An expanded Bell state generator can generate a Bell state on four output modes of a set of m output modes, where m is greater than four. Some expanded Bell state generators can receive inputs on any four of a set of 2m input modes. Subsets of the m output modes can be multiplexed to reduce the number of modes to four. According to some embodiments, a set of 2×2 muxes can be used to rearrange the output modes prior to reducing the number of modes.

An optical fiber adapter and method of fabricating the same from a wafer including a double silicon-on-insulator layer structure. The optical fiber adapter may include a mode converter, a trench, and a V-groove, the V-groove and the trench operating as passive alignment features for an optical fiber, in the transverse translational and rotational degrees of freedom, and in the longitudinal translational degree of freedom, respectively. The mode converter may include a buried tapered waveguide.

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.

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.

An optical circuit element formed on a substrate, the optical circuit element includes a first waveguide and a second waveguide, the second waveguide having a shape in a width direction, the shape being asymmetrical to the first waveguide. The first waveguide includes a first segment and a second segment, the first segment having a width that changes along a light propagation direction, the second segment continuous with the first segment. The second waveguide includes a coupled waveguide adjacent to the second segment of the first waveguide. At least one of the second segment and the coupled waveguide has a shape with a width that changes along the light propagation direction.

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 device includes a grating coupler with a grating constant, two light sources, and a planar waveguide, which are configured to couple light with two different wavelengths λ.sub.1, λ.sub.2 into the waveguide. The waveguide has a waveguiding layer disposed adjacent to a substrate layer and a cover layer. The waveguiding layer has a thickness d and effective refractive indices of N(λ.sub.k, j.sub.k), wherein λ.sub.k is one of the wavelengths and j.sub.k is an order of a waveguide mode, wherein the coupled light of the wavelength λ.sub.k has a coupling angle α.sub.k into the waveguide, and wherein an amount of difference between the coupling angles is a divergence angle Δα. Guiding of waveguide modes of the order j.sub.k>0 is possible for a wavelength of the coupled light. The waveguiding layer is arranged to couple the light via the grating coupler under a divergence angle of Δα<6.

Optical chips and packages are described. The optical chips and packages described herein are configured to output high-power, single mode optical outputs for use by integrated photonics packages. Some embodiments relate to an optical chip or package including a light source array configured to output a plurality of first optical signals and an optical combiner configured to receive the plurality of first optical signals from the light source array and to output a second optical signal that is a combination of the received plurality of first optical signals. The optical combiner may include at least one tunable element configured to increase an optical power of the output second optical signal.

Low spherical aberration of a Mikaelian lens makes it suitable for focusing off-optical-axis light propagating in higher order modes. A Mikaelian lens can be used as a mode-size converter to expand light in a semiconductor waveguide before coupling light out of the waveguide. For example, a Mikaelian lens can be used in a waveguide to expand light from a 1 μm wide multimode waveguide to a 20 μm wide multimode grating coupler in a shorter distance than an adiabatic taper. 3D FDTD simulation results show that an embodiment of a 12 μm long, subwavelength mode-size converter has comparable first-order mode transmission as a 600 μm adiabatic taper.

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.