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.

The invention relates to photonic circuits, in particular to photonic circuits where light is escalated transferred between optical waveguides which are coupled to photonic devices. A first waveguide on a silicon substrate is provided having a first thickness and a first refractive index. A tapered second waveguide having a second thickness less than the first thickness and a second refractive index higher than said first refractive index is deposited on the first waveguide. At least one layer of an optically active material comprising a photonic device is deposited on the first waveguide adjacent to the second waveguide. The photonic device is interfaced with the wide end of the tapered second waveguide to provide an optical coupling, and the opposite narrow end of the tapered second waveguide is interfaced on top of the first waveguide to provide adiabatic light transfer between said first and second waveguides.

Various polarization rotator splitter (PRS) configurations are disclosed. In an example embodiment, a system includes a PRS that includes a silicon nitride (SiN) rib waveguide core that includes a rib and a ridge that extends vertically above the rib, the SiN rib waveguide core having a total height h.sub.SiN from a bottom of the rib to a top of the ridge, a rib height h.sub.rib from the bottom of the rib to a top of the rib, a rib width w.sub.rib, and a top width w.sub.SiN of the ridge. The rib width w.sub.rib varies along at least a portion of a length of the SiN rib waveguide core.

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.

In one embodiment, a waveguide includes an upstream portion, a downstream portion, and an intermediate portion between the upstream portion and the downstream portion. A first band is disposed on an insulating layer, the first band oriented along a first direction. A first lateral strip and a second lateral strip are disposed on either side of the first band, the first lateral strip and the second lateral strip being thinner or interrupted along the intermediate portion.

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 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 output filter section is provided to prevent light from reentering the output waveguide after being squeezed out. An integrated light absorber/deflector may be coupled to the outer waveguiding regions.

A system may include a polarization rotator combiner. The polarization rotator combiner may include a first stage, a second stage, and a third stage. The first stage may receive a first component of light with a TE00 polarization and a second component of light with the TE00 polarization. The first stage may draw optical paths of the first and second components together. The second stage may receive the first component and the second component from the first stage. The second stage may convert the polarization of the second component from the TE00 polarization to a TE01 polarization. The third stage may receive the first component and the second component from the second stage. The third stage may convert polarization of the second component from the TE01 polarization to a TM00 polarization. The third stage may output the first component and output the second component.

A device for coupling a first waveguide with a second waveguide, wherein the core of the second guide includes an end portion having at least a flat end wall rotated facing, and preferably, in contact with the core of the first guide, a flared part of convex shape extending the end wall by extending from the first guide, the flared part having a section which increases by extending from the first guide, a narrowing, a main portion, extending the end portion by extending from the first guide and having a substantially constant section.

A spot-size converter includes a first part of a waveguiding structure to couple to a first waveguide to receive light from or transmit light to the first waveguide in a first propagation mode, wherein the first part of the waveguiding structure has a lower waveguiding structure with a varying effective refractive index that decreases away from the first waveguide; and a second part of the waveguiding structure to couple to a second waveguide to transmit light to or receive light from the second waveguide in a second propagation mode, the second part of the waveguiding structure includes an upper waveguiding structure with a plurality of high-index elements arranged therein, an overlap region is between the first part and the second part, the first propagation mode progressively transforms into the second propagation mode in the overlap region.