Granted Patent B2

US 7,075,695 · App. 10/790,620 · Granted Jul 11, 2006

Abstract

Claims (34)

1. A method of controlling a bias voltage of a Mach-Zender modulator (MZM) performing a non-return-to-zero (NRZ) modulation of an optical signal, comprising:

generating a digital pilot signal;

modulating the MZM using the digital pilot signal;

coupling a portion of an optical output signal from the MZM to a light detector;

processing an output signal of the light detector using a digital correlation filter to recover the digital pilot signal; and

demodulating the recovered digital pilot signal to produce a feedback signal controlling the bias voltage of the MZM.

2. The method of claim 1 wherein the digital pilot signal is a digitized sinusoidal signal.

3. The method of claim 1 wherein the processing step further comprises:

filtering the output signal of the light detector using a band-path filter

digitizing the output signal of the light detector using an analog-to-digital converter;

sampling the output signal of the analog-to-digital converter; and

applying a digital correlating technique recover at least one of the digital pilot signal or a first harmonic of the digital pilot signal.

4. The method of claim 3 wherein the digital correlating technique further comprises:

time-domain averaging of a pre-determined number of samples of the output signal of the analog-to-digital converter.

5. The method of claim 1 wherein the demodulating step further comprises:

using a digital synchronous demodulating technique, and

generating a signal while maintaining a bias voltage of the MZM at a quadrature bias point.

6. A method of controlling bias voltages of an input Mach-Zender modulator (MZM) and an output MZM coupled for performing a return-to-zero (RZ) modulation or a carrier suppressed RZ (CSRZ) modulation of an optical signal, comprising:

generating a digital pilot signal;

modulating sequentially the input MZM or the output MZM using the digital pilot signal;

coupling a portion of an optical output signal from the output MZM to a light detector;

processing an output signal of the light detector using a digital correlation filter to recover the digital pilot signal; and

demodulating the detected digital pilot signal to produce a feedback signal controlling a bias voltage of an MZM modulated using the digital pilot signal during at least a data sampling period of the processing step.

7. The method of claim 6 wherein the digital pilot signal is a digitized sinusoidal signal.

8. The method of claim 6 wherein the processing step further comprises:

filtering the output signal of the light detector using a band-path filter

digitizing the output signal of the light detector using an analog-to-digital converter;

sampling the output signal of the analog-to-digital converter; and

applying a digital correlating technique recover at least one of the digital pilot signal or a first harmonic of the digital pilot signal.

9. The method of claim 8 wherein the digital correlating technique further comprises:

time-domain averaging of a pre-determined number of samples of the output signal of the analog-to-digital converter.

10. The method of claim 6 wherein the demodulating step further comprises:

using a digital synchronous demodulating technique, and

generating a signal while maintaining a bias voltage of the MZM at a quadrature bias point.

Assignments (8)