Digital compensation for optical transmission system
AssigneeNortel Networks Limited
InventorsSeb J Savory, James Whiteaway
Life of this patent
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Abstract
A receiver for an optical transmission system, has a polarization diverse and phase diverse coherent optical receiver, and a digital adaptive equalizer for compensating for distortions in the optical signal introduced by the optical path. The entire field of the optical signal is mapped including phase and polarization information, to enable more complete compensation for impairments such as chromatic dispersion and PMD. Furthermore, it can also reduce the problems which have so far held back coherent optical detection from widespread implementation, such as polarization alignment and phase tracking. This can be applied to upgrade existing installed transmission routes to increase capacity without the expense of replacing the old fiber.
Claims15
A receiver for an optical transmission system, having a polarization diverse and phase diverse coherent optical receiver, for receiving an optical input signal on an optical path and generating digital electrical outputs,
- a digital adaptive equalizer coupled to the digital outputs, for compensating for distortions in the optical signal introduced by the optical path, in which the optical receiver has four outputs, in-phase and quadrature on two polarizations, and
- the optical signal has two or more information channels modulated orthogonally, the adaptive equalizer being arranged to maximise an orthogonality of information channels.
A receiver for an optical transmission system, having
- a polarization diverse and phase diverse coherent optical receiver, for receiving an optical input signal on an optical path and generating digital electrical outputs,
- a digital adaptive equalizer coupled to the digital outputs, for compensating for distortions in the optical signal introduced by the optical path, the adaptive equalizer being a transversal filter, and
- the transversal filter being adapted by iteration of a limited set of independent variables including three defining the orientation and magnitude of PMD, and one each for the chromatic dispersion, the orientation of polarizing element at the receiver, and the phase of a local oscillator used for phase diverse detection in the optical receiver.
Dependencies are inferred from the claim text.