Ultrahigh-resolution optical vector analyzer for multiple parallel measurements based on frequency-domain analysis

An ultrahigh-resolution optical vector analyzer (OVA) is reported for multiple parallel measurements based on frequency-domain analysis (FDA). In the proposed system, an optical linearly frequency modulated waveform generated via electro-optic modulation and optical injection locking is launched into an unbalanced Mach-Zehnder interferometer (MZI), in which multiple devices under test (DUTs) are cascaded with different time delays in one arm and a delay reference line in the other arm. The optical signals from the two arms of the MZI are sent to a balanced photo-detector, where a series of electrical signals with different frequencies is generated. With the use of the FDA, the optical spectral response of the DUTs can be separately extracted from the generated electrical signals. An experimental demonstration is performed, in which the frequency responses of a hydrogen cyanide (HCN) gas cell, a phase-shifted fiber Bragg grating, and an optical reflector are characterized simultaneously. The measurement results show that the proposed OVA has a simultaneous characterization capacity of multiple devices at a frequency resolution as high as 200 kHz, a measurement time as short as 490 µs, and a frequency measurement range as wide as 18.5 GHz.