# US 8,543,006 B2 · System and method for reducing polarization dependent loss > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,543,006 B2 - Document ID: US8543006B2 - Status: Granted - Kind: B2 - Application number: 12/879,762 - Filed: 2010-09-10 - Published: 2012-03-15 - Granted: 2013-09-24 - Earliest claimed: 2010-09-10 - Assignees: Fujitsu Limited - Applicants: Olga I Vassilieva; Youichi Akasaka - Inventors: Olga I Vassilieva; Youichi Akasaka - Web page: https://patentgrep.com/patent/US8543006B2 ## CPC - H04B 10/2572: {due to forms of polarisation-dependent distortion other than PMD} - H04J 14/02216: {by gain equalization} - H04J 14/06: Polarisation multiplex systems - H04J 14/0201: {Add-and-drop multiplexing} - H04B: TRANSMISSION - H04J: MULTIPLEX COMMUNICATION (transmission in general H04B; peculiar to transmission of digital information H04L5/00; systems for the simultaneous or sequential transmission of more than one television signal H04N7/08; in exchanges H04Q11/00; stereophonic systems H04S) ## Abstract A method is provided for reducing polarization dependent loss experienced by an optical signal comprises monitoring a power level of a polarization multiplexed optical signal. The method further comprises detecting a power spike based on the monitored power. The power spike is induced by misalignment of a polarization component axis of the optical signal with a polarization dependent loss (PDL) axis of one or more network elements. The method further comprises rotating the polarization orientation of the optical signal such that the power spike is reduced. ## Claims ### Claim 1 A method for reducing polarization dependent loss experienced by an optical signal comprising: monitoring a power level of a polarization division multiplexed optical signal after the optical signal leaves one or more polarization dependent loss (PDL) inducing components; detecting a power spike based on the monitored power, the power spike induced by misalignment of a polarization component of the optical signal with a PDL axis associated with the one or more PDL inducing components; and rotating the polarization orientation of the optical signal before the optical signal reaches the one or more PDL inducing components such that the power spike is reduced, wherein detecting a power spike further comprises detecting at least a twenty-five percent increase in the monitored power level. ### Claim 2 (depends on 1) The method of claim 1, wherein rotating the polarization further comprises rotating the polarization until the power spike is reduced such that the monitored power is equal to a baseline power level. ### Claim 3 (depends on 1) The method of claim 1, wherein rotating the polarization further comprises rotating the polarization in increments. ### Claim 4 (depends on 1) The method of claim 1, wherein the signal comprises a wavelength division multiplexed (WDM) signal that comprises a plurality of channels, wherein the method further comprises: monitoring a power level for each of the plurality of channels; detecting whether a power spike has occurred for each of the plurality of channels based on the monitored power of each of the plurality of channels; and rotating the polarization of each of the channels experiencing a power spike. ### Claim 5 (depends on 4) The method of claim 4, further comprising sweeping through each channel with a scanning filter to allow sequential power level monitoring of each channel. ### Claim 6 (depends on 1) The method of claim 1, wherein rotating the polarization further comprises rotating the polarization such that the polarization component axis of the signal is substantially aligned with the axis of the PDL to reduce the power spike. ### Claim 7 (depends on 1) The method of claim 1, wherein rotating the polarization further comprises rotating the polarization such that a polarization component axis of the signal is aligned with the axis of the PDL within a twenty degree angle to reduce the power spike. ### Claim 8 (depends on 1) The method of claim 1, wherein monitoring the power level further comprises monitoring the power before the signal enters an optical fiber. ### Claim 9 (depends on 1) The method of claim 1, further comprising determining an average power level of the signal based on the monitored power and wherein detecting a power spike further comprises detecting the power spike based on the average power. ### Claim 10 A system for reducing polarization dependent loss experienced by an optical signal comprising: a power monitor configured to monitor power of a polarization division multiplexed optical signal after the optical signal leaves one or more polarization dependent loss (PDL) inducing components; a polarization controller configured to rotate a polarization of the optical signal before the optical signal reaches the one or more PDL inducing components; a control unit coupled to the power monitor and polarization controller and configured to: determine a power spike based on the monitored power, the power spike induced by misalignment of a polarization component axis of the signal with a PDL axis associated with the one or more PDL inducing components; and control the polarization controller to rotate the polarization orientation of the signal such that the power spike is reduced, wherein the control unit is further configured to detect a power spike based on at least a twenty-five percent increase in the monitored power level. ### Claim 11 (depends on 10) The system of claim 10, wherein the control unit is further configured to control the polarization controller to rotate the polarization orientation of the signal until the power spike is reduced such that the monitored power is equal to a baseline power level. ### Claim 12 (depends on 10) The system of claim 10, wherein the control unit is further configured to control the polarization rotator to rotate the polarization in increments. ### Claim 13 (depends on 10) The system of claim 10, wherein the signal comprises a wavelength division multiplexed (WDM) signal that comprises a plurality of channels; wherein the power monitor is configured to monitor the power of each channel; wherein the polarization controller further comprises: a de-multiplexer configured to split the WDM signal into its constituent channels; and a plurality of polarization controllers coupled to the de-multiplexer, each polarization controller configured to rotate the polarization of a different channel; and wherein the control unit is further configured to determine a power spike and control rotation of the polarization with respect to each of the plurality of channels. ### Claim 14 (depends on 13) The system of claim 13 further comprising a scanning filter coupled to the power monitor and configured to sweep through each channel of the WDM signal to allow sequential power level monitoring of each channel. ### Claim 15 (depends on 10) The system of claim 10, wherein the control unit is further configured to control the rotation of the polarization such that the polarization component axis of the signal is substantially aligned with the axis of the PDL to reduce the power spike. ### Claim 16 (depends on 10) The system of claim 10, wherein the control unit is further configured to control the rotation of the polarization such that a polarization component axis of the signal is aligned with an axis of the PDL within a twenty-degree angle to reduce the power spike. ### Claim 17 (depends on 10) The system of claim 10, wherein the control unit is further configured to determine an average power level of the signal based on the monitored power and determine the power spike based on the average power level. ### Claim 18 (depends on 10) The system of claim 10, wherein the power monitor is further configured to monitor the power before the signal enters an optical fiber.