Beam steering using delays generated from an optical OAM mode shifting recirculating loop

Abstract

This paper investigates the performance of generated delays from an orbital angular momentum mode shifting recirculating delay loop (OAM-SL) in simulation using Kirchhoff-Fresnel diffraction (KFD) and the delays applicability for RF signal beam steering applications. OAM-SL is a novel structure that has been recently reported to produce multiple delayed signal replicas on independent OAM carriers using a single compact system. The objective of this research is to explore the impact of several limiting factors on the quality of OAM-SL delays for beam steering applications, such as where there is (i) displacement of the OAM mode shifter, (ii) displacement of the center of the OAM mode demultiplexer at the loop output, and (iii) the limited resolution. The methodology includes: (i) simulating the beam propagation using KFD, (ii) producing the output as a coherent summation of the recirculating beams, and (iii) characterizing the SCR by dividing the power of the recirculating beam (ρ) on its OAM mode by the power accumulated from the other recirculating beams. Our findings show that delays generated from a system with lin=−30, lshift=+1, and a resolution of 1024 pixels can steer a 100 MHz signal at a steering angle of 11.5° in a four antenna system with 0.1° error if loop alignment is perfect. Also, for steering the 100 MHz signal in an eight antenna system, we analyze the system assuming the system loss can be compensated, and a similar result of 0.1° error is obtained. Additionally, we report the beam steering performance at 23.6° and 36.8°.