Microwave Photonic Filter Research Articles

Performance Comparison of Seed Generation Techniques of Stimulated Brillouin Scattering-Based Microwave Photonics Amplifier and Filter

This work presents a Brillouin amplification performance comparison of seed generation techniques using double-sideband suppressed carrier (DSB-SC) and single-sideband suppressed carrier (SSB-SC) modulations. The SSB-SC is obtained using an optical bandpass filter (OBPF) and in-phase and quadrature Mach-Zehnder modulator (IQ-MZM). All three techniques provide high amplification performance with optical signal-to-noise ratio (OSNR) enhancement of 37.47 dB, 33.14 dB, and 32.67 dB using DSB-SC, SSB-SC/OBPF, and SSB-SC/IQ-MZM, respectively. The best seed generation technique is using the DSB with a signal amplification of 62.47 dB. The technique presents ~4 dB higher OSNR enhancement due to the dual-energy transfer obtained from the beating process of the DSB than SSB. A ~3 dB OSNR reduction is found when pump linewidth (LW) was changed from 1kHz to 50 MHz, which suggests using a low-cost pump source whenever the OSNR reduction is not critical. The work also shows that the three techniques required 10 dBm stimulated Brillouin scattering threshold (SBST) to stimulate the process. An additional analysis of DSB-SC shows that a high-carrier suppression during the seed generation technique using MZMs is insignificant to the amplification performance. The high-carrier suppression produces a high seed signal power that distorts the Brillouin gain spectrum (BGS) and the pump depletion region, hence reducing the Brillouin gain (BG). Since carrier suppression is not a primary consideration, a cost-effective MZM with a modest extinction ratio requirement is allowed. The relaxed requirement of the pump’s linewidth and MZM’s extinction ratio suggest a cost-effective development of the SBS-based optical amplifier with narrow filter bandwidth.

Magnetic field measurement with temperature compensation based on a fiber ring microwave photonic filter and Vernier effect.

We proposed, a novel, to the best of our knowledge, magnetic field measurement with temperature compensation based on a fiber ring microwave photonic filter (FR-MPF) and a Vernier effect. The sensing head is made up by attaching the fiber Bragg grating (FBG) on the magnetostrictive material. Based on the wavelength division multiplexing, two FR-MPFs with different optical carriers can eliminate the influence of the temperature. The Linear chirped FBG (LCFBG) in the FR can transfer the magnetic field variation to the time delay change as well as the frequency shift. Two FR-MPFs with close free spectral ranges can implement the Vernier effect, which can improve the sensitivity. The experimental results show the sensitivity is 58.3 kHz/Oe and the magnification factor is 214. The proposed sensor has merits of high resolution, high sensitivity and low cross-sensitivity, which has potential applications requiring high precision detections.

Tunable microwave photonic filters based on stimulated Brillouin scattering for radio over fiber applications

Tunable microwave photonic filters based on stimulated Brillouin scattering for radio over fiber applications

Vector magnetic field measurement based on fiber ring microwave photonic filter with the Vernier effect

A vector magnetic field sensor based on enhanced Vernier effect is experimentally demonstrated. The Vernier effect is generated from two microwave photonic filters (MPFs) with close free spectral range (FSR), which is constructed by the fiber ring (FR) and the optical carrier microwave interferometry (OCMI). Linear chirped fiber Bragg grating (LCFBG) is inserted in the FR to act as the dispersion element to provide time delay. By attaching the fiber Bragg grating (FBG) on the magnetostrictive material (MA), the magnetic field can be transferred into the wavelength shift, as well as the time delay of the FR and the frequency response of the FR-MPF. By choosing opposite dispersion of LCFBGs and closer FSRs, cascaded FR-MPFs based sensor can greatly improve the sensitivity. The sensitivities for the magnetic field intensity and direction are 127.71 kHz/Oe, the magnification factor of which is 432, and 418.16 kHz/deg. The proposed scheme has merits of high sensitivity and interference immunity, which is suitable for high precision measurement.

Performance Analysis of Microwave Photonic Spectral Filters based on Optical Microcombs

AbstractMicrowave transversal filters, which are implemented based on the transversal filter structure in digital signal processing, offer a high reconfigurability for achieving a variety of signal processing functions without changing hardware. When implemented using microwave photonic (MWP) technologies, also known as MWP transversal filters, they provide competitive advantages over their electrical counterparts, such as large operation bandwidth, strong immunity to electromagnetic interference, and low loss when processing signals at high frequencies. Recent advances in high‐performance optical microcombs provide compact and powerful multi‐wavelength sources for MWP transversal filters that require a larger number of wavelength channels to achieve high performance, allowing for the demonstration of a diverse range of filter functions with improved performance and new features. Here, a comprehensive performance analysis for microcomb‐based MWP spectral filters based on the transversal filter approach is presented. First, the theoretical limitations are investigated in the filter spectral response induced by finite tap numbers. Next, the distortions are analyzed in the filter spectral response resulting from experimental error sources. Finally, the influence of input signal's bandwidth on the filtering errors is assessed. These results provide a valuable guide for the design and optimization of microcomb‐based MWP transversal filters for a variety of applications.

Fully tunable microwave photonic narrow bandpass filter using an on-chip dual-drive microring resonator

We propose and experimentally demonstrate a fully tunable microwave photonic narrow bandpass filter based on phase modulation to intensity modulation (PM-IM) conversion. In the filter implementation, an on-chip dual-drive microring resonator (MRR) is a key component. This resonator leverages a multimode waveguide to enable a high Q-factor. A metallic micro-heater and a lateral PN junction are simultaneously created for resonance wavelength tuning. When one driving signal is applied to the micro-heater, a large tuning range of the resonance wavelength is resulted; when another driving signal is applied to the PN junction, a fast tuning speed of the resonance wavelength is caused. By jointly using two different tuning mechanisms, the realized microwave photonic filter features a large frequency tuning range as well as a fast tuning speed. In addition, the filter bandwidth can also be tuned. A silicon-based dual-drive high-Q racetrack MRR chip is designed, fabricated, and evaluated. By incorporating the chip in a microwave photonic filter system, a bandpass filter with a narrow bandwidth of 1.27 GHz is achieved. An ultra-wide frequency tuning range from 3 to 51 GHz, an ultra-fast tuning speed less than 0.54 ns, and a tunable bandwidth from 1.27 to 4.47 GHz is experimentally demonstrated. This fully tunable filter offers significant potential in future radar and next-generation wireless communication applications.

Electrically interfaced Brillouin-active waveguide for microwave photonic measurements

New strategies for converting signals between optical and microwave domains could play a pivotal role in advancing both classical and quantum technologies. Traditional approaches to optical-to-microwave transduction typically perturb or destroy the information encoded on intensity of the light field, eliminating the possibility for further processing or distribution of these signals. In this paper, we introduce an optical-to-microwave conversion method that allows for both detection and spectral analysis of microwave photonic signals without degradation of their information content. This functionality is demonstrated using an optomechanical waveguide integrated with a piezoelectric transducer. Efficient electromechanical and optomechanical coupling within this system permits bidirectional optical-to-microwave conversion with a quantum efficiency of up to −54.16 dB. Leveraging the preservation of the optical field envelope in intramodal Brillouin scattering, we demonstrate a multi-channel microwave photonic filter by transmitting an optical signal through a series of electro-optomechanical waveguide segments, each with distinct resonance frequencies. Such electro-optomechanical systems could offer flexible strategies for remote sensing, channelization, and spectrum analysis in microwave photonics.

Enhancement of Brillouin nonlinearities with a coupled resonator optical waveguide.

Stimulated Brillouin scattering (SBS) is a nonlinear optical phenomenon mediated from the coupling of photons and phonons. It has found applications in various realms, yet the acousto-optic interaction strength remains relatively weak. Enhancing the SBS with resonant structures could be a promising solution, but this method faces strict constraints in operational bandwidth. Here, we present the first demonstration to our knowledge of the broadband enhancement of Brillouin nonlinearities by a suspended coupled resonator optical waveguide (CROW) on an SOI platform. By comprehensively balancing the Brillouin gain and operational bandwidth, a 3-fold enhancement for the Brillouin gain coefficient (GB) and a broad operational bandwidth of over 80 GHz have been achieved. Furthermore, this 1.1 mm device shows a forward Brillouin gain coefficient of 2422 m-1W-1 and a high mechanical quality factor (Qm) of 1060. This approach marks a pivotal advancement toward wide bandwidth, low energy consumption, and compact integrated nonlinear photonic devices, with potential applications in tunable microwave photonic filters and phonon-based non-reciprocal devices.

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.

Research on frequency response effect of microwave photonic filter based on Brillouin effect

Stimulated Brillouin Scattering (SBS) effect is a typical third-order optical nonlinearity that can be generated in various media through the excitation by intense light. Due to the excellent characteristics of the SBS laser, such as low threshold, wide ultra-narrow line width, and counter-propagating scattering light of adjacent orders, it has been widely applied in fields like high-resolution spectrometry, optical sensing, and quantum computing. This paper utilizes the OptiSystem software for simulation and explores the integration of microwave filters with the SBS effect. Experimental results demonstrate the feasibility of adjusting the pump branch laser frequency to achieve tunable filter passband characteristics.

Wideband-tunable microwave photonic filter using dissipative self-interference microring resonators

We propose and demonstrate a widely tunable microwave photonic filter with controlled frequency agility, bandwidth reconfigurability and flexible switching functions. It is based on the self-interference microring aided by an asymmetric Mach–Zehnder interferometer, breaking the fundamental microring footprint limit and achieving a doubled free spectral range (123.2 GHz) with a strong out-of-band rejection. Simulation results show that a bandpass microwave photonic filter can be tuned across a 60 GHz frequency range with a varied 3-dB bandwidth from 2.13 GHz to 40.7 GHz in a cascaded dual-ring topology. Its RF out-of-band rejection ratio is improved by more than 60 dB in the high frequency region due to a perfect residual phase cancellation. A dual-band notch microwave photonic filter with an extinction ratio of about 50 dB and a frequency tunable range of about 27.7 GHz is also demonstrated, showing its broadly applicability. Our method highlights its suitability to improve chip-scale wideband and high-performance RF receiver systems.

Microwave photonic multitap filter with bipolar coefficients based on dual‐input Mach–Zehnder modulator

AbstractThis article introduces and experimentally validates a novel microwave photonic filter featuring multiple taps and employing bipolar coefficients. The filter utilizes a dual‐input modulator and a laser array for coefficient adjustment. Experimental verification of the proposed concept showcases a three‐tap bipolar microwave photonic notch filter with a reduced notch width and a flat passband. The innovative design of this filter offers benefits such as a straightforward configuration and enhanced system stability.

Instantaneous frequency measurement system based on quantum dash mode-locked laser

We present the theory and experimental results of a microwave photonic (MWP) filter based instantaneous frequency measurement system. A quantum dash mode-locked laser is used as an optical frequency comb source. With up to 41 flat comb lines and a real-time feedback loop for comb shaping, a set of MWP filters with linear frequency responses for either linear unit or dB unit are experimentally demonstrated. The maximum measurement frequency can be up to 20 GHz limited by the available test-and-measurement instruments. By using one MWP filter, the root-mean-square error is 51∼66 MHz, which can be improved to 42.2 MHz for linear unit, and 30.7 MHz for dB unit by using two MWP filters together.

Slow-light-enhanced Brillouin scattering with integrated Bragg grating.

Advancements in photonic integration technology have enabled the effective excitation of simulated Brillouin scattering (SBS) on a single chip, boosting Brillouin-based applications such as microwave photonic signal processing, narrow-linewidth lasers, and optical sensing. However, on-chip circuits still require large pump power and centimeter-scale waveguide length to achieve a considerable Brillouin gain, making them both power-inefficient and challenging for integration. Here, we exploit the slow-light effect to significantly enhance SBS, presenting the first, to the best of our knowledge, demonstration of a slow-light Brillouin-active waveguide on the silicon-on-insulator (SOI) platform. By integrating a Bragg grating with a suspended ridge waveguide, a 2.1-fold enhancement of the forward Brillouin gain coefficient is observed in a 1.25 mm device. Furthermore, this device shows a Brillouin gain coefficient of 1,693 m-1W-1 and a mechanical quality factor of 1,080. The short waveguide length reduces susceptibility to inhomogeneous broadening, enabling the simultaneous achievement of a high Brillouin gain coefficient and a high mechanical quality factor. This approach introduces an additional dimension to enhance acousto-optic interaction efficiency in the SOI platform and holds significant potential for microwave photonic filters and high spatial resolution sensing.

Surface Acoustic Microwave Photonic Filters on Etchless Lithium Niobate Integrated Platform

AbstractLithium niobate on insulator emerges as a promising platform for integrated microwave photonics because of its capability of ultralow‐loss guidance and high‐efficiency modulation of light. Chip‐level integration of microwave filters is important for signal processing in the 5G/6G wireless communication. Here, by employing bound states in the continuum for low‐loss waveguiding, high‐performance microwave photonic filters are realized on an etchless lithium niobate integrated platform. These microwave photonic filters consist of a high‐quality photonic microcavity modulated by piezoelectrically excited surface acoustic waves. Acoustic time delays from 21 to 106 ns and passbands with bandwidth as narrow as 0.89 MHz are achieved in the fabricated filters operating at gigahertz frequencies. This demonstration may open up new applications on the lithium niobate integrated platform, such as optical communication, signal processing, and beam steering.

Multitap microwave photonic filter based on a DFB laser array using photonic wire bonding

We propose and experimentally demonstrate a multitap microwave photonic filter (MPF) based on a distributed feedback (DFB) laser array using photonic wire bonding (PWB). Through the application of the PWB technique, an eight-wavelength DFB laser array with wavelength spacing of 400 GHz was hybrid-integrated with an arrayed waveguide grating multiplexer. Remarkably, the insertion losses of all eight channels are maintained below 5 dB. In the experiments, the larger wavelength spacing allowed us to achieve a sinc MPF with a lower 3 dB bandwidth of 0.22 GHz using only eight taps. Further, Gaussian apodization enabled the out-of-band rejection of the filter to reach 24 dB. These results indicate that the proposed scheme could provide a promising guideline for the MPFs that demand high reconfigurability and greatly reduced size and complexity.

Highly precise FBG wavelength demodulation method with strong multiplexing ability and positioning function based on time-domain detection.

Based on the theory of the microwave photonic filter (MPF), to our knowledge, a novel fiber Bragg grating (FBG) wavelength demodulation method based on time-domain detection is proposed. The method uses VNA (vector network analyzer) to measure the S21 parameter of the sensor system, and converts them to the time-domain through inverse discrete Fourier transform (IDFT), The wavelength demodulation and positioning of FBG can be realized by measuring the amplitude and position of the time-domain peak. In order to improve the number of FBG multiplexes, a method is proposed to eliminate the effect of spectrum overlap by normalization in the case of two FBGs and three FBGs. The experimental results show that the temperature sensitivity is 0.00503 RAC/°C, the positioning resolution of the system is 1.25 cm, and the limit of the wavelength difference between two FBGs allowed by the system is 0.25 nm. This method has the advantages of high demodulation precision, strong multiplexing ability and high precision positioning, and has broad application prospects.

Si3N4-Based Narrowband and High Peak Rejection Microwave Photonic Filter With Adjustable Bandwidth

Si₃N₄-Based Narrowband and High Peak Rejection Microwave Photonic Filter With Adjustable Bandwidth

High resolution and large measurement range voltage sensing based on an optoelectronic oscillator utilizing an unbalanced Mach-Zehnder interferometer.

A voltage sensor with high resolution and large measurement range based on an optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. The key component in the cavity to select the oscillating signal is a finite impulse response (FIR)-microwave photonic filter (MPF) which consists of a sinusoidal broadband optical signal, an unbalanced Mach-Zehnder interferometer (MZI), a section of dispersion compensating fiber, and a photodetector. The center frequency of the FIR-MPF is mainly determined by the free spectral range (FSR) of the FIR-MPF. In the lower arm of the MZI, a cylindrical piezoelectric ceramic (PZT) wrapped with a section of optical fiber acts as voltage sensing head. Due to the inverse piezoelectric effect of PZT, the variation of the voltage will cause radial deformation of the cylindrical PZT and then lead to the change of the FSR of the MZI, determining the shift of center frequency of FIR-MPF as well as the frequency of the oscillating signal of the OEO. Thus, by monitoring the shift of the oscillation frequency of the OEO using an electric spectrum analyzer or a digital signal processor, a high-speed interrogation and high-resolution voltage measurement can be realized. Additionally, in the proposed scheme, an infinite impulse response (IIR)-MPF consisting of a fiber ring resonator is cascaded with the FIR-MPF to ensure the single-mode oscillation of the OEO. The experimental results show that a total range of 1700 V voltage sensing from - 200 V to 1500 V is accomplished with the voltage sensitivity of 0.25 GHz/100 V and the resolution of 0.3 V. By adjusting the proportion of the length of single mode fiber between two branches of MZI, the impact of temperature can be greatly reduced. The proposed sensor offers advantages such as a large measurement range, high resolution, high-speed interrogation, and stability to temperature disturbances, making it highly suitable for sensing applications in smart grids.

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.