A first waveguide and a second waveguide including a first layer and a second layer are provided. In a first longitudinal segment, the first layer gradually approaches a first waveguide in a first transverse direction. In a second longitudinal segment, the first and second waveguides are longitudinally oriented. In a third longitudinal segment, the first layer includes a length portion having a width in the first transverse direction that gradually decreases along the third longitudinal segment, and the second layer includes a length portion having a width in the first transverse direction that gradually increases along the third longitudinal segment.

A wavelength demultiplexer includes a photonic circuit and a control circuit that adjusts wavelength characteristics of the photonic circuit. The photonic circuit converts two orthogonal polarized waves contained in the incident light into two same polarized waves, which are supplied to a first optical demultiplexing circuit and a second optical demultiplexing circuit provided in the photonic circuit and having the same configuration. The photonic circuit supplies a total output power of monitor lights extracted from the same positions in the first optical demultiplexing circuit and the second optical demultiplexing circuit to the control circuit. The control circuit controls a first wavelength characteristic of the first optical demultiplexing circuit and a second wavelength characteristic of the second optical demultiplexing circuit based on the total output power of the monitor lights.

A wavelength demultiplexer includes a photonic circuit and a control circuit that adjusts wavelength characteristics of the photonic circuit. The photonic circuit converts two orthogonal polarized waves contained in the incident light into two same polarized waves, which are supplied to a first optical demultiplexing circuit and a second optical demultiplexing circuit provided in the photonic circuit and having the same configuration. The photonic circuit supplies a total output power of monitor lights extracted from the same positions in the first optical demultiplexing circuit and the second optical demultiplexing circuit to the control circuit. The control circuit controls a first wavelength characteristic of the first optical demultiplexing circuit and a second wavelength characteristic of the second optical demultiplexing circuit based on the total output power of the monitor lights.

An optical waveguide (100) is disclosed, for guiding light in a photonic circuit comprising a layer of phase change material (101) for modulating the phase of the guided light. The phase change material (101) is switchable between at least a stable crystalline state and a stable amorphous state each with different refractive indexes. The phase change material (101) exhibits an extinction coefficient of less than 0.1 in both states for wavelengths greater than 1000 nm.

An optical waveguide (100) is disclosed, for guiding light in a photonic circuit comprising a layer of phase change material (101) for modulating the phase of the guided light. The phase change material (101) is switchable between at least a stable crystalline state and a stable amorphous state each with different refractive indexes. The phase change material (101) exhibits an extinction coefficient of less than 0.1 in both states for wavelengths greater than 1000 nm.

A photonic polarization splitter rotator (PSR) includes a substrate, a first optical waveguide disposed in the substrate on a first layer, the first optical waveguide having a curved portion between a first end of the first optical waveguide and a second end of the first optical waveguide, and a second optical waveguide disposed in the substrate on a second layer, above the first layer, the second optical waveguide having a substantially rectangular shape and longitudinally arranged between the first end of the first optical waveguide and the second end of the first optical waveguide.

A photonic polarization splitter rotator (PSR) includes a substrate, a first optical waveguide disposed in the substrate on a first layer, the first optical waveguide having a curved portion between a first end of the first optical waveguide and a second end of the first optical waveguide, and a second optical waveguide disposed in the substrate on a second layer, above the first layer, the second optical waveguide having a substantially rectangular shape and longitudinally arranged between the first end of the first optical waveguide and the second end of the first optical waveguide.

A manufacturing method of an optical waveguide device that allows light to propagate through a core formed within a cladding formed on a substrate, the core having a higher refractive index than the cladding, includes: layering a first cladding-material layer for the cladding and a core-material layer for the core sequentially on the substrate; forming the layered core-material layer into the core having a waveguide shape, and removing a first part of the core, the first part being positioned at a portion where a slit is to be formed, to thereby form a gap in the core; layering a second cladding-material layer for the cladding to cover the first cladding-material layer and the core; and removing, by dry-etching, a second part of the first and second cladding-material layers, the second part being positioned at the portion where the slit is to be formed, to thereby form the slit.

A manufacturing method of an optical waveguide device that allows light to propagate through a core formed within a cladding formed on a substrate, the core having a higher refractive index than the cladding, includes: layering a first cladding-material layer for the cladding and a core-material layer for the core sequentially on the substrate; forming the layered core-material layer into the core having a waveguide shape, and removing a first part of the core, the first part being positioned at a portion where a slit is to be formed, to thereby form a gap in the core; layering a second cladding-material layer for the cladding to cover the first cladding-material layer and the core; and removing, by dry-etching, a second part of the first and second cladding-material layers, the second part being positioned at the portion where the slit is to be formed, to thereby form the slit.

A single photon source comprises a photon emitter (10), an excitation waveguide (30) arranged to direct excitation photons having a first polarisation direction into the photon emitter, and a collection waveguide (42) arranged to collect photons having a second polarisation direction from the photon emitter. The first polarisation direction is coupled to a first exciton state of the photon emitter and the second polarisation direction is non-parallel to the first polarisation direction and is coupled to a second exciton state of the photon emitter, and the first and second exciton states have substantially equal energies.