Pilot tone bias control
View Patent ↗A method and apparatus for dynamically compensating for phase deviations using two synchronous rectifiers in a quadrature constellation and a delay line.
1. A method for dynamically compensating for phase deviations of a modulated optical data signal, comprising:
shifting the phase of a pilot tone by 90 degrees;
combining the shifted pilot tone with a modulated signal;
filtering the combined signal to extract a control signal for a delaying element;
delaying the pilot tone in response to the control signal; and
providing the adjusted pilot tone as a reference signal to a first synchronous rectifier in a demodulator.
2. The method of claim 1 , wherein the first rectifier produces a feedback signal.
3. The method of claim 1 , wherein the modulated signal is a return-to-zero (RZ) signal.
4. The method of claim 1 , wherein the pilot tone is obtained from a tone generator.
5. The method of claim 1 , wherein the step of combining is performed by a multiplier.
6. The method of claim 1 , wherein the delaying is accomplished by adjusting the phase of the pilot tone.
7. The method of claim 1 , wherein the delaying is accomplished by a time delay to the pilot tone.
8. The method of claim 1 , wherein the control signal is a DC offset and the delay is determined by an amount of the DC offset.
9. An optical demodulator, comprising:
a first synchronous rectifier comprising:
a first multiplier, for multiplying a modulated signal with a reference signal; and
a first filter, for filtering the first multiplied signal, thereby providing a feedback signal; and
a second synchronous rectifier comprising:
a second multiplier, for multiplying the modulated signal with a pilot tone that has been phase shifted 90 degrees by a phase shifter; and
a second filter, for filtering the second multiplied signal, thereby extracting a control signal for a delay element, wherein the element delays the pilot tone thereby producing the reference signal.
10. The demodulator of claim 9 , further comprises a tone generator for providing the pilot tone.
11. The demodulator of claim 9 , wherein the modulated signal is a return-to-zero (RZ) signal.
12. The demodulator of claim 9 , wherein the first and second filters are low pass filters.
13. The demodulator of claim 9 , wherein the delay element adjusts the phase of the pilot tone.
14. The demodulator of claim 9 , wherein the delay element adjusts the pilot tone by a time delay.
15. The demodulator of claim 9 , wherein the control signal is a DC offset and the delay is determined by an amount of the DC offset.
16. An apparatus for dynamically compensating for phase deviations of a modulated optical data signal, comprising:
a phase shifter, for shifting the phase of a pilot tone by 90 degrees;
a multiplier, for multiplying the shifted pilot tone with a modulated signal;
a filter, for filtering the multiplied signal to extract a delay element control signal;
a delay element, for delaying the pilot tone in response to the delay element control signal; and
a first synchronous rectifier, for processing the adjusted pilot tone and the modulated signal to produce thereby a feedback signal.
17. The apparatus of claim 16 , wherein the modulated signal comprises a return-to-zero (RZ) signal.
18. The apparatus of claim 16 , wherein the delaying is accomplished by adjusting the phase of the pilot tone.
19. The apparatus of claim 16 , wherein the delaying is accomplished by a time delay to the pilot tone.
20. The apparatus of claim 16 , wherein the control signal comprises a DC offset and the delay is determined by an amount of the DC offset.