Self-calibrated optical vector analyzer with a largely extended measurement range based on linearly frequency-modulated waveform and recirculating frequency shifter

We propose and experimentally demonstrate a novel method to realize an optical vector analyzer (OVA) with a largely increased measurement range based on linearly frequencymodulated (LFM) waveform and a recircuiting frequency shifter (RFS) loop. An optical LFM signal is sent into an RFS loop to extend its frequency range by circulating in the loop. At the output of the RFS, the frequency-extended optical LFM signal is launched into a Mach-Zehnder interferometer (MZI1) with the device under test (DUT) incorporated in one arm and a delay line in the other arm. By beating the optical signals from the MZIs at a pair of balanced photodetectors, low-frequency signals are generated, from which the frequency responses of the DUT can be extracted using post-digital signal processing. To eliminate the unwanted influence from the measurement system, another MZI (MZI2) sharing the delay line arm with the MZI1 is used for system self-calibration. Thanks to the largely extended frequency range of the optical LFM signal with the use of the RFS loop, the measurement range of the OVA is highly increased. As a proof of the concept, an experiment is performed in which the magnitude and phase responses of a narrow-band fiber ring resonator (FRR) and a hydrogen cyanide (HCN) gas chamber are measured with the proposed OVA. The measurement results show that a measurement range as broad as 418 GHz and a frequency resolution as high as 0.5 MHz are achieved with a measurement time as short as 400 μs. The key advantages of the proposed OVA include a largely extended measurement range, high measurement speed and high resolution.