Laser wavelength control device

• US 5,943,152 A
• Filed: 05/08/1997
• Issued: 08/24/1999
• Est. Priority Date: 02/23/1996
• Status: Expired due to Term

• Current Assignee: Ciena Corporation
• Original Assignee: Ciena Corporation
• Inventors: Mizrahi, Victor, Harmon, Stephen R.
• Primary Examiner(s): NEGASH, KINFE MICHAEL
• Application Number:
  US08/848,423
• Time in Patent Office: 838 Days
• Field of Search: 359/110, 359/124, 359/157, 359/161, 359/187, 385/24, 372/34
• US Class Current: 398/196
• CPC Class Codes: G02B 6/2932 comprising a directional router, e.g. directional coupler, circulator
• CPC Class Codes: G02B 6/29361 Interference filters, e.g. multilayer coatings, thin film filters, dichroic splitters or mirrors based on multilayers, WDM filters
• CPC Class Codes: G02B 6/2938 for multiplexing or demultiplexing, i.e. combining or separating wavelengths, e.g. 1xN, NxM
• CPC Class Codes: G02B 6/29395 configurable, e.g. tunable or reconfigurable switching G02B6/35
• CPC Class Codes: G02B 6/29398 Temperature insensitivity
• CPC Class Codes: G02B 6/4246 Bidirectionally operating package structures
• CPC Class Codes: H01S 5/0687 Stabilising the frequency of the laser
• CPC Class Codes: H01S 5/4025 Array arrangements, e.g. constituted by discrete laser diodes or laser bar H01S5/42 takes precedence
• CPC Class Codes: H04B 10/505 using external modulation
• CPC Class Codes: H04B 10/5057 using a feedback signal generated by analysing the optical output
• CPC Class Codes: H04B 10/506 Multiwavelength transmitters
• CPC Class Codes: H04B 10/572 Wavelength control

Abstract

A laser control system is disclosed including a microprocessor, which precisely adjusts the wavelength of light output from the laser by monitoring the transmissivity of an in-fiber Bragg grating coupled to the output of the laser. The Bragg grating is fabricated to have a minimum transmissivity at the desired output wavelength of the laser. The microprocessor continually adjusts the wavelength of the laser output to obtain substantially minimal transmissivity through the grating. At which point, the laser is locked to the desired wavelength. Alternatively, the microprocessor can monitor light reflected from the grating, and continually adjust the wavelength of the laser output to lock the laser at a wavelength providing substantially maximum reflectance by the grating.

Claims

1. An optical device, comprising:

a first source of light, said light having a first wavelength dependent upon a temperature of said first source;

a filtering element coupled to said first source of said light;

a first photoelectric conversion device configured to detect a portion of said light transmitted through said filtering element and generate an electrical sense signal in response thereto;

a control circuit coupled to said first photoelectric conversion device;

a temperature regulating device coupled to receive a control signal generated by said control circuit in response to said electrical sense signal, said temperature regulating device adjusting a temperature of said first light source in response to said control signal to thereby adjust said first wavelength;

a second source of light at a second wavelength different than said first wavelength;

a second photoelectric conversion device coupled to said second source and generating a detection signal in response to said light at said second wavelength for modulating said light at said first wavelength; and

a circuit coupled to said second photoelectric conversion device, said second photoelectric conversion device supplying said detection signal to said circuit, said circuit being configured to facilitate modulation of said light at said first wavelength.

2. An optical device in accordance with claim 1, wherein said circuit further comprising:

a modulation circuit coupled to receive said detection signal, said modulation circuit outputting a modulation signal in accordance with said detection signal; and

an optical modulator configured to receive said modulation signal to thereby modulate said light at said first wavelength.

3. An optical device in accordance with claim 1, wherein said source of light comprises a laser.

4. An optical device in accordance with claim 1, wherein said filtering element comprises an in-fiber Bragg grating.

5. An optical device in accordance with claim 1, wherein said filtering element has a transmission characteristic whereby a minimum transmittance is obtained at a predetermined wavelength, said first wavelength being substantially equal to said predetermined wavelength.

6. An optical device in accordance with claim 1, wherein said optical modulator comprises a Mach-Zehnder interferometer.

38. An optical device in accordance with claim 4, wherein said in-fiber Bragg grating has a spectral width substantially equal to one angstrom.

7. An optical device comprising:

a first source of light at a first wavelength, said first wavelength being dependent upon a temperature of said first source;

a reflective element coupled to said source of said first light;

a first photoelectric conversion device configured to detect a portion of said light reflected by said reflective element and generate an electrical sense signal in response thereto;

a control circuit coupled to said first photoelectric conversion device;

a temperature regulating device coupled to receive a control signal generated by said control circuit in response to said electrical sense signal, said temperature regulating device adjusting a temperature of said first light source in response to said control signal to thereby adjust said first wavelength;

a second source of light at a second wavelength different than said first wavelength;

a second photoelectric conversion device coupled to said second source and generating a detection signal in response to said light at said second wavelength for modulating said light at said first wavelength!; and

a circuit coupled to said second photoelectric conversion device, said second photoelectric conversion device supplying said detection signal to said circuit, said circuit being configured to facilitate modulation of said light at said first wavelength.

8. An optical device in accordance with claim 7, wherein said circuit further comprising:

a modulation circuit coupled to receive said detection signal, said modulation circuit outputting a modulation signal in accordance with said detection signal; and

an optical modulator configured to receive said modulation signal to modulate said light at said first wavelength.

9. An optical device in accordance with claim 7, wherein said reflective element comprises an in-fiber Bragg grating.

10. An optical device in accordance with claim 7, wherein said reflective element has a reflectivity characteristic whereby a maximum reflectance is obtained at a predetermined wavelength, said control circuit adjusting said wavelength to be substantially equal to said predetermined wavelength.

11. An optical device in accordance with claim 7, wherein said optical modulator circuit comprises a Mach-Zehnder interferometer.

12. An optical device comprising:

a first source of light at a first wavelength;

a partially reflective element coupled to said first source of said light at said first wavelength;

a first photoelectric conversion device configured to detect a first portion of said light at said first wavelength transmitted through said partially reflective element and generating a first electrical sense signal;

a second photoelectric conversion device configured to detect a second portion of said light at said first wavelength reflected by said partially reflective element and generating a second electrical sense signal;

a comparator circuit configured to receive said first and second electrical sense signals and generating an output signal corresponding to a comparison between said first and second electrical sense signals;

a control circuit coupled to said comparator circuit, said control circuit adjusting said first wavelength of said light in response to said output signal;

a second source of light at a second wavelength different than said first wavelength;

a third photoelectric conversion device coupled to said second source and generating a detection signal in response to said light at said second wavelength; and

a circuit coupled to said second photoelectric conversion device, said second photoelectric conversion device supplying said detection signal to said circuit, said circuit being configured to facilitate modulation of said light at said first wavelength.

13. An optical device in accordance with claim 12, wherein said first source comprises a laser.

14. An optical device in accordance with claim 12, wherein said partially reflective element comprises an in-fiber Bragg grating.

15. An optical device in accordance with claim 12, wherein said first wavelength of said light is dependent upon a temperature of said first source, said optical device further comprising:

a temperature regulating device coupled to receive a control signal generated by said control circuit in response to said output signal, said temperature regulating device adjusting a temperature of said first source in response to said control signal to thereby adjust said first wavelength.

16. An optical device in accordance with claim 12, wherein said circuit comprises:

a modulation circuit coupled to receive said detection signal, said modulation circuit outputting a modulation signal in accordance with said detection signal; and

an optical modulator configured to receive said modulation signal to modulate said light at said first wavelength.

17. An optical device in accordance with claim 16, wherein said optical modulator comprises a Mach-Zehnder interferometer.

18. A method of regulating a wavelength of light output from a laser, comprising the steps of:

transmitting said light through a partially transmissive element having a transmission characteristic whereby a minimum transmissivity is obtained at a predetermined wavelength;

increasing said wavelength in first increments until a transmissivity of said light increases at a first wavelength;

decreasing said wavelength in second increments until said transmissivity of said light increases at a second wavelength; and

adjusting said wavelength to be a third wavelength between said first and second wavelengths.

19. A method in accordance with claim 18, further comprising the steps of:

changing said wavelength in third increments less than said first increments until said transmissivity of said light through said filtering element increases at a fourth wavelength between said first and third wavelengths;

changing said wavelength in fourth increments less than said second increments until said transmissivity of said light through said filtering element increases at a fifth wavelength between said second and third wavelengths; and

adjusting said wavelength to be sixth wavelength between said fourth and fifth wavelengths.

20. A method in accordance with claim 18, wherein if said first increments are equal to a predetermined value, said method further comprising the steps of:

changing said wavelength in said first increments until said transmissivity of said light through said filtering element increases at a fourth wavelength between said first and third wavelengths;

changing said wavelength in said second increments until said transmissivity of said light through said filtering element increases at a fifth wavelength between said second and third wavelengths; and

adjusting said wavelength to be a sixth wavelength between said fourth and fifth wavelengths.

21. A method in accordance with claim 18, wherein said increasing step further comprises the steps of:

monitoring a temperature of said laser; and

delaying successive ones of said first increments of said wavelength at least until said temperature of said laser is substantially constant.

22. A method in accordance with claim 18, wherein said partially transmissive element comprises an in-fiber Bragg grating, said method further comprising the steps of:

monitoring a temperature of said in-fiber Bragg grating; and

discontinuing said increasing and decreasing steps when said temperature exceeds a first value or falls below a second value.

23. A method in accordance with claim 18, further comprising the step of generating an alarm signal when an intensity of said light output from said laser exceeds a first value or falls below a second value.

24. A method of regulating a wavelength of light output from a laser, comprising the steps of:

reflecting said light off a partially reflective element having a reflectivity characteristic whereby a maximum reflectivity is obtained at a predetermined wavelength;

increasing said wavelength in first increments until a reflectivity of said partially reflective element decreases at a first wavelength;

decreasing said wavelength in second increments until said reflectivity of reflective element decreases at a second wavelength; and

adjusting said wavelength to be a third wavelength between said first and second wavelengths.

25. A method in accordance with claim 24, further comprising the steps of:

changing said wavelength in third increments less than said first increments until said reflectivity of said partially reflective element decreases at a fourth wavelength between said second and third wavelengths;

changing said wavelength in fourth increments less than said second increments until said reflectivity of said partially reflective element decreases at a fifth wavelength; and

adjusting said wavelength to be a sixth wavelength between said fourth and fifth wavelengths.

26. A method in accordance with claim 24, wherein if said first increments are equal to a predetermined value, said method further comprising the steps of:

changing said wavelength in said first increments until said reflectivity of said partially reflective element decreases at a fourth wavelength;

changing said wavelength in said second increments until said reflectivity of said partially reflective element decreases at a fifth wavelength; and

adjusting said wavelength to be a sixth wavelength between said fourth and fifth wavelengths.

27. A method in accordance with claim 24, wherein said increasing step further comprises the steps of:

monitoring a temperature of said laser; and

delaying successive ones of said first increments of said wavelength at least until said temperature of said laser is substantially constant.

28. A method in accordance with claim 24, wherein said partially reflective element comprises an in-fiber Bragg grating, said method further comprising the steps of:

monitoring a temperature of said in-fiber Bragg grating; and

discontinuing said increasing and decreasing steps when said temperature exceeds a first value or falls below a second value.

29. A method in accordance with claim 24, wherein said method further comprising the step of generating an alarm signal when an intensity of said light output from said laser exceeds a first value or falls below a second value.

30. An optical device, comprising:

a laser;

an optical filtering element coupled to an output of said laser, said optical filtering element having a transmissivity characteristic in which a minimum transmissivity is obtained at a predetermined wavelength;

means, coupled to said laser, for increasing a wavelength of light output from said laser in first increments until a transmissivity of said optical filtering element increases at a first wavelength;

means, coupled to said laser, for decreasing said wavelength in second increments until a transmissivity of said optical filtering element increases at a second wavelength; and

means, coupled to said laser, for adjusting said wavelength to be a third wavelength between said first and second wavelengths.

31. An optical device in accordance with claim 30, wherein said optical filtering element comprises an in-fiber Bragg grating.

32. An optical device, comprising:

a laser;

a reflective element coupled to an output of said laser, said reflective element having a reflectivity characteristic in which a maximum reflectivity is obtained at a predetermined wavelength;

means, coupled to said laser, for increasing a wavelength of light output from said laser in first increments until a reflectivity of said reflective element decreases at a first wavelength;

means, coupled to said laser, for decreasing said wavelength in second increments until a reflectivity of said reflective element decreases at a second wavelength; and

means, coupled to said laser, for adjusting said wavelength to be a third wavelength between said first and second wavelengths.

33. An optical device in accordance with claim 32, wherein said filtering element comprises an in-fiber Bragg grating.

34. An optical device, comprising:

a laser;

an optical filtering element coupled to an output of said laser, said optical filtering element having a transmissivity characteristic in which a minimum transmissivity is obtained at a predetermined wavelength and a reflectivity characteristic in which a peak reflectivity is obtained at said predetermined wavelength;

means for detecting a first portion of said output of said laser reflected from said optical filtering element and generating a first detection signal;

means for detecting a second portion of said light output from said laser transmitted through said optical filtering element and generating a second detection signal;

means for comparing said first and second detection signals;

means for increasing a wavelength of light output from said laser in first increments in response to said comparison until a transmissivity of said optical filtering element increases at a first wavelength;

means for decreasing said wavelength in second increments in response to said comparison until a transmissivity of said optical filtering element increases at a second wavelength; and

means, coupled to said laser, for adjusting said wavelength to be a third wavelength between said first and second wavelengths.

35. An optical device in accordance with claim 34, wherein said optical filtering element comprises an in-fiber Bragg grating.

36. An optical device, comprising:

a laser;

an optical filtering element coupled to an output of said laser, said optical filtering element having a transmissivity characteristic in which a minimum transmissivity is obtained at a predetermined wavelength and a reflectivity characteristic in which a peak reflectivity is obtained at said predetermined wavelength;

means for detecting a first portion of said output of said laser reflected from said optical filtering element and generating a first detection signal;

means for detecting a second portion of said light output from said laser transmitted through said optical filtering element and generating a second detection signal;

means for comparing said first and second detection signals;

means for increasing a wavelength of light output from said laser in first increments in response to said comparison until a reflectivity of said optical filtering element decreases at a first wavelength;

means for decreasing said wavelength in second increments in response to said comparison until a reflectivity of said optical filtering element decreases at a second wavelength; and

means, coupled to said laser, for adjusting said wavelength to be a third wavelength between said first and second wavelengths.

37. An optical device in accordance with claim 36, wherein said optical filtering element comprises an in-fiber Bragg grating.