A compact polarization beam rotator includes a converter waveguide comprising a first segment and a second segment both in corresponding taper rib shapes sharing a first middle plane and configured to receive an input optical signal with TM polarization mode from an input plane and convert the TM polarization mode to TE1 polarization mode comprising a first arm mode and a second arm mode at a second middle plane. The polarization beam rotator additionally includes a splitter waveguide coupled to the second middle plane for separating the first arm mode and the second arm mode at a third plane respectively coupled to a first branch waveguide to deliver the first arm mode in phase and a second branch waveguide to reverse the second arm mode phase by 180, and a 21 MMI coupler waveguide to combine both arm modes in phase to an output optical signal with TE polarization mode.

A polarization mode converter includes a rectangular waveguide, a first tapered waveguide, and a second tapered waveguide. A height of the rectangular waveguide is a first height (H1). A side of the first tapered waveguide is coupled to the rectangular waveguide. A width of the first tapered waveguide changes gradually. A height of the first tapered waveguide is a second height (H2), and H2 is less than H1. The second tapered waveguide is detached from the rectangular waveguide and the first tapered waveguide. A width of the second tapered waveguide changes gradually. A height of the second tapered waveguide is H1. The first tapered waveguide is located between the rectangular waveguide and the second tapered waveguide.

An optical waveguide adapter assembly comprises a solid core optical waveguide extending between a free end and a coupled end and having a solid waveguiding core with an associated first optical mode field size; a hollow core optical waveguide extending between a free end and a coupled end and having a hollow waveguiding core with an associated second optical mode field size; and an optical mode field adapter extending between a first end and a second end and having a waveguiding core configured to change an optical mode field of a waveguided optical signal substantially between the first optical mode field size at the first end of the optical mode field adapter and the second optical mode field size at the second end of the optical mode field adapter.

An apparatus includes a first coupler configured to input input light through an input waveguide and branch the input light into first and second branch waveguides; a second coupler configured to combine the first and second branch waveguides and to output the output light through an output waveguide; a phase adjuster having a birefringent property, provided to the second branch waveguide; and a polarization converter having a birefringent property, provided to the output waveguide and configured to, when reflected light corresponding to the output light is input to the output waveguide, convert a polarization state of the reflected light such that a first part of the reflected light for traveling through the first path and a second part of the reflected light for traveling through the second path are in antiphase at the input waveguide.

An optical waveguide coupler is provided that includes an InP substrate, a guiding core layer disposed on the InP substrate, a top cladding layer disposed on the guiding core layer, where the guiding core layer and the top cladding layer are disposed in a photosensitive housing waveguide, and a mode coupling region having a lateral taper of the guiding core layer and the top cladding layer disposed above a region where the InP substrate is at least partially removed to create an air-cladding, where a low-to-high refractive index contrast transition (RICT) InP-based waveguide device is established to minimize light leakage into the InP substrate.

A functional optical device is disclosed. The optical functional device integrates a coupling unit, a light-receiving element and an optical waveguide on a semiconductor substrate. The coupling unit extracts an optical signal by interfering between signal light and local light. The optical waveguide carries the optical signal from the coupling unit to the light-receiving element. The light-receiving element receives the optical signal. The semiconductor substrate provides a heavily doped conducting layer and a buffer layer that is un-doped or lightly doped with impurities by density smaller than density of impurities in the conducting layer. The conducting layer and the buffer layer continuously and evenly expand from the optical waveguide to the light-receiving element.

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 spot-size converter having a waveguiding structure. The first part of the waveguiding structure receives light from or transmits light to a first waveguide in a first propagation mode. The first part of the waveguiding structure has a longitudinally varying effective refractive index that decreases away from the first waveguide. The second part of the waveguiding structure transmits light to or receives light from a second waveguide in a second propagation mode. The second part of the waveguiding structure has a number of high-index elements arranged in a single plane, extending along a longitudinal waveguiding axis and at least partially overlapping the first part of the waveguiding structure. The first propagation mode of the first waveguide progressively transforms into the second propagation mode of the second waveguide along the longitudinal waveguiding axis through an overlap region between the first part and the second part of the waveguiding structure.

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 photonic polarizing beamsplitter is disclosed. The beamsplitter comprises a first waveguide, a second waveguide located above the first waveguide, and a birefringent coupler between the first waveguide and the second waveguide. The birefringent coupler has an effective refractive index for a TM mode which is greater than a refractive index of the first waveguide, and an effective refractive index for a TE mode which is less than the refractive index of the first waveguide. The second waveguide comprises a plurality of outwardly tapering legs with a gap between adjacent legs that are connected downstream to a body. The vertical beamsplitter uses less surface area.