Apparatus and method for duobinary transmission

1. An optical duobinary transmitter apparatus comprising:

a precoder;

an amplifier coupled to the precoder; and

a low bandwidth modulator coupled to the amplifier having a bandwidth of less than about 60% of the transmission bit rate of the transmitters,

wherein the apparatus combines the effect of residual dispersion in an optical system with that of the low bandwidth modulator in order to achieve a low pass filtering operation without additional electrical filters for duobinary transmission.

2. The apparatus of claim 1 wherein the low bandwidth modulator is a Mach-Zehnder modulator.

3. An optical duobinary transmitter apparatus comprising:

a low bandwidth modulator having a bandwidth of less than about 60% of the transmission bit rate of the transmitter,

wherein the apparatus combines the effect of residual dispersion in an optical system with that of the low bandwidth modulator in order to achieve a low pass filtering operation without additional electrical filters for duobinary transmission in an optical fiber transmission system having a predetermined amount of residual dispersion, such that the residual dispersion substantially compensates for signal distortions from the low bandwidth modulator.

4. The apparatus of claim 3 wherein the low bandwidth modulator is a Mach-Zehnder modulator.

5. The apparatus of claim 3 wherein signal distortions from the low bandwidth modulator include substantial response ripple.

6. A method for optical duobinary transmission in a transmitter comprising:

providing a precoder means;

providing an amplifier means coupled to the precoder;

providing a low bandwidth modulator means coupled to the amplifier means having a bandwidth of less than about 60% of the transmission bit rate of the transmitter; and

operating the modulator means to provide low pass filtering for low pass filtered duobinary transmission in an optical fiber transmission system having residual dispersion, wherein the transmitter combines the effect of residual dispersion in the optical transmission system with that of the modulator means in order to achieve a low pass filtering operation without additional electrical filters.

7. The method of claim 6 wherein the low bandwidth modulator is a Mach-Zehnder modulator.

8. A method for optical duobinary transmission in a transmitter comprising:

transmitting an optical duobinary signal using a low bandwidth modulator having a bandwidth of less than about 60% of the transmission bit rate of the transmitter;

wherein the modulator is operable to provide low pass filtering for low pass filtered duobinary transmission in an optical fiber transmission system having residual dispersion, the transmitter combining the effect of residual dispersion in the optical transmission system with that of the modulator means in order to achieve a low pass filtering operation without additional electrical filters.

9. The method of claim 8 wherein the low bandwidth modulator is a Mach-Zehnder modulator.

10. An optical duobinary transmitter apparatus comprising:

a precoder means;

an amplifier means coupled to the precoder; and

a low bandwidth modulator means coupled to the amplifier means having a bandwidth of less than about 60% of the transmission bit rate of the transmitter,

wherein the modulator means is operable to provide low pass filtering for low pass filtered duobinary transmission in an optical fiber transmission system having residual dispersion, the apparatus combining the effect of residual dispersion in the optical transmission system with that of the modulator means in order to achieve a low pass filtering operation without additional electrical filters.

11. An optical duobinary transmitter apparatus comprising:

a low bandwidth modulator means having a bandwidth of less than about 60% of the transmission bit rate of the transmitter,

wherein the modulator means is operable to provide low pass filtering for low pass filtered duobinary transmission in an optical fiber transmission system having a predetermined amount of residual dispersion, such that the residual dispersion substantially compensates for signal distortions from the low bandwidth modulator, thereby achieving low pass filtering without substantial additional electrical filters, the apparatus combining the effect of residual dispersion in the optical transmission system with that of the modulator means in order to achieve a low pass filtering operation without additional electrical filters.

12. The apparatus of claim 3 , wherein high frequency response of the modulator is predominantly limited by a velocity mismatch between microwave and optical field propagation constants in a modulator interaction region.

13. The apparatus of claim 12 , wherein frequency response is further limited by electrode loss.

14. The apparatus of claim 6 , wherein high frequency response of the modulator means is predominantly limited by a velocity mismatch between microwave and optical field propagation constants in a modulator interaction region.

15. The apparatus of claim 14 , wherein frequency response is further limited by electrode loss.

16. The apparatus of claim 8 , wherein high frequency response of the modulator is predominantly limited by a velocity mismatch between microwave and optical field propagation constants in a modulator interaction region.

17. The apparatus of claim 16 , wherein frequency response is further limited by electrode loss.

18. The apparatus of claim 10 , wherein high frequency response of the modulator means is predominantly limited by a velocity mismatch between microwave and optical field propagation constants in a modulator interaction region.

19. The apparatus of claim 18 , wherein frequency response is further limited by electrode loss.