Monolithically-integrated, polarization-independent circulator

A method for an optical isolator and/or circulator, the method comprising:

• receiving light at a first port from a laser, wherein the first port is part of a first coupler, wherein:
• the first coupler is part of a first splitter;
• and
• the first splitter comprises the first coupler, a second coupler, a first waveguide between the first coupler and the second coupler, and a second waveguide between the first coupler and the second coupler, wherein:
• the first waveguide has a maximum cross-sectional width that is less than a maximum cross-sectional width of the second waveguide;
• the maximum cross-sectional width of the first waveguide and the maximum cross-sectional width of the second waveguide are measured in a direction orthogonal to a direction of beam propagation and halfway between the first coupler and the second coupler;
• and
• the maximum cross-sectional width of the first waveguide is less than a height of the first waveguide;
• splitting, using the first coupler, received light from the first port into the first waveguide and the second waveguide;
• receiving, at the second coupler, light from the first waveguide and the second waveguide;
• transmitting light, received by the second coupler, into a first path and a second path, wherein:
• a first non-reciprocal polarization rotator is in the first path between the first splitter and a second splitter;
• a first reciprocal polarization rotator is in the first path between the first splitter and the second splitter;
• a second non-reciprocal polarization rotator is in the second path between the first splitter and the second splitter;
• a second reciprocal polarization rotator is in the second path between the first splitter and the second splitter;
• receiving light from the first path and the second path, at the second splitter, wherein the laser, the first coupler, the second coupler, the first waveguide, the second waveguide, the second splitter, the first non-reciprocal polarization rotator, the first reciprocal polarization rotator, the second non-reciprocal polarization rotator, and the second reciprocal polarization rotator are integrated on a semiconductor substrate;
• and
• combining, at the second splitter, light received from the first path and from the second path to exit a second port.

A device for an optical isolator and/or circulator, the device comprising:

• a laser;
• a first splitter comprising:
• a first coupler configured to receive light from the laser at a first port and split light received at the first port into a first waveguide and a second waveguide;
• a second coupler configured to:
• receive light from the first waveguide and from the second waveguide;
• and
• transmit light received from the first coupler by the first waveguide and the second waveguide to propagate along a first path and along a second path;
• the first waveguide;
• and
• the second waveguide;
• and
• a second splitter configured to:
• receive light from the first path and from the second path;
• and
• combine light received from the first path and from the second path to exit a second port, wherein:
• the first waveguide has a maximum cross-sectional width that is less than a maximum cross-sectional width of the second waveguide;
• the maximum cross-sectional width of the first waveguide and the maximum cross-sectional width of the second waveguide are measured in a direction orthogonal to a direction of beam propagation and halfway between the first coupler and the second coupler;
• and
• the maximum cross-sectional width of the first waveguide is less than a height of the first waveguide.