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 larger-mode region is configured to propagate at least a first optical mode characterized by a first mode field diameter at a first position along a propagation axis of the larger-mode region. A smaller-mode region comprises one core structure embedded within the cladding positioned to couple optical modes guided by the smaller-mode region characterized by a second mode field diameter smaller than the first mode field diameter to the first optical mode over a coupling region within the cladding in which the larger-mode region is in proximity to the smaller-mode region. Stress-modifying formations are arranged within or in proximity to one or both of the larger-mode region or the coupling region, and modify a stress within a portion of the cladding along a first transverse axis with respect to a stress within the portion of the cladding along a second transverse axis.

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.

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 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.

An example optical fiber signal mode conversion apparatus includes a non-single-mode optical fiber and a single-mode optical fiber. The single-mode optical fiber forms, with the non-single-mode optical fiber, a first coupling region and a second coupling region along a signal transmission direction in the non-single-mode optical fiber, where an effective refractive index of a fundamental mode signal of the single-mode optical fiber in the first coupling region is equal to an effective refractive index of a signal in a first mode, the signal in the first mode is coupled to a fundamental mode channel of the single-mode optical fiber, and an effective refractive index of the fundamental mode signal of the single-mode optical fiber in the second coupling region is equal to an effective refractive index of a signal in a second mode.

Low loss fiber-to-chip interfaces for lithium niobate photonic integrated circuits are provided. An optical circuit includes a waveguide comprising an electro-optical material. The waveguide includes an elevated ridge and a slab underlying the elevated ridge, the elevated ridge and the slab extending along a central axis toward an optical interface. The elevated ridge and the slab each have a plurality of cross-sections along the central axis, each cross-section having a width measured perpendicular to the central axis, wherein the width of elevated ridge is smaller than the width of the slab for every cross-section along the central axis. The elevated ridge includes a tapered portion having a first taper, wherein the cross-section of the elevated portion decreases along the central axis toward the optical interface. The slab includes a tapered portion having a second taper, wherein the cross-section of the slab decreases along the central axis toward the optical interface. The slab extends beyond the elevated ridge along the central axis to the optical interface.

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.

An optical device includes a substrate having a first region and a second region in a surface thereof, a first waveguide for inputting light, and at least one second waveguide for outputting light. The second region surrounds the first region. The first waveguide and the second waveguide are optically coupled to the first region. The substrate includes a first layer and a second layer sequentially stacked one on top of the other in the first region. The second layer has a plurality of holes. A depth of each of the holes is half of a thickness of the second layer or smaller. The substrate does not have the second layer and has the first layer in the second region.

An optical phased array comprises photonic components for on-chip beam forming and steering, and is adapted to use an input optical field of a beam having a wavelength which ranges from visible light to a short-wavelength infrared region. The photonic component comprises at least a waveguide and a plurality of scatterers, with each scatterer having a diagonal which is at most about one-tenth the wavelength of the input optical field.