Automatic bias control of an optical transmitter

1. An apparatus comprising:

an electro-absorption modulator configured to receive an optical light from an optical light source and output a modulated optical signal, the electro-absorption modulator including a bias voltage used to set a predetermined modulation performance and an output power of the electro-absorption modulator; and

a controller configured to measure a DC value of the output power provided by the electro-absorption modulator and use the DC value as a reference to automatically control the bias voltage of the electro-absorption modulator to maintain the predetermined modulation performance and the output power of the electro-absorption modulator when a detuning change occurs between the electro-absorption modulator and the optical light source.

2. The apparatus of claim 1 , further comprising:

an automatic power control circuit that controls a bias current of the optical light source to maintain a same output power from the optical light source.

3. The apparatus of claim 2 , wherein a wavelength of the optical light source is changed by changing the bias current of the optical light source.

4. The apparatus of claim 1 , wherein the bias voltage is controlled to maintain a constant photocurrent generated by the electro-absorption modulator.

5. The apparatus of claim 1 , wherein the controller comprises:

a monitor configured to monitor the photocurrent of the electro-absorption modulator;

a processor configured to set a reference voltage; and

bias control logic configured to control the electro-absorption modulator bias voltage based on the reference voltage.

6. The apparatus of claim 1 , wherein the controller comprises:

a monitoring circuit that measures the photocurrent of the electro-absorption modulator without using an optical coupler and a photodetector;

an electrical feedback circuit that generates a reference signal based on the photocurrent and a targeted photocurrent level; and

a voltage source or current source that controls the bias voltage of the electro-absorption modulator based on the reference signal.

7. The apparatus of claim 1 , wherein an output power of the electro-absorption modulator is maintained by controlling the bias voltage of the electro-absorption modulator.

8. The apparatus of claim 1 , wherein the controller maintains modulation linearity by controlling the bias voltage.

9. The apparatus of claim 1 , wherein the controller minimizes second order distortion changes that occur based on the detuning change by controlling the bias voltage.

10. The apparatus of claim 1 , wherein the controller minimizes even order distortion that occurs based on the detuning change by controlling the bias voltage.

11. The apparatus of claim 1 , further comprising:

a temperature control circuit configured to maintain a temperature of the optical light source and the electro-absorption modulator.

12. The apparatus of claim 1 , wherein the optical light source comprises a distributed feedback laser (DFB) laser.

13. The apparatus of claim 1 , wherein the optical light source and the electro-absorption modulator are located in a same package.

14. The apparatus of claim 1 , further comprising a temperature control circuit configured to set and maintain a temperature of both the optical light source and the electro-absorption modulator.

15. The apparatus of claim 1 , wherein the optical light source and the electro-absorption modulator form an electro-absorption modulated laser.

16. A method comprising:

receiving, at an electro-absorption modulator, an optical light from an optical light source and outputting a modulated optical signal, the electro-absorption modulator including a bias voltage used to set a predetermined modulation performance and an output power of the electro-absorption modulator; and

measuring a DC value of the output power provided by the electro-absorption modulator; and

using the DC value as a reference to automatically control the bias voltage of the electro-absorption modulator to maintain the predetermined modulation performance and the output power of the electro-absorption modulator when a detuning change occurs between the electro-absorption modulator and the optical light source.

17. The method of claim 16 , wherein the bias voltage is controlled to maintain a constant photocurrent generated by the electro-absorption modulator.

18. The method of claim 17 , further comprising:

monitoring the photocurrent of the electro-absorption modulator;

setting a reference voltage; and

controlling the bias voltage based on the reference voltage.

19. The method of claim 16 , wherein the bias voltage is controlled to maintain a constant photocurrent generated by the electro-absorption modulator.

20. A system comprising:

an optical light source configured to output an optical light;

an electro-absorption modulator configured to receive the optical light and output a modulated optical signal, the electro-absorption modulator including a bias voltage used to set a predetermined modulation performance and an output power of the electro-absorption modulator; and

a controller configured to measure a DC value of the output power provided by the electro-absorption modulator and use the DC value as a reference to automatically control the bias voltage of the electro-absorption modulator to maintain the predetermined modulation performance and the output power of the electro-absorption modulator when a detuning change occurs between the electro-absorption modulator and the optical light source.