Delay jitter and dispersion are two important factors that impact the quality of radio over fiber transmission. In this paper, a simultaneous perception method for these two factors based on matched filtering is proposed. The proposed method effectively combines the precision of RF matched filtering process with the broadband advantages of microwave photonics technology, which can enable an accurate perception of both. The effectiveness of the proposed perception method is verified through experiments.
A microwave photonic (MWP) pulse radar system for high-resolution target detection is proposed and experimentally demonstrated in this article. In the transmitter, a pulsed linearly-frequency-modulated (LFM) wave is generated based on optical frequency operation module (OFOM), which can generate LFM waves with ultra-flexibly tunable center frequency. In the receiver, optical-domain down-conversion is employed to convert the incoming echo to an intermediate frequency signal by a microwave photonic frequency mixer, which can free the receiver from high-speed ADC and provide an excellent wideband processing. Experimentally, a Ku-band pulsed LFM wave with a bandwidth of 840 MHz is generated and received through self-closed-loop and target detection test by the constructed system. The performance verifies that the proposed pulsed MWP radar has the potential of supporting high-resolution detection and recognition of distant targets.
A method of dual-broadband signal generation based on the same optoelectronic oscillator with different tuning mechanisms is proposed in this paper. The structure includes a compatible dual-passband microwave photonic filter based on stimulated Brillouin Scattering effect (SBS) and phase-shifted Bragg fiber (PS-FBG). By implementing the Fourier-domain mode-locked mechanism, the proposed optoelectronic oscillator can simultaneously generate signals in different frequency bands with adjustable center frequency and bandwidth. The effectiveness of the proposed method is verified by experiments. Oscillating signals with bandwidth of 600 MHz and center frequencies at 5 GHz and 6 GHz are generated.
A single sideband (SSB) phase-modulated link with an improved spurious-free dynamic range (SFDR) is proposed and experimentally demonstrated. By generating a single-sideband phase-modulated signal containing a specific spectrum for demodulation, the third-order intermodulation distortion (IMD3) is effectively suppressed. The theoretical analysis is presented, and the experimental results show that a carrier-to-interference ratio of 62.45 dB is achieved. The improved SFDR is 120.25 dB · Hz4/5, which is 14.47 dB higher than that of a conventional SSB phase-modulated link.
An ultra-wideband random OEO using both stimulated Brillouin effect and Rayleigh scattering effect is proposed, which can generate random oscillating microwave signals covering all frequency bands. By using stimulated Brillouin scattering effect to amplify weak reverse Rayleigh scattering, the microwave signals with random characteristics which is independent of fixed cavity length can be generated. Experimentally, the work realized the generation of ultra-wideband (DC up to 32 GHz) random microwave signals. Compared with previous methods,the proposed random OEO mechanism is realized in an easier way, which can avoid using 1450 nm laser and promote its application in electronic interference.
We propose and experimentally demonstrate a pulse radar signal generation based on the Fourier domain mode-locked optoelectronic oscillator (FDML-OEO). In this method, two low-frequency control signals generated by a direct digital synthesizer (DDS) are adopted to control the tunable laser source (TLS) and the bias voltage of Mach-Zehnder modulators (MZM) respectively. The broadband pulse signals are generated by directly truncating the broadband signals on the basis of a FDML-OEO by controlling the frequency and amplitude of the bias voltage of the MZM. In the experiment, the broadband radar pulse signals with tunable duty cycle and the center frequency are demonstrated. In particular, the center frequency of signals are tuned by changing the initial phase of pulse driving signal and the triangular wave or the wavelength of TLS, which have greatly potential in improving the detection capability of the radar system.
A phase-coded microwave signal generation method based on parallel Mach-Zehnder modulator (MZM) with tunable frequency multiplication factor is proposed and demonstrated. By controlling the modulation index and the optical power ratio of the parallel MZMs, phase-coded microwave signals with frequency multiplication factors of 1, 3 and 5 are obtained. The feasibility of this approach is demonstrated by theoretical analysis and simulation, in which binary phase-coded signals with carrier frequency of 1GHz, 3GHz or 5GHz are respectively generated under 1GHz radio frequency (RF) signal input.
A single sideband phase modulated radio over fiber link with improved spurious-free dynamic range is propsed, in which an optical processor is used for IMD3 suppression. A theoretical analysis is presented and the simulation experiment results indicate that the SFDR is up to 126.3 dB·Hz4/5.
We propose a fiber Bragg grating sensor interrogation system based on a Fourier domain mode-locked optoelectronic oscillator (FDML-OEO). The FDML is achieved by synchronizing the period of the driving current of the laser with the round-trip time of the OEO loop. By employing a narrow band electrical filter with the central frequency located within the sweeping frequency of the FDML-OEO, pulsed microwave output can be obtained. The wavelength shift of the phase-shift fiber Bragg grating (PS-FBG) can be interrogated by measuring the pulse interval variation. The experimental results indicate that the pulse interval of the generated signal has a linear relationship with the axial strain applied to the PS-FBG and a sensitivity as high as 0.42 μs/με is achieved.
A photonic approach to generate triangular frequency modulated microwave waveform (TFMMW) using frequency-scanning (FS) laser and dual-output dual-parallel Mach-Zehnder modulator (DO-DPMZM) is proposed and demonstrated. In the scheme, a DO-DPMZM followed by a time delayer and a polarization beam combiner is utilized to generate orthogonally polarized -1rst-order sideband and +1rst-order sideband with time delay. After that, a TFMMW with large time-bandwidth product (TBWP) can be generated by photoelectric balanced detection. In the simulation experiments, Ka band TFMMW with TBWP of 9830.4 is generated and its ambiguity function is investigated
A simple single sideband (SSB) analog optical link with enhancement spurious free dynamic range (SFDR) is proposed. By coupling the independent optical carrier and +1st, +2nd order phase-modulated optical sidebands to be demodulation, the suppression of IMD3 is achieved. An theoretical model is established and the simulation results show that the carrier-to-interference ratio (CIR) presents a 32dB improvement and the corresponding improved SFDR is 123.5 dB·HZ2/3 , which is 18.6 dB larger than that of conventional single sideband phase-modulated link. In particular, the proposed SSB link can avoid the periodic power attenuation caused by dispersion, presenting great potential usage in modern radar system.
Detecting targets with long distance and high resolution is the goal of radar techniques. Traditional electrical radar which has a long working distance always work at low frequency and thus has a limited bandwidth. We demonstrate a microwave photonic radar system which can realize larger bandwidth at low-frequency band based on optical-domain frequency operation. P-band and C-band radio-frequency (RF) signals with 700-MHz and 4-GHz bandwidths, respectively are generated, while the latter is adopted to detect space-separated corner reflectors to demonstrate the effectiveness of the proposed system.
An approach for photonic generation dual-chirp microwave waveform (DCMW) with frequency and bandwidth multiplication without filtering is proposed and demonstrated. A continuous-wave (CW) optical signal is sent to a polarization division multiplexing modulator. In the modulator, one part of the CW optical signal is modulated by the radio-frequency (RF) driving signals to generate ±2 nd-order single-frequency sidebands, while another one is modulated by the baseband chirped signals to generate ±2 nd-order chirped sidebands. After that, a frequency-doubled and bandwidth-quadrupled DCMW can be generated by photoelectric balanced detection. In the simulation experiments, by using a RF driving signal at 5GHz and a baseband single-chirp signal with bandwidth of 0.5GHz as the input electrical signals, a DCMW with central frequency of 10GHz and bandwidth of 2GHz is generated.
An optical length measuring method exploiting microwave interrogated cascaded fiber Mach-Zehnder interferometer (MZI) is proposed. The frequency response of the filter with respect to the fiber length change of MZI is studied and an length measuring sensitivity of 2.580 GHz/mm is obtained. The proposed sensing configuration is with high sensitivity, easy to implement and shows the capability for other parameters measurement such as temperature, strain, and vibration.
Generation of phase-coded chirped microwave waveforms by an improved frequency-sweeping optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. In the proposed system, an upgraded frequency-sweeping OEO has function to generate not only a linearly chirped microwave waveform (LCMW) but also to output an optical sideband and the latter is then modulated in phase by a binary phase-coded electrical signal. By beating the phase modulated signal and a portion of the frequency-sweeping laser light at a high-speed photodetector, a phase-coded chirped microwave waveform is generated. In order to realize large time-bandwidth product (TBWP), the key significance of the improved frequency-sweeping OEO is that a near-zero-dispersion single-mode-fiber (SMF) introduced into the loop which can not only avoid the limitation of high frequency oscillation caused by dispersion, but also construct long OEO delay loop to realize large time duration. Finally, phase-coded chirped microwave waveform with a bandwidth of 6 GHz and a TBWP of 130,392 is experimentally demonstrated.
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