# US 9,520,952 B2 · Polarization mode dispersion (PMD) tolerant optical signaling > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,520,952 B2 - Document ID: US9520952B2 - Status: Granted - Kind: B2 - Application number: 14/607,276 - Filed: 2015-01-28 - Published: 2016-07-28 - Granted: 2016-12-13 - Earliest claimed: 2015-01-28 - Assignees: Ciena Corporation - Applicants: Kevin Farley - Inventors: Kevin Farley - Web page: https://patentgrep.com/patent/US9520952B2 ## CPC - H04B 10/6162: {Compensation of polarization related effects, e.g., PMD, PDL} - H04B 10/2569: due to polarisation mode dispersion [PMD] - H04B 10/6166: {Polarisation demultiplexing, tracking or alignment of orthogonal polarisation components} - H04B: TRANSMISSION ## Abstract A method of receiving an optical signal through an optical communication system. The optical signal is transmitted by a transmitter of the optical communication system with a predetermined State of Polarization in a succession of signalling intervals. The SoP in each signalling interval is selected to excite two orthogonal eigenvectors of Polarization Mode Dispersion (PMD) of the optical communication system. The SoP in one signalling interval may be different from the SoP in at least one other signalling interval. Modulation of the optical signal is detected in two orthogonal polarization directions. Modulation components associated with one of the two orthogonal eigenvectors are selected and used to recover data. ## Claims ### Claim 1 In a receiver of an optical communication system, a method comprising: detecting modulation of a received optical signal in two orthogonal polarization directions, the optical signal having been transmitted by a transmitter of the optical communication system with a predetermined State of Polarization (SoP) in a succession of signalling intervals, the SoP in each signalling interval exciting two orthogonal eigenvectors of Polarization Mode Dispersion (PMD) of the optical communication system; and recovering data from modulation components of a selected one of the two orthogonal eigenvectors, based on the detected modulation of the received optical signal. ### Claim 2 (depends on 1) The method as claimed in claim 1, wherein the SoP in a first signalling interval is different from the SoP in a second signalling interval. ### Claim 3 (depends on 1) The method as claimed in claim 1, wherein detecting modulation of the received optical signal comprises: a polarization beam splitter dividing the received optical signal into a pair of linearly polarized optical signals having a mutually orthogonal polarization orientations; a photodetector block detecting respective modulation of each one of the linearly polarized optical signals; and an Analog-to Digital converter block generating a respective polarization sample stream associated with each one of the linearly polarized optical signals, based on the modulation detected by the photodetector block. ### Claim 4 (depends on 1) The method as claimed in claim 1, wherein the signalling interval corresponds with a sample period of the transmitter. ### Claim 5 (depends on 1) The method as claimed in claim 1, wherein the signalling interval corresponds with a symbol period of the optical signal. ### Claim 6 (depends on 1) The method as claimed in claim 1, wherein a symbol period of the optical signal corresponds with a plurality of signalling intervals. ### Claim 7 (depends on 1) The method as claimed in claim 1, wherein selecting modulation components associated with one of the two orthogonal eigenvectors comprises discarding modulation components associated with the other one of the two orthogonal eigenvectors. ### Claim 8 (depends on 2) The method as claimed in claim 2, wherein the predetermined State of Polarization (SoP) is polarized in each signalling interval. ### Claim 9 (depends on 3) The method as claimed in claim 3, wherein recovering data from modulation components associated with the selected one of the two orthogonal eigenvectors comprises: rotating the polarization sample streams to generate respective modulation sample streams of each eigenvector; and selecting the respective modulation sample stream of one of the eigenvectors based on a predetermined criterion. ### Claim 10 (depends on 9) The method as claimed in claim 9, wherein the predetermined criterion comprises any one or more of a Bit Error Rate (BER) and a Signal to Noise Ratio (SNR). ### Claim 11 (depends on 9) The method as claimed in claim 9, wherein rotating the polarization sample streams comprises: estimating an angle between the two orthogonal polarization directions and the eigenvectors; calculating at least one rotation vector based on the estimated angle; and applying the at least one rotation vector to each polarization sample stream to generate the modulation sample streams of each eigenvector. ### Claim 12 A receiver of an optical communication system, the receiver comprising: a detector configured to detect modulation of a received optical signal in two orthogonal polarization directions, the optical signal having been transmitted by a transmitter of the optical communication system with a predetermined State of Polarization (SoP) in a succession of signalling intervals, wherein the SoP in each signalling interval exciting two orthogonal eigenvectors of Polarization Mode Dispersion (PMD) of the optical communication system; and a processor configured to recover data from modulation components of a selected one of the two orthogonal eigenvectors, based on the detected modulation of the received optical signal. ### Claim 13 (depends on 12) The receiver as claimed in claim 12, wherein the SoP in a first signalling interval is different from the SoP in a second signalling interval. ### Claim 14 (depends on 12) The receiver as claimed in claim 12, wherein the detector comprises: a polarization beam splitter dividing the received optical signal into a pair of linearly polarized optical signals having a mutually orthogonal polarization orientations; a photodetector block detecting respective modulation of each one of the linearly polarized optical signals; and an Analog-to Digital converter block generating a respective polarization sample stream associated with each one of the linearly polarized optical signals, based on the respective modulation detected by the photodetector block. ### Claim 15 (depends on 12) The receiver as claimed in claim 12, wherein the predetermined State of Polarization (SoP) is polarized in each signalling interval. ### Claim 16 (depends on 12) The receiver as claimed in claim 12, wherein the signalling interval corresponds with a sample period of the transmitter. ### Claim 17 (depends on 12) The receiver as claimed in claim 12, wherein the signalling interval corresponds with a symbol period of the optical signal. ### Claim 18 (depends on 12) The receiver as claimed in claim 12, wherein a symbol period of the optical signal corresponds with a plurality of signalling intervals. ### Claim 19 (depends on 12) The receiver as claimed in claim 12, wherein the processor is further configured to discard modulation components of the other one of the two orthogonal eigenvectors. ### Claim 20 (depends on 14) The receiver as claimed in claim 14, wherein the processor comprises: a polarization rotator configured to rotate the polarization sample streams to generate respective modulation sample streams of each eigenvector; and a selector configured to select the respective modulation sample stream of one of the eigenvectors based on a predetermined criterion. ### Claim 21 (depends on 20) The receiver as claimed in claim 20, wherein the predetermined criterion comprises any one or more of a Bit Error Rate (BER) and a Signal to Noise Ratio (SNR). ### Claim 22 (depends on 20) The receiver as claimed in claim 20, further comprising an update block configured to: estimate an angle between the two orthogonal polarization directions and the eigenvectors; and calculate at least one rotation vector based on the estimated angle; wherein the polarization rotator is configured to apply the at least one rotation vector to each polarization sample stream to generate the modulation sample streams of each eigenvector.