Frequency-tunable Microwave Research Articles

Broadband Tunable Microwave Frequency Comb Generation Based on Modulated Optical Injection Semiconductor Laser

Broadband Tunable Microwave Frequency Comb Generation Based on Modulated Optical Injection Semiconductor Laser

Frequency-Tunable Pulsed Microwave Waveform Generation Based on Unbalanced Single-Arm Interferometer Excited by Near-Infrared Femtosecond Laser

Femtosecond laser-excited generation of frequency-tunable microwave pulses, based on an unbalanced single-arm interferometer with frequency-to-time mapping, has been proposed and demonstrated with easy-to-obtain commercial devices. The optical wave-to-microwave frequency conversion, which involves continuous tuning in the range from 2.0 GHz to 19.7 GHz, was achieved based on simple spatial–optical group delay adjustment. Additionally, the pulse duration of the microwave waveform was measured to be 24 ns as the length of the linear dispersion optical fiber was fixed at 20 km. In addition, owing to the designs of the single-arm optical path and polarization-independent interference, the generated microwave pulse train had better stability in terms of frequency and electrical amplitude. Furthermore, a near-triangular-shaped microwave pulse at 4.5 GHz was experimentally obtained by the superposition of two generated sinusoidal signals, which verified the potential of this system to synthesize special microwave waveform pulses.

Tunable Microwave Conductance of Nanodomains in Ferroelectric PbZr0.2Ti0.8O3 Thin Film

AbstractFerroelectric materials exhibit spontaneous polarization that can be switched by electric field. Beyond traditional applications as nonvolatile capacitive elements, the interplay between polarization and electronic transport in ferroelectric thin films has enabled a path to neuromorphic device applications involving resistive switching. A fundamental challenge, however, is that finite electronic conductivity may introduce considerable power dissipation and perhaps destabilize ferroelectricity itself. Here, tunable microwave frequency electronic response of domain walls injected into ferroelectric lead zirconate titanate (PbZr0.2Ti0.8O3) on the level of a single nanodomain is revealed. Tunable microwave response is detected through first‐order reversal curve spectroscopy combined with scanning microwave impedance microscopy measurements taken near 3 GHz. Contributions of film interfaces to the measured AC conduction through subtractive milling, where the film exhibited improved conduction properties after removal of surface layers, are investigated. Using statistical analysis and finite element modeling, we inferred that the mechanism of tunable microwave conductance is the variable area of the domain wall in the switching volume. These observations open the possibilities for ferroelectric memristors or volatile resistive switches, localized to several tens of nanometers and operating according to well‐defined dynamics under an applied field.

Photonic-Assisted Microwave Frequency Measurement With Adjustable Channel Bandwidth Based on Spectrum-Controlled Brillouin Phase Shift

A photonics-based channel bandwidth tunable microwave frequency measurement (MFM) is analyzed and verified, which is implemented based on the principle of the frequency-to-phase-slope mapping (FTPSM) in stimulated Brillouin scattering (SBS). The spectrum-controlled Brillouin phase shift curve is created by using an optical frequency comb (OFC) pump instead of a single pump. As a result, the Brillouin phase shift response is superimposed to further realize a flexible and adjustable measurement bandwidth. Meanwhile, thanks to the relationship between the OFC pump and the unknown signal, the frequency measurement can be achieved by the property of monotonous frequency-to-phase-slope mapping. A proof-of-concept experiment is performed to verify the feasibility of the approach. By changing the number of OFC lines, the channel bandwidths of 500, 700, or 900 MHz are demonstrated, with a measurement error lower than 35 MHz. We believe that this FTPSM-based MFM system is a promising solution for radio frequency (RF) channelized receiver.

Tunable Photonic Microwave Up-Converter Using Opto-Electronic Oscillator Based on Monolithic Integrated Three-Section Laser

A tunable photonic microwave frequency up-conversion scheme using opto-electronic oscillator (OEO) based on a monolithic integrated three-section laser without any electro-optic modulator (EOM) or filter is proposed. By adjusting the monolithic integrated three-section laser to operate in the period-one (P1) dynamical state, the signal carrier frequency up-converted from the intermediate frequency (IF) to the frequency at the difference and the summation between the oscillation frequency of OEO and IF can be realized. The tunability of the up-converted frequency can also be greatly guaranteed just by altering the control currents of the monolithic integrated three-section laser induced P1 frequency. In this paper, an IF of 2 GHz with 10 Msymbol/s 16-QAM signals is successfully up-converted to 16 GHz and 20 GHz simultaneously. The up-converted frequencies can be tuned from 16 GHz/20 GHz to 19 GHz/23 GHz, and the error vector magnitudes (EVMs) of all those up-converted signals satisfy the limitation in satellite communication.

Design and Modelling of Carbon Fiber Grid Structure based Carbon/Epoxy Composites for Enhanced Microwave Absorbing Properties

Frequency Tunable Microwave absorbers in desired low thickness is a critical requirement in electronics, radar and military applications where Electro Magnetic Interference has become a major concern. Composite are obvious choice of absorbers in above applications. The aim of this paper is to investigate the use of carbon fiber grid layers as Frequency Selective Surface (FSS) on Carbon Filler based Glass-Epoxy composites. In this work, three key points are highlighted, first is design, modeling of FSS grid, using equivalent circuit model and Transmission Line Theory, second is the use of fillers including Milled Carbon Fibers and Carbon Nano Tubes (CNTs) for microwave absorption, third is to have the desired reflection loss at specified thickness of around 6-7 mm which is low as compared to recent trends. It is found that the factors like the number of grid layers , their unit cell dimensions, type of filler, and the top surface layer, affects the resonance frequency and hence the microwave absorption characteristics of the composite laminates. The results are satisfactory showing minimum of -9.8 Db of Reflection Loss at 6-7 mm thickness laminates, for varied range of frequency.

Low-field microwave absorption in Ga-doped polycrystalline La0.6Sr0.4MnO3 in the frequency range from 0.1 to 4 GHz

We investigated the magnetic-field-dependent microwave absorption in polycrystalline La0.6Sr0.4Mn1-xGaxO3 samples (x = 0.0–0.3) over a wide frequency spectrum (f = 0.1–4 GHz) and up to a magnetic field of Hdc= 2.5 kOe at room temperature. The field dependence of microwave power absorption (ΔP) in each sample exhibits a peak at a critical value of Hdc and the peak moves towards higher fields as frequency increases. The shift is at a faster rate for x = 0.2 and 0.3 compared to x = 0.01 and 0.1. Based on the line shape analysis, we attribute the observed features to ferromagnetic resonance for x ≤ 0.1 and a combined effect of electron spin resonance and superparamagnetic resonance for x ≥ 0.2. Our results are also verified by magnetic resonance spectra recorded using a coplanar waveguide spectrometer. We extracted the gyromagnetic ratio, saturation magnetization, and anisotropy field in our samples. Frequency-tunable microwave absorption at resonance found in these materials will be of interest for high-frequency device applications.

Dynamics of optical injection in an external cavity based FP-LD for wide tunable microwave signal generation.

In this paper, we analyze the dynamics of optical injection in an external cavity based Fabry-Pérot laser diode (ECFP-LD) for wide tunable microwave signal generation. The ECFP-LD is a specially designed FP-LD that has a self-locked single dominant mode. The injected beam power is varied to analyze the dynamics of optical beam injection on the ECFP-LD. The ECFP-LD shows the interesting behavior of red-shift followed by hopping to another self-injected mode equivalent to FP-LD external and internal cavity modes separation, which provides the fine and coarse tuning of the self-injected mode. The optical beating of the injected beam and the self-injected mode, whether it is the fine red-shifted self-injected mode or the hopped self-injected mode equivalent to the external or internal cavity mode separation, provides a wide tunable range of microwave generation. We obtained fine tuning of 3 GHz for every self-injected mode, and coarse tuning of 15 GHz and 150 GHz, which is equivalent to the free spacing tuning of the external cavity (0.12 nm) and internal FP-LD cavity (1.17 nm), with change in the power of the injected beam. The maximum coarse tuning range is about 3.72 nm, and the corresponding beating frequency tuning range is 330 GHz. Hence, a wide tunable microwave frequency can be obtained by optical beating of the shifted/hopped self-injected mode and the injected beam.

Generation of Tunable Microwave Frequency Comb Utilizing a Semiconductor Laser Subject to Optical Injection from an SFP Module Modulated by an Arbitrary Periodic Signal

In this paper, a microwave frequency comb (MFC) is generated from a semiconductor laser subject to optical injection from a commercial small form-factor pluggable (SFP) optical module which is modulated by an arbitrary periodic signal. A sinusoidal signal or square wave signal is employed as the arbitrary periodic signal instead of the electric pulse signal adopted in the former references. When the frequency of the modulated signal is 1 GHz, the MFC with a maximal bandwidth of 15 GHz can be obtained. In addition, taking a sinusoidal signal as an example, the influence of the injection optical power to the slave laser and the modulation frequency of the optical module on the generation of the MFC is analyzed in detail. Finally, the results of MFC generated with a square wave signal injection are presented. The experimental results of this paper provide an important reference for the practical applications of MFC.

Parity-time-symmetric frequency-tunable optoelectronic oscillator with a single dual-polarization optical loop.

We propose and experimentally demonstrate a parity-time (PT)-symmetric frequency-tunable optoelectronic oscillator (OEO) in which the PT symmetry is implemented based on a single dual-polarization optical loop. By employing the inherent birefringence of a z-cut lithium niobate (LiNbO3) phase modulator (PM), two mutually coupled optoelectronic loops supporting orthogonally polarized light waves with one experiencing a gain and the other a loss are implemented. By controlling the gain, loss, and the coupling coefficients between the two loops, the PT symmetry breaking condition is met, which enables the OEO to operate in single mode without using an ultranarrow passband optical or microwave filter. The frequency tunability is realized using a microwave photonic filter (MPF) implemented using the PM and a phase-shifted fiber Bragg grating (PS-FBG). The proposed PT-symmetric OEO is experimentally evaluated. A stable and frequency-tunable microwave signal from 2 to 12 GHz is generated. The phase noise of the generated signal at 11.8 GHz is measured, which is -124dBc/Hz at a frequency offset of 10 kHz.

Hierarchical Cobalt Selenides as Highly Efficient Microwave Absorbers with Tunable Frequency Response.

Microwave absorbing materials have attracted much attention in solving electromagnetic interference and pollution problems. Hierarchical cobalt selenides have been obtained through a facile selenization annealing process. The as-prepared samples exhibit distinct reflection losses (RL) and frequency responses via tailoring their crystalline configurations, with excellent absorption in Ku, X, or C band. All of the samples show RL greater than or near -50 dB with effective bandwidths more than 4 GHz, indicating that they may serve as high-efficient and frequency-tunable microwave absorbers. Especially, the sample annealed at 400 °C shows a competitive RL of -62.04 dB at 9.92 GHz with a thickness of 2.25 mm; meanwhile, its effective absorption bandwidth reaches 5.36 GHz with a thickness as small as 1.56 mm. The cobalt selenides as microwave absorbers exhibit a promising prospect applied in complex electromagnetic environments.

Rational design of mesoporous MnO2 microwave absorber with tunable microwave frequency response

To design a single-component absorber with optimizing reflections loss and tunable absorption frequency, the unique lightweight MnO 2 microspheres are successfully synthesized by a template-free method. The as-synthesized MnO 2 microspheres are of mesoporous in diverse specific surface area. By controlling the pH value of the reacting solution, the specific surface area of MnO 2 microspheres is adjustable. The maximum specific surface area of MnO 2 microspheres with mesoporous nature being 90.52 m 2 /g for specimens is obtained from solution of pH = 5. The complex permittivity and permeability of manganese dioxide are tailored to obtain proper impedance matching. Thus, the resultant MnO 2 microspheres exhibit remarkable microwave characteristic in a wax matrix. The minimum reflection loss reaches −31.79 dB at 14.60 GHz, with the effective absorbing bandwidth below −10 dB being 5.78 GHz with a 2 mm thickness. The effective absorption broadband also changes from 10.27 to 13.75 GHz to 12.56–18.00 GHz as the increasing pH value. Such an outstanding microwave absorption performance ascribes to the unique mesoporous structure with designable specific surface area, giving rise to the multiple scattering and reflecting, interfacial polarization, and dielectric relaxation from the abundant interfaces and curved surfaces and impedance matching. • Mesoporous MnO 2 microspheres are facilely synthesized instead of tedious process. • Diverse specific surface area is obtained through adjusting pH of reaction system. • Specific surface area controls property and tunable absorption frequency response. • Maximum specific surface area is 90.52 m 2 /g, pore size concentrates on 4.909 nm. • Minimum reflection loss reaches −31.79 dB with effective bandwidth 5.78 GHz at 2 mm.

Frequency-tunable high-Q superconducting resonators via wireless control of nonlinear kinetic inductance

Frequency-tunable microwave resonators are in great demand especially in hybrid systems where precise frequency alignment of resonances is required. Here, we present frequency-tunable high-Q superconducting resonators fabricated from thin niobium nitride and niobium titanium nitride films. The resonant frequency is tuned by applying a magnetic field perpendicular to the hole structures in the resonator's inductor wire, whose kinetic inductance is modified by wirelessly induced DC supercurrents. A continuous in situ frequency tuning of over 300 MHz is achieved for a 10 GHz resonator with a moderate magnetic field of 1.2 mT. The planar resonator design and the noncontact tuning scheme greatly ease the fabrication complexity and can be widely applied in many hybrid systems for coupling microwave modes with other forms of excitations such as optical photons, phonons, magnons, and spins.

A Frequency-Tunable $V$ -Band Radial Relativistic Backward-Wave Oscillator

In this paper, we propose a novel frequency-tunable ${V}$ -band radial-line backward-wave oscillator (BWO). It operates in two high-order modes (i.e., TM02 or TM03 modes) so as to achieve a high power capacity, the reflector of which can effectively reduce the microwave leakage from the radial slow wave structure (SWS) to the diode region. The SWS is segmented into two sections, which can enhance the interaction between the electron beam and microwaves. The drift tube in between is capable of adjusting the operation frequency. In particle simulations, with the tube length of 6.1 mm, high-power microwaves with a frequency of 60.56 GHz are obtainable and the output power is 1.5 GW. The electron beam voltage is 524 kV and the beam current is 16.27 kA. By simply shrinking the tube to 3.9 mm, the operation frequency is tuned to 78.89 GHz and the microwave power yielded is 586.75 MW. This work validates the feasibility of tuning a radial-line BWO between two high-order modes, which will enlighten the design of other future frequency-tunable high-power microwave sources.

Tunable microwave generation utilizing monolithic integrated two-section DFB laser

Tunable microwave generation and frequency up-conversion are demonstrated utilizing a monolithically integrated two-section DFB laser. The frequency of the microwave signal is tuned from 13 GHz to 40 GHz, which can be further improved by adjusting the wavelengths of the DFB lasers. Utilizing the sideband optical injection locking technique, frequency-doubled microwave signals with low phase noise of −100.9 dBc/Hz at 10 kHz and narrow linewidth of 102 Hz are obtained. In addition, the tunable range of frequency-doubled and frequency-quadrupled microwave signals are also investigated respectively.

Generation of Tunable and Ultra-Broadband Microwave Frequency Combs Based on a Semiconductor Laser Subject to Pulse Injection From a Current Modulated Laser

We have experimentally demonstrated and characterized the generation of tunable and ultra-broadband microwave frequency combs (MFCs) based on a slave laser (SL) subject to regular pulse injection from a current modulated master laser (ML). Under modulation frequency fm = 1.2 GHz and modulation power Pm = 22 dBm, the current modulated ML is driven into a regular pulse state, and a seed MFC with 14.4 GHz bandwidth within a ±5 dB amplitude variation can be obtained. Such a seed MFC is then injected into the SL for producing final MFC with higher performances. For a fixed detuning frequency fi = 0 GHz and optimized injection power Pi = 2060 μ W, the bandwidth of the final MFC is increased to 33.6 GHz, and the single-sideband phase noises of all comb lines of the MFC within the bandwidth can be decreased to below –90.9 dBc/Hz@10 kHz. Additionally, the influences of Pi and fm on the MFC bandwidth are also analyzed. The experimental results are in agreement with numerical simulations to a certain extent.

Wideband frequency-tunable optoelectronic oscillator with a directly modulated AlGaInAs/InP integrated twin-square microlaser.

We propose and demonstrate an optoelectronic oscillator with a directly modulated AlGaInAs/InP integrated twin-square microlaser for generating wideband frequency-tunable microwave signals with low phase noise. Apart from the relaxation oscillation peak, the modulation response of the twin-square microlaser working at the mutual optical injection state exhibits a significant enhancement around the beating frequency of the lasing modes in the two square cavities owing to the photon-photon resonance. A self-sustaining oscillation can be generated around the modulation response peak with the lowest loop loss occurring at the relaxation oscillation frequency or the beating frequency, depending on the practical state of the twin-square microlaser. High-quality tunable microwave signals ranging from 2.22 to 19.52 GHz are generated with single sideband phase noises below -110 dBc/Hz at the 10 kHz offset frequency and side-mode suppression ratios of approximately 40 dB by tuning the injection currents of the twin-square microlaser.

Tunable microwave magnetic field detection based on Rabi resonance with a single cesium-rubidium hybrid vapor cell

We experimentally investigated continuously frequency-tunable microwave (MW) magnetic field detection based on Rabi resonance with a single cesium-rubidium hybrid vapor cell. The multispecies atomic systems, with their tunable abilities in transition frequencies, enabled this atomic sensing head to cover a broader detectable MW field scope compared to the use of a single alkali atom. Here, we demonstrated the simultaneous observation of atomic Rabi resonance signals with 85Rb, 87Rb, and 133Cs in the same vapor cell. Using an experimentally feasible static magnetic field (DC field) below 500 G, we realized a MW magnetic field strength detection with a bandwidth of 4.8 GHz around 8.1 GHz. The use of a hybrid cell system cell also enabled the detection of an identical MW field for different atomic species with the help of the DC field, allowing us to perform a perfect comparison for different applications that require the same electromagnetic environment. The results may be useful for the realization and application of many atomic detectors based on different physical principles.

Optically Tunable Microwave Frequency Downconversion Based on an Optoelectronic Oscillator Employing a Phase-Shifted Fiber Bragg Grating

We demonstrate an approach to achieve optically tunable microwave frequency downconversion based on an optoelectronic oscillator (OEO) incorporating a tunable microwave photonic filter. The wideband tunable local oscillation (LO) is generated in the OEO through simply tuning the frequency difference between the optical carrier and the reflection notch of a phase-shifted fiber Bragg grating (PS-FBG). The LO and the input radio-frequency (RF) signal are combined and added to the OEO loop by a single-phase modulator. Through transmitting one modulation sideband of the LO via the reflection notch of the PS-FBG and combining it with the optical carrier split from the laser source, the oscillation of the LO in the OEO is maintained. The reflected modulation sidebands of the LO and the RF signal from the PS-FBG are exported out of the OEO loop and enter a narrow-band photodetector to achieve optically tunable microwave frequency downconversion. Our method is experimentally evaluated, in which optically tunable LOs in the frequency range 6-15 GHz are generated, and RF signals in the frequency range 7-16 GHz are successfully downconverted to intermediate frequency band around 1 GHz.

Breaking the limitation of mode building time in an optoelectronic oscillator

An optoelectronic oscillator (OEO) is a microwave photonic system with a positive feedback loop used to create microwave oscillation with ultra-low phase noise thanks to the employment of a high-quality-factor energy storage element, such as a fiber delay line. For many applications, a frequency-tunable microwave signal or waveform, such as a linearly chirped microwave waveform (LCMW), is also needed. Due to the long characteristic time constant required for building up stable oscillation at an oscillation mode, it is impossible to generate an LCMW with a large chirp rate using a conventional frequency-tunable OEO. In this study, we propose and demonstrate a new scheme to generate a large chirp-rate LCMW based on Fourier domain mode locking technique to break the limitation of mode building time in an OEO. An LCMW with a high chirp rate of 0.34 GHz/μs and a large time-bandwidth product of 166,650 is demonstrated.