Optical dispersion compensation in the electrical domain in an optical communications system

• US 10,164,707 B2
• Filed: 11/27/2017
• Issued: 12/25/2018
• Est. Priority Date: 10/03/2002
• Status: Active Grant

• Current Assignee: Ciena Corporation
• Original Assignee: Ciena Corporation
• Inventors: Roberts, Kim B., O'Sullivan, Maurice, McNicol, John, Parsons, Kieran, Strawczynski, Leo
• Primary Examiner(s): Li, Shi K
• Application Number:
  US15/822,252
• Publication Number:
  US 20180076887A1
• Time in Patent Office: 393 Days
• CPC Class Codes: H04B 10/07951 Monitoring or measuring chromatic dispersion or PMD
• CPC Class Codes: H04B 10/07953 Monitoring or measuring OSNR, BER or Q
• CPC Class Codes: H04B 10/25137 using pulse shaping at the transmitter, e.g. pre-chirping or dispersion supported transmission [DST]
• CPC Class Codes: H04B 10/505 using external modulation
• CPC Class Codes: H04B 10/50597 to control the phase of the modulating signal
• CPC Class Codes: H04B 10/508 Pulse generation, e.g. generation of solitons
• CPC Class Codes: H04B 10/6161 Compensation of chromatic dispersion

Abstract

A compensation function mitigates a substantial portion of the dispersion imparted to a communications signal by an optical communications system. A digital input signal is digitally processed using the compensation function to generate a predistorted signal. An amplitude and a phase of an optical signal are modulated using a pair of orthogonal signal components to generate a predistorted optical signal for transmission. In one implementation, the pair of orthogonal signal components are components of the predistorted signal. In another implementation, the predistorted signal is processed using a non-linear compensator to generate a further distorted signal and the pair of orthogonal signal components are components of the further distorted signal. In that implementation, the non-linear compensator is configured to substantially compensate for nonlinearities in one or both of an optical modulator of a transmitter of the system and an optical-to-electrical converter of a receiver of the system.

Claims

1. A method of compensating chromatic dispersion of a communications signal conveyed through an optical communications system, the method comprising:

digitally processing a digital input signal using a Fast Fourier Transform (FFT) filter and a compensation function to generate a predistorted signal comprising a pair of orthogonal signal components, in-phase (I) and quadrature (Q), wherein the compensation function mitigates the chromatic dispersion of a plurality of spans, each span having a distance greater than 40 kilometers; and

modulating in-phase (I) and quadrature (Q) components of an optical signal using the in-phase (I) and quadrature (Q) components of the predistorted signal,

wherein a data rate of the communications signal exceeds 2 Gb/s.

2. The method as recited in claim 1, further comprising removing part of the chromatic dispersion via linear electrical filtering at a coherent receiver of the optical communications system.

3. The method as recited in claim 1, wherein the compensation function is nonlinear.

4. The method as recited in claim 3, wherein nonlinearity of the compensation function significantly mitigates component or fiber nonlinearities.

5. The method as recited in claim 3, further comprising removing part of the chromatic dispersion via linear electrical filtering at a coherent receiver of the optical communications system.

6. A dispersion compensation system for compensating dispersion of a communications signal conveyed through an optical communications system, the dispersion compensation system comprising:

a processor configured to digitally process a digital input signal using a Fast Fourier Transform (FFT) filter and a compensation function to generate a predistorted signal comprising a pair of orthogonal signal components, in-phase (I) and quadrature (Q), wherein the compensation function mitigates the dispersion of a plurality of spans, each span having a distance greater than 40 kilometers; and

a multi-dimensional optical modulator configured to modulate in-phase (I) and quadrature (Q) components of an optical signal using the in-phase (I) and quadrature (Q) components of the predistorted signal,

wherein a data rate of the communications signal exceeds 2 Gb/s.

7. The dispersion compensation system as recited in claim 6, wherein the processor comprises:

a pair of serial-to-parallel converters configured to convert successive bits of the digital input signal into two parallel bit streams each having a width of N bits; and

a pair of digital-to-analog converters configured to convert streams of successive numerical values to respective ones of the pair of orthogonal signal components.

8. The dispersion compensation system as recited in claim 6, further comprising a coherent receiver configured to remove part of the chromatic dispersion via linear electrical filtering.

9. The dispersion compensation system as recited in claim 6, wherein the compensation function is nonlinear.

10. The dispersion compensation system as recited in claim 9, wherein the nonlinear aspect of the compensation function significantly mitigates component or fiber nonlinearities.

11. The dispersion compensation system as recited in claim 9, further comprising a coherent receiver configured to remove part of the chromatic dispersion via linear electrical filtering.