Disclosed is a Chinese knot-like porous fiber core ultra-high birefringence THz optical fiber. The optical fiber comprises a substrate, claddings and fiber cores, wherein the claddings and the fiber cores are arranged in the substrate, and the fiber cores are embedded in the centers of the claddings; and the fiber core comprises a first fiber core region, a second fiber core region and a third fiber core region, the center of the first fiber core region 4 serves as the origin of coordinates, and the first fiber core region 4 is composed of six regular hexagon units with overlapped boundaries in the x-axis direction. In the present disclosure, the fiber core comprises a first fiber core region, a second fiber core region and a third fiber core region, and the three regions jointly form a fiber core region of a Chinese knot-like porous fiber core.

Disclosed is a Chinese knot-like porous fiber core ultra-high birefringence THz optical fiber. The optical fiber comprises a substrate, claddings and fiber cores, wherein the claddings and the fiber cores are arranged in the substrate, and the fiber cores are embedded in the centers of the claddings; and the fiber core comprises a first fiber core region, a second fiber core region and a third fiber core region, the center of the first fiber core region 4 serves as the origin of coordinates, and the first fiber core region 4 is composed of six regular hexagon units with overlapped boundaries in the x-axis direction. In the present disclosure, the fiber core comprises a first fiber core region, a second fiber core region and a third fiber core region, and the three regions jointly form a fiber core region of a Chinese knot-like porous fiber core.

Certain aspects of the present disclosure generally relate to an optical reference element having a wavelength spectrum comprising a plurality of wavelength functions having wavelength peaks spaced over a range of wavelengths, wherein adjacent wavelength functions are due to two orthogonal birefringence axes in the optical reference element. Aspects of the present disclosure may eliminate the drift issues associated with residual polarization and polarization dependent loss (PDL) with respect to grating-based sensor and reference element measurements.

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.

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.

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.

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.