Optical coupler with different waveguide materials

An apparatus comprising:

• a first layer comprising silicon;
• a second layer comprising silicon and nitrogen, the second layer on the first layer, wherein the second layer has a first axis that defines a first end and a second end of the second layer;
• and
• a third layer comprising silicon, the third layer on the first layer, wherein the third layer has a second axis that defines a first end and a second end of the third layer, and wherein the first end of the second layer is adjacent to the first end of the third layer, and wherein the first axis and second axis are at a non-zero first angle to one another, wherein the first end of the second layer terminates at a non-zero second angle from a plane that is orthogonal to the first axis, and wherein the non-zero first angle and the non-zero second angle are related to one another based on modal effective indices of a plurality of modes.

An optical coupler comprising:

• a silicon substrate;
• a silicon waveguide separated from the silicon substrate by an oxide layer, wherein the oxide layer has a first thickness between the silicon substrate and the silicon waveguide;
• and
• a silicon nitride waveguide configured to receive an optical signal from an optical source and output the optical signal to the silicon waveguide, wherein the silicon nitride waveguide includes:
• a first portion, wherein the first portion is separated from the silicon substrate by the oxide layer, and wherein the oxide layer has a second thickness between the silicon substrate and the first portion of the silicon nitride waveguide;
• and
• a second portion adjacent to the silicon waveguide, wherein the second portion is separated from the silicon substrate by the oxide layer, and wherein the oxide layer has the first thickness between the silicon substrate and the second portion of the silicon nitride waveguide, wherein the silicon nitride waveguide and the silicon waveguide are configured to guide the optical signal along respective axes that are at a non-zero first angle to one another, wherein an output end of the silicon nitride waveguide terminates at a non-zero second angle from a plane that is orthogonal to an axis of the silicon nitride waveguide, and wherein the non-zero first angle and the non-zero second angle are related to one another based on modal effective indices of a plurality of modes of the optical signal.