Polarization diversity detection of optical signals transmitted through a polarization-mode dispersive medium
First Claim
1. An apparatus for detecting an optical signal transmitted over a medium having polarization-dependent transmission properties, the apparatus comprising:
- a polarization controller arranged in an optical signal path of the optical signal;
a polarization beam splitter arranged in the optical signal path after the polarization controller to separate the optical signal into a first polarization component and a second polarization component Of generally unequal relative strengths; and
means for generating a control signal corresponding to a phase difference between the first and second polarization components, wherein the phase difference is measured between electrical data streams superimposed on the first and second polarization components in a manner independent of the relative strengths of the first and second polarization components, wherein the control signal is supplied to the polarization controller to adjust the polarization of the optical signal.
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Abstract
An apparatus and method which utilize polarization diversity detection to compensate for polarization-mode dispersion (PMD) introduced in an optical signal propagating over a medium such as optical fiber. A received optical signal is separated into first and second polarization components by a polarization beam splitter (PBS). A control signal corresponding to a phase difference between the polarization components is used to drive at least one polarization controller located in the optical signal path before the PBS, such that the two polarization components are aligned with the PSPs of the received optical signal. The control signal may also be used to adjust a variable delay element such that phases of the two polarization components are aligned before the components are combined to provide a PMD-compensated output signal. Other aspects of the invention are directed to polarization control using a rotator element with low numerical aperture input and output signal coupling, and to the use of feedback control to compensate for variations in loss through a polarization controller.
91 Citations
19 Claims
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1. An apparatus for detecting an optical signal transmitted over a medium having polarization-dependent transmission properties, the apparatus comprising:
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a polarization controller arranged in an optical signal path of the optical signal; a polarization beam splitter arranged in the optical signal path after the polarization controller to separate the optical signal into a first polarization component and a second polarization component Of generally unequal relative strengths; and means for generating a control signal corresponding to a phase difference between the first and second polarization components, wherein the phase difference is measured between electrical data streams superimposed on the first and second polarization components in a manner independent of the relative strengths of the first and second polarization components, wherein the control signal is supplied to the polarization controller to adjust the polarization of the optical signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A method of detecting an optical signal comprising the steps of:
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separating the optical signal into a first polarization component and a second polarization component; generating a control signal corresponding to a phase difference between the first and second polarization components of generally unequal strengths, wherein the phase difference is measured between electrical data streams superimposed on the first and second polarization components in a manner independent of the relative strengths of the first and second polarization components; and adjusting the polarization of the optical signal in response to the control signal prior to separating the optical signal into first and second polarization components. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19)
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Specification