Phased array radar has important applications in military and civil fields. In order to improve the performance of radar systems, there is a growing demand for increased the signal bandwidth. However, with the larger bandwidth, the traditional phased array system based on microwave phase shifter will have obvious beam squint phenomenon when realizing beam pointing adjustment. Hence, the microwave photonic broadband phased array with the core of light-controlled microwave technology has become a much-appreciated realization of broadband phased array. For the beam squint phenomenon caused by broadband signals, this paper proposes a scheme of using the true time delay introduced by a continuously tunable Mach-Zehnder interferometer for compensation in optical domain. Four different bandwidth with different center frequencies were designed and validated to achieve a squint free beamforming within the scanning angles of ±30°.
In this paper, we propose and demonstrate a novel Tilted Fiber Bragg grating (TFBG) sensing demodulation scheme based on microwave photonic technique. In the proposed approach, the optical power spectrum from BBS (Broadband source) is shaped by a TFBG and then sent to a dispersive element to perform the linear wavelength-to-time mapping. A nonuniform microwave photonic filter with the center frequency depending on the shaped optical spectrum is obtained at the output of a high-speed photodetector. The central frequency and the envelope of the generated microwave photonic filter will shift according to the change of environment. Theory and a proof-of-principle experiment are implemented to verify the proposed approach.
A compact dual-loop optoelectronic oscillator (OEO) employing a dual-output Mach–Zehnder intensity modulator (DOMZM) and a balanced photodetector (BPD) is theoretically analyzed and experimentally demonstrated. The fundamental idea of the scheme is based on double loops formed by two complementary output ports of DOMZM and two input ports of BPD, which could be naturally combined without any additional optical coupler or polarization beam splitter devices. This simple structure makes it possible to enhance side-mode suppression ratio (SMSR) and reduce phase noise of the OEO. Compared with the traditional dual-loop OEO (SO-OEO) based on single-output Mach–Zehnder modulator (MZM), optical coupler, and BPD, the advantages of our proposed dual-loop OEO (DO-OEO) with DOMZM and BPD are presented. Experimental results show that a 16-GHz single-mode OEO is obtained with measured SMSR of 72 dB and phase noise of −133.2 dBc/Hz at 10-kHz frequency offset.
A microwave photonic link (MPL) with spurious-free dynamic range (SFDR) improvement utilizing the nonlinearity of a distributed feedback (DFB) laser is proposed and demonstrated. First, the relationship between the bias current and nonlinearity of a semiconductor DFB laser is experimentally studied. On this basis, the proposed linear optimization of MPL is realized by the combination of the external intensity Mach–Zehnder modulator (MZM) modulation MPL and the direct modulation MPL with the nonlinear operation of the DFB laser. In the external modulation MPL, the MZM is biased at the linear point to achieve the radio frequency (RF) signal transmission. In the direct modulation MPL, the third-order intermodulation (IMD3) components are generated for enhancing the SFDR of the external modulation MPL. When the center frequency of the input RF signal is 5 GHz and the two-tone signal interval is 10 kHz, the experimental results show that IMD3 of the system is effectively suppressed by 29.3 dB and the SFDR is increased by 7.7 dB.
A novel optical single-sideband (OSSB) signal generation with simultaneous IF signal up conversion technique is proposed to overcome the fiber dispersion problem. With this up-conversion technique, a high frequency OSSB signal is generated by using two low bandwidth intensity modulators in combination with fiber gratings. The low frequency local oscillator (LO) signal is modulated by employing frequency doubling technique or frequency quadrupling technique respectively. The OSSB radio frequency (RF) signal generated by mixing the intermediate frequency (IF) signal and low frequency local oscillator (LO) signal, is transmitted over standard single-mode fiber successfully. The received signal error vector magnitude (EVM) is 5.8% rms and 13% rms.
KEYWORDS: Signal generators, Singular optics, Modulators, Modulation, Radio optics, Single mode fibers, Microwave radiation, Eye, Signal detection, Optical amplifiers
A novel method is proposed for optical up-converted single-sideband (OSSB) signal generation in radio over fiber links, which can realize optical carrier reuse synchronously. The OSSB signal is generated in order to overcome the fiber dispersion problem by using two intensity modulators in combination with fiber gratings. With this up-conversion technique, a 25 GHz OSSB radio frequency signal is generated by mixing an intermediate frequency signal (5 GHz) and low frequency local oscillator signal (10 GHz). The signal is transmitted over 25 km standard single-mode fiber successfully. And the received signal error vector magnitude is 5.8% root mean square, with eye diagram widely open.
KEYWORDS: Microwave radiation, Single mode fibers, Time division multiplexing, Optical amplifiers, Optical switching, Dispersion, Switches, Modulators, Signal detection, Signal attenuation
We propose a novel photonic technique for unknown microwave frequency measurement by employing an optical group delay line. The 7-bit optical delay line composed of several magneto-optical switches and 1.6 km single-mode fiber is designed as a tunable dispersive medium in the measurement system. In our scheme, the measurable frequency range of 1 to 20 GHz with a measurement error less than ±40 MHz was demonstrated experimentally. Also, we studied the sensitivity of the whole measurement system, and the minimum detectable power reached −50 dBm .
A novel technique for instantaneous frequency measurement of unknown microwave signal based on both phase
modulation and intensity modulation is theoretically and experimentally demonstrated. Based on the output microwave
power through dispersive fiber links, three amplitude comparison functions (ACFs) are established, which are combined
to measure the frequency of input microwave signal with improved measurable range and accuracy. In the frequency
estimation process, the measured calibration ACFs are utilized as the look-up table. The experiment results show that
measurement error smaller than 200 MHz can be obtained for the frequency from 0.5 GHz to 20 GHz.
A novel photonic approach for measuring microwave frequency over a wide bandwidth, based on intensity-modulated link with output microwave interference detection, is proposed. In this simple measurement system, a tunable laser and a fixed-wavelength laser are used with a single-mode fiber as the dispersive medium. By scanning the wavelength of a tunable laser, the frequency of the modulated microwave signal can be obtained directly through analyzing the interference intensity of the microwave signal at the output of the photodetector. The proposed approach is demonstrated experimentally by obtaining the unknown microwave frequency in the range of 1 to 20 GHz with a measurement accuracy of several tens of MHz.
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