Out-of-band communication channel for sub-carrier-based optical communication systems

1. An apparatus, comprising:

a laser operable to supply an optical signal;

a digital signal processor operable to supply digital signals;

digital to analog circuitry operable to provide analog signals based on the digital signals;

driver circuitry coupled to the digital to analog circuitry, the driver circuitry operable to supply at least one drive signal; and

a modulator operable to:

receive said at least one drive signal,

modulate the optical signal based on said at least one drive signal to provide a plurality of optical subcarriers,

collectively amplitude modulate the plurality of optical subcarriers at a first frequency to carry first control information, and

collectively amplitude modulate the plurality of subcarriers at a second frequency to carry second control information.

2. An apparatus in accordance with claim 1 , wherein each of the plurality of optical subcarriers is a Nyquist subcarrier, each of the plurality of optical subcarriers including first and second polarization components having the same frequency.

3. An apparatus in accordance with claim 1 , wherein the first frequency is in a range of 3 MHz to 4 MHz and the second frequency is in a range of 6 MHz to 7 MHz.

4. An apparatus in accordance with claim 1 , wherein the plurality of optical subcarriers is a first plurality of optical subcarriers, the apparatus further including a receiver operable to receive a second plurality of optical subcarriers, each of which is amplitude modulated at a third frequency.

5. An apparatus in accordance with claim 4 , wherein the first frequency is within a first band and the second frequency is within a second band, the third frequency being within the first band or the second band.

6. An apparatus in accordance with claim 4 , wherein the second plurality of optical subcarriers is further amplitude modulated at a fourth frequency different than the third frequency.

7. An apparatus in accordance with claim 6 , wherein the first frequency is within a first band and the second frequency is within a second band, the third frequency being within the first band and the fourth frequency being within the second band.

8. An apparatus, comprising:

an optical hybrid circuit operable to:

receive a plurality of optical subcarriers, the plurality of optical subcarriers being collectively amplitude modulated at a first frequency to carry first control information and collectively amplitude modulated at a second frequency to carry second control information,

receive a local oscillator signal, and

provide mixing products based on the local oscillator signal and the plurality of optical subcarriers;

a photodiode circuit operable to provide first electrical signals based on the mixing products;

analog to digital conversion circuitry operable to output digital signals based on the first electrical signals;

a digital signal processor operable to provide data associated with the plurality of optical subcarriers; and

circuitry operable to receive second electrical signals based on first electrical signals and output the first and second control information based on the first electrical signals.

9. An apparatus in accordance with claim 8 , wherein each of the plurality of optical subcarriers is a Nyquist subcarrier each of the plurality of optical subcarriers including first and second polarization components having the same frequency.

10. An apparatus in accordance with claim 8 , wherein the first frequency is in a range of 3 MHz to 4 MHz and the second frequency is in a range of 6 MHz to 7 MHz.

11. An apparatus in accordance with claim 8 , wherein the plurality of optical subcarriers is a first plurality of optical subcarriers, the apparatus further including a receiver operable to receive a second plurality of optical subcarriers, each of which is amplitude modulated at a third frequency.

12. An apparatus in accordance with claim 11 , wherein the first frequency is within a first band and the second frequency is within a second band, the third frequency being within the first band or the second band.

13. An apparatus in accordance with claim 11 , wherein the second plurality of optical subcarriers is further amplitude modulated at a fourth frequency different than the third frequency.

14. An apparatus in accordance with claim 13 , wherein the first frequency is within a first band and the second frequency is within a second band, the third frequency being within the first band and the fourth frequency being within the second band.

15. An apparatus, in accordance with claim 8 , further comprising a plurality of filter circuits, each of which has a corresponding one of a plurality of passbands, wherein the plurality of optical subcarriers is further amplitude modulated at a third frequency different than the first and second frequencies, the plurality of filter circuits blocking signals being associated with the third frequency.

16. An apparatus, comprising:

a transmitter including:

a laser operable to supply an optical signal,

a digital signal processor operable to supply digital signals,

digital to analog circuitry operable to provide analog signals based on the digital signals,

driver circuitry coupled to digital to analog circuitry, the driver circuitry operable to supply at least one drive signal, and

a modulator operable to:

receive said at least one drive signal,

modulate the optical signal based on said at least one drive signal to provide a first plurality of optical subcarriers,

collectively amplitude modulate the first plurality of subcarriers at a first frequency to carry first control information, and

collectively amplitude modulate the first plurality of subcarriers at a second frequency to carry second control information; and

a receiver including:

an optical hybrid circuit operable to:

receive a second plurality of optical subcarriers, the second plurality of optical subcarriers being amplitude modulated at a third frequency to carry third control information and amplitude modulated at a fourth frequency to carry fourth control information,

receive a local oscillator signal, and

provide mixing products based on the local oscillator signal and the plurality of optical subcarriers;

a photodiode circuit operable to provide first electrical signals based on the mixing products;

analog to digital conversion circuitry operable to output digital signals based on the first electrical signals;

a digital signal processor operable to provide data associated with the plurality of optical subcarriers; and

circuitry operable to receive second electrical signals based on first electrical signals and output the third and fourth control information based on the first electrical signals.

17. An apparatus in accordance with claim 16 , wherein the laser is further operable to supply the local oscillator signal.

18. An apparatus in accordance with claim 16 , wherein each of the plurality of optical subcarriers is a Nyquist subcarrier each of the plurality of optical subcarriers including first and second polarization components having the same frequency.

19. An apparatus in accordance with claim 16 , wherein the first frequency is in a range of 3 MHz to 4 MHz and the second frequency is in a range of 6 MHz to 7 MHz.

20. An apparatus in accordance with claim 16 , wherein the second plurality of optical subcarriers is further amplitude modulated at a third frequency.

21. An apparatus in accordance with claim 20 , wherein the first frequency is within a first band and the second frequency is within a second band, the third frequency being within the first band or the second band.

22. An apparatus in accordance with claim 20 , wherein the second plurality of optical subcarriers is further amplitude modulated at a fourth frequency different than the third frequency.

23. An apparatus in accordance with claim 22 , wherein the first frequency is within a first band and the second frequency is within a second band, the third frequency being within the first band and the fourth frequency being within the second band.