Simultaneous Measurement of AOA and Frequency Based on Stimulated Brillouin Scattering and Frequency-to-Time Mapping

A photonic system for simultaneous measurement of angle-of-arrival (AOA) and frequency based on stimulated Brillouin scattering and frequency-to-time mapping is proposed and experimentally demonstrated. A continuous-wave light is firstly modulated by microwave signals received from antennas with unknown AOAs and frequencies. A frequency-sweeping signal is modulated onto the light using carrier-suppressed single-sideband modulation, serving as a frequency-sweeping optical probe. Another laser diode is introduced as the Brillouin pump source and a coil of single-mode fiber is employed as the Brillouin gain medium. During the period when the gain spectrum is overlapped by the frequency-sweeping sideband of the probe wave, a pulse is generated in the time domain. The frequencies and AOAs are mapped onto the time positions and peak amplitudes of the pulses, consequently. The time ambiguity can be avoided by introducing a reference RF signal. The proposed system can avoid the RF power fading induced by dispersion and double-sideband modulation and is suitable for scenarios with separated remote antenna units and central offices. In the experiment, frequency measurement covering 11-17 GHz with a maximum error of 8 MHz and AOA measurement covering -69.0 degrees to +69.0 degrees with a maximum error of 2.5 degrees are realized. The primary advantage of our proposed approach lies in its ability to simultaneously measure the AOAs and frequencies of multiple signals with a tunable frequency range.