Non-magnetic optical isolator
Approaches to a 3-port circulator / optical isolator require breaking optical reciprocity. One technique involves leveraging an intrinsic magnetic response in a material using the magneto-optic effect, requiring permanent magnets or a current loop: neither of which are compatible with low loss Si3N4 processes. We explore isolation based on a discrete spatial-temporal index modulation of three coupled high-Q Si3N4 low-loss rings using stress induced modulation. Aluminum nitride (AlN) and PZT type piezoelectric actuators are fabricated in order to tune the optical resonances.
An index modulation Δε is implemented in a ring, which normally has degenerate modes. The modulation imposes an effective spin to the ring resonator, with angular velocity, breaking reciprocity by introducing an asymmetric phase shift for counter propagating modes.
- High-Q, coupled cavities give high isolation
- Distributed design decouples RF drive frequency requirements from ring FSR
- Low through loss using Si3N4
- Planar wafer-scale waveguide fabrication platform with under etching
Waveguide and 3-Ring Design
- AlN as stress-optic material for piezo phase tuning of the resonator
- PZT as an alternative
- Can tune optical wavelength by 2 pm with 3 nW
- Can achieve blue- and red-tuning of optical resonance
- CMOS compatible