In this paper, we propose a fiber link delay mismatch detection method for the fiber-optic phase-aligned transmission system of broadband microwave signals. Different from the conventional pulse time-of-flight method to solve the problem of periodic ambiguity for a sine signal, an adjustable frequency signal is adopted as the reference in the process of phase discrimination. The main frequency is employed to extract the fiber delay difference and its fluctuation within the corresponding period. Meanwhile, the auxiliary frequency is introduced to deal with the periodic ambiguity for the delays beyond one period. A proof of principle system with an equivalent 5 km outdoor transmission length is implemented to verify the feasibility and effectiveness of the proposed method. Broadband microwave signals received at eight antenna ends are transmitted to the central station through wavelength division multiplexing. At the central station, each link delay is obtained in turn from the incorporated reference frequency signal. Then, the phases of each broadband microwave signals are set in line by the corresponding adjustable optical delay lines. According to the experimental demonstration, the phase consistency is better than 8.68° for a 10 GHz transmitted frequency.
At present, the deficiency of large size and bad environmental adaption etc. hinders the engineering application of optoelectronic oscillator (OEO). By hybrid integration of photonic chips and electronic ones, a significantly miniaturized OEO with low phase noise is achieved and presented in this paper. Meanwhile, a frequency stabilization configuration based on hybrid optoelectronic phase locking is designed to improve the capability of environmental adaptation. Therefore, the OEO frequency can follow the external reference signal at real time and keep high stability as well. The performance for the OEO prototype with a volume of Φ100 mm×200 mm is investigated in detail. The spur suppression is over 70 dBc for the oscillation frequency of 10 GHz. And the phase noise of -145.9 dBc/Hz@10 kHz is reached.
For the true time delay (TTD) of optical fiber changes with temperature, integrated optical chips are proposed to improve the delay consistency among channels. A 5-bit TTD chip is proposed in this paper. By using cascaded switches and optical waveguides, the chip is switchable and wavelength independent. A beamforming system operating at 6GHz is established for demonstration. 7 beam directions covering ±15° is obtained with proper mainside lobe ratio.
Microwave photonic (MWP) based radio frequency (RF) channel is usually composed of three parts: microwave pre-processing part, electro-optical interconversion part and microwave post-processing part. The nonlinearity of active components causes serious harmonics at the output of MWP based RF channels. This paper mainly analyzes the harmonic distortions produced in the external-modulated optical transmission link and studies the variation of output harmonic power in the RF channel by changing the modulator bias point. According to the experiment, it is verified that the second harmonic can be effectively suppressed when the modulator is biased at high power point.
Microwave photonic mixer is a potential solution for wideband information systems due to the ultra-wide operating bandwidth, high LO-to-RF isolation, the intrinsic immunity to electromagnetic interference, and the compatibility with exsiting microwave photonic transmission systems. The spurious response of microwave photonic mixer cascading in series a pair of Mach-Zehnder interferometric intensity modulators has been simulated and analyzed in this paper. The low order spurious products caused by the nonlinearity of modulators are non-negligible, and the proper IF frequency and accurate bias-controlling are of great importance to mitigate the impact of spurious products.
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