Coherent optical communications technology for recovery of 1D and 2D formatted optical signals. For example, 1D or 2D formatted signals that travel through fiber optic media may be recovered by separating the light into X- and Y-polarization components, rotating one polarization component (e.g., Y-component) into the polarization space of the other component (e.g., Y-component into the X-polarization space), delaying the rotated component enough to avoid destructive interference and combining the delayed component with the undelayed component to form a folded optical signal, which may then be processed as a X-polarized signal.

An optical reception apparatus includes an optical coherent reception unit that generates an I-axis component of a reception signal and a Q-axis component of the reception signal based on an optical signal subjected to continuous phase frequency shift keying, a conversion unit that generates a digital signal of the I-axis component of the reception signal and a digital signal of the Q-axis component of the reception signal, a differential detection unit that generates a differential detection signal, a frequency offset compensation unit that derives a phase change amount or a temporal change in the Q-axis component of the differential detection signal whose component of a frequency offset has been compensated, a clock error detection unit that detects an amount of shift of a sampling phase of the differential detection signal whose component of the frequency offset has been compensated, based on the phase change amount or the temporal change in the Q-axis component of the differential detection signal, and a reception clock generation unit that generates the clock at a frequency adjusted such that the amount of shift becomes small.

Apparatus and method for digital signal constellation transformation are provided herein. In certain configurations, an integrated circuit includes an analog front-end that converts an analog signal vector representing an optical signal into a digital signal vector, and a digital signal processing circuit that processes the digital signal vector to recover data from the optical signal. The digital signal processing circuit generates signal data representing a signal constellation of the digital signal vector. The digital signal processing circuit includes an adaptive gain equalizer that compensates the signal data for distortion of the signal constellation arising from biasing errors of optical modulators used to transmit the optical signal.

An optical reception apparatus includes: an optical coherent reception unit that receives a frequency-modulated optical signal whose optical intensity is approximately constant and generates an I-axis component of a reception signal and a Q-axis component of the reception signal based on the optical signal; a conversion unit that generates a digital signal of the I-axis component of the reception signal and a digital signal of the Q-axis component of the reception signal; a differential detection unit that generates a differential detection signal by controlling a delay amount of the digital signal of the I-axis component and a delay amount of the digital signal of the Q-axis component so that a distance between symbols on an IQ plane is increased and by performing differential detection on the digital signal of the I-axis component whose delay amount is controlled and on the digital signal of the Q-axis component whose delay amount is controlled; and an inter-symbol-distance measuring unit that measures a distance between the symbols based on a phase change amount of the differential detection signal and feeds the distance between the symbols back to the differential detection unit.

An optical access network includes an optical hub having at least one processor, and a plurality of optical fiber strands. Each optical fiber strand has a first strand end connected to the optical hub. The network further includes a plurality of nodes connected to at least one segment of a first fiber strand of the plurality of optical fiber strands. Each node is sequentially disposed at respective locations along the first fiber strand at different differences from the optical hub, respectively. The network further includes a plurality of end-points. Each end-point includes a receiver. Each respective receiver (i) has a different optical signal-to-noise ratio (OSNR) from the other receivers, (ii) is operably coupled with at least one node of the plurality of nodes, and (iii) is configured to receive the same optical wavelength signal from the first fiber strand as received by the other receivers.

Techniques are described for determining pre-compensation parameters to compensate for signal integrity degradation along a signal path. A processor generates a first digital signal and receives a second digital signal. The second digital signal is generated from an optical-to-electrical conversion of a feedback optical signal that is generated from an electrical-to-optical conversion of an electrical signal by an optical module. The processor determines the pre-compensation parameters based on the first and second digital signals.

A network or system in which a hub or primary node may communicate with a plurality of leaf or secondary nodes. The hub node may operate or have a capacity greater than that of the leaf nodes. Accordingly, relatively inexpensive leaf nodes may be deployed to receive data carrying optical signals from, and supply data carrying optical signals to, the hub node. One or more connections may couple each leaf node to the hub node, whereby each connection may include one or more spans or segments of optical fibers, optical amplifiers, optical splitters/combiners, and optical add/drop multiplexer, for example. Optical subcarriers may be transmitted over such connections, each carrying a data stream. The subcarriers may be generated by a combination of a laser and a modulator, such that multiple lasers and modulators are not required, and costs may be reduced. As the bandwidth or capacity requirements of the leaf nodes change, the number of subcarriers, and thus the amount of data provided to each node, may be changed accordingly. Each subcarrier within a dedicated group of subcarriers may carry OAM or control channel information to a corresponding leaf node, and such information may be used by the leaf node to configure the leaf node to have a desired bandwidth or capacity.

A nonlinear compensation unit (300) includes a first compensation unit (350) and a second compensation unit (360). The first compensation unit (350) compensates for each of two polarization signals E.sub.x and E.sub.y so as to cancel a first amount of phase rotation which is the amount of phase rotation calculated based on the signal strength of the two polarization signals E.sub.x and E.sub.y. The second compensation unit (360) compensates for each of the two polarization signals E.sub.x and E.sub.y so as to cancel a second amount of phase rotation which is the amount of phase rotation calculated based on the perturbative component of the two polarization signals E.sub.x and E.sub.y. The first compensation unit (350) includes a strength calculation unit (302), a first filter unit (304), and a first phase modulation unit (306). The second compensation unit (360) includes a perturbative component calculation unit (316), a second filter unit (318), a second phase modulation unit (322), and a third phase modulation unit (330).

Disclosed herein is a monolithically integrated coherent receiver chip which has a geometric arrangement of the on-chip components that significantly improves the performance and the manufacturability of a coherent receiver module for Dual Polarization Quadrature Phase Shift Keyed (DP-QPSK) applications and other optical coherent detection systems. The coherent receiver chip comprises two optical hybrids, three optical inputs and eight electrical outputs with the two optical hybrids oriented perpendicular to the optical inputs and the electrical outputs which are widely spaced and arranged in a co-linear fashion that simplifies module design and assembly. The proposed geometric arrangement also replaces any optical waveguide crossings with vertical electrical-optical crossings and includes electrical transmissions which are used to minimize channel skew. The proposed configuration also has the additional benefit of improved thermal management by separating the module's trans-impedance amplifiers.

An apparatus comprises a front end configured to receive an optical signal, and convert the optical signal into a plurality of digital signals, and a processing unit coupled to the front end and configured to determine a best-match chromatic dispersion (CD) estimate in the optical signal by optimizing a cost function based on signal peaks of the plurality of digital signals.