Fig. 4: Si3N4 optical isolator via spatiotemporal modulation.
From: Hybrid integrated photonics using bulk acoustic resonators
a Schematic showing directionally dependent coupling between two optical modes a and b in ω–k space, induced by a rotating modulation wave. b In the forward direction, light transmits at resonance due to mode splitting from the strong coupling between modes a and b. Light in the backwards direction, however, will be absorbed due to phase mismatch and inefficient mode coupling. c Simplified schematics of measurement setup. The inset is the optical microscopy image of the fabricated device. Three AlN piezoelectric actuators are driven with fixed phase differences, generating a synthetic circulating wave along the ring. FPCs control the polarization of input and output light, and the polarization beam splitter (PBS) filters out unwanted modulation sidebands. d Optical transmission showing one pair of TE and TM resonant modes that are closely spaced by only 3.36 GHz. e Optical transmission of TE mode in forward and backward directions (with respect to off-chip input laser of −3 dBm) under +36 dBm RF driving. A 17 dB isolation is achieved at resonance with a bandwidth of 1 GHz.
