The present disclosure relates to system-level integration of lasers, electronics, integrated photonics-based optical components and a sensing chip. Novel waveguide design on the integrated photonics chip, acting as a front-end chip, ensures precise detection of phase change in a fiber coil or a sensing chip having a waveguide coil or ring resonator, where the sending chip is coupled to the front end chip. Strip waveguides are designed to primarily select TE mode over TM mode when laser light is coupled into the integrated photonics chip. A plurality of mode-selective filters, based on multi-mode interference (MMI) filter, a serpentine structure, or other types of waveguide-based mode-selective structure, are introduced in the system architecture. Additionally, implant regions are introduced around the waveguides and other optical components to block unwanted/stray light into the waveguides and optical signal leaking out of the waveguide.

A photonic device has a polarization-dependent region and a device layer including a first cladding film, a second cladding film, and a core film. The core film includes one of (1) a material having an index n.sub.M and (2) alternating layers of a first material having a first index and second material having a second index. The alternating layers have an effective index for TE polarized light n.sub.TE and an effective index for TM polarized light n.sub.TM. Each of the first cladding film and the second cladding film include the other of (1) the material having the index of refraction n.sub.M and (2) the alternating layers n.sub.TM<n.sub.M<n.sub.TE, and the indices of the upper cladding and the lower cladding are less than n.sub.TM, n.sub.M and n.sub.TE. A polarizer, polarizing beam splitter and coupler using clipped coupling can employ the material having an index n.sub.M and the alternating layers.

A photonic device has a polarization-dependent region and a device layer including a first cladding film, a second cladding film, and a core film. The core film includes one of (1) a material having an index n.sub.M and (2) alternating layers of a first material having a first index and second material having a second index. The alternating layers have an effective index for TE polarized light n.sub.TE and an effective index for TM polarized light n.sub.TM. Each of the first cladding film and the second cladding film include the other of (1) the material having the index of refraction n.sub.M and (2) the alternating layers n.sub.TM<n.sub.M<n.sub.TE, and the indices of the upper cladding and the lower cladding are less than n.sub.TM, n.sub.M and n.sub.TE. A polarizer, polarizing beam splitter and coupler using clipped coupling can employ the material having an index n.sub.M and the alternating layers.

An optical fiber device may include a unitary core including a primary section and a secondary section, wherein at least a portion of the secondary section is offset from a center of the unitary core, wherein the unitary core twists about an optical axis of the optical fiber device along a length of the optical fiber device, and wherein a refractive index of the primary section is greater than a refractive index of the secondary section; and a cladding surrounding the unitary core.

Many embodiments in accordance with the invention are directed towards waveguides implementing birefringence control. In some embodiments, the waveguide includes a birefringent grating layer and a birefringence control layer. In further embodiments, the birefringence control layer is compact and efficient. Such structures can be utilized for various applications, including but not limited to: compensating for polarization related losses in holographic waveguides; providing three-dimensional LC director alignment in waveguides based on Bragg gratings; and spatially varying angular/spectral bandwidth for homogenizing the output from a waveguide. In some embodiments, a polarization-maintaining, wide-angle, and high-reflection waveguide cladding with polarization compensation is implemented for grating birefringence. In several embodiments, a thin polarization control layer is implemented for providing either quarter wave or half wave retardation.

A photonic integrated circuit comprises an input interface adapted for receiving an optical input signal and splitting it into two distinct polarization modes and furthermore adapted for rotating the polarization of one of the modes for providing the splitted signals in a common polarization mode. The PIC also comprises a combiner adapted for combining the first mode signal and the second mode signal into a combined signal and a decohering means adapted for transforming at least one of the first mode signal and the second mode signal such that the first mode signal and the second mode signal are received by the combiner in a mutually incoherent state. A processing component for receiving and processing said combined signal is also comprised.

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.

In an example, a photonic system includes a Si PIC with a Si substrate, a SiO.sub.2 box formed on the Si substrate, a first layer, and a second layer. The first layer is formed above the SiO.sub.2 box and includes a SiN waveguide with a coupler portion at a first end and a tapered end opposite the first end. The second layer is formed above the SiO.sub.2 box and vertically displaced above or below the first layer. The second layer includes a Si waveguide with a tapered end aligned in two orthogonal directions with the coupler portion of the SiN waveguide such that the tapered end of the Si waveguide overlaps in the two orthogonal directions and is parallel to the coupler portion of the SiN waveguide. The tapered end of the SiN waveguide is configured to be adiabatically coupled to a coupler portion of an interposer waveguide.

A polarization-sensitive photonic splitter may include a lower cladding layer and a device layer formed from a first waveguide supporting TE and TM light, a second waveguide, a third waveguide, and a transition core. The first waveguide core and the second waveguide core are formed from one of a first core structure or a second core structure, and the third waveguide is formed from the other structure. The first core structure has an index of refraction n.sub.M. The second core structure is formed as alternating layers providing an effective index of refraction for TE light n.sub.TE and an effective index of refraction for TM light n.sub.TM, where n.sub.TM<n.sub.M<n.sub.TE. The transition core is formed from the first core structure adjacent to the second core structure and is coupled to the first transition core at one and the second and third transition cores at the other end.

A photonic device may include a lower cladding layer and a device layer. The device layer may include a first waveguide supporting TE and TM light, and a second waveguide, where a portion of a second waveguide core is proximate to a first waveguide core to provide evanescent coupling. The first waveguide core is formed from one of a first core structure or a second core structure, and the second waveguide core is formed from the other structure. The first core structure has an index of refraction n.sub.M. The second core structure is formed as alternating layers providing an effective index of refraction for TE polarized light n.sub.TE and an effective index of refraction for TM polarized light n.sub.TM, where n.sub.TM<n.sub.M<n.sub.TE such that one of TM or TE light is preferentially evanescently coupled between the first waveguide and the second waveguide.