, several performance metrics have been optimized and improved, offering superior performance for FDML laser-based applications. This paper reviews the principles and key performance indicators of FDML lasers, as well as the recent progress made in some important applications, and highlights further research directions for FDML lasers in the future.

A Real-Time Signal Measurement System Using FPGA-Based Deep Learning Accelerators and Microwave Photonic

A Real-Time Signal Measurement System Using FPGA-Based Deep Learning Accelerators and Microwave Photonic

Integrated lithium niobate Vernier micro-ring filter with wide and fast tuning capabilities

Tunable optical micro-ring filters play significant roles in optical communications, microwave photonics, and photonic neural networks. Typical micro-ring filters are based on either a thermo-optic (TO) effect with microsecond timescales or an electro-optic (EO) effect with a limited tuning range. Here, we report a continuously tunable lithium niobate on insulator (LNOI) Vernier cascaded micro-ring filter with wire-bonded packaging integrated with both TO and EO tuning electrodes, featuring a 40-nm free spectral range (FSR), 2.3 GHz EO bandwidth, and a high sidelobe suppression ratio of 21.7 dB, simultaneously. Our high-performance optical micro-ring filter could become an important element in future LNOI photonic circuits with applications in high-capacity wavelength-division multiplexing (WDM) systems, broadband microwave photonics, fast-tunable external-cavity lasers, and high-speed photonic neural networks.

Investigation of jitter in an optoelectronic oscillator with suppressed parasitic harmonics

The increasing demands on the level of phase noise and frequency stability of microwave signals in radar and communication systems have led to the search for new solutions beyond standard microwave devices. One of the perspective fields to respond to modern challenges is microwave photonics, which combines the principles and approaches of microwave technology with the application of a photonic component base. Optoelectronic oscillators (OEO) have a low level of phase noise, and as a result, low jitter, which corresponds to the high stability of the generated microwave signals. The principle of operation of the OEO is based on the circulation of a microwave signal through a microwave photonic ring resonator consisting of microwave and optical paths. The resonator with a high Q-factor, a wide frequency range between the resonant harmonics and feedback, that ensures a balance of amplitudes, is necessary to use in order to implement the OEO. Over the two decades, many methods have been proposed to reduce phase noise and jitter of OEO, among that not only an increase in the quality factor of the resonator, but also the suppression of parasitic harmonics, have been discussed. However, nowadays the multi-ring configurations of the OEO for suppression of parasitic harmonics have clearly not been sufficiently studied. The purpose of this work is to investigate the suppression of parasitic harmonics and jitter reduction in two-ring OEO. A dual-ring OEO with a parallel configuration of fiber-optic delay lines with different lengths was chosen as the object of research. The proposed configuration is based on an interference circuit on fiber-optic lines with passive optical amplification. The parameters of the interference circuit were selected in order to suppress the second harmonic to -25 dB, while a low noise level is hold on. It is shown that a dual-ring OEO with fiber-optic delay lines of 600 m and 531 m long has a jitter of 434 fs in the frequency range from 100 Hz to 7 GHz. The proposed design can be used to reduce the jitter of an optoelectronic oscillator.

Guest Editorial Guest Editorial for the Special Issue on Microwave Photonics

Guest Editorial Guest Editorial for the Special Issue on Microwave Photonics

High-Performance Integrated Microwave Photonic Transceiver for Dual-Band Synthetic Aperture Radar

High-Performance Integrated Microwave Photonic Transceiver for Dual-Band Synthetic Aperture Radar

Tunable Microwave Photonic Filter With Ultra-Narrow Passband and High Out-of-Band Rejection

Tunable Microwave Photonic Filter With Ultra-Narrow Passband and High Out-of-Band Rejection

Microwave Photonic Adaptive Complex Wideband Self-Interference Cancellation Enabled by Digital Pre-Modeling Search and Two-Tap Delay Adjustment

Microwave Photonic Adaptive Complex Wideband Self-Interference Cancellation Enabled by Digital Pre-Modeling Search and Two-Tap Delay Adjustment

Dual-Functional Microwave Photonic System for Target Detection and Frequency Measurement

Dual-Functional Microwave Photonic System for Target Detection and Frequency Measurement

Integrated Pockels Modulators on Silicon Photonics Platform

AbstractElectro‐optic (EO) modulators are essential components in various fields, including optical communication, free‐space communication, microwave photonics, sensing, and light detection and ranging. The EO modulation enables the fast conversion of electric signals into optical signals, facilitating the precise manipulation of light. With advancements in fabrication processing techniques, next‐generation integrated EO modulators have demonstrated substantial improvements in modulation efficiency, bandwidth, and footprint. Here, the latest research progress in integrated EO modulation, focusing on the principle of the Pockels effect, key modulation metrics, novel EO thin‐film material platforms, and innovative device architectures is overviewed. Finally, it is evaluated different schemes and provide perspectives on future trends in developing integrated EO modulators, highlighting both the advantages and challenges of integrated EO modulation, including waveguide and electrode engineering, integrated methods, and other applications for large‐scale photonic integrated circuits.

Fivefold increased power handling in waveguide UTC-PDs using dual-injection shared CPW PD-arrays.

This work presents two circuit-based solutions to enhance the power handling capabilities of waveguide-integrated uni-travelling carrier photodetectors (WG-UTC-PDs). Compared to a baseline WG-UTC-PD, these solutions achieve a fivefold increase in photocurrent before thermal breakdown. First, dual-injection improves the optical power distribution within a baseline WG-UTC-PD, raising the photocurrent threshold before thermal breakdown. Second, an array of four optically parallel WG-UTC-PDs, electrically connected to a single coplanar waveguide (CPW) line, further increases the maximum photocurrent by distributing the input optical power across multiple PDs. The design omits a termination resistor, as the arrays do not rely on a traveling wave configuration, maximizing photocurrent without a 50% reduction of bandwidth. Both 4-PD single-injection and dual-injection arrays were designed, fabricated, and characterized. Compared to a baseline UTC-PD, with a maximum photocurrent of 1.8 mA at a 3 dB bandwidth of 55 GHz, the 4-PD single-injection circuit achieved 5.1 mA at 43 GHz. The dual-injection array further increased the photocurrent to 9.2 mA at a bandwidth of 35 GHz. Electrical reflection measurements confirmed the negative effects of CPW losses on RF performance. These power handling improvements enable compact, high-power integrated solutions for microwave photonics.

High Sensitivity Long Pulse Envelope Detector Assisted by Microwave Photonics

This article presents a concept of a long pulse envelope detector (ED) with a high sensitivity value based on Microwave Photonics (MWP). The process of envelope detecting of RF signals is achieved by the translation of the RF spectrum to the optical spectrum range followed by optical filtering to cut the lower sideband and the carrier, finally beating the remaining upper sideband into a low-speed photodetector (LSPD). The LSPD output signal is amplified by transimpedance gain. This approach depends only on the RF passing band of the phase modulator (PM) and the optical filter transfer function. This concept is experimentally demonstrated reaching envelope detector tangential signal sensitivity (TSS) values around to -40 dBm for RF input frequency range from 10 GHz to 20 GHz. The proposed architecture does not use any optical or video signal amplifier. The implementation of this approach is simple, employs few components, and Commercial off-the-Shelf (COTS).

Proposal of Anti-Radiation Missile Decoy Assisted by Microwave Photonics

This article proposes the concept of a decoy that could be used against anti-radiation missiles (ARMs). The bait signals are generated remotely and transmitted to the sacrificial antenna site over a fiber optic network. This network has the possibility to support broadband radar signals in the range of a few GHz. This study postulated a distance of 1 km in relation to its park of antennas, however, this distance may be greater. This analog fiber link was designed for radar signal transmission in the frequency range of 0.3 to 3 GHz. The theoretical results were compared with the experimental ones and it was observed that the behavior of the radar signal power gain in the studied range is straight, thus the signal does not present distortions. The system proposed in this study is promising as a distraction for ARMs.

High-Linearity Dual-Parallel Mach–Zehnder Modulators in Thin-Film Lithium Niobate

Microwave photonic (MWP) systems are inseparable from conversions of microwave electrical signals into optical signals, and their performances highly depend on the linearity of electro-optic modulators. Thin-film lithium niobate (TFLN) is expected to be an ideal platform for future microwave photonic systems due to its compact size, low optical loss, linear electro-optic effect, and high bandwidth. In this paper, we propose a TFLN modulator with a low voltage–length product (VπL) of 1.97 V·cm and an ultra-high-linearity carrier-to-distortion ratio (CDR) of 112.33 dB, using a dual-parallel Mach–Zehnder interferometer configuration. It provides an effective approach to fully suppress the third-order intermodulation distortions (IMD3), leading to 76 dB improvement over a single Mach–Zehnder modulator (MZM) in TFLN. The proposed TFLN modulator would enable a wide variety of applications in integrated MWP systems with large-scale integration, low power consumption, low optical loss, and high bandwidth.