Ultrahigh-resolution optical vector analysis using fixed low-frequency electrical phase-magnitude detection.

An ultrahigh-resolution optical vector analyzer (OVA) is proposed and experimentally demonstrated based on microwave photonic frequency downconversion and fixed low-frequency electrical phase-magnitude detection. In the proposed OVA, two optical single-sideband (OSSB) signals are generated by two RF signals with a fixed frequency spacing. One propagates through an optical device under test (DUT) and is then combined with the other before entering to a low-speed photodetector. By photodetection, a low-frequency and frequency-fixed photocurrent carrying the spectral responses is achieved. Hence, a low-frequency electrical phase-magnitude detector is sufficient to extract the magnitude and phase. Sweeping the frequency of the RF signals, the spectral responses of the DUT can be obtained. As compared with the conventional OSSB- and optical double-sideband-based OVA, the proposed OVA avoids the use of high-speed photodetection and broadband electrical phase-magnitude detection. In addition, it is inherently immune to the measurement errors induced by high-order sidebands and has the capability of measuring arbitrary spectral responses. In an experiment, the proposed OVA is implemented based on an electrical phase-magnitude detector working at 10 MHz. The measurement resolution is 1 MHz, and the measurement range is larger than 45 GHz.