We propose a compact, high extinction ratio, and low-loss polarization beam splitter (PBS) on a lithium-niobate-on-insulator (LNOI) platform, based on an asymmetrical directional coupler and using a silicon nitride nanowire assisted waveguide (WG) and a grooved WG. By properly designing nanowires and grooved LN WGs, TE polarization meets the phase matching condition, while significant mismatching exists for TM polarization. Numerical simulations show that the PBS has an ultra-high extinction ratio (ER) of and (larger than 40 dB and 50 dB, respectively). The device extinction ratios are larger than 10 dB over 100 nm wavelength ranges. Moreover, the device has an ultra-low insertion loss (IL less than 0.05 dB) at the wavelength of 1550 nm and maintains ILs less than 0.4 dB over 100 nm wavelength ranges.
A simple photonics-based dual-channel system is proposed to simultaneously measure the Doppler frequency shift (DFS) and angle of arrival (AOA) of microwave signals. The system applies two parallel push–pull Mach–Zehnder modulators (MZMs) for carrier suppression dual-sideband (CS-DSB) modulation. The introduction of the reference signal results in a DFS measurement without direction ambiguity. The DFS can be determined by measuring the frequency of the down-converted intermediate frequency (IF) signal, and the AOA can be calculated by comparing the phase shift of the two channels. A proof-of-concept experiment shows that the DFS measurement error is less than 0.4 Hz during ±100 kHz, and the AOA measurement error is within 1.5° in a range of 0–70°.
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