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.

Structures including a grating coupler and methods of fabricating a structure including a grating coupler. The structure includes structure includes a dielectric layer on a substrate, a first waveguide core positioned in a first level over the dielectric layer, and a second waveguide core positioned in a second level over the dielectric layer. The second level differs in elevation above the dielectric layer from the first level. The first waveguide core includes a tapered section. The structure further includes a grating coupler having a plurality of segments positioned in the second level adjacent to the second waveguide core. The segments of the grating coupler and the tapered section of the first waveguide core are positioned in an overlapping arrangement.

Structures including a grating coupler and methods of fabricating a structure including a grating coupler. The structure includes structure includes a dielectric layer on a substrate, a first waveguide core positioned in a first level over the dielectric layer, and a second waveguide core positioned in a second level over the dielectric layer. The second level differs in elevation above the dielectric layer from the first level. The first waveguide core includes a tapered section. The structure further includes a grating coupler having a plurality of segments positioned in the second level adjacent to the second waveguide core. The segments of the grating coupler and the tapered section of the first waveguide core are positioned in an overlapping arrangement.

An optical interconnect device and the method of fabricating it are described. The device includes an in-plane laser cavity transmitting a light beam along a first direction, a Franz Keldysh (FK) optical modulator transmitting the light beam along the first direction, a mode-transfer module including a tapered structure disposed after the FK optical modulator along the first direction to enlarge the spot size of the light beam to match an external optical fiber and a universal coupler controlling the light direction. The tapered structure can be made linear or non-linear along the first direction. The universal coupler passes the laser light to an in-plane external optical fiber if the fiber is placed along the first direction, or it is a vertical coupler in the case that the external optical fiber is placed perpendicularly to the substrate surface. The coupler is coated with highly reflective material.

A mode multiplexing/demultiplexing optical circuit with a reduced inter-mode crosstalk is provided. A mode multiplexing/demultiplexing optical circuit includes a Port 1 through which light from a light source is input to a waveguide, a Port 3 through which light propagating through a first waveguide is output, a mode conversion unit located adjacent to the first waveguide, and configured to convert a first-order mode light input from the Port 3 to a second-order mode, and Port 2 configured to convert, via a waveguide located adjacent to the mode conversion unit, second-order mode light input to the mode conversion unit to a zeroth-order mode.

An optical semiconductor device including an optical waveguide; a light absorbing region coupled to the optical waveguide; a first conductive region and a second conductive region disposed at both sides of the light absorbing region so as to sandwich the light absorbing region; and a conductor coupled to the first conductive region and the second conductive region to let the first conductive region and the second conductive region short-circuit. With this configuration, the optical semiconductor device provides effects that absorption saturation is less likely to occur even if the light intensity increases, so that reflection return light can be reliably suppressed without using an external power source.

An optical device comprises first, second and third elements fabricated on a common substrate. The first element comprises an active waveguide structure supporting a first optical mode, the second element, fabricated on a planarized top surface of the first element, comprises a passive waveguide structure supporting a second optical mode, and the third element, at least partly butt-coupled to the first element, comprises an intermediate waveguide structure, positioned such that a top surface of the intermediate structure underlies a bottom surface of the passive waveguide structure. If the first optical mode differs from the second optical mode by more than a predetermined amount, a tapered waveguide structure in at least one of the second and third elements facilitates efficient adiabatic transformation between the first optical mode and the second optical mode. Mutual alignments of the first, second and third elements are defined using lithographic alignment marks.

A method for fabricating an integrated structure, using a fabrication system having a CMOS line and a photonics line, includes the steps of: in the photonics line, fabricating a first photonics component in a silicon wafer; transferring the wafer from the photonics line to the CMOS line; and in the CMOS line, fabricating a CMOS component in the silicon wafer. Additionally, a monolithic integrated structure includes a silicon wafer with a waveguide and a CMOS component formed therein, wherein the waveguide structure includes a ridge extending away from the upper surface of the silicon wafer. A monolithic integrated structure is also provided which has a photonics component and a CMOS component formed therein, the photonics component including a waveguide having a width of 0.5 μm to 13 μm.

A SOI device may include a waveguide adapter that couples light between an external light source—e.g., a fiber optic cable or laser—and 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 device—e.g., the waveguide adapter is formed before heat-sensitive components are added to the silicon surface layer.

Optical circuits support reconfigurable spatial rearrangement (also referred to as “spatial multiplexing”) for a group of photons propagating in waveguides. According to some embodiments, a set of 2×2 muxes can be used to rearrange a pattern of photons on a first set of waveguides into a usable input pattern for a downstream optical circuit.