Two path digital wavelength stabilization

• US 6,384,947 B1
• Filed: 03/09/1999
• Issued: 05/07/2002
• Est. Priority Date: 03/09/1999
• Status: Expired due to Term

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Agere Systems Guardian Corp. (Broadcom, Inc.)
• Inventors: Przybylek, George John, Ackerman, David Alan, Broutin, Scott L., Plourde, James Kevin, Stayt, John William Jr.
• Primary Examiner(s): Chan, Jason
• Assistant Examiner(s): Bello, Agustin
• Application Number:
  US09/265,291
• Time in Patent Office: 1,155 Days
• Field of Search: 359/127, 359/132, 359/187, 372/32, 372/28
• US Class Current: 398/192
• CPC Class Codes: H04B 10/506 Multiwavelength transmitters
• CPC Class Codes: H04B 10/572 Wavelength control

Abstract

A method and apparatus for stabilizing the wavelength of a laser are disclosed. The invention provides a way to stabilize a laser for applications in dense wavelength division multiplexing (DWDM) systems where frequency spacing is crucial. The invention accomplishes laser stabilization by generating an optical path which is passed through a filter to obtain a signal which is a function of frequency. A second optical path which does not contain a filter is generated to obtain a signal which is a function of power. The signals are then converted from optical to electrical and from analog to digital, and a microcontroller is used to normalize the frequency path with respect to the optical power path, process the signals via software code, and generate a signal which provides feedback to the laser for stabilization. By using a microcontroller; elements that lead to wavelength or frequency drift, or manufacturing component variations can be taken into account and the input signal to the laser can be adjusted accordingly.

Claims

1. A method for stabilizing the wavelength of a laser source, the method comprising the steps of:

photo-coupling a first path from an output of a laser and passing said first path through an optical filter to derive a first optical signal, said first optical signal being a function of the frequency and the optical power of the output of the laser;

photo-coupling a second path from the output of the laser to derive a second optical signal, said second optical signal being a function of the optical power of the output of the laser independent of the frequency;

converting the optical signal from said first path and the optical signal from said second path to electrical signals;

converting the electrical signal from said first path and the electrical signal from said second path from analog to digital; and

using a microcontroller to process said first path digital signal and said second path digital signal to determine frequency variations in the output of said laser, and develop a signal capable of adjusting the output of the laser.

2. The method of claim 1, wherein:

said microcontroller uses said second digital path to normalize said first digital path.

3. The method of claim 2, further comprising:

amplifying the electrical signals from said first and second paths.

4. The method of claim 2, further comprising:

converting the electrical signals from said first and second paths from current to voltage.

5. The method of claim 4, further comprising:

amplifying the electrical signals from said first and second paths.

6. The method of claim 1, further comprising:

converting the output of said microcontroller from digital to analog.

7. The method of claim 1, wherein said microcontroller is configured to run software code to process said first path digital signal and said second path digital signal to determine frequency variations in the output of said laser, and develop said signal capable of adjusting the output of the laser.

8. The method of claim 1, said step of using said microcontroller further comprises using said microcontroller to accommodate for the effect of component variations in said first and second paths.

9. The method of claim 1, said step of using said microcontroller further comprises using said microcontroller to compensate for the voltage levels of the electrical signals from said first and second paths.

10. The method of claim 7, further comprising:

updating said software code.

11. The method of claim 1, wherein said step of using a microcontroller comprises the steps of:

normalizing said first path digital with said second path digital signal;

integrating said normalized first path digital signal; and

developing said signal capable of adjusting the output of the laser, said signal based on said integrated normalized signal.

12. An apparatus for stabilizing the wavelength of a laser source, the apparatus comprising:

a laser source having an output;

first and second optical paths coupled from the output of the laser;

an optical filter positioned within the first optical path to produce a filter output signal having a power that is a function of the wavelength and power of the laser source;

a first photo-detector coupled to the output of the filter in the first optical path to detect said filter output signal;

a second photo-detector coupled to the second optical path to detect the power of the laser source independent of frequency;

first and second analog-to-digital converters attached to the output of the first and second photo-detectors, respectively; and

a microcontroller with inputs connected to the outputs of the first and second analog-to-digital converters, said microcontroller having means for processing data at the inputs to determine frequency variations in the output of the laser and generate a signal for controlling the laser responsive thereto.

13. The apparatus of claim 12, further comprising:

a first current-to-voltage converter electrically connected between the first photo-detector and the first analog-to-digital converter, and a second current-to-voltage converter electrically connected between the second photo-detector and the second analog-to-digital converter.

14. The apparatus of claim 13, further comprising:

a first amplifier electrically connected between the first current-to-voltage converter and the first analog-to-digital converter, and a second amplifier electrically connected between the second current-to-voltage converter and the second analog-to-digital converter.

15. The apparatus of claim 12, further comprising:

a first amplifier electrically connected between the first photo-detector and the first analog-to-digital converter, and a second amplifier electrically connected between the second photo-detector and the second analog-to-digital converter.

16. The apparatus of claim 15, further comprising:

a first current-to-voltage converter electrically connected between the first photo-detector and the first amplifier, and a second current-to-voltage converter electrically connected between the second photo-detector and the second amplifier.

17. The apparatus of claim 12, wherein:

said generated signal is converted from digital to analog by a digital-to-analog converter.

18. The apparatus of claim 12, said means for processing data comprising at least software code for use by said microcontroller.

19. The apparatus of claim 18, said microcontroller having a remote input for updating said software code.

20. A method for stabilizing the wavelength of a laser source, the method comprising the steps of:

photo-coupling a first path from an output of a laser and passing said first path through an optical filter to derive a first optical signal, said output having a frequency and an optical power;

photo-coupling a second path from the output of said laser to derive a second optical signal;

converting the optical signal from said first path and the optical signal from said second path to electrical signals;

converting the electrical signal from said first path and the electrical signals from said second path from analog to digital, said first path digital signal being a function of the frequency and the optical power of the output of the laser and said second path digital signal being a function of the optical power of the output of the laser independent of frequency;

normalizing said first path digital signal with said second path digital signal to derive a normalized signal, said normalized signal being a function of the frequency of the output of the laser;

integrating said normalized signal; and

developing a signal capable of adjusting the output of the laser, said signal based on said integrated normalized signal.

21. The method of claim 20, wherein said integrating step comprises the steps of:

selecting a period of time for integration; and

integrating said normalized signal over said period of time.

22. The method of claim 21, wherein said period of time is selected from a group consisting of hours, days, months, and years.

23. The method of claim 20, further comprising the step of:

accommodating variations in said first path digital signal and said second path digital signal.