摘要:
A WDM system having at least two channels, each of which employs two polarizations, is arranged so that the start times of symbols carried by one polarization of a channel are displaced in time from the start times of symbols carried by the other polarization of that channel, e.g., the start time for each symbol on one polarization is not substantially synchronized with the closest-in-time symbol start time on the other polarization of that channel. Preferably, the data signals are modulated using a return-to-zero (RZ) format and the start times of the symbols of the data signal carried by one polarization of a channel is offset from the start time of the symbols data signal carried by the other polarization of that channel by between 20% to 80%—preferably 50%—of the symbol period of the data signals, when the data signals have the same symbol period.
摘要:
A WDM system having at least two channels, each of which employs two polarizations, is arranged so that the start times of symbols carried by one polarization of a channel are displaced in time from the start times of symbols carried by the other polarization of that channel, e.g., the start time for each symbol on one polarization is not substantially synchronized with the closest-in-time symbol start time on the other polarization of that channel. Preferably, the data signals are modulated using a return-to-zero (RZ) format and the start times of the symbols of the data signal carried by one polarization of a channel is offset from the start time of the symbols data signal carried by the other polarization of that channel by between 20% to 80%—preferably 50%—of the symbol period of the data signals, when the data signals have the same symbol period.
摘要:
In one embodiment, an optical receiver has a bulk dispersion compensator and a butterfly equalizer serially connected to one another to perform dispersion-compensation processing and electronic polarization de-multiplexing. The bulk dispersion compensator has a relatively large dispersion-compensation capacity, but is relatively slow and operates in a quasi-static configuration. The butterfly equalizer has a relatively small dispersion-compensation capacity, but can be dynamically reconfigured on a relatively fast time scale to track the changing conditions in the optical-transport link. The optical receiver has a feedback path that enables the configuration of the bulk dispersion compensator to be changed based on the configuration of the butterfly equalizer in a manner that advantageously enables the receiver to tolerate larger amounts of chromatic dispersion and/or polarization-mode dispersion than without the use of the feedback path.
摘要:
In an over-sampled maximum-likelihood sequence estimation (MLSE) receiver system, the optimal sample spacing is determined for a variety of conditions. In an illustrative implementation, the system includes an optical filter for tightly filtering an incoming optical data signal with an on-off-keying (OOK) non-return-to-zero (NRZ) format, followed by an optical-to-electrical converter, an electrical filter, a sampler, and a MLSE receiver. The sampler samples the filtered electrical data signal twice each bit period with unequal sample spacings. For wide optical filtering bandwidths, the optimal sample spacing occurs at less than 50% of a bit period. For narrow bandwidths, the optimal sample instances occur closer to the maximum eye opening.
摘要:
A representative optical receiver of the invention receives an optical transverse-mode-multiplexed (TMM) signal through a multimode fiber that supports a plurality of transverse modes. The optical receiver has a plurality of optical detectors operatively coupled to a digital signal processor configured to process the TMM signal to determine its modal composition. Based on the determined modal composition, the optical receiver demodulates each of the independently modulated components of the TMM signal to recover the data encoded onto the TMM signal at the remote transmitter.
摘要:
An optical receiver comprising an optical-to-electrical converter and a digital processor having one or more equalizer stages. The optical-to-electrical converter is configured to mix an optical input signal and an optical local-oscillator signal to generate a plurality of electrical digital measures of the optical input signal. The digital processor is configured to process the electrical digital measures to recover the data carried by the optical input signal. At least one of the equalizer stages is configured to perform signal-equalization processing in which the electrical digital measures and/or digital signals derived from the electrical digital measures are being treated as linear combinations of arbitrarily coupled signals, rather than one or more pairs of 90-degree phase-locked I and Q signals. The latter feature enables the digital processor to more-effectively mitigate the receiver-, link-, and/or transmitter-induced signal impairments because various orthogonality-degrading effects can be mitigated in a relatively straightforward manner.
摘要:
A representative optical receiver of the invention receives an optical transverse-mode-multiplexed (TMM) signal through a multimode fiber that supports a plurality of transverse modes. The optical receiver has a plurality of optical detectors operatively coupled to a digital signal processor configured to process the TMM signal to determine its modal composition. Based on the determined modal composition, the optical receiver demodulates each of the independently modulated components of the TMM signal to recover the data encoded onto the TMM signal at the remote transmitter.
摘要:
An optical communication system having an optical transmitter and an optical receiver optically coupled via a multi-path fiber. The optical transmitter launches, into the multi-path fiber, an optical transverse-mode-multiplexed (TMM) signal having a plurality of independently modulated components by coupling each independently modulated component into a respective transverse mode of the multi-path fiber. The TMM signal undergoes inter-mode mixing in the multi-path fiber before being received by the optical receiver. The optical receiver processes the received TMM signal to reverse the effects of inter-mode mixing and recover the data carried by each of the independently modulated components.
摘要:
An optical communication system having an optical transmitter and an optical receiver optically coupled via a multi-path fiber. The optical transmitter launches, into the multi-path fiber, an optical transverse-mode-multiplexed (TMM) signal having a plurality of independently modulated components by coupling each independently modulated component into a respective transverse mode of the multi-path fiber. The TMM signal undergoes inter-mode mixing in the multi-path fiber before being received by the optical receiver. The optical receiver processes the received TMM signal to reverse the effects of inter-mode mixing and recover the data carried by each of the independently modulated components.
摘要:
An example method includes modulating an optical signal using a Phase Shift Keying (PSK) signal constellation, wherein signal points of the PSK signal constellation are located on at least two rings. The first ring has a first radius r1 and a second ring has a second radius r2, wherein the first radius and second radius differ, and wherein the signal points are not located on a regular n-dimension lattice, where n is an integer. The regular n-dimension lattice is formed from a minimum number of lines parallel to an axis for each of the n-dimensions that connect ones of the signal points of the PSK signal constellation on either side of an origin of the axis. The second radius may be greater than the first radius, with the second radius a non-integer multiple of the first ring radius.