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光学工程
一种基于光子学技术的微波频率测量方法

Novel photonic approach to microwave frequency measurement using tunable group delay line

A photonic approach for measuring microwave frequency over a wide bandwidth is proposed. An optic group delay line composed of several magneto-optical switches and a 1.6-km single-mode fiber is used as a tunable dispersive medium in the measurement setup. A minimum frequency accuracy of 80 MHz in the range of 1–20 GHz is achieved experimentally.

   OCIS codes: 130.0250, 350.4010, 060.5625.

   doi: 10.3788/COL201109.081301.

    The photonic technique has been considered an alternative approach to processing radar signals in electronic warfare[1]. The optical processing of microwave signals offers more advantages over conventional electronic systems, such as reduction of device size and weight, increase in signal bandwidths, low loss, and immunity to electromagnetic interference. One of the basic applications of this technique is microwave frequency measurement. Previously, a tunable Fabry-Perot interferometer was used for microwave frequency measurement[2]. In the last few years, several other experimental approaches based on amplitude comparison function were developed for measuring the frequency of a microwave signal[3?7] . Some of these methods suffer from the measurement range restriction[5,6]. Microwave frequency measurement was also attained by analyzing the photodetector direct current (DC) voltage[8] and photonic Hilbert transform[9]. The measurement accuracy of these methods can be achieved from several megahertz to tens of megahertz over a wide frequency range. Recently, a measured error within ±400 kHz over a narrow band has been realized[10]. However, the measurement systems often use a tunable laser source and tens of kilometers of single-mode fibers (SMF) or photonic filters, making these systems costly, bulky, complex, and unsuitable for some applications.

   A novel photonic approach for measuring microwave frequency has been proposed recently[11]. A phase difference of the two optical carriers with the same microwave signal is induced by chromatic dispersion. By tuning one of the optical wavelengths, the interference microwave power of the two signals is tuned per