Research on Ultra-Fast Optical Vector Analysis Based on Microwave Photonic Frequency Sweeping

An ultra-fast and high-resolution optical vector analysis scheme has been proposed and experimentally demonstrated. In the scheme, a broadband optical frequency-sweeping signal is generated by injecting a linearly frequency-modulated signal into one radio-frequency (RF) port of a dual-drive Mach-Zehnder electro-optic modulator, which is used to achieve fast scanning of the frequency response characteristic of the device under test (DUT). A single-tone microwave signal is injected into the other RF port of the modulator to realize down-conversion of the frequency-sweeping signal. The down-converted signal is then digitized by an analog-to-digital converter, and is processed through Hilbert transform to extract the amplitude- and phase-frequency response of the DUT. In the proof-of-concept experiment, the amplitude- and phase-frequency response of the Brillouin gain in a section of non-zero dispersion shifted fiber with a length of 3 km is accurately measured, where the measurement time is only 20 μs, and the frequency resolution reaches 20 kHz.