A quantum communications system includes a quantum key generation system having a photonic quantum bit generator, a dispersion compensating optical fiber link, and a photon detector unit and a communications network having a signal generator, a signal channel, and a signal receiver. The dispersion compensating optical fiber link extends between and optically couples the photonic quantum bit generator and the photon detector unit. Further, the dispersion compensating optical fiber link is structurally configured to induce dispersion at an absolute dispersion rate of about 9 ps/(nm)km or less and induce attenuation at an attenuation rate of about 0.18 dB/Km or less such that the quantum key bit information of a plurality of photons output by the one or more photonic quantum bit generators is receivable at the photon detector unit at a bit rate of at least about 10 Gbit/sec.

A quantum communications system includes a quantum key generation system having a photonic quantum bit generator, a dispersion compensating optical fiber link, and a photon detector unit and a communications network having a signal generator, a signal channel, and a signal receiver. The dispersion compensating optical fiber link extends between and optically couples the photonic quantum bit generator and the photon detector unit. Further, the dispersion compensating optical fiber link is structurally configured to induce dispersion at an absolute dispersion rate of about 9 ps/(nm)km or less and induce attenuation at an attenuation rate of about 0.18 dB/Km or less such that the quantum key bit information of a plurality of photons output by the one or more photonic quantum bit generators is receivable at the photon detector unit at a bit rate of at least about 10 Gbit/sec.

A method (200) of controlling compensation of chromatic dispersion in an optical transport network. The method comprises determining (202) whether a residual dispersion, RD, of a first path (3) within the network is within a defined RD range and if the RD of the first path is outside the defined RD range the method comprises identifying (204) a first tuneable dispersion compensation module, TDCM, crossed by the first path (3), configured to apply a respective value of dispersion compensation. The method also comprises determining (206) a different value of dispersion compensation to be applied by the first TDCM to bring the RD of the first path within the defined RD range; if (208) the first TDCM is crossed by at least one other path (1, 2), checking (210) that the respective RD of said at least one other path is within a respective defined RD range for said different value of dispersion compensation; and generating (212) a control signal comprising instructions configured to set the first TDCM to apply said different value of dispersion compensation.

A first optical transceiver includes a transmission signal processor that generates a multi-valued pulse amplitude modulation signal including a fixed bit pattern. The first optical transceiver includes an optical transmitter that transmits the multi-valued pulse amplitude modulation signal as an optical transmission signal. The first optical transceiver includes an optical receiver that receives an optical adjustment signal from a second optical transceiver to reproduce an adjustment signal from the optical adjustment signal. The first optical transceiver includes a first controller that controls the transmission signal processor based on a bit error rate included in the optical adjustment signal to adjust light power at each level of the optical transmission signal.

An optical transmission system is an optical transmission system for transmitting a signal from an optical transmitter to an optical receiver via at least a transmission line among one or more optical nodes and the transmission line, wherein the optical transmitter includes a digital filter that compensates for, between ripple components that are micro-fluctuating components in a frequency region representing a transmission characteristic of the signal in the optical transmitter and the optical receiver and non-ripple components of the transmission characteristic, at least the ripple components of the transmission characteristic, and at least one of the optical node and the optical transmitter includes an optical filter that compensates for the non-ripple components of the transmission characteristic.

An optical transmission system is an optical transmission system for transmitting a signal from an optical transmitter to an optical receiver via at least a transmission line among one or more optical nodes and the transmission line, wherein the optical transmitter includes a digital filter that compensates for, between ripple components that are micro-fluctuating components in a frequency region representing a transmission characteristic of the signal in the optical transmitter and the optical receiver and non-ripple components of the transmission characteristic, at least the ripple components of the transmission characteristic, and at least one of the optical node and the optical transmitter includes an optical filter that compensates for the non-ripple components of the transmission characteristic.

An optical Digital Signal Processor (DSP) circuit includes a digital core configured to implement digital signal processing functionality and configured to operate at a plurality of baud rates including a full baud rate and a half-baud rate; and an analog interface including a Digital-to-Analog Converter (DAC) section and an Analog-to-Digital Converter (ADC) section, wherein the analog interface is connected to the digital core and is configured to operate at the full baud rate when the digital core is configured to operate at any of the plurality of baud rates.

A method of dispersion compensation for an optical link includes establishing communication using a first symbol rate over the optical link, determining a dispersion compensation for the optical link based on the communication at the first symbol rate, and establishing communication using a second symbol rate over the optical link using the determined dispersion compensation, wherein the second symbol rate is higher than the first symbol rate.

A method of dispersion compensation for an optical link includes establishing communication using a first symbol rate over the optical link, determining a dispersion compensation for the optical link based on the communication at the first symbol rate, and establishing communication using a second symbol rate over the optical link using the determined dispersion compensation, wherein the second symbol rate is higher than the first symbol rate.

Described herein are systems and methods that perform coarse chromatic dispersion (CD) compensation by applying precomputed coarse front-end equalizer (FEE) tap weights to a receiver based on an assumed propagation distance. After a waiting period, the FEE tap weights are applied, and it is determined whether the FEE tap weights cause a decision-directed tracking of channel rotations to satisfy a stability metric. In response to the stability metric not being satisfied, the assumed propagation distance is adjusted and used to obtain updated FEE tap weights. Conversely, if the stability metric is satisfied, a fine CD compensation is performed that comprises maintaining the updated FEE tap weights; performing an iterative least-mean-squared (LMS) error adaption to adjust Back-End Equalizer (BEE) tap weights and obtain updated BEE tap weights; and using the updated BEE tap weights to adjust the FEE tap weights to, ultimately, have the BEE output an equalized data bit stream.