A width-tunable single-frequency fiber laser light source for coherent optical orthogonal frequency division multiplexing system including a chirped fiber grating with high reflectivity, a high gain optical fiber, a chirped fiber grating with low reflectivity, a single-mode semiconductor pump laser, an optical wavelength division multiplexer, an optical coupler, an optical circulator, and a tunable optical filter module is provided. The chirped fiber grating with low reflectivity and the chirped fiber grating with high reflectivity together serve as a front cavity mirror and a back cavity mirror of a resonant cavity to realize laser oscillation. After a laser with broad spectrum output from the optical wavelength division multiplexer is split by the optical coupler, a part of the laser passes through the optical circulator to enter the tunable optical filter module. A wavelength corresponding to any nominal center frequency stipulated by the ITU-T is selected by the tunable optical filter module, with a 3 dB spectral width of less than 0.1 nm, and is then injected back into the resonant cavity via the optical circulator and the optical coupler, and the resonant cavity is subjected to a self-injection locking.

An optical communication system comprises a plurality of linked single-wavelength coherent optical transceivers configured to communicate via short-reach data-center links at a common reference wavelength, each transceiver including a single single-wavelength laser source that is used to produce a source beam at a source beam wavelength, the source beam being used to produce transmit beams sent by the transceiver and for mixing with one or more receive beams received by the transceiver; wherein each of the transceivers includes a thermo-electric cooler configured to control a temperature of the single-wavelength laser source around a temperature setpoint that locks the source beam wavelength to the common reference wavelength; wherein each transceiver includes a wavelength deviation detector configured to detect a wavelength deviation between the source beam wavelength and the wavelength or wavelengths of the one or more receive beams or between the source beam wavelength and the common reference wavelength, wherein the wavelength deviation detector is configured to detect a threshold amount of wavelength deviation that is indicative that the single-wavelength laser source is problematic or a single-wavelength laser source of a separate transceiver coupled to send the one or more receive beams is problematic, wherein each transceiver is configured to indicate the wavelength deviation or problematic characteristic in order to identify problematic laser sources and thereby prevent the linked network of transceivers from communicating at a linked network wavelength that is marginal or out-of-range in relation to the common reference wavelength.

A receiver that may include a receiver front end arranged to receive (a) a received signal, (b) a reference signal generated by a local oscillator laser, and to output a first intermediate signal; a carrier phase estimator that is arranged to receive the first intermediate signal and to generate a phase estimation signal that represents a phase difference between the received signal and the reference signal; wherein the carrier phase estimator comprises a multi-symbol-differential-detection module and a carrier phase demodulator; and an output circuit arranged to receive the phase estimation signal and to apply a slicing operation to provide an output signal of the carrier phase estimator.

It becomes difficult to regenerate transmitting signals depending on modulation systems for the optical phase modulation in a polarization multiplexed optical communication system employing the optical digital coherent communication system, therefore, an optical transmitter according to an exemplary aspect of the invention includes first optical quadrature modulation means for performing a phase modulation on a first continuous light beam and outputting a first transmitting light beam; second optical quadrature modulation means for performing a phase modulation on a second continuous light beam belonging in the same frequency band as that of the first continuous light beam and outputting a second transmitting light beam; optical phase difference adding means for adding an optical phase difference varying temporally between the first transmitting light beam and the second transmitting light beam; and polarization multiplexing means for polarization-multiplexing the first transmitting light beam and the second transmitting light beam in the state where their polarizations are made to be orthogonal to each other and outputting a polarization multiplexed transmitting light beam.

An apparatus comprising a first analog multiplexer configured to provide a respective one of a plurality of first input signals as a first output signal based on a first control signal, a second analog multiplexer configured to provide a respective one of a plurality of second input signals as a second output signal based on a second control signal, and a combiner configured to combine the first output signal and the second output signal to obtain a third output signal.

A coherent optical injection locking (COIL) apparatus generates multiple optical source outputs from a single optical source generated by a parent laser. The COIL apparatus includes a plurality of optical source generators each having a child laser, of lesser performance than the parent laser, that is injection locked to the single optical source. The optical source generators may have one or both of a shared configuration and a cascaded configuration that replicates the single optical source, or a single wavelength of the single optical source when it is a comb source.

A coherent optical injection locking (COIL) apparatus generates multiple optical source outputs from a single optical source generated by a parent laser. The COIL apparatus includes a plurality of optical source generators each having a child laser, of lesser performance than the parent laser, that is injection locked to the single optical source. The optical source generators may have one or both of a shared configuration and a cascaded configuration that replicates the single optical source, or a single wavelength of the single optical source when it is a comb source.