Embodiments relate to an apparatus that includes: an input stage with an input Si slab height, an input Si waveguide height, and an input height difference between the input Si slab height and the input Si waveguide height; an output stage with an output Si slab height that is different from the input Si slab height, an output Si waveguide height that is different from the input Si waveguide height, and an output height difference between the output Si slab height and the output Si waveguide height that is different from the input height difference; and a transition stage positioned between the input stage and the output stage, wherein the transition stage has a transition Si slab height, a transition Si waveguide height, and a transition height difference between the transition Si slab height and the transition Si waveguide height. Other embodiments may be described and/or claimed.

Techniques for forming a facet optical coupler that includes a waveguide formed over a trench of a silicon substrate are described. The trench is formed in a silicon substrate and then filled with a dielectric material. The waveguide is patterned on the dielectric material over the trench such that the waveguide is disposed a distance from the first surface. A first end of the waveguide has a first size and a second end of the waveguide distal the first end has a second size different than the first size. A material of the waveguide and the first size define a mode size of the waveguide.

A bent taper is provided that includes one or more waveguide bends, at least one of which has a tapering waveguide width along at least a portion thereof. In one embodiment, the bent taper is an S-shaped bent taper that is configured as a TE0-TE1 mode convertor. Such a bent taper can be combined with a linear bi-layer taper configured as a TM0-TE1 mode converter to form a TM0-TE0 polarization rotator.

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 photonic device for converting optical modes of optical beams includes a first port to receive a first beam having a first mode, a mode converter and a second port to transmit the first beam. The mode converter is configured to broaden the first beam to convert the first mode into a second mode and narrow the broadened first beam at an output side of the mode converter, wherein the mode converter includes a guide material having a first refractive index and perturbation segments each having a second refractive index, wherein the first refractive index is greater than the second refractive index, wherein the perturbation segments are arranged in the guide material to cross the first beam.

A polarization splitter-rotator (PSR) is described. The PSR having a silicon nitride based waveguide including a first silicon nitride segment comprising a tapered width in a longitudinal direction and a ridge extending in a transverse direction and an adiabatic coupler coupled with the first silicon nitride segment.

Provided is an optical waveguide device including an optical waveguide, and a spot size converter connected to the optical waveguide, in which a propagation loss is further suppressed even in a case where an insulating layer covering the optical waveguide is disposed. An optical waveguide device includes an optical waveguide 2 formed on a substrate 1, and a spot size converter SSC that changes a mode field diameter of a light wave propagating through the optical waveguide in at least one end of the optical waveguide 2, in which an insulating layer IL that covers at least an upper surface of the optical waveguide is provided, and the insulating layer IL is continuously disposed to the spot size converter SSC along the optical waveguide.

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 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 photonic circuit including a structure of coupling to an external device, the structure including a main waveguide and at least two secondary waveguides, each secondary waveguide having a first portion substantially parallel to the main guide arranged in the vicinity of the main guide to perform an evanescent wave coupling between the main guide and the secondary guide, the first portion extending in a second portion having an end opposite to the first portion defining a coupling surface of the secondary guide, emerging at the level of an external surface of the circuit.