Apparatus and method for measurement and adaptive control of polarization mode dispersion in optical fiber transmission systems
First Claim
1. An optical fiber transmission system for transmitting an optical signal with reduced polarization mode dispersion (PMD) along an optical transmission path subject to PMD comprising:
- an optical source of at least one optical signal;
an optical fiber transmission path optically coupled to the source for transmitting the signal;
a PMD measuring device optically coupled to the path downstream of the source for providing a measure signal indicative of the PMD-induced change in different polarization components of the signal; and
a tunable PMD compensating device tunably responsive to the measure signal for compensating PMD in the optical signal.
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Abstract
In accordance with the invention, an optical fiber transmission system is provided with a new method and apparatus to measure PMD and then to use the measurements to control adaptive optical filters that minimize system signal degradation. The measurements provide accurate information to compensate for distortions and thereby permit higher transmission rates. The new technique can obtain phase information without optical heterodyning and without bandlimiting. In a first embodiment, an optical signal transmitter, such as a laser/modulator pair, is driven by a data signal combined with a test signal, in the form of a comb of tones with known relative magnitude and phase relationships. Tunable all pass filters recover phase and magnitude information to control an adaptive filter for precise compensation. In a second embodiment, no changes are made to the transmitted signal. The relative delay between orthogonal polarizations of a modulated signal can be obtained by using a polarization beam splitter (PBS), flipping (rotating by 90°) the polarization of one output, sweeping a narrowband optical filter (NBF) across the signal spectrum and detecting the interference between polarizations. Additional detectors can obtain the magnitude versus frequency for the orthogonal components, x and y.
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Citations
20 Claims
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1. An optical fiber transmission system for transmitting an optical signal with reduced polarization mode dispersion (PMD) along an optical transmission path subject to PMD comprising:
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an optical source of at least one optical signal;
an optical fiber transmission path optically coupled to the source for transmitting the signal;
a PMD measuring device optically coupled to the path downstream of the source for providing a measure signal indicative of the PMD-induced change in different polarization components of the signal; and
a tunable PMD compensating device tunably responsive to the measure signal for compensating PMD in the optical signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
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Specification