The rapid development of integrated photonic circuits demands for a technique to extract the magnitude and phase responses of the optical devices with ultrahigh resolution. Several methods, such as the modulation phase-shift approach and the interferometry approach, were proposed, which have a resolution of tens or hundreds of MHz. However, the bandwidth of the narrowest fiber Bragg grating (FBG) fabricated to date is below 9 MHz, and the Q-value of the optical micro-resonators has reached 6×10^10. To obtain sub-MHz measurement resolution, an optical vector analysis (OVA) based on microwave photonics to measure the phase and magnitude responses of the optical devices was proposed. With the electrical-to-optical and optical-to-electrical conversions, the relatively low-resolution laser wavelength sweeping in the optical domain can be replaced by ultrahigh resolution microwave frequency sweeping in the electrical domain. The measurement resolution of the OSSB-based OVA reaches 78 kHz in experiment and several hertz in theory.
In this paper, the most recent works for extending the measurement range, increasing the measurement accuracy and enlarging the dynamic ranges of the microwave-photonics-based OVA are reviewed. An optical frequency comb (OFC) is used to extend the measurement range by segmental measurement, and the measurement errors caused by the high-order sidebands are eliminated by introducing a frequency shift to the optical carrier or adding a phase change to the sidebands in the left and right sides of the optical carrier. A prototype of the OVA was built, which was used for high-fineness devices fabrication, high-precision optical sensing, and on-chip optical signal processing. The prospective of this technique is discussed.