Showing papers by "Ninghua Zhu published in 2019"

Dual-chirp Fourier domain mode-locked optoelectronic oscillator

Abstract: Optoelectronic oscillators (OEOs) have been widely investigated to generate ultra-pure single-frequency microwave signals. Here, we propose and experimentally demonstrate a dual-chirp Fourier domain mode-locked (FDML) OEO to generate dual-chip microwave waveforms. In the proposed FDML OEO, a frequency-scanning dual-passband microwave photonics filter based on phase-modulation-to-intensity-modulation conversion using an optical notch filter and two laser diodes is incorporated into the OEO cavity. Fourier domain mode-locking operation is achieved by synchronizing the scanning period of the filter to the cavity round-trip time. Tunable dual-chirp microwave waveforms with a large time-bandwidth product are generated directly from the FDML OEO cavity in the experiment, which can be used in modern radar systems to improve its range-Doppler resolution.

Photonic generation of background-free binary phase-coded microwave pulses

Abstract: We report a photonic scheme to generate background-free frequency-doubled binary phase-coded microwave pulses. The key component is a dual-polarization dual-parallel Mach–Zehnder modulator that is used to realize phase modulation and carrier-suppressed double second-order sideband modulation at two orthogonal polarization states, respectively. The π phase jump of the frequency-doubled phase-coded microwave pulse is dependent on the polarity of the coding signal rather than its amplitude. Besides, the generated microwave pulses are free from the baseband-modulated signals, because the optical power launched to a photodetector (PD) keeps constant all the time. Since no electrical or optical filters are involved, the photonic generator can ensure a broad operation bandwidth and wide tunability. Our scheme is theoretically analyzed and experimentally verified. The 4 Gb/s at 16 GHz and 7 Gb/s at 28 GHz background-free frequency-doubled phase-coded microwave pulses have been successfully generated.

Multiple-frequency measurement based on a Fourier domain mode-locked optoelectronic oscillator operating around oscillation threshold

Abstract: We propose and experimentally demonstrate a photonic-assisted approach to microwave frequency measurement based on frequency-to-time mapping using a Fourier domain mode-locked optoelectronic oscillator (FDML OEO) operating around oscillation threshold. A relationship between the frequency of the unknown input microwave signals and the time difference of the output pulses is established with the help of the frequency scanning capability of the FDML OEO and, thus, can be used for microwave frequency measurement. The proposed scheme is characterized as having broad bandwidth, high resolution, multiple-frequency detection capability, and tunable measurement range. Microwave frequency measurement with a measurement range up to 16 GHz and a low measurement error of 0.07 GHz is realized.

Harmonically Fourier Domain Mode-Locked Optoelectronic Oscillator

Abstract: We experimentally demonstrate a harmonically Fourier domain mode-locked optoelectronic oscillator (FDML OEO). Harmonic Fourier domain mode locking operation is achieved when the cavity round-trip time is equal to integer multiples of the scanning period of the filter in the OEO loop. Compared with a fundamentally FDML OEO, frequency scanning microwave signals with increased tuning speed and large bandwidth can be easily generated by the proposed harmonically FDML OEO, which can find applications in spread-spectrum communication and modern radar systems. Up to fourth order, harmonic Fourier domain mode locking operation is achieved in the experiment. The time-bandwidth product of the harmonically FDML OEO is as large as tens of thousands. The maximum chirp rate of the generated $X$ -band linearly chirped microwave waveform is 0.725 GHz/ $\mu \text{s}$ , which is four times higher than that of the fundamentally FDML OEO.

Photonic Radio Frequency Self-Interference Cancellation and Harmonic Down-Conversion for In-Band Full-Duplex Radio-Over-Fiber System

Abstract: We report a photonic radio frequency (RF) self-interference cancellation (SIC) and harmonic down-conversion (HDC) scheme based on a dual-parallel dual-drive Mach-Zehnder modulator (DDMZM). The proposed scheme can eliminate the chromatic-dispersion induced power fading (CDIP) effect and thus is very suitable for in-band full-duplex (IBFD) radio-over-fiber (ROF) system. The self-interference RF signal is directly cancelled in optical domain, which overcomes the electronics bottleneck limitation of electrical SIC. Moreover, the HDC allows us to use a cost-effective low frequency local oscillation (LO) source to down-convert a high-frequency RF signal into an intermediate frequency (IF) band. In addition, the harmonic odd-order single-sideband (SSB) down-conversion is naturally free from the CDIP effect. The proposed photonic SIC+HDC system is theoretically analyzed and experimentally verified.

Chromatic-dispersion-induced power-fading suppression technique for bandwidth-quadrupling dual-chirp microwave signals over fiber transmission.

Abstract: We report a technique to overcome chromatic-dispersion-induced power fading (CDIP) for bandwidth-quadrupling dual-chirp microwave signals over fiber transmission. Normally, dual-chirp microwave signals are generated using double-sideband (DSB) modulation. However, DSB modulation suffers from CDIP significantly. We propose a carrier-frequency shift method to suppress the CDIP based on a dual-polarization dual-parallel Mach–Zehnder modulator. In addition, the bandwidth of the dual-chirp signal can be quadrupled by properly setting the biases of the modulator. The proposed technique is theoretically analyzed and experimentally verified. Our technique is promising for improving the range-Doppler resolution of radars for one-to-multi base stations transmission.

Advanced Digital Signal Processing for Reach Extension and Performance Enhancement of 112 Gbps and Beyond Direct Detected DML-Based Transmission

Abstract: 112 Gbps per wavelength, amplification free Four-level Pulse Amplitude Modulation (PAM-4) transmissions are experimentally demonstrated with advanced digital signal processing (DSP) algorithms. Two DSP architectures are investigated for Directly Modulated Lasers (DMLs): 1) the regular DSP with Feed Forward Equalization (FFE) and Decision Feedback Equalization (DFE), and 2) the enhanced DSP with Maximum Likelihood Sequence Estimation (MLSE) equalizer. The experimental results show that with advanced DSP technologies the conventional DML can achieve 40 km transmissions with Bit Error Rate (BER) under 2.4 × 10−4 that meets RS (544, 514) Forward Error Correction (FEC) requirement; with regular-DSP the advanced DML can achieve 40 km transmissions with BER under 3.8 × 10−3, with stronger FEC. 112 Gbps and beyond per lambda DML based transmission is a promising low power, low-cost solution for 800 GbE or 1.6 TbE Ethernet.

Large-capacity and low-loss integrated optical buffer

Abstract: Temporarily storing light occupies a pivotal position in all-optical packet switching network and microwave photonics. An integrated optical buffer with large capacity and low loss is demonstrated on a silica wafer. The optical buffer consists of four silica waveguide delay lines connected by five thermo-optic switches. With different switch combinations applied, related delay lines are selected to realize a different storage time in the buffer, and a storage time up to 100 ns with a 10-ns step size is implemented. By optimizing the fabrication process and introducing the offsets between straight and bending waveguides, the propagation loss as low as ~1.08 dB/m is achieved. This large-capacity and low-loss buffer enables broad applications in optical communications and microwave photonics.

Accuracy-Enhanced Wideband Optical Vector Network Analyzer Based on Double-Sideband Modulation

Abstract: We report a method to significantly improve the accuracy of an optical vector network analyzer (OVNA) with double-sideband (DSB) modulation. The measurement errors of the DSB-OVNA mainly derive from optical carrier uncertainty and the beating between higher order optical sidebands. We propose a three-step measurement method and an accuracy-enhanced algorithm to eliminate these measurement errors perfectly. A theoretical model is built to analyze the potential measurement errors as well as to find a way to remove them. Excellent accuracy improvement of the OVNA is confirmed by a proof-of-concept experiment. The OVNA shows an ultrahigh resolution of 667 kHz over a wideband measurement range of 80 GHz.

Photonic-based microwave hybrid combiner with arbitrarily tunable phase shift and power combining ratio.

Abstract: We report a broadband photonic-based microwave hybrid combiner (PMHC) using a dual-polarization dual-parallel Mach-Zehnder modulator. The broadband PMHC with arbitrarily tunable phase shift and power combining ratio can overcome several limitations of conventional microwave combiners in terms of tunability and bandwidth. By simply adjusting the biases of the modulator, the phase shift and power ratio of the two combined microwave signals are independently, continuously, and freely tunable. The proposed PMHC is theoretically analyzed and experimentally verified. In a proof-of-concept experiment, two sinusoidal microwave waveforms are successfully combined to form rectangular and triangular waveforms, respectively.

Temporal Cloak Without Synchronization

Abstract: Considered to only exist in fairy tales in the past, invisibility cloaks have been successively converted into reality no matter in the spatial domain or the temporal domain. Inspired by the spatial cloaking, time gaps are utilized to hide temporal events. However, a sophisticated synchronization for cloaking is indispensable in these cloaking techniques, therefore leaving inconvenience for the realization of the temporal cloak. Here, by exploiting the temporal Talbot effect, we propose a brand new scheme and concept to achieve a temporal cloak without any synchronization for the cloaking process, under which the intensity-modulated event is directly turned into invisibility in intensity through temporal averaging effect induced by the Talbot effect. We successfully realize the temporal cloak for periodic and pseudo-random signals. We also find that the higher order temporal Talbot effect is beneficial to the cloaking performance. Due to the transformed information on the phase, the data could be recovered from the intensity-cloaked waveform, leading to a non-full-field cloak. This method and its concept render a distinct perspective for the temporal cloak, extend temporal cloak to the pulsed-wave, and promote the development of confidential communication.

Tunable Single-Notch Microwave Photonic Filter Based on Nonsliced ASE Source

Abstract: We propose a novel single-notch microwave photonic filter (MPF) using a nonsliced amplified spontaneous emission (ASE) source and a laser diode (LD). The nonsliced ASE is used for implementation of a phase tunable bandpass MPF, where the participation of an LD enables the simultaneous realization of an allpass MPF, without adding more devices into the system. By destructive interfering between the bandpass MPF and the allpass MPF, a single-notch MPF can be achieved with tunable center frequency. Compared with previous approach based on ASE source, the proposed approach has a broader tunable frequency range and a much simpler configuration since it is free from both the wavelength-division-multiplexer (WDM) and polarization processing. The proposed method is theoretically analyzed and experimentally demonstrated.

A Novel Optical Frequency-Hopping Scheme Based on a Flexible Structure for Secure Optical Communications

Abstract: A novel optical frequency-hopping scheme based on a flexible structure for secure optical communications is proposed and demonstrated. In the proposed scheme, critical users' data are divided into a lot of segments, and these segments are transmitted by different optical wavelengths in time domain. In other words, one channel optical carrier carries different users' data segments. A flexible structure was demonstrated and used in optical frequency-hopping system to simplify the structure and decrease the cost of the security system. In this paper, the viability of a four-wavelength-frequency-hopping secure optical communication system with a 25-Gb/s error-free transmission through a 32-km single-mode fiber and a 8-km dispersion compensation fiber was demonstrated and verified by simulation tools.

Photonic generation of frequency-doubled triangular waveforms based on a dual parallel Mach–Zehnder modulator

Abstract: We propose a photonic approach to generating frequency-doubled triangular waveforms using a dual-parallel Mach–Zehnder modulator (DPMZM). Most previous modulator-based schemes require additional processing of optical sidebands using filters or a dispersive element. In our work, optical processing of optical components is no longer necessary. The triangular waveforms with a repetition rate twice the frequency of the applied microwave signal can be directly generated by properly setting the bias and driven signal of the DPMZM. Since there is no additional optical processing, the proposed structure is cost effective. The repetition rate of the generated waveform is freely tunable over a wide bandwidth since there is no optical or electrical filter involved. The proposed approach is theoretically analyzed and experimentally demonstrated. Triangular waveforms with the repetition rates of 6, 8, and 10 GHz are successfully generated.

Fourier domain mode-locked photoelectric oscillator

Abstract: A Fourier domain mode-locked photoelectric oscillator comprises a laser controller, a tunable laser, a phase modulator, an optical notch filter, an optical fiber, a photoelectric detector, an electricamplifier and a power divider, wherein the tunable laser, the phase modulator, the optical notch filter and the photoelectric detector form a microwave photonic filter together, and the transmissionband of the microwave photonic filter is determined by the difference value of wavelengths corresponding to the notch positions of the tunable laser and the optical notch filter. According to the invention, the tunable laser, the phase modulator, the optical notch filter and the photoelectric detector form a quickly tuned microwave photon filter, the rapid tuning of the transmission band of the microwave photonic filter is realized through the rapid tuning of the laser, and the change of the transmission band of the filter is matched with the time delay of a signal transmitted for a circle ina photoelectric oscillator loop, so that the Fourier domain mode locking is realized, and a chirp microwave signal with an adjustable broadband can be outputted.

Ultra-Fast Wavemeter for CW Laser Based on Wavelength-to-Time Mapping

Abstract: An ultra-fast continuous wave (CW) wavemeter with the 51 MHz update rate is proposed and demonstrated based on wavelength-to-time mapping and optical heterodyne. The system consists of a mode-locked laser (MLL) as the probe source and a reference tunable laser. The mode-locked pulses emitted from the MLL are first stretched in a dispersive element and its spectrum is mapped into time-domain. Then, the stretched pulses beat with reference beam and the beam under test in two arms, respectively. By measuring the time delay between the beating results in two arms, the wavelength information can be obtained. In the meantime, we introduce cross correlation to our data processing to improve the measurement resolution. A resolution of about 0.03 nm is achieved. The spectral range of the ultra-fast wavelength meter is about 10 nm. Using the proposed scheme, we successfully trace the wavelength variation of a linearly chirped laser source with the 125 kHz repetition rate.

Fast-Switching Microwave Photonic Filter Using an Integrated Spectrum Shaper

Abstract: A fast-switching single passband microwave photonic finite impulse response filter (MPF) using an incoherent broadband optical source (BOS) and an integrated spectrum shaper is proposed and experimentally demonstrated. The key component of our proposed MPF is the silica-on-silicon integrated spectrum shaper, which is used to slice the spectrum of the BOS. The performance of the integrated spectrum shaper is measured in terms of time delay, power consistency, and switching speed. A number of spectral shapes with the free spectrum range from 1.88 to 0.058 nm can be flexibly switched by changing the driving voltage of the optical switches. With the dispersion compensating fiber as dispersion medium, a fast-switching MPF with the switching speed up to 1.4-KHz is demonstrated in a wide tunable range from 1 to 12 GHz and the sidelobe suppression is up to 35 dB, which shows a great agreement with the theoretical result.

Optically controlled phase array antenna [Invited]

Abstract: To overcome the beam squint in wide instantaneous frequency, we review a number of system-level optical controlled phase array antennas for beam forming. The optical delay network based on a fiber device in terms of topological structure of an N-bit optical switch, fiber grating, high-dispersion fiber, and vector-sum technology is discussed, respectively. Lastly, an integrated circuit is simply summarized.

Photonic generation and transmission of phase-modulated microwave signals

Abstract: In modern radar system, pulse compression technique has been widely used to increase the detection distance and range resolution. To enlarge the pulse compression ratio, the microwave signals are often phase modulated, such as phase-coded or frequency chirped. Conventionally, the phase-modulated microwave signals generated by electrical methods suffer from low microwave carrier frequency, limited bandwidth, low data rate and high transmission loss. Photonic-assisted generation and transmission of phase-modulated signals is a promising candidate to overcome these limitations In this paper, we review our recent works about the photonic generation and transmission of phase-modulated microwave signals, including the simultaneously frequency up-conversion and phase-coding, background-free frequency-doubled phase-coded microwave signal generation, phase-coded microwave pulse generator by optoelectronic oscillation (OEO), as well as transmission of dual-chirped microwave signals with chromatic-dispersion-induced power fading (CDIP) compensation and elimination technology. These works represent the new progresses in photonic approaches to generate and transmit phase-modulated microwave signals, which has great potential in the modern radar system.

Double chirped Fourier domain mode-locked photoelectric oscillator and application thereof and communication system

Abstract: The invention relates to a double chirped Fourier domain mode-locked photoelectric oscillator and an application thereof and a communication system, which relate to the technical field of microwave photonics. The double chirped Fourier domain mode-locked photoelectric oscillator comprises two lasers, an optical coupler, a modulator, an optical filter, an optical delay line, a photoelectric detector, a power divider and an electric amplifier. The two lasers, the modulator, the optical fiber and the photoelectric detector constitute a double-pass-band sweep-frequency microwave photonic filter, of which the sweep frequency is realized by the sweep frequency of the two lasers or is realized by the sweep frequency of the optical filter. The double chirped Fourier domain mode-locked photoelectric oscillator provided by the invention does not need a high-speed electronic device. The output signals can be tuned. Broadband fast chirped microwave signals can be output.

Tunable notch microwave photonic filter based on interferometry of a single low-incoherence source.

Abstract: We present a method to realize a single-notch microwave photonic filter (MPF) based on interferometry of a single, low-coherence broadband optical source (BOS). Normally, a notch MPF based on low-coherence interferometry requires independent control of two optical sources located in different wavebands. In this work, we use a single BOS to accurately perform destructive interference between a bandpass and an all-pass MPF. A frequency and bandwidth freely tunable single-notch MPF can thus be realized. The proposed method is theoretically analyzed and experimentally demonstrated. A notch depth of more than 30 dB and a continuously tunable frequency range from 2 to 18 GHz was demonstrated in the proof-of-concept experiment.

Integrated fourier domain mode-locked optoelectronic oscillator, application and communication system

Abstract: The invention discloses an integrated Fourier domain mode-locked photoelectric oscillator, an application and a communication system, and relates to the technical field of microwave photonics. The integrated Fourier domain mode-locked photoelectric oscillator comprises a photoelectric chip and an electronic chip; the photoelectric chip comprises a laser, a modulator, an optical notch filter and aphotoelectric detector which are connected through optical waveguides; the electronic chip comprises an electric amplifier and a power divider which are connected through a coplanar microwave waveguide. All devices needed by a Fourier domain mode-locked photoelectric oscillator are integrated on the chips, so that the size, the weight and the power consumption of the Fourier domain mode-locked photoelectric oscillator are greatly reduced; the tunable frequency sweeping microwave signal output can be realized; the frequency sweeping speed of an output signal is increased; and the integrated Fourier domain mode-locked photoelectric oscillator can be applied to a radar and the communication system.