Microwave Signal Generation Research Articles

Photonic Generation of Background-Free Phase-Coded Microwave Pulses with Elimination of Power Fading

We report a novel photonic scheme to generate background-free phase-coded microwave pulses with elimination of power fading by cascading a dual-polarization dual-parallel Mach–Zehnder modulator (DP-DPMZM) and a polarization modulator (PolM). The DP-DPMZM is driven by a radio frequency (RF) signal to generate two first-order optical sidebands with an orthogonal polarization state, while the PolM is driven by a three-level electrical coding signal. By properly adjusting the polarization state, a series of background-free frequency-doubled phase-coded microwave pulses can be generated after optical-to-electrical conversion. Benefiting from the carrier-suppressed single-sideband (CS-SSB) modulation, the proposed signal generator can suppress the chromatic-dispersion-induced power-fading effect, which has excellent potential for long-distance fiber transmission. In addition, the system can directly generate phase-coded microwave signals in pulse mode by truncating continuous wave (CW) microwave signals. Moreover, the microwave signal generator has wideband tunability since no optical filter is involved in our scheme. The proposed method was theoretically analyzed and experimentally verified. Phase-coded microwave pulses centered at 14 GHz and 19.2 GHz with a bit rate of 0.5 Gb/s were successfully generated.

High Power Microwave Signal Generation Based on Recursive Balanced Power Amplifier

High Power Microwave Signal Generation Based on Recursive Balanced Power Amplifier

МЕТОД ГЕНЕРАЦИИ СВЕРХШИРОКОПОЛОСНЫХ СВЧ-СИГНАЛОВ С ЛИНЕЙНО-ЧАСТОТНОЙ МОДУЛЯЦИЕЙ НА ОСНОВЕ САМОГЕТЕРОДИНИРОВАНИЯ ИЗЛУЧЕНИЯ ЛАЗЕРНОГО ДИОДА

In this paper, microwave photonic technique of ultrawideband linearly frequency modulated signals generation is proposed. The proposed method based on direct modulation of the laser diode current, which provides a periodic change in the emission frequency. The Michelson interferometer summarizes laser signal and its replica with time delay exceeding 10 ms, which, in turn, is defined by time difference between arms. Optoelectronic conversion is performed in high-speed high-power photodiode. The proposed approach makes it possible to generate microwave signals with linear frequency modulation in the frequency range up to several tens of gigahertz by means of laser pump current modulation in the frequency range less than 100 MHz. The method of ultra-wideband microwave signals generation is implemented using a Michelson fiber-optic interferometer with Faraday mirrors. Such interferometer topology provides a doubling of the path length, and reduced gyroscopic effects due to a counter-propagating double pass. Changing the parameters of the generated microwave ultrawideband signals with frequency modulation is achieved by pump current shape and amplitude control. It is also proposed to use real-time oscilloscope without need of changing of the internal structure of such generator to pre-tune it. Time-frequency analysis is used to extract frequency versus time dependence. By so doing, direct impulse response estimation is performed. This method allows to characterize laser diode frequency response for arbitrary microwave waveform generation by means of pump current waveform calculation from experimental data.

Microwave signal generation from a parity-time-symmetric optoelectronic oscillator with optical injection locking.

A parity-time (PT) symmetric optoelectronic oscillator (OEO) with optical injection locking is proposed and experimentally demonstrated to generate single-mode microwave signals. A distributed feedback laser is injection locked, which functions as a frequency multiplier for the coarse mode selection of the PT-symmetric OEO. The PT symmetry in the OEO is implemented by using a polarization-dependent Sagnac loop to form two identical loops for coupling. By tuning the two polarization controllers in the Sagnac loop, the gain/loss and coupling coefficient of the two loops can be controlled, and single-mode oscillation in the OEO could be achieved at the broken PT-symmetry condition. Microwave signal generation at the frequency of 6.427GHz is obtained from the proposed OEO. The phase noise is about -105dBc/Hz at an offset frequency of 10kHz.

Generation of a high chirp rate microwave signal by using external optical modulation technique for RADAR application: theory and experiment

Generation of a high chirp rate microwave signal by using external optical modulation technique for RADAR application: theory and experiment

Frequency-modulated microwave signal generation by dual-wavelength-injection period-one laser dynamics.

In this Letter, dual-wavelength-injection period-one (P1) laser dynamics is proposed for the first time, to the best of our knowledge, to generate frequency-modulated microwave signals. By injecting light with two different wavelengths into a slave laser to excite P1 dynamics, the P1 oscillation frequency can be modulated without external control of the optical injection strength. The system is compact and stable. The frequency and bandwidth of the generated microwave signals can be easily adjusted by tuning the injection parameters. Through both simulations and experiments, the properties of the proposed dual-wavelength injection P1 oscillation are revealed, and the feasibility of the frequency-modulated microwave signal generation is verified. We believe that the proposed dual-wavelength injection P1 oscillation is an extension of laser dynamics theory, and the signal generation method is a promising solution for generating broadband frequency-modulated signals with good tunability.

Multifunction spin transfer nano-oscillator based on elliptical skyrmion

As microwave signal generators, the spin transfer nano-oscillator (STNO) based on magnetic skyrmion has attracted huge interest recently. However, the circular magnetic skyrmion-based oscillator only produces a microwave signal with a single oscillation frequency, and detecting the precession of skyrmion in the entire nanodisk is also a challenge. In the paper, we propose an STNO based on elliptical skyrmion, which can simultaneously generate a single frequency or multiple frequency oscillation signal, and the oscillation frequency also can be increased to some extent. Moreover, to reduce the difficulty of detection, the method to restrict elliptical skyrmion moving in a specific orbit is suggested. Our results provide a possible candidate to design the spintronic devices.

Quantum Microwave Photonics

By combing photonics and radiofrequency (RF) engineering, microwave photonics has been widely studied in the past few decades for the generation, processing, control and distribution of microwave and RF signals using photonic techniques. In parallel with the continuous hot research on classic microwave photonic systems, cross research between microwave photonics and other disciplines is also a promising research spot for scientists in this area. Here we review emerging advances in recent years in cross research between microwave photonics and quantum technology, i.e., quantum microwave photonics that harnessing quantum technology to achieve features or functions that are very complex or even not possible using traditional microwave photonic technology and vice versa. Key motivations of quantum microwave photonics are discussed. The basic operation principle of the quantum single-photon detection scheme, which is the main building block of current quantum microwave photonic systems, is provided. Selected recent advances, including weak microwave signal detection, microwave photonic phase shifting and filtering, nonlocal frequency-to-time mapping, RF compressed sensing, and quantum key distribution, are summarized. Challenges and future prospects of quantum microwave photonics are also discussed.

Single-modulator Based Multi-Format Switchable Signal Generator Without Background Noise

A photonic multi-format background-free binarily modulated microwave signal generator using a single dual-polarization dual-parallel Mach–Zehnder modulator is proposed and demonstrated. The proposed generator features good reconfiguration and switchability. By simply adjusting the direct current biases of the modulator, amplitude shift keying (ASK), phase shift keying (PSK) and frequency-shift keying (FSK) microwave signals can be generated. Benefiting from the complementary intensity modulation, there is no residual baseband modulated signal in the generated binarily modulated signals. The system does not involve any optical or electrical filters, which ensures good tunability of the generator. By changing the frequency of the driven microwave carrier and bit rate of the electrical coded signal, the frequency and rate of the generated multi-format signals can be adjusted accordingly. The multi-format switchable signal generator has great potential in multi-functional communication and radar systems.

Driving system for Mach-Zehnder electro-optic modulators in microwave photonics.

In order to obtain a modulation signal with high bandwidth and highly stable output power without distortion, an electro-optic modulator driving system with quick response to the input signal is designed in this paper. The system mainly includes three parts: power supply module, microwave signal generation module, and automatic gain control (AGC) module. The power supply module provides appropriate voltage and current for other two modules. The microwave signal generation module is used to generate microwave signals. The AGC module adopts the digital AGC control structure and the PID control principle to achieve stable control of the output power of the microwave signal. The hardware is developed, and the software algorithm is integrated into the driving system to verify the effectiveness and stability. The experimental results show that the bandwidth of the AGC module reaches 20 GHz. The proposed AGC module can effectively stabilize the output power of the microwave signal at 10 dBm with fluctuations less than ±1.5 dB, and its stability is improved by 74.95% compared to existing instrument. When the input power changes at 10 KHz, the system can still achieve stable control performance and has exhibited excellent dynamic response characteristics.

Theoretical and Experimental Investigations of Tunable Microwave Signal Generation Based on a 1-GHz All-Polarization-Maintaining Mode-Locked Fiber Laser

Photonics-based microwave generation brings the advantages of photonic oscillators, such as high stability, wide bandwidth, and low loss, to the microwave domain. In this paper, the generation of tunable microwave signals was investigated both theoretically and experimentally based on an all-polarization-maintaining 1-GHz mode-locked fiber laser. Based on beating between two highly chirped optical pulse trains with a relative time delay at the photodetector, tunable microwave signals could be obtained. The numerical simulations show that 40 GHz or higher microwave signals could be obtained by tuning the time delay and dispersion. To experimentally validate the theoretical model, the generation of tunable microwave signals from 2–4 GHz was demonstrated. Due to the utilization of polarization-maintaining devices, the optical output has a high degree of linear polarization of more than 99%, which verifies the enhanced system stability. These demonstrations are imperative for solidifying the advancements of recent years and could promote the utilization of photonics-based microwave generation in microwave photonics.

Optical Generation and Transmission of mmWave Signals in 5G ERA: Experimental Evaluation Paradigm

We demonstrate the generation, of a mmWave signal via the injection of an optical frequency comb (OFC) into an integrated tunable dual distributed Bragg reflector (DBR) laser as well as the fiber transmission and the processing of this signal by an optical beamforming network (OBFN). The dual DBR laser is based on a hybrid indium phosphide (InP) – polymer photonic integrated circuit (PIC). Two different cases have been examined in which the microwave signal is centered around 39 GHz and 60 GHz respectively, carrying quadrature amplitude modulation (QAM) formats at 0.5 Gbaud. In this proof-of-concept scenario, the OBFN consists of two optical paths, where the relative true time delay is induced by an optical delay line (ODL). Extensive comparison between the back-to-back (B2B) case and scenarios with transmission over 25 km of standard single-mode fiber (SSMF) has been made using the error-vector magnitude (EVM) and the bit-error ratio (BER) as evaluation criteria. In all cases, error-free transmission was suggested for all QPSK signals, whereas a worst-case EVM of 11.8% was observed for 16-QAM transmission, successfully showcasing the concept’s potential. The generated microwave signal’s frequency can be set arbitrarily high, provided that high-speed photodetection equipment is available for the detection and down-conversion of the signal. Extension to higher antenna elements (AEs) numbers is straight-forward, relying only on the number of available photodetectors.

Microwave Photonics Advancements in Radar Application

Microwave photonics (MWP) Technology brings Microwave and optical domains together. Due to its extraordinary capabilities and solution especially towards generation, transmission and processing of Microwave signals, the MWP field has potential to break barrier, which was not possible with RF technology alone. MWP technologies provide new opportunities in many areas like 5G networks, Advanced Radar and Internet of things. As demand for multi-functionality and reduced size is growing in every field, Radar is no exception. Radar systems capabilities in terms of functionality, precision, response time have significantly improved in past decades. MWP technologies are one of the key factors in that. With Modern photonics technologies Radar performance in terms of Speed, resolution, coverage, precise target identification has improved drastically. To understand the photonics technologies in detail, this paper is designed, which highlights the important features of Microwave photonics techniques applied in Radar and its subsystems

IOT-Based Injection-Locked Microwave Photonic Frequency Division Signal Processing

When building an injection-locked microwave photonic frequency division signal processing model for the Internet of Things, the waveform and frequency of the microwave have an important impact on its performance. How to optimize and adjust the injection-locked microwave photonic frequency division signal processing effect needs more research and exploration. Taking the traditional mode architecture as a reference, this paper constructs an injection-locked microwave photonic frequency division signal processing model based on the Internet of Things. In this paper, the popular deep analysis method is used to optimize the model, and the photonic technology is matched with the microwave analysis. The purpose of this construction is to weaken the microwave integration error and improve the calculation accuracy to a higher level. In addition, aiming at the difficult problem of microwave signal generation, this paper uses the optical injection method to lock the microwave photons and generate waveform signals, which makes the model data more representative, so as to solve the problems of unstable microwave signals and high transmission costs. This paper also discusses the possibility of microwave photon filtering and frequency division signal processing of microwaves. The optimal solution is determined by analyzing the experimental results of various technical means, thus proving that the injection-locked microwave photonic frequency division signal processing means has better stability and a higher fitting degree.

Broad tunable photonic microwave signal generation using optically-injected 1310 nm spin-VCSELs

We theoretically propose and demonstrate photonic microwave signal generation with a very broad tunability range from below 2.5 GHz to around 100 GHz. The proposed scheme is based on sustained oscillation dynamics produced in spin-VCSELs under right circularly polarized optical injection. The generated microwave frequencies can be tuned by detuning the frequency of the optical injection signal. The system also takes the advantage of polarization switching phenomena to generate broader microwave frequencies where the generated frequencies are equal to the sum of the absolute detuning frequency and the birefringence split between the spin-VCSEL modes which is 47.7 GHz. Sustained oscillation dynamics provokes tunable periodical oscillations through the adjustment of the frequency detuning and injection strength which can be used as a microwave signal generator. Enhancement of the RF power of the oscillations can be achieved by increasing the injection strength towards the locking regions. The microwave linewidth is reduced from 58 MHz to a medium linewidth of about 14 MHz under optical injection technique. This simple configuration paves the way for potential uses of spin-VCSELs in Radio-over-Fiber (RoF) applications and future technologies.

A Rational Harmonic Mode-Locking Optoelectronic Oscillator for Microwave Frequency Comb Generation

Recently, optoelectronic oscillators (OEOs) have shown good behavior in microwave signal generation. In this letter, we propose a rational harmonic mode-locking OEO (RHML-OEO) to generate microwave frequency combs (MFCs) with tunable comb intervals. By embedding an extra Mach–Zehnder modulator (MZM) into the OEO cavity, the intensity of the oscillating mode can be modulated by the signal applied on the MZM, and sidebands having fixed phase differences are produced in addition to the oscillating mode. A main feature of the RHML-OEO is that there is a frequency detuning between the modulation signal and longitudinal mode spacing of the OEO. Consequently, MFCs with large comb intervals can be generated even with a low-frequency modulation signal. In our experiment, third-order, fifth-order, and tenth-order RHML-OEOs are realized to generate MFCs with different frequency intervals of 1.128, 1.88, and 3.76 MHz when the modulation frequencies are 564, 940 kHz, and 1.253 MHz, respectively.

Boundary-free spin torque nano-oscillators based on ferrimagnetic skyrmions

Skyrmion-based spin torque nano-oscillators have great potential as microwave signal generators in communication technology. In this work, we propose a spin torque nano-oscillator based on ferrimagnetic skyrmions, where the current-induced force can be easily balanced by the controllable Magnus force due to the ferrimagnetic nature, resulting in a stable motion around the edge of the area with applied current. The direction of such a motion is switchable by tuning the ferrimagnet across the compensation point. The oscillation frequency is found to rely on the magnetization and can exceed 1.5 GHz around the angular momentum compensation point. In contrast to previous proposals based on ferromagnetic or antiferromagnetic skyrmions, our ferrimagnetic nano-oscillator does not require a shaped magnetic working layer, thus suggesting that the ferrimagnet could be a potential platform for building oscillator arrays and studying interaction between them.

Multi-band microwave signals generation based on a photonic sampling with a flexible ultra-short pulse source.

We propose and experimentally demonstrate a photonic sampling-enabled multi-band microwave signals generation scheme. The intermediate-frequency input signal is up-converted to high frequency output signals in multiple frequency bands, after being optically sampled by an ultra-short optical pulse train and subsequently being detected by a photodetector (PD). The ultra-short pulse source, realized by using an electro-optic modulation-based time lens with the chirp compensation, can be flexibly adjusted to enhance the performance of multi-band frequency up-conversion. In the experiment, after optimizing the optical ultra-short pulse source with a repetition frequency of 8 GHz, ten phase-coded up-converted microwave signals with a 13-bit Barker code were successfully generated within a frequency range from 7 GHz to 41 GHz. The power fluctuation among the generated microwave signals in multi-band is measured to be 5.9 dB. The experiment results indicate that, our proposed scheme can realize the multi-band up-conversion with a high fidelity.

Optoelectronic oscillator with improved sidemode suppression by joint use of spectral Vernier effect and parity-time symmetry.

An optoelectronic oscillator (OEO) with improved sideband suppression by joint use of the spectral Vernier effect and parity-time (PT) symmetry is proposed and experimentally demonstrated. The spectral Vernier effect is implemented using two mutually coupled loops with different loop lengths, to increase the effective free spectral range (FSR). To further increase the mode selection capability to ensure stable single-frequency oscillation with an increased sidemode suppression ratio (SMSR), PT symmetry is implemented, in which the two mutually coupled loops are controlled with balanced gain and loss. Thanks to the combined effects, stable single-mode oscillation with a significantly increased SMSR is achieved. The proposed OEO is studied theoretically and evaluated experimentally. The results show that for a generated microwave signal at 10 GHz, the SMSR is 67.68 dB, which is increased by 11.20 dB or 26.05 dB, when using only the spectral Vernier effect or only the PT symmetry. Thanks to the long length of the longer loop, good phase noise performance is still maintained. The measurement shows that a phase noise as low as -124.5 dBc/Hz at an offset frequency of 10 kHz is achieved.

Non-Hermitian tunable exceptional point system based on coupled fiber-optic Fabry-Pérot microcavities for broadband microwave signal generation

Appearance of exceptional points (EPs) in photonics arises enormous attention as a result of the counterintuitive phenomena occurring around EP. In particular, adiabatically encircling EP contributes to accumulation of Berry phase, leading to mode switching and strong chirality. Therefore, it would be of significance to develop a photonic system with tunable EP states, which helps to implement versatile functionalities for various applications. Here we propose a non-Hermitian tunable system based on coupled fiber-optic Fabry-Pérot microcavities with distributed gain/loss to host quasi-static EP-encirclement and parity-time (PT) symmetry schemes. Analytical calculations for the case of EP encircling along the path in the vicinity of EP are compared with their counterparts on the boundaries of the parameter space based on quasi-adiabatic theory, revealing mode switching and chirality relevant to the system singularity. And moreover, tunable coupling between microcavities enables tunability of EPs under PT symmetry regime, based on which generation of broadband microwave signals ranging from 0 to 75GHz could be achieved and the maximum frequency tuning sensitivity up to the magnitude of 106GHz/RIU could be reached for specific refractive index ranges, providing clues for manipulating EPs in non-Hermitian fiber-optic systems and designing novel EP-based photonic devices.