Equalizer for an optical transmission system

Patent metadata

Field	Value
Publication number	US-9166703-B2
Application number	US-200913148309-A
Country	US
Kind code	B2
Filing date	Feb 20, 2009
Priority date	Feb 20, 2009
Publication date	Oct 20, 2015
Grant date	Oct 20, 2015

Abstract

An equalizer ( 60 ) processes, in the electrical domain, a signal obtained from a path of an optical transmission system. The equalizer comprises N cascaded stages (where N≧1). At least one of the stages comprises a cascade of a linear equalization element ( 61 ) and a non-linear equalization element ( 62 ). The equalizer ( 60 ) is able to compensate for both linear impairments, such as dispersion, and non-linear impairments. The cascaded linear and non-linear elements can simulate the effect of signal propagation through a fiber which has the opposite propagation parameters (e.g. attenuation, dispersion, non-linearity) to those of the propagation path experienced by a signal in the transmission system. The non-linear equalization element ( 62 ) can be a non-linear phase rotator which rotates phase of an input signal proportional to the squared modulus of the input signal amplitude. The linear equalization element ( 61 ) can comprise a digital filter, such as an Infinite Impulse Response (HR) filter or a Finite Impulse Response (FIR) filter.

First claim

The invention claimed is:

1. An equalizer for processing, in a digital electrical domain, a signal obtained from a path of an optical transmission system, the equalizer disposed in a digital signal processor and comprising a plurality of cascaded stages, where at least two of the plurality of cascaded stages each comprise a cascade of:
a linear equalization element; and
a non-linear equalization element, the linear equalization element and the non-linear equalization element each comprising adjustable parameters,
wherein the digital signal processor is configured to monitor a performance parameter of the equalizer and to control values of the adjustable parameters to optimize the performance parameter,
wherein the non-linear equalization element is a non-linear phase rotator, and
wherein the linear equalization element compensates for dispersion and the non-linear equalization element compensates for nonlinearity in each of the at least two of the plurality of cascaded stages.

2. The equalizer of claim 1 , wherein the non-linear equalization element has an input for receiving an input signal and is arranged to rotate a phase of the input signal proportional to a squared modulus of an amplitude of the input signal.

3. The equalizer of claim 1 , wherein the linear equalization element is one of a finite impulse response filter and an infinite impulse response filter.

4. The equalizer of claim 1 , wherein, in at least one of the cascaded stages that comprises the cascade of the linear equalization element and the non-linear equalization element, the linear equalization element is an infinite impulse response filter.

5. The equalizer of claim 4 , wherein the linear equalization element is an all-pass infinite impulse response filter.

6. The equalizer of claim 1 , wherein, in at least one of the cascaded stages that comprises the cascade of the linear equalization element and the non-linear equalization element, the linear equalization element is a finite impulse response filter.

7. The equalizer of claim 1 , wherein each of the plurality of cascaded stages comprise a cascade of:
a linear equalization element; and
a non-linear equalization element.

8. The equalizer of claim 1 , wherein each of the plurality of cascaded stages comprises a cascade of:
a first-order infinite impulse response filter having configurable parameters; and
a non-linear element configured to be selectively bypassed.

9. The equalizer of claim 8 , wherein a configurable parameter of the first-order infinite impulse response filter in each cascaded stage is configurable to cause the filter to perform as a first-order finite impulse response filter.

10. The equalizer of claim 1 , wherein at least one of the plurality of cascaded stages comprises only a linear equalization element.

11. The equalizer of claim 1 , wherein the plurality of cascaded stages comprises 10 cascaded stages.

12. The equalizer of claim 1 , wherein the plurality of cascaded stages comprises 50 cascaded stages.

13. A system, comprising:
an equalizer for processing, in a digital electrical domain, a signal obtained from a path of an optical transmission system, the equalizer comprising a plurality of cascaded stages, where at least two of the plurality of cascaded stages each comprise a cascade of:
an adaptable linear equalization element; and
an adaptable non-linear equalization element, the linear equalization element and the non-linear equalization element each comprising a plurality of adjustable parameters; and
a processor in communication with the linear equalization element and the non-linear equalization element of each of the plurality of cascaded stages to monitor a performance parameter of the equalizer and to control values of the plurality of adjustable parameters to optimize the performance parameter,
wherein the non-linear equalization element is a non-linear phase rotator, and
wherein the linear equalization element compensates for dispersion and the non-linear equalization element compensates for nonlinearity in each of the at least two of the plurality of cascaded stages.

14. The system of claim 13 , wherein the processor is arranged to adaptively determine values for the parameters during operation of the optical transmission system.

15. A node for an optical transmission system, comprising:
an equalizer for processing, in a digital electrical domain, a signal obtained from a path of an optical transmission system, the equalizer disposed in a digital signal processor and comprising a plurality of cascaded stages, where at least two of the plurality of cascaded stages each comprise a cascade of:
a linear equalization element; and
a non-linear equalization element, the linear equalization element and the non-linear equalization element each comprising adjustable parameters,
wherein the node is configured to monitor a performance parameter of the equalizer and to control values of the adjustable parameters to optimize the performance parameter,
wherein the non-linear equalization element is a non-linear phase rotator, and
wherein the linear equalization element compensates for dispersion and the non-linear equalization element compensates for nonlinearity in each of the at least two of the plurality of cascaded stages.

16. The node of claim 15 , further comprising a receiver, the receiver comprising:
an input for receiving an optical signal from a transmission path of the optical transmission system; and
an optical-to-electrical converter for converting the received optical signal into an electrical signal;
wherein the equalizer is arranged to process the electrical signal.

17. The node of claim 15 , further comprising a transmitter, wherein the equalizer is arranged to process a communication signal in the electrical domain, and the transmitter comprises:
an electrical-to-optical converter for converting a processed communication signal into an optical signal; and
an output for transmitting the optical signal onto a transmission path of the optical transmission system.

18. A method of equalizing, in a digital electrical domain, a signal obtained from a path of an optical transmission system, the method comprising:
processing the signal by digital signal processer comprising a plurality of cascaded processing stages, wherein at least two of the plurality of cascaded processing stages performs:
processing the signal with a linear equalization function; and
processing the signal with a non-linear equalization function, the linear equalization function and the non-linear equalization function comprising configurable parameters,
wherein a performance parameter is monitored and values of the configurable parameters are adjusted to optimize the performance parameter,
wherein the non-linear equalization function is a non-linear phase rotator, and
wherein the processing of the signal with the linear equalization function compensates for dispersion and the processing of the signal with the non-linear equalization function compensates for nonlinearity in each of the at least two of the plurality of cascaded processing stages.

19. The method of claim 18 , further comprising:
receiving an optical signal from a transmission path of the optical transmission system; and
converting the optical signal into an electrical signal;
wherein the method of equalizing is performed on the electrical signal.

20. The method of claim 18 , wherein the method of equalizing is performed on an electrical signal to form an equalized electrical signal,

Assignees

• Secondini Marco
• Forestieri Enrico
• Ericsson Telefon Ab L M

Inventors

• Secondini Marco
• Forestieri Enrico

Classifications

• H04L25/03133

  with a non-recursive structure (H04L25/03127 takes precedence) · CPC title

• H04B10/6971 Primary

  using equalisation · CPC title