An optical waveguide connection structure connects a Si waveguide and an optical fiber to each other with a bonding layer interposed therebetween. The Si waveguide has a core whose cross-sectional area in the direction perpendicular to the direction of propagation of light decreases toward the optical fiber, and a cladding that covers the core. The optical fiber has a fiber core, a fiber cladding that covers the fiber core, and a recess formed in an end face opposed to the Si waveguide. The bonding layer fills a gap between the end face of the Si waveguide and the end face of the optical fiber and the recess, and the bonding layer has a refractive index greater than the refractive index of the fiber core of the optical fiber.

In conventional hybrid lasers large back refection may lead to a degradation of relative intensity noise (RIN), linewidth broadening, mode hopping, etc. To solve the aforementioned problem a hybrid laser includes a mode converter for converting a higher-back-reflection mode of the light to a mode providing less back reflection to the gain chip. The mode converter may comprise a polarization rotator, a waveguide converter, or high-order mode converter. A routing waveguide may be provided including a phase shifter, e.g. a doped waveguide, for adjusting a cavity length of the laser cavity.

In conventional hybrid lasers large back refection may lead to a degradation of relative intensity noise (RIN), linewidth broadening, mode hopping, etc. To solve the aforementioned problem a hybrid laser includes a mode converter for converting a higher-back-reflection mode of the light to a mode providing less back reflection to the gain chip. The mode converter may comprise a polarization rotator, a waveguide converter, or high-order mode converter. A routing waveguide may be provided including a phase shifter, e.g. a doped waveguide, for adjusting a cavity length of the laser cavity.

An optical coupler (40; 50) comprises a substrate (41). A first waveguide element (45) is provided in a first layer with respect to the substrate, wherein the first waveguide element (45) comprises a first end (45a) and a second end (45b), and wherein the first end (45a) of the first waveguide element (45) is coupled to input/output light to/from a first end of the optical coupler. A second waveguide element (43) is provided in a second layer, the second layer arranged adjacent to the first layer, wherein the second waveguide element (43) comprises a first end (43a) and a second end (43b), and wherein the first end (43a) of the second waveguide element (43) is coupled to input/output light to/from a second end of the optical coupler. The first waveguide element (45) is configured to extend from the first end of the optical coupler towards the second end of the optical coupler, and the second waveguide element (43) is configured to extend from the second end of the optical coupler towards the first end of the optical coupler, such that the first waveguide element (45) partly overlaps with the second waveguide element (43) to adapt light passing between the first end (45a) of the first waveguide element (45) and first end (43a) of the second waveguide element (43).

Structures with waveguides in multiple levels and methods of fabricating a structure that includes waveguides in multiple levels. A waveguide crossing has a first waveguide and a second waveguide arranged to intersect the first waveguide. A third waveguide is displaced vertically from the waveguide crossing, The third waveguide includes a portion having an overlapping arrangement with a portion of the first waveguide. The overlapping portions of the first and third waveguides are configured to transfer optical signals between the first waveguide and the third waveguide.

A device, such as an electroabsorption modulator, can modulate a light intensity by controllably absorbing a selectable fraction of the light. The device can include a substrate. A waveguide positioned on the substrate can guide light. An active region positioned on the waveguide can receive guided light from the waveguide, absorb a fraction of the received light, and return a complementary fraction of the received light to the waveguide. Such absorption produces heat, mostly at an input portion of the active region. The input portion of the active region can be thermally coupled to the substrate, which can dissipate heat from the input portion, and can help avoid thermal runaway of the device. The active region can be thermally isolated from the substrate away from the input portion, which can maintain a relatively low thermal mass for the active region, and can increase efficiency when heating the active region.

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.

The present application discloses a polarization beam splitter (PBS). The PBS includes a silicon substrate and a planar structure formed thereon characterized by an isosceles trapezoid shape with a first parallel side and a second parallel side connected by two tapered sides. The first parallel side has longer width than the second parallel side, both of which is separated by a length no greater than 100 m along a line of symmetry bisecting the pair of parallel sides. The PBS further includes a pair of input ports coupled to the first parallel side and a pair of output ports coupled to the second parallel side. The planar structure is configured to receive an input light wave of any wavelength in C-band via one input port and split to a TE-mode light wave and a TM-mode light wave respectively outputting to the pair of output ports.

An optical mode converter and method of fabricating the same from wafer including a double silicon-on-insulator layer structure. The method comprising: providing a first mask over a portion of a device layer of the DSOI layer structure; etching an unmasked portion of the device layer down to at least an upper buried oxide layer, to provide a cavity; etching a first isolation trench and a second isolation trench into a mode converter layer, the mode converter layer being: on an opposite side of the upper buried oxide layer to the device layer and between the upper buried oxide layer and a lower buried oxide layer, the lower buried oxide layer being above a substrate; wherein the first isolation trench and the second isolation trench define a tapered waveguide; filling the first isolation trench and the second isolation trench with an insulating material, so as to optically isolate the tapered waveguide from the remaining mode converter layer; and regrowing the etched region of the device layer.

Systems, apparatus and methods for a neural implant are provided. In one embodiment, a neural implant that can both optically stimulate neurons and record electrical signals from neurons is provided, including a wide band gap semiconductor optoelectronic microarray, such optoelectronic microarray including a plurality of needles, each providing both optical transparency and electrical conductivity; a flexible optical conduit from the optoelectronic microarray to an optical signal source; a flexible electrical conduit from the optoelectronic microarray to an electrical signal sensor; integration of the optical and electrical conduits to a single monolithic optical cable; a circuit assembly coupled to the electrical signal source and the optical signal source; and a processor for providing control of at least one of the electrical signal sensor and the optical signal source. Further embodiments are described herein.