A spot-size converter for coupling light between a first waveguide and a second waveguide extends along a longitudinal waveguiding axis and includes a transition region. The transition region includes a first part of waveguiding structure, which is coupled to the first waveguide, and a second part of waveguiding structure, which is coupled to the second waveguide. The second part of waveguiding structure includes high-index elements arranged in multiple vertically spaced rows and horizontally spaced columns, and extends along the longitudinal waveguiding axis at least partially over the first part of waveguiding structure so as to define a low-index region where the mode of the first waveguide progressively transforms into the mode of the second waveguide, thereby enabling light propagation via a mode of the combined system of the first and second parts of waveguiding structures.

A SOI bent taper structure is used as a mode convertor. By tuning the widths of the bent taper and the bend angles, almost lossless mode conversion is realized between TE0 and TE1 in a silicon waveguide. The simulated loss is <0.05 dB across C-band. This bent taper can be combined with bi-layer TM0-TE1 rotator to reach very high efficient TM0-TE0 polarization rotator. An ultra-compact (9 m) bi-layer TM0-TE1 taper based on particle swarm optimization is demonstrated. The entire TM0-TE0 rotator has a loss <0.25 dB and polarization extinction ratio >25 dB, worst-case across the C-band.

A waveguide mode expander couples a smaller optical mode in a semiconductor waveguide to a larger optical mode in an optical fiber. The waveguide mode expander comprises a shoulder and a ridge. In some embodiments, the ridge of the waveguide mode expander has a plurality of stages, the plurality of stages having different widths at a given cross section.

A low loss high extinction ratio on-chip polarizer is disclosed. The polarizer includes an input waveguide taper having an outer waveguiding region that widens in the direction of light propagation along at least a portion of the taper length, and a core waveguiding region that narrows in the direction of light propagation along at least a portion of the taper length, so as to selectively squeeze out light of undesired modes into the outer regions while preserving light of a desired mode in the waveguide core. An integrated light absorber/deflector may be coupled to the outer waveguiding regions.

A spot-size converter for coupling light between a first waveguide and a second waveguide extends along a longitudinal waveguiding axis and includes a transition region. The transition region includes a first part of waveguiding structure, which is coupled to the first waveguide, and a second part of waveguiding structure, which is coupled to the second waveguide. The second part of waveguiding structure includes high-index elements arranged in multiple vertically spaced rows and horizontally spaced columns, and extends along the longitudinal waveguiding axis at least partially over the first part of waveguiding structure so as to define a low-index region where the mode of the first waveguide progressively transforms into the mode of the second waveguide, thereby enabling light propagation via a mode of the combined system of the first and second parts of waveguiding structures.

Provided are a spot-size converter structure and a photonic device. The spot-size converter structure comprises: a first end face configured to be coupled to an integrated optical waveguide, and a second end face parallel to the first end face configured to be coupled to an optical fiber and. The spot-size converter structure comprises: a substrate; an isolation layer located on one side of the substrate; a waveguide layer located on one side of the isolation layer away from the substrate; and a covering layer located on one side of the waveguide layer away from the substrate and covering the waveguide layer.

Embodiments of the present disclosure are directed toward techniques and configurations for an optical coupler. In some embodiments, the device may include an optical waveguide to transmit light input from a light source. The optical waveguide may include a semiconductor layer, having a trench with one facet that comprises an edge formed under an approximately 45 degree angle and another facet formed substantially normal to the semiconductor layer. The edge may interface with another medium to form a mirror to receive inputted light and reflect received light substantially perpendicularly to propagate the received light. Other embodiments may be described and/or claimed.

A spot-size converter for coupling light between first and second waveguides respectively supporting first and second propagation modes having substantially different dimensions is provided. The spot-size converter includes a lower and an upper waveguiding structure each characterized by an effective refractive index. The lower waveguiding structure is coupled to the first waveguide to receive light therefrom or transmit light thereto in the first propagation mode. The upper waveguiding structure is coupled to the second waveguide to transmit light thereto or receive light therefrom in the second propagation mode. The upper waveguiding structure includes a plurality of longitudinally extending high-index elements arranged in multiple vertically spaced rows. At least part of the upper waveguiding structure extends at least partially over the lower waveguiding structure so as to define a coupling region wherein an effective refractive index crossing occurs, thereby enabling evanescent coupling of light between the lower and upper waveguiding structures.

A SOI device may include a waveguide adapter that couples light between an external light sourcee.g., a fiber optic cable or laserand a silicon waveguide on the silicon surface layer of the SOI device. In one embodiment, the waveguide adapter is embedded into the insulator layer. Doing so may enable the waveguide adapter to be formed before the surface layer components are added onto the SOI device. Accordingly, fabrication techniques that use high-temperatures may be used without harming other components in the SOI devicee.g., the waveguide adapter is formed before heat-sensitive components are added to the silicon surface layer.

A low loss high extinction ratio on-chip polarizer is disclosed. The polarizer includes an input waveguide taper having an outer waveguiding region that widens in the direction of light propagation along at least a portion of the taper length, and a core waveguiding region that narrows in the direction of light propagation along at least a portion of the taper length, so as to selectively squeeze out light of undesired modes into the outer regions while preserving light of a desired mode in the waveguide core. An integrated light absorber/deflector may be coupled to the outer waveguiding regions.