Ultrafast and ultrahigh-resolution optical vector analysis using linearly frequency-modulated waveform and dechirp processing

We propose and experimentally demonstrate an ultrafast and ultrahigh-resolution optical vector analyzer (OVA) using linearly frequency-modulated (LFM) waveform and dechirp processing. An optical LFM signal, achieved by modulating an electrical LFM signal on an optical carrier via carrier-suppressed optical single-sideband (OSSB) modulation, is separated into two portions. One portion (denoted as the reference signal) directly goes through the reference path, and the other (denoted as the probe signal) undergoes magnitude and phase changes by an optical device under test (DUT) in the measurement path. After balanced photodetection, the reference signal and the probe signal are mixed to perform a dechirp operation. A relatively low-frequency electrical signal is generated, which can be sampled by a low-speed analog-to-digital converter. As a result, the frequency responses of the DUT can be extracted at a high speed by post digital signal processing. Thanks to the large chirp rate of the electrical LFM signal and the dechirp processing, the proposed LFM-based OVA enables ultrafast measurement speed and ultrahigh frequency resolution. We perform an experiment in which a narrowband tunable optical filter is characterized. The measurement speed reaches 1 ns/point, and the frequency resolution is 1.6 MHz.