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 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.
Photonic generation approach of linearly chirped microwave waveform(LCMW) with tunable frequency and bandwidth multiplication factor(FBMF) based on parallel Mach-Zehnder modulator(MZM) is proposed. Theoretical analysis show that LCMW with FBMF of 4, 8 and 12 can be obtained by properly adjusting the amplitude of linearly chirped microwave drive signal and direct current(DC) drive signal. The scheme greatly reduce the frequency and bandwidth of electrical linearly chirped microwave drive signal. Due to no filter is employed, so the generation LCMW has a large frequency and bandwidth tunable range. Furthermore, the feasibility of the approach is demonstrated by the simulation based on OptiSystem platform.
KEYWORDS: Modulators, Microwave photonics, Modulation, Intermodulation, Phase shift keying, Radio optics, Single mode fibers, Signal attenuation, Phase modulation, Local area networks
A novel phase modulator-based microwave photonics link (MPL) with improved spurious-free dynamic range (SFDR) is proposed, in which a parallel optical sideband processing path is used to generate the opposite third-order intermodulation distortion (IMD3) for destructive combination. By controlling the magnitude of the generated IMD3 term via attenuator in one path, the suppression of IMD3 term was achieved. A theoretical analysis is presented and the simulation experiment results indicate that the SFDR is up to 128.582 dB•HZ2/3, which has an improvement of 23.66 dB compared with the nonlinearized link.
A Ka-band microwave photonic imaging radar demonstrator with 10.02 GHz-bandwidth is proposed and experimentally demonstrated. Continuous linear frequency waveform is optically generated in the transmitter and processed in the receiver. The range resolution of the demonstrator is tested to be 1.68 cm. Out-field tests while demonstrator works at inverse synthetic aperture radar (ISAR) and synthetic aperture radar (SAR) mode are carried out to image different targets.
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