An apparatus and method for wavelength conversion of a signal, for example, a dual-polarization signal, is disclosed. The apparatus implements a single-loop counter-propagating wavelength conversion scheme which provides both up-conversion and down-conversion of the signal within the same loop. Nonlinear wavelength conversion devices in the loop provide both up-conversion and down-conversion of the polarization components of the signal within the loop depending on whether the polarization component travels through the nonlinear conversion device in a clockwise or a counter-clockwise direction. The wavelength-converted signal is available to be extracted from the wavelength-conversion loop. An all-optical wavelength-division multiplexing transponder based on the wavelength-conversion scheme is also disclosed.

An object is to be capable of housing an optical fiber that connects between components not to exceed a bending limit of the optical fiber in a housing of a pluggable optical module. A pluggable electric connector (11) is configured to be insertable into and removable from an optical communication apparatus (93). An optical output module (12) outputs an optical signal (LS1) and a local oscillation light (LO). An optical reception module (13) outputs a communication data signal (DAT) generated by demodulating using the local oscillation light (LO). A pluggable optical receptor (15) is configured in such a manner that optical fibers are insertable thereinto and removable therefrom. A first optical fiber (F11) is connected between the optical output module (12) and the pluggable optical receptor (15). A second optical fiber (F12) is connected between the optical output module (12) and the optical reception module (13). A third optical fiber (F13) is connected between the optical reception module (13) and the pluggable optical receptor (15). Optical fiber housing means winds extra lengths of the first to third optical fibers (F11 to F13) around a guide.

A demodulator can include an optical resonator. The optical resonator can include a resonant cavity that extends between a first surface that is partially reflective and a second surface that is at least partially reflective. The first surface can receive a phase-modulated optical signal that has a time-varying phase. The resonant cavity can accumulate resonant optical signal energy based at least in part on the phase-modulated optical signal. The first surface can direct a fraction of the resonant optical signal energy out of the optical resonator to form an intensity-modulated optical signal that has a time-varying intensity. A data detector can receive at least a portion of the intensity-modulated optical signal and, in response, generate an intensity-modulated electrical signal that has a time-varying intensity that corresponds to the time-varying phase of the phase-modulated optical signal.

A demodulator can include an optical resonator. The optical resonator can include a resonant cavity that extends between a first surface that is partially reflective and a second surface that is at least partially reflective. The first surface can receive a phase-modulated optical signal that has a time-varying phase. The resonant cavity can accumulate resonant optical signal energy based at least in part on the phase-modulated optical signal. The first surface can direct a fraction of the resonant optical signal energy out of the optical resonator to form an intensity-modulated optical signal that has a time-varying intensity. A data detector can receive at least a portion of the intensity-modulated optical signal and, in response, generate an intensity-modulated electrical signal that has a time-varying intensity that corresponds to the time-varying phase of the phase-modulated optical signal.

An off-axis optical system includes an optical source to generate a light beam and an off-axis optical element arranged at a first angle with respect to a normal to the light beam. The off-axis optical element deflects the light beam onto a target. The off-axis optical element can be a thin-film reflective element having a combined deflection and lens profile.

An off-axis optical system includes an optical source to generate a light beam and an off-axis optical element arranged at a first angle with respect to a normal to the light beam. The off-axis optical element deflects the light beam onto a target. The off-axis optical element can be a thin-film reflective element having a combined deflection and lens profile.

A reception apparatus includes: a receiving unit configured to coherently detect an optical signal and output an electrical signal containing a modulated signal and a pilot signal; a first compensating unit configured to detect a frequency of the pilot signal by performing a DFT of the electrical signal, and determine and compensate for frequency error in the electrical signal based on a reference frequency; a frequency converting unit configured to convert the frequency of the pilot signal after the compensating such that the frequency of the pilot signal is lowered by the reference frequency; and a second compensating unit configured to determine frequency error in the modulated signal after the compensating by performing a DFT on the pilot signal after the frequency converting and detecting a frequency of the pilot signal after the frequency converting.

Disclosed are optical communications systems and optical receivers including one or more optical cavity resonators. In particular, disclosed are methods and apparatus that allow for beam pointing to be maintained while permitting the receiver to tune the optical resonator to suit the wavelength, data rate and modulation format of the incoming optical signal, without requiring a coherent receiver or adaptive optics in addition to optical resonators.

Disclosed are optical communications systems and optical receivers including one or more optical cavity resonators. In particular, disclosed are methods and apparatus that allow for beam pointing to be maintained while permitting the receiver to tune the optical resonator to suit the wavelength, data rate and modulation format of the incoming optical signal, without requiring a coherent receiver or adaptive optics in addition to optical resonators.

To provide an optical 90-degree hybrid formed of a silicon waveguide capable of suppressing an optical loss and a phase error, and facilitating electronic packaging and optical packaging. In the optical 90-degree hybrid circuit including two optical branching units facing each other and two optical coupling units facing away from each other, four arm waveguides are arranged including bent waveguides each of which guides an output light of the optical branching unit to the optical coupling unit, and is formed in a curved shape.