Heterodyne Light Source Using Two Tandem Acousto-Optic Modulators Under Bragg Diffraction Conditions

We propose a novel heterodyne light source architecture employing two tandem acousto-optic modulators (AOM) operating under Bragg-diffraction conditions. A mirror and a half-wave plate are strategically positioned between the AOMs. By fine-tuning the angle of the mirror relative to the AOMs, only the +1st- or −1st-order light is generated, allowing the two light beams to coincide. The beat frequency is determined by the difference in modulation frequencies. In order to demonstrate the feasibility of this architecture, we use this light source in common-path heterodyne interferometry (CPHI) to measure the gold film thickness of a surface plasmon resonance (SPR) sensor. The experimental results are in good agreement with the outcomes of mathematical simulations.