On-chip multi-beam frequency shifter through sideband separation

Abstract

In this paper, we introduce a novel method to realize a multi-beam optical frequency shifting component for photonic integrated circuits, utilizing an array of parallel optical modulators and a free-propagation region (FPR), such as a slab waveguide-based star coupler. This component generates multiple optical beams with different frequency shifts, making it suitable for various systems, such as multi-beam laser Doppler vibrometry (LDV). We thoroughly elaborate on the working principle of the component through theoretical analysis and demonstrate that by applying periodic wave-like modulation in the modulator array, the discrete harmonic content of the light can be selectively directed to different outputs based on the delay between consecutive modulators. A design comprising a 16-element modulator array and 5 outputs will be presented. Simulations show that this design can generate and collect 5 different harmonics (-2, -1, 0, +1, +2) in the different outputs with a side band suppression ratio of 20 dB to 30 dB for each output. Our proposed design is just one possibility and the component can be modified and optimized for specific applications.