An interface for optical communication, including an input waveguide in which light input from an outside is guided, an output waveguide including a first part abutting against one end of the input waveguide and a second part connected to the first part and a substrate including a Buried oxide (BOX) layer connected to a lower side of the output waveguide, wherein the one end of the input waveguide includes a tapered structure of which a cross-sectional area is reduced by a predetermined angle.

An avalanche photodiode includes a silicon layer on a substrate; a germanium layer on the silicon layer; a cathode and an anode on any of the silicon layer and the germanium layer; and a plurality of contacts on the germanium layer, in addition to the cathode and the anode. The silicon layer can include a highly doped region at each end, an intrinsic doped region in a middle, and an intermediately doped region between the highly doped region at each end and the intrinsic doped region, and the cathode and the anode are each at a respective a highly doped region at each end. The germanium layer can include a plurality of highly doped regions with each including one of the plurality of contacts.

Provided is a photodetector which can be manufactured in a standard process of a mass-produced CMOS foundry. The photodetector includes a silicon (Si) substrate; a lower clad layer; a core layer including a waveguide layer configured to guide signal light, and including a first Si slab doped with first conductive impurity ions and a second Si slab doped with second conductive impurity ions; a germanium (Ge) layer configured to absorb light and including a Ge region doped with the first conductive impurity ions; an upper clad layer; and electrodes respectively connected to the first and second Si slabs and the Ge region. A region of the core layer sandwiched between the first Si slab and the second Si slab operates as an amplification layer.

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.

A bent taper is provided that includes one or more waveguide bends, at least one of which has a tapering waveguide width along at least a portion thereof. In one embodiment, the bent taper is an S-shaped bent taper that is configured as a TE0-TE1 mode convertor. Such a bent taper can be combined with a linear bi-layer taper configured as a TM0-TE1 mode converter to form a TM0-TE0 polarization rotator.

Tapered waveguides made of high-index material attached to a tapered optical fiber are provided, enabling access to the optical modes of large, high-index resonators. In some embodiments, an optical fiber having a central axis, a tapered portion, and an untapered portion is provided. The tapered portion is configured to expose an evanescent field. An elongated waveguide is optically coupled to the optical fiber along the tapered portion and parallel to the central axis of the optical fiber. The elongated waveguide has a substantially triangular cross section perpendicular to the central axis of the optical fiber.

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.

According to various embodiments, there is provided an optical device including a first waveguide configured to guide a light wave along a longitudinal axis; a first grating at least partially formed in the first waveguide, the first grating arranged away from the longitudinal axis in a first direction; and a second grating at least partially formed in the first waveguide, the second grating arranged away from the longitudinal axis in a second direction; wherein the second direction is different from the first direction.

Structures for an optical power splitter and methods of forming a structure for an optical power splitter. A first waveguide core provides an input port, and second and third waveguide cores provide respective output ports. A non-linear waveguide taper is coupled to the first waveguide core at a first interface and is coupled to the second and third waveguide cores at a second interface. The non-linear waveguide taper includes a first curved section having a first width dimension that increases with increasing longitudinal distance from the first interface. The non-linear waveguide taper includes a second curved section having a second width dimension that increases with increasing longitudinal distance from the second interface. The first and second curved sections join at a longitudinal location at which the first and second width dimensions are each equal to a maximum width of the non-linear waveguide taper.

An optical coupling may involve orienting a waveguide and a lens such that light rays are focused on a surface. The lens may involve the use of a material having a variable refractive index to focus rays of light along first axis and a curved surface to focus the rays of light along a second axis.