A coherent optical data receiver having a digital signal processor (DSP) capable of mitigating equalization-enhanced phase noise (EEPN). In an example embodiment, the DSP mitigates EEPN by applying individual phase adjustments to different spectral slices of a digital stream carrying CD-compensated digital samples of the received optical data signal. In different embodiments, the individual phase adjustments can be dynamically selected based on symbol decisions taken prior to EEPN mitigation, based on transmitted pilot symbols, and/or using moving averages computed for different spectral slices. Some embodiments are suitable for handling polarization-division-multiplexed optical data signals. Some embodiments are advantageously capable of producing an effective SNR gain of approximately 1 dB.

A system for laser phase noise compensation for a fibered communication path, the system being configured for connection with a node of the fibered communication path, including at least one signal splitter optically coupled to a laser source of the fibered communication path, the at least one signal splitter having two output communication path, the communication paths having a path difference therebetween; an integrated coherent receiver (ICR) optically coupled to the first output communication path and the second output communication path; and a digital signal processor (DSP) communicatively connected to the ICR, the ICR being configured to determine, based signals received from the first and second output communication paths, at least one phase noise indication related to phase noise of the laser source, the DSP being configured to determine an estimated laser phase noise based on at least the at least one phase noise indication.

The present invention relates to a fiber branch structure for spatial optical communication for transmitting information by emitting communication light. The fiber branch structure is provided with: a light emitter configured to emit communication light; a light emission controller configured to control the light emitter; an optical fiber configured to transmit the light emitted from the light emitter; a distributor configured to distribute the light, the distributer being optically coupled to an output terminal of the optical fiber; and an optical fiber group optically coupled to a plurality of output terminals of the distributor. According to the present invention, a communication area can be established without blind spots. That is, the fiber branch structure for spatial optical communication according to the present invention includes an optical fiber group optically coupled to a plurality of output terminals of the distributor. A communication area can be established more assuredly by such an optical fiber group, which prevents the optical communication from being interrupted.

An optical transmission system including: N transmitters, each of the N transmitters being configured to convert one of N electrical signals indicating data sequences different from one another into an optical signal; a signal generator configured to cause N optical splitters to split the N optical signals output from the N transmitters to convert the N optical signals into M optical signals; a multiplexer configured to convert the M optical signals converted by the signal generator into one mode-multiplexed signal that is excitable in at least M modes; a demultiplexer configured to convert the mode-multiplexed signal converted by the multiplexer into M optical signals; M receivers, each of the M receivers being configured to convert one of the M optical signals converted by the demultiplexer into the electrical signal; and a signal detector configured to perform signal separation on the M electrical signals converted by the M receivers to extract the N data sequences.

In order to improve free space optical communications, an optical communication terminal includes a laser source, a photo detecting apparatus and an optical input/output assembly. These components are controlled by a control logic. In order to have the optical communication terminal to be self-compatible, the optical input/output assembly selectively routes the outgoing beam and incoming beam depending on their respective beam polarization. To this end, the optical input/output assembly may include a polarizing beam splitter together with a quarter-wave plate.

An optical reception device including: a wavelength selection unit configured to split an optical signal amplified by an optical amplifier into different paths according to wavelengths by using a wavelength multiplexer/demultiplexer, and control a passage state of a passage target optical switch through which the optical signal is to be passed, out of a plurality of optical switches provided on the respective paths, to select an optical signal of a path where the optical signal entered and output the optical signal to a receiver; and a wavelength detection unit configured to detect the wavelength of an optical signal by using each of a plurality of optical detectors, determine the passage target optical switch based on a detection result, and output, to the determined passage target optical switch, a control signal for controlling the passage target optical switch so as to enter the passage state, the optical detectors being respectively provided on different paths that are different from the paths on which the plurality of optical switches are provided and that respectively correspond to wavelengths into which the optical signal is split by a wavelength multiplexer/demultiplexer.

Various embodiments of a monolithic transceiver are described, which may be fabricated on a semiconductor substrate. The monolithic transceiver includes a coherent receiver module (CRM), a coherent transmitter module (CTM), and a local oscillation splitter to feed a local oscillation to the CRM and the CTM with a tunable power ratio. The monolithic transceiver provides tunable responsivity by employing photodiodes for opto-electrical conversion. The monolithic transceiver also employs a polarization beam rotator-splitter (PBRS) and a polarization beam rotator-combiner (PBRC) for supporting modulation schemes including polarization multiplexed quadrature amplitude modulation (PM-QAM) and polarization multiplexed quadrature phase shift keying (PM-QPSK).

A wavelength division multiplexing structure includes: a first reflecting surface; a second reflecting surface; a first optical filter; a second optical filter; and a pretreatment device. The light that is incident on the first reflecting surface forms a first C-shaped light path in C-shaped or approximately C-shaped and enters the first optical filter. The light that is incident on the first reflecting surface forms a non-coplanar straight line with the light that is reflected by the second reflecting surface. The light that is incident on the pretreatment device forms a pretreatment light path, enters the first optical filter. The light in the pretreatment light path coincides with the light in the first C-shaped light path that is incident on the first optical filter from the second reflecting surface.

A communication network includes a coherent optics transmitter, a coherent optics receiver, an optical transport medium operably coupling the coherent optics transmitter to the coherent optics receiver, and a coherent optics interface. The coherent optics interface includes a lineside interface portion, a clientside interface portion, and a control interface portion.

A spatial optical transmitter modulates an optical signal of a single wavelength in accordance with a signal to be transmitted, divides the modulated optical signal into two, rotates polarizations of the two divided optical signals, and transmits the two optical signals as optical signals of two orthogonal polarizations to space.