Wideband optical vector network analyzer based on polarization modulation

We propose a polarization modulator (PolM) -based optical vector network analyzer (OVNA) with extended measurement bandwidth. The combined use of the PolM, a polarization controller (PC) and a polarizer performs phase-and-intensity hybrid modulation of optical signal with double-sideband (DSB) modulation. The ratio between phase and intensity modulations is controlled by the PC, leading to different modulation formats. The frequency response of a device-under-test (DUT) can be obtained by processing the results of two measurements under two arbitrarily different modulation formats. The significance of this work lies in that the measurement of a DUT with bandpass response can be simply achieved, which is a huge challenge for the conventional single-sideband (SSB)-based OVNAs. In addition, the measurement bandwidth is doubled compared with the conventional SSB-based OVNA. Moreover, the PolM-based OVNA can avoid the bias drifting problem using conventional Mach-Zehnder modulator (MZM)-based scheme. The proposed method is theoretically and experimentally demonstrated. A proof-of-concept experiment is carried out and a DUT with bandpass response is successfully measured using the proposed scheme.