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.

Operation Diagram
Operation Diagram

Our Approach

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
Device Design
Device Design

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