Conventional systems use a polarization-maintaining fiber (PMF) in order to maintain the light in the same polarization between a laser light source and an optical waveguide on a photonic integrated circuit (PIC). A polarization controller may be provided at an input port of the PIC configured for the manipulation of one or both of the TE.sub.0 and TM.sub.0 polarized light modes. The polarization controller may include a polarization beam splitter/rotator (PBSR), including a plurality of phase tuners and a plurality of couplers which are coupled together by waveguides, all of which are integrated in a device layer on the PIC.

Example polarization splitter and rotator devices are described. In one example, an optical apparatus includes a splitter configured to split a light signal into a first signal having a first polarization and a second signal having a second polarization, a polarization rotator configured to rotate the second polarization of the second signal into a third polarization, and a polarization mode converter configured to convert the third polarization of the second signal into the first polarization. In certain aspects of the embodiments, the splitter can be a curved multi-mode inference (MMI) polarization splitter, and the polarization rotator comprises input and output ports, with the output port being wider than the input port. The polarization mode converter can be an asymmetrical waveguide taper mode converter. The devices described herein can overcome the deficiencies of conventional devices and provide low insertion loss, flat and/or wide wavelength response, high fabrication tolerance, and compact size.

Embodiments herein describe reverse biasing one or more PIN junctions formed in at least one layer of a PSR. The resulting electric fields in the PIN junctions overlap with the optical path of the optical signal and sweep away photo-generated hole-electron free carriers away. That is, the electric fields in the PIN junctions remove the free carriers from the path of the optical signal and reduces the population of the free carriers, thereby mitigating the negative impact of free-carrier absorption (FCA).

Example polarization splitter and rotator devices are described. In one example, an optical apparatus includes a splitter configured to split a light signal into a first signal having a first polarization and a second signal having a second polarization, a polarization rotator configured to rotate the second polarization of the second signal into a third polarization, and a polarization mode converter configured to convert the third polarization of the second signal into the first polarization. In certain aspects of the embodiments, the splitter can be a curved multi-mode inference (MMI) polarization splitter, and the polarization rotator comprises input and output ports, with the output port being wider than the input port. The polarization mode converter can be an asymmetrical waveguide taper mode converter. The devices described herein can overcome the deficiencies of conventional devices and provide low insertion loss, flat and/or wide wavelength response, high fabrication tolerance, and compact size.

Embodiments herein describe reverse biasing one or more PIN junctions formed in at least one layer of a PSR. The resulting electric fields in the PIN junctions overlap with the optical path of the optical signal and sweep away photo-generated hole-electron free carriers away. That is, the electric fields in the PIN junctions remove the free carriers from the path of the optical signal and reduces the population of the free carriers, thereby mitigating the negative impact of free-carrier absorption (FCA).

An integrated photonics optical gyroscope fabricated on a silicon nitride (SiN) waveguide platform comprises a first straight waveguide to receive incoming light and to output outgoing light to be coupled to a photodetector to provide an optical signal for rotational sensing. The gyroscope comprises a first microresonator ring proximate to the first straight waveguide. Light evanescently couples from the first straight waveguide to the first microresonator ring and experiences propagation loss while circulating as a guided beam within the first microresonator ring. The guided beam evanescently couples back from the first microresonator ring to the first straight waveguide to provide the optical signal for rotational sensing after optical gain is imparted to guided beam to counter the propagation loss. In a coupled-ring configurations, the first microresonator ring acts as a loss ring, and optical gain is imparted to a second microresonator ring which acts as a gain ring.

A mode coupling connector system that includes a first and second fiber connector each coupled to a coupler housing. The first and second fiber connectors are positioned in first and second receiving cavities of the coupler housing, respectively. The first and second fiber connector each have a ferrule with a fiber receiving hole extending from an outer end to an inner end of the ferrule. The fiber receiving hole of the first and second fiber connector are in axial alignment. The mode coupling connector system further includes a mode coupling plate having a phase mask array of a plurality of phase masks. The mode coupling plate is positioned in a plate receiving hole of the coupler housing between the first and second receiving cavity and at least two phase masks of the phase mask array are circumscribed by the fiber receiving hole of both the first and second fiber connector.

An optical integrated device includes a substrate a passive waveguide region and an active region. The active region and the passive waveguide region include a first mesa structure having an upper cladding portion formed of a same material as the upper cladding layer. The passive waveguide region includes a second spot size converter having the first mesa structure, a second mesa structure having a first core portion, a lower cladding portion, and a second core portion that are formed of same materials as the first core layer, the lower cladding layer, and the second core layer, respectively. The second mesa structure has a width wider than a width of the first mesa structure, and the width of the first mesa structure continuously changes along a longitudinal direction in which light is guided through the second core portion, the width being along a direction perpendicular to the longitudinal direction.

An optical device that can be used as an optical hybrid, e.g., in CMOS-compatible PICs. In an example embodiment, the optical device has a single optical input and four optical outputs. The two optical input signals to be mixed in the optical device are applied to the single optical input as transverse electric (TE) and transverse magnetic (TM) polarization components, respectively, of the corresponding polarization-multiplexed optical input signal. In response to the latter, the optical device causes the four outputs to receive four different relative-phase combinations of the two optical input signals, each combination being coupled into a TE waveguide mode at the respective optical output. A PIC having one or more instances of the optical device can be used, e.g., to implement a coherent optical receiver, wherein the TE and TM polarization components of the optical input signal are populated by a communication signal and a local-oscillator signal.

A light detection and ranging (LiDAR) system according to the present disclosure comprises an optical source to emit an optical beam. The LiDAR system comprises a PSR comprising a silicon nitride based waveguide to split and rotate a target return signal of the optical beam from a target. The silicon nitride based waveguide includes a first silicon nitride segment and a second silicon nitride segment. The first silicon nitride segment includes a first layer and a second layer. The first silicon nitride segment has tapered widths along a longitudinal direction. The second silicon nitride segment includes a silicon nitride adiabatic coupler. The LiDAR system further comprises an optical element to generate a local oscillator (LO) signal and a PD to mix the target return signal with the LO signal to generate a heterodyne signal to extract information of the target.