Beam Steering for Terahertz Time-Domain Spectroscopy Using Optical Ring Resonators

In this work, we circumvent the bandwidth limitation of an optical ring resonator (ORR) as a delay element by exploiting the periodicity of its group delay response and simulate wideband beam steering for terahertz time-domain spectroscopy (THz-TDS) driven by a mode-locked laser diode (MLLD). First, we derive the transfer matrix of a Mach-Zehnder modulator-based ORR and calculate the delays that the ORRs in the photonic beam steering network introduce to the individual laser modes. Second, we use the delayed laser pulses in a simulation of a ten-element array. In the simulation, the resulting terahertz beam is successfully steered in the desired direction without any beam squint across a bandwidth of 1 THz.