Microwave Photonics Research Articles

Low-Loss Waveguide Crossing for Complicated On-Chip Microwave Photonic Processor

Low-Loss Waveguide Crossing for Complicated On-Chip Microwave Photonic Processor

Silicon Photonic Filters: A Pathway from Basics to Applications

Silicon photonics has found a profound place among emerging technologies in the past few decades due to several advantages. Due to a series of breakthroughs and increased funding from private and government sectors, the development of silicon photonics has accelerated especially starting from the two years 2004–2005 with a persisting and ever‐growing momentum. Among various components, the silicon photonic filters that selectively pass or block particular wavelengths with a finite bandwidth have found particular interest as they are useful in signal processing in different fields ranging from optical communication to microwave photonics and quantum photonics. Herein, a comprehensive review of silicon photonic filters focusing on the four most commonly used architectures, such as microring resonators, waveguide Bragg grating, Mach–Zehnder interferometers, and arrayed waveguide grating, encapsulating basics, and guidelines, in terms of simulating tools and topologies, of realizing reconfigurable and high‐performing filters for several applications, is provided. The novelty of this review relies on the fact that it summarizes these filter architectures covering a broad range of applications concisely and constructively and includes the basics, growth, and future trends, providing a clear understanding and importance of silicon photonic filters from research to commercialization perspective.

Broadband Beam-Scanning Phased Array Based on Microwave Photonics

A one-dimensional active broadband phased array based on microwave photonics that works in the Ku band is proposed to achieve a large instantaneous bandwidth. The phased array uses a feeding network based on microwave photonics to provide the true time delay and a wide operating bandwidth. The array is mainly composed of a broadband horn antenna, an RF transmitting/receiving module, an optical network module, and a temperature control module. The form of a horn was selected for the antenna unit, and it was fed through a waveguide to obtain a wide operating bandwidth. An optical fiber delay line that could realize the true time delay at different frequencies was adopted for the time-delay module of the optical network. To obtain a large time delay and small quantization error, a hybrid time-delay diagram utilizing electrical and optical time delays was used in the design. In addition, a temperature control module was added to the antenna system to enhance the stability of the photonic time-delay module. For verification, a prototype of the presented antenna system was designed, fabricated, and measured. The experimental results showed that the optical phased array antenna was able to scan ±20° from 12 GHz to 17 GHz, and the beam pointing did not appear to be offset over the wide operating bandwidth.

Microwave photonics frequency measurement with improved accuracy based on an artificial neural network.

Photonics-assisted techniques for microwave frequency measurement (MFM) show great potential for overcoming electronic bottlenecks, with wild applications in radar and communication. The MFM system based on the stimulated Brillouin scattering (SBS) effect can measure the frequency of multiple high-frequency and wide-band signals. However, the accuracy of the MFM system in multi-tone frequency measurement is constrained by the SBS bandwidth and the nonlinearity of the system. To resolve this problem, a method based on an artificial neural network (ANN) is suggested, which can establish a nonlinear mapping between the measured two-tone signal spectra and the theoretical frequencies. Through simulation verification, the ANN optimized frequencies within the range of (0.5, 27) GHz of the MFM system show 79%, 76%, 70%, 44% reduction in errors separately under four spectral signal-to-noise ratios (SNR) conditions, 20dB, 15dB, 10dB, 0dB, and the frequency resolution is improved from 30MHz to 10MHz.

Algorithmically calibrated optical switch with high-extinction-ratio and low-polarization-dependence on 3-μm-thick SOI platform

Crosstalk, calibration complexity, and polarization dependence obstacle the precision of optical networks such as microwave photonics beamforming networks (MPBNs). The optical switch presented in this work, boasting high tolerance and polarization insensitivity, utilizes multimode interferometers (MMIs), a thermo-optical phase shifter, and variable optical attenuators (VOAs) on the 3 μm-thick silicon-on-insulator (SOI) platform. The switch exhibits extinction ratio (ER) exceeding 32.5 dB within 140 nm bandwidth, with maximum ER of 50 dB, accompanied by 0.4 dB loss, and features switching speed of 16 μs/21 μs In 10-layer networks, the VOA-assist golden-section algorithm enables optimal calibration within 170 iterations, serving as fundamental component for establishing precise optical networks.

Microwave photonics doppler speed measurement based on sagnac loops and four-wave mixing effect in a highly nonlinear fiber

Photonic radars are increasingly being developed and offer a promising replacement for traditional RF radars. They feature higher precision, and smaller size compared to the current microwave radars. One important part of a moving target indicating (MTI) radar is the Doppler shift measurement used to measure the radial velocity of a moving target. Therefore, for any photonic radar operating at MTI mode, it is necessary to have a Doppler measurement subsystem. In this paper, a microwave photonic Doppler frequency measurement system is conceived and implemented for this purpose specifically. The operation is based on making a Doppler shift-dependent yet low-frequency voltage component. It is all-optical and hence has the potential to be integrated into many electronic warfare systems. This feature not only makes the system independent of any sophisticated electrical device but also makes the measurement time lower than that of the electrical counterparts. The specific design presented here provides a much better stability compared to the recent works. An error as low as 0.012 Hz at a 10 GHz radar frequency was obtained, and the system performance was demonstrated up to 40 GHz, at which a 4.75 Hz error was recorded.

Photonic chip-based low-noise microwave oscillator

Numerous modern technologies are reliant on the low-phase noise and exquisite timing stability of microwave signals. Substantial progress has been made in the field of microwave photonics, whereby low-noise microwave signals are generated by the down-conversion of ultrastable optical references using a frequency comb1–3. Such systems, however, are constructed with bulk or fibre optics and are difficult to further reduce in size and power consumption. In this work we address this challenge by leveraging advances in integrated photonics to demonstrate low-noise microwave generation via two-point optical frequency division4,5. Narrow-linewidth self-injection-locked integrated lasers6,7 are stabilized to a miniature Fabry–Pérot cavity8, and the frequency gap between the lasers is divided with an efficient dark soliton frequency comb9. The stabilized output of the microcomb is photodetected to produce a microwave signal at 20 GHz with phase noise of −96 dBc Hz−1 at 100 Hz offset frequency that decreases to −135 dBc Hz−1 at 10 kHz offset—values that are unprecedented for an integrated photonic system. All photonic components can be heterogeneously integrated on a single chip, providing a significant advance for the application of photonics to high-precision navigation, communication and timing systems.

Silicon Integrated Microwave Photonic Mixer Based on Cascaded Microring Resonator Modulators

Silicon Integrated Microwave Photonic Mixer Based on Cascaded Microring Resonator Modulators

Integrated lithium niobate microwave photonic processing engine.

Integrated microwave photonics (MWP) is an intriguing technology for the generation, transmission and manipulation of microwave signals in chip-scale optical systems1,2. In particular, ultrafast processing of analogue signals in the optical domain with high fidelity and low latency could enable a variety of applications such as MWP filters3-5, microwave signal processing6-9 and image recognition10,11. An ideal integrated MWP processing platform should have both an efficient and high-speed electro-optic modulation block to faithfully perform microwave-optic conversion at low power and also a low-loss functional photonic network to implement various signal-processing tasks. Moreover, large-scale, low-cost manufacturability is required to monolithically integrate the two building blocks on the same chip. Here we demonstrate such an integrated MWP processing engine based on a 4 inch wafer-scale thin-film lithium niobate platform. It can perform multipurpose tasks with processing bandwidths of up to 67 GHz at complementary metal-oxide-semiconductor (CMOS)-compatible voltages. We achieve ultrafast analogue computation, namely temporal integration and differentiation, at sampling rates of up to 256 giga samples per second, and deploy these functions to showcase three proof-of-concept applications: solving ordinary differential equations, generating ultra-wideband signals and detecting edges in images. We further leverage the image edge detector to realize a photonic-assisted image segmentation model that can effectively outline the boundaries of melanoma lesion in medical diagnostic images. Our ultrafast lithium niobate MWP engine could provide compact, low-latency and cost-effective solutions for future wireless communications, high-resolution radar and photonic artificial intelligence.

Machine-Learning-Assisted Instantaneous Frequency Measurement Method Based on Thin-Film Lithium Niobate on an Insulator Phase Modulator for Radar Detection.

A simple microwave photonic, reconfigurable, instantaneous frequency measurement system based on low-voltage thin-film lithium niobate on an insulator phase modulator is put forward and experimentally demonstrated. Changing the wavelength of the optical carrier can realize the flexibility of the frequency measurement range and accuracy, showing that during the ranges of 0-10 GHz, 3-15 GHz, and 12-18 GHz, the average measurement errors are 26.9 MHz, 44.57 MHz, and 13.6 MHz, respectively, thanks to the stacked integrated learning models. Moreover, this system is still able to respond to microwave signals of as low as -30 dBm with the frequency measurement error of 62.06 MHz, as that low half-wave voltage for the phase modulator effectively improves the sensitivity of the system. The general-purpose, miniaturized, reconfigurable, instantaneous frequency measurement modules have unlimited potential in areas such as radar detection and early warning reception.

Towards large-scale programmable silicon photonic chip for signal processing

Abstract Optical signal processing has been playing a crucial part as powerful engine for various information systems in the practical applications. In particular, achieving large-scale programmable chips for signal processing are highly desirable for high flexibility, low cost and powerful processing. Silicon photonics, which has been developed successfully in the past decade, provides a promising option due to its unique advantages. Here, recent progress of large-scale programmable silicon photonic chip for signal processing in microwave photonics, optical communications, optical computing, quantum photonics as well as dispersion controlling are reviewed. Particularly, we give a discussion about the realization of high-performance building-blocks, including ultra-low-loss silicon photonic waveguides, 2 × 2 Mach–Zehnder switches and microring resonator switches. The methods for configuring large-scale programmable silicon photonic chips are also discussed. The representative examples are summarized for the applications of beam steering, optical switching, optical computing, quantum photonic processing as well as optical dispersion controlling. Finally, we give an outlook for the challenges of further developing large-scale programmable silicon photonic chips.

Ultrabroadband high-resolution silicon RF-photonic beamformer

Microwave photonics aims to overcome the limitations of radiofrequency devices and systems by leveraging the unique properties of optics in terms of low loss and power consumption, broadband operation, immunity to interference and tunability. This enables versatile functions like beam steering, crucial in emerging applications such as the Internet of Things (IoT) and 5/6G networks. The main problem with current photonic beamforming architectures is that there is a tradeoff between resolution and bandwidth, which has not yet been solved. Here we propose and experimentally demonstrate a novel switched optical delay line beamformer architecture that is capable of achieving the desired maximum resolution (i.e., 2M pointing angles for M-bit coding) and provides broadband operation simultaneously. The concept is demonstrated by means of a compact (8 × 3 mm2) 8 (5-bit) delay line Silicon Photonic chip implementation capable of addressing 32 pointing angles and offering 20 GHz bandwidth operation.

Maximization of rf-signal recovery in quantum microwave photonics systems

Maximization of rf-signal recovery in quantum microwave photonics systems

Fast-reconfigurable frequency comb generation based on AlGaAsOI waveguide with electro-optic time lens

Tunable optical frequency combs offer a flexible solution for specific applications such as dual-comb spectroscopy, optical communications and microwave photonics, delivering improved precision, compatibility, and performance. However, previously, there has been a trade-off between reconfigurability and system simplicity in comb generation. Here, we present a fast-switched repetition rate frequency comb system that utilizes an electro-optic modulation time-lens technique with a high third-order nonlinear AlGaAsOI waveguide. Only one stage of modulator is used in the time-lens system which significantly reduces the complexity of the overall system. Our system allows for tuning of the center wavelength from 1542 nm to 1556 nm, as well as independent adjustment of the repetition rates from 18 GHz to 26.5 GHz, enabling fast-switching capabilities. Additionally, our system exhibits a high pump-to-comb conversion efficiency of up to 67.9%. It also demonstrates robustness to temperature changes and environmental instability. All the involved devices can be integrated onto a single chip, making this comb suitable for various applications.

Ultrabroadband vernier cascaded microring filters based on dispersive Si3N4 waveguides

A viable candidate for use in silicon photonics and microwave photonics is the hybrid external cavity laser (ECL) chip, which offers a high extinction ratio, ultrabroadband mode-hopping-free tuning range, and small linewidth. It requires a photonic filter device with an ultrabroadband operating bandwidth and adjustable frequency selection capability. The Vernier cascaded microring filter is a prevailing filter technique that usually ignores chromatic dispersion and will result in noticeable frequency variations, particularly over a large frequency range. Based on dispersive Si3N4 waveguides, we develop ultrabroadband Vernier cascaded microring filters and examine the impact of chromatic dispersion. For the same waveguide geometry, the filter’s effective free spectral range (FSR) varies by more than 400 GHz with and without the dispersion. Furthermore, these Vernier filters, which are made of anomalous and normal dispersive waveguides respectively, exhibit mode hopping at the opposite frequency side. It leads to a sudden mode number leap and, consequently, a diversified dispersion condition for the convoluted filtering frequency. We show that this phenomenon is caused by the interplay between half of the FSR difference, and the accumulated frequency difference caused by the chromatic dispersion. Finally, the use of thermal-optical tuning enables accurate frequency tuning. Our findings offer a valuable resource for the engineering of hybrid ECLs at the chip scale.

Satellite Communication Payload Based on Microwave Photonics: Benefits, Architecture, and Technologies

Satellite Communication Payload Based on Microwave Photonics: Benefits, Architecture, and Technologies

Broadband Microwave Photonic Mixer With High Spurs Suppression and Image Rejection

Broadband Microwave Photonic Mixer With High Spurs Suppression and Image Rejection

Temperature-Insensitive Fiber-Optic Refractive Index Sensing System With High Sensitivity by Using EFPI-Based Microwave Photonic Filter

Temperature-Insensitive Fiber-Optic Refractive Index Sensing System With High Sensitivity by Using EFPI-Based Microwave Photonic Filter

Ultra-compact acousto-optic modulation using on-chip integrated Bragg gratings on lithium niobate-chalcogenide hybrid platform.

An ultra-compact and efficient acousto-optic modulator based on a thin-film lithium niobate-chalcogenide (ChG) hybrid platform was designed and realized. In this approach, π phase-shift Bragg grating has an ultra-short effective interaction length of only ∼ 300 µm and a compact footprint of 200 × 300 µm2. The strong microwave-acoustic coupling and superior photo-elastic property of the ChG allow us to achieve a half-wave voltage of Vπ = 1.08 V (4.07 V) for the π phase-shift Bragg grating (waveguide Bragg grating), corresponding to VπL = 0.03 V·cm (0.09 V·cm). This acousto-optic modulator exhibits a compact size, and low power consumption, and can be used for on-chip optical interconnects and microwave photonics.

All optical tunable RF filter using elemental antimony

Abstract In the past decade, the proliferation of modern telecommunication technologies, including 5G, and the widespread adoption of the Internet-of-things (IoT) have led to an unprecedented surge in data generation and transmission. This surge has created an escalating demand for advanced signal processing capabilities. Microwave photonic (MWP) processors offer a promising solution to satisfy this unprecedented demand for data processing by capitalising on the high bandwidth and low latency achievable by optical systems. In this work, we introduce an integrated MWP processing unit for all-optical RF filtering using elemental antimony. We exploit the crystallisation dynamics of antimony to demonstrate a photonic leaky integrator, which is configured to operate as a first-order low-pass filter with a bandwidth of 300 kHz and ultra-compact footprint of 16 × 16 μm2. We experimentally demonstrate the implementation of such a filter as an envelope detector to demodulate an amplitude-modulated signal. Finally, a discussion on achieving bandwidth tunability is presented.