The disclosed technology can be implemented in photonics integrated circuit (PIC) to provide an optical frequency detection device for measuring an optical frequency of light using two Mach-Zehnder interferometer where the delay imbalance in the first interferometer is configured to be one quarter wavelength longer than that of the second interferometer to produce an additional phase difference between the two arms. The two outputs of each interferometer are then detected by two photodetectors to produce two complementary interference signals. The difference between the two complementary interference signals of the first interferometer is a sine function of the optical frequency while the difference between the two complementary interference signals of the second interferometer is proportional to a cosine function of the optical frequency. Using the sine/cosine interpretation algorithm commonly used for the rotation encoders/decoders, any increments in optical frequency can be readily obtained.

An optical circuit for routing a signal includes a coupler and first and second waveguides. The coupler has an input for the signal and has first and second outputs. The first waveguide has a first optical connection to the first output, and the second waveguide has a second optical connection to the second output. Both waveguides have the same propagation length. The first and second waveguides include different widths at the respective optical connections to the respective outputs. This coupler can be used with another input couplers, two additional waveguides, and two 2×2 output couplers to provide a 90-degree hybrid for mixing signal light and local oscillator light in a coherent receiver or the like.

An optical circuit for routing a signal includes a coupler and first and second waveguides. The coupler has an input for the signal and has first and second outputs. The first waveguide has a first optical connection to the first output, and the second waveguide has a second optical connection to the second output. Both waveguides have the same propagation length. The first and second waveguides include different widths at the respective optical connections to the respective outputs. This coupler can be used with another input couplers, two additional waveguides, and two 2×2 output couplers to provide a 90-degree hybrid for mixing signal light and local oscillator light in a coherent receiver or the like.

Disclosed is an all-fiber optical vortex laser based on resonance of orbital angular momentum modes. The all-fiber optical vortex laser has an annular cavity structure, and includes a narrow-linewidth pump laser, an optical amplifier, an orbital angular momentum mode generator, a first polarization controller, an optical fiber circulator, an optical fiber coupler, a second polarization controller and a vortex optical fiber. The orbital angular momentum mode generator (3) realizes directional conversion from a fundamental transverse mode in a single-mode optical fiber into an orbital angular momentum mode with a specific topological charge in a vortex optical fiber. The optical fiber coupler can realize directional coupling from an orbital angular momentum mode in one vortex optical fiber to an orbital angular momentum mode in another vortex optical fiber; the vortex optical fiber is an optical fiber supporting stable transmission of an orbital angular momentum model.

Optical protection devices are provided for protecting client equipment in an optical communication system. According to one implementation, a protection device includes a passive optical coupler configured to combine optical signals from a plurality of input paths, where the passive optical coupler is further configured to provide the output signals along an optical output path. The exemplary protection device further includes one or more interrupters configured to allow at most one input from a plurality of optical inputs via the plurality of input paths to be provided to the passive optical coupler at one time.

A flexible TOF processing block having power measurement circuitry comprising separate modules that can be modified using parameterizable registers, without complete reconstruction, allows development to continue while the overall design is optimized.

An optical wavelength-division multiplexing (WDM) device utilizing a mechanism of folded optical-path includes multiple collimators, optical filters, prism, and glass plate. The collimators are capable of collimating optical lights for facilitating free-space optical communication. The optical filters optically coupled with the collimators provide filtering functions to separate optical wavelengths in accordance with the configurations or characteristics of optical filters. The prism having an interface surface and two side surfaces is configured to direct or redirect optical beams based on the angle of incidence (AOI) of each optical beam received. The glass plate, in one embodiment, physically configured to be situated in parallel with the collimators is capable of providing free-space optical paths for facilitating separation of wavelengths.

Disclosed is an all-fiber optical vortex laser based on resonance of orbital angular momentum modes. The all-fiber optical vortex laser has an annular cavity structure, and includes a narrow-linewidth pump laser, an optical amplifier, an orbital angular momentum mode generator, a first polarization controller, an optical fiber circulator, an optical fiber coupler, a second polarization controller and a vortex optical fiber. The orbital angular momentum mode generator (3) realizes directional conversion from a fundamental transverse mode in a single-mode optical fiber into an orbital angular momentum mode with a specific topological charge in a vortex optical fiber. The optical fiber coupler can realize directional coupling from an orbital angular momentum mode in one vortex optical fiber to an orbital angular momentum mode in another vortex optical fiber; the vortex optical fiber is an optical fiber supporting stable transmission of an orbital angular momentum mode.

An optical signal isolation device comprising a common port, an isolated diagnostic port, an integrated circulator comprising an input circulator fiber, an output circulator fiber, and a fiber-to-fiber optical coupler configured to couple an isolated optical signal propagating along the input circulator fiber to the output circulator fiber for propagation along the output circulator fiber, a multi-fiber alignment body that secures at least portions of each of the multi-signal fiber, the isolated diagnostic signal fiber, the input circulator fiber, and the output circulator fiber, and a wavelength-selective optical assembly including an optical signal filter, fiber-to-filter focusing optics, and a communications signal reflector. The integrated circulator and the wavelength selective optical assembly are configured such that the communications component is retro-reflected back to the common port and the diagnostic component is passes out of the isolated diagnostic port.

Devices and methods are described for selecting a level of entanglement between two nondegenerate photons. The method may include receiving two non degenerate photons through a single input port of a directional photonic coupler; adjusting one of a first-order coupler dispersion M or a power splitting ratio (00) of the directional optical coupler to select a ; and, emitting the photons from corresponding output ports of the directional optical coupler, wherein the emitted photons have a spectral entanglement corresponding to the selected .