High-resolution microwave photonic vector analyzer with low-frequency splitting of probing signal

Variants of high-resolution microwave photonic vector analyzer based on the modulation splitting of the optical probing frequency into a small fixed value of the MHz range and the amplitude-phase determination of the device under test spectrum by the parameters of the radio signal on the specified frequency after photo detection are proposed and experimentally demonstrated. In the proposed OVA, either a two-frequency optical single-sideband signal (OSS) with a fixed low splitting frequency, or an optical double-sideband signal (DSS) is formed, consisting of two split components for probing the DUT, respectively, of arbitrary and symmetrical shapes. In both cases, the probing radiation is divided into two channels, the first of which is measuring, the radiation propagates through the DUT, the second is the reference one, the radiation is taken from the DUT input. The output radiation of the channels is fed to the inputs of a balanced photo detector. The frequency of the optical carrier when analyzing a DUT of an arbitrary shape must be outside its spectrum, and in the case of a DUT of a symmetrical shape, at its center frequency. By tuning the frequency of the subcarrier, which lies in the spectrum band of the DUT, and in the process of generating probing signals, as well as the carrier, it is suppressed, it is possible to obtain the spectral characteristics of the DUT with high resolution. For this purpose, after the photodetector, the low-frequency signal and the signal fixed at the splitting frequency is processed in the corresponding low-frequency electronic amplitude-phase detector. Thus, in comparison with the known single-sideband and two-side OVA, the proposed analyzer uses a low-frequency element base, which significantly reduces its cost. In the experiment, both versions of OVA (with a splitting frequency of 5 MHz and a laser linewidth of 50 kHz) were implemented. The subcarrier frequency tuning in the symmetrical OVA was carried out in steps of 0.5 MHz, which determined its resolution in the range up to 20 GHz (40,001 points).