Tunable semiconductor laser having cavity with ring resonator mirror and mach-zehnder interferometer

• US 6,690,687 B2
• Filed: 01/02/2001
• Issued: 02/10/2004
• Est. Priority Date: 01/02/2001
• Status: Expired due to Fees

• Current Assignee: Spectrasensors, Inc. (Endress+Hauser AG)
• Original Assignee: Spectrasensors, Inc. (Endress+Hauser AG)
• Inventors: Ksendzov, Alexander, May, Randy Dean
• Primary Examiner(s): Scott, Jr., Leon
• Application Number:
  US09/753,285
• Publication Number:
  US 20020085609A1
• Time in Patent Office: 1,134 Days
• Field of Search: 372/20, 372/32, 372/92, 372/98, 372/93, 372/94
• US Class Current: 372/20
• CPC Class Codes: H01S 5/0687 Stabilising the frequency of the laser
• CPC Class Codes: H01S 5/1028 Coupling to elements in the cavity, e.g. coupling to waveguides adjacent the active region, e.g. forward coupled [DFC] structures
• CPC Class Codes: H01S 5/1032 Coupling to elements comprising an optical axis that is not aligned with the optical axis of the active region
• CPC Class Codes: H01S 5/141 using a wavelength selective device, e.g. a grating or etalon H01S5/146 takes precedence

Abstract

A semiconductor laser is provided having a cavity including a gain chip, a Mach-Zehnder wide tuning port, and a ring resonator mirror. Optical signals generated by the gain chip propagate through the Mach-Zehnder wide tuning port and into the ring resonator mirror where the optical signals are reflected back through the Mach-Zehnder wide tuning port to the gain chip. The ring resonator is configured to reflect only those optical signals back into the laser cavity having wavelengths within a set of sharp peaks and the laser cavity therefore can resonate only within one of the sharp peaks. The ring resonator mirror is heated to adjust its dimensions so as to maintain one of the sharp peaks at a selected emission wavelength. As optical signals reflected from the ring resonator pass through the Mach-Zehnder wide tuning port, the signals are split between two channels of differing lengths resulting in optical interference. The optical interference limits the ability of the laser cavity to resonate at wavelengths other than near the center of a single broad peak determined by the relative lengths of the two channels. The Mach-Zehnder wide tuning port is heated to vary the relative lengths of the two channels so as to maintain the single broad peak at the selected transmission wavelength. In this manner, the laser cavity is controlled to resonate substantially only at the selected wavelength. Resonance at the other sharp resonance peaks permitted by the ring resonator is significantly reduced, thereby significantly reducing transmission sidebands generated by the laser.

Claims

1. A semiconductor laser having a cavity comprised of:

a gain chip for providing radiant energy within the cavity;

an interferometric wide tuning port for generating resonances within the cavity and having at least two interferometric optical channels, with at least one of the interferometric optical channels having an adjustable length, to selectively generate resonances at selectable wavelengths, wherein the interferometric wide tuning port has a coarse tuning profile to generate a broad peak for limiting the radiant energy generated by the gain chip to a single broad peak;

a ring resonator for generating resonances within the cavity and receiving radiant energy with a single broad peak from the interferometric wide tuning port, having a ring-shaped optical channel with an adjustable diameter and at least two ring resonator channels, wherein the at least two ring resonator channels are formed sufficiently close to opposing sides of the ring-shaped optical channel to selectively permit evanescent coupling of radiant energy propagating therein at frequencies dependent upon the diameter of the ring-shaped optical channel, wherein the ring resonator has a fine tuning profile to generate a set of sharp peaks which further limit resonances within the cavity; and

wherein the interferometric tuning port aligns a wavelength of the broad peak of the coarse tuning profile at a selected wavelength and the ring resonator is aligned to a wavelength of one of the sharp peaks also at the selected wavelength so that the ring resonator may reflect light having a sharp peak at the selected wavelength through the interferometric wide tuning port and the gain chip for emission by the laser.

2. The semiconductor laser of claim 1 wherein the gain chip is formed on a III/IV material chip.

3. The semiconductor laser of claim 1 wherein the interferometric tuning port is a Mach-Zehnder interferometer.

4. The semiconductor laser of claim 3 wherein the Mach-Zehnder interferometer comprises:

an input optical channel;

a splitter for splitting the input optical channel into the at least two interferometric optical channels;

wherein the at least two interferometric optical channels are of differing lengths; and

a combining section for combining the at least two interferometric optical channels into a single output channel.

5. The semiconductor laser of claim 4 further comprising a wide tuning control unit configured to adjust an optical path length difference between the at least two interferometric optical channels of the Mach-Zehnder interferometer to maintain alignment of the broad peak of the wide tuning profile with the selected wavelength.

6. The semiconductor laser of claim 5 further comprising a heating element configured to thermally adjust the optical path length difference of the at least two interferometric optical channels.

7. The semiconductor laser of claim 5 further comprising a wavelength detector coupled to the wide tuning control unit configured to detect the wavelength of a signal output by the laser.

8. The semiconductor laser of claim 3 wherein the Mach-Zehnder interferometer is formed on a separate planar wave guide chip.

9. The semiconductor laser of claim 1 wherein the ring resonator further comprises:

an input optical channel;

a splitter for splitting the input optical channel into the at least two channels; and

wherein the pair of channels formed sufficiently close to opposing sides of the ring-shaped optical channel to permit evanescent coupling of radiant energy propagating therein.

10. The semiconductor laser of claim 9 further including a fine tuning control unit configured to adjust the diameter of the ring-shaped optical channel to maintain alignment of one of the sharp peaks at the selected wavelength.

11. The semiconductor laser of claim 10 further comprising a heating element configured to thermally adjust resonance frequencies of the ring-shaped optical channel.

12. The semiconductor laser of claim 10 further comprising a wavelength detector coupled to the fine tuning control unit configured to detect the wavelength of a signal output by the laser.

13. The semiconductor laser of claim 9 wherein a difference in length between the pair of channels is approximately 20 μ

m.

14. The semiconductor laser of claim 1 wherein the ring resonator is formed using planar wave guides.

15. The semiconductor laser of claim 1 further comprising a gain chip control unit configured to control the output of the gain chip.

16. The semiconductor laser of claim 1 wherein an intensity emitted by the laser at the selected wavelength is 30 dB greater than sideband wavelengths emitted by the laser.

17. The semiconductor laser of claim 1 wherein the ring resonator has a diameter of approximately 300 μ

m.

18. The semiconductor laser of claim 1 wherein the sharp resonance peaks generated by the ring resonator have a spacing of approximately 1.5 nm.

19. The semiconductor laser of claim 1 wherein the gain chip is an InGaAsP gain chip.

20. The semiconductor laser of claim 1 wherein the inteferometric wide tuning port and the ring resonator are provided on a tuning chip having a plurality of channels, wherein each channel is formed from stacks of dielectric material.

21. The semiconductor laser of claim 20 further comprising a silicon substrate and wherein the stacked dielectric material comprises a first layer of silicon dioxide mounted on the silicon substrate, a layer of silicon oxynitride deposited on the first layer of silicon dioxide, and a second layer of silicon dioxide deposited on the layer of silicon oxynitride.

22. The semiconductor laser of claim 21 wherein the layer of silicon oxynitride comprises a first rib portion on a side opposite from the silicon substrate abutting outwards from the silicon;

and wherein the second layer of silicon dioxide is deposited on the silicon oxynitride to form a second rib portion on a side opposite from the silicon abutting outwards from the silicon substrate.

23. The semiconductor laser of claim 22 wherein the width of the silicon substrate is approximately 0.3 mm, the width of the first layer of silicon dioxide is approximately 5 μ

m, the width of the layer of silicon oxynitride layer is approximately 0.5 μ

m, and the width of the second layer of silicon dioxide is approximately 1 μ

m in width.

24. The semiconductor laser of claim 22 wherein the first rib portion extends approximately 600 Angstroms from other portions of the layer of silicon oxynitride.

25. The semiconductor laser of claim 1 wherein the width of the broad peak is approximately 41 nm.

26. The semiconductor laser of claim 1 wherein the interferometric wide tuning port and the ring resonator are provided on a silicon tuning chip.

27. The semiconductor laser of claim 26 wherein the silicon tuning chip comprises a unitary structure of silicon.

28. The semiconductor laser of claim 1 further comprising:

first heating means for heating the interferometric wide tuning port; and

second heating means for heating the ring resonator.

35. The semiconductor laser of claim 24 wherein the means for adjusting an optical path length difference of the at least two interferometric optical channels includes a heating element.

29. A semiconductor laser having a cavity comprised of:

means for providing radiant energy and gain for resonances within the cavity;

wide tuning means for generating resonances within the cavity based on a wide tuning profile having a broad peak having at least two interferometric optical channels with at least one of the interferometric optical channels having an adjustable length to selectively interfere resonances generated by the gain chip; and

fine tuning means for further limiting resonances within the cavity to within a set of sharp resonance peaks having a ring-shaped optical channel with an adjustable diameter and at least two fine tuning channels, wherein the at least two channels are formed sufficiently close to opposing sides of the ring-shaped optical channel to selectively permit evanescent coupling of radiant energy propagating therein at frequencies dependent upon the diameter of the ring-shaped optical channel; and

wherein the wide tuning means is configured to align a wavelength of the broad peak of the wide tuning profile at a selected wavelength and the fine tuning means configured to align a wavelength of one of the sharp peaks also at the selected wavelength so that the fine tuning means may reflect light having a sharp peak at the selected wavelength through the wide tuning means and the means for providing radiant energy for emission by the laser.

30. The semiconductor laser of claim 29 wherein the means for providing radiant energy and gain is a gain chip.

31. The semiconductor laser of claim 30 wherein the gain chip is formed on a III/IV material chip.

32. The semiconductor laser of claim 29 wherein the wide tuning means is a Mach-Zehnder interferometer.

33. The semiconductor laser of claim 32 wherein the Mach-Zehnder interferometer comprises:

an input optical channel;

a splitter for splitting the input optical channel into he at least two interferometric optical channels of differing lengths; and

a combining section for combining the at least two interferometric optical channels into a single output channel.

34. The semiconductor laser of claim 33 further including means for controlling the wide tuning means to adjust an optical path length difference between the at least two interferometric optical channels of the Mach-Zehnder interferometer so as to maintain alignment of the broad peak of the wide tuning profile with a selected wavelength.

36. The semiconductor laser of claim 32 wherein the Mach-Zehnder interferometer is formed on a separate planar wave guide chip.

37. The semiconductor laser of claim 29 wherein the fine tuning means is a ring resonator.

38. The semiconductor laser of claim 37 wherein the ring resonator comprises:

an input optical channel;

a splitter for splitting the input optical channel into the at least two fine tuning channels; and

wherein the at least two fine tuning channels are formed sufficiently close to opposing sides of the ring-shaped optical channel to permit evanescent coupling of radiant energy propagating therein.

39. The semiconductor laser of claim 38 further including means for controlling the fine tuning means includes means to adjust the length of the ring-shaped optical channel so as to maintain alignment of one of the sharp peaks at the selected wavelength.

40. The semiconductor laser of claim 39 wherein the means for adjusting resonance frequencies of the ring-shaped optical channel includes a heating element.

41. The semiconductor laser of claim 37 wherein the ring resonator is formed using planar wave guides.

42. A method for operating a semiconductor laser having a cavity formed from a gain chip, a Mach-Zehnder interferometer and a ring resonator, comprising the steps of:

controlling the gain chip to provide radiant energy for resonance within the cavity;

controlling the Mach-Zehnder interferometer to limit resonance within the cavity based on a wide tuning profile having a broad peak set to a selected wavelength, wherein the Mach-Zehnder interferometer includes a pair of optical channels of differing lengths and wherein the step of controlling the Mach-Zehnder interferometer is performed by adjusting an optical path length difference between the pair of optical channels; and

controlling the ring resonator to further limit resonance within the cavity to within a set of sharp resonance peaks, with a wavelength of one of the sharp peaks also set to the selected wavelength, wherein the ring resonator includes a ring-shaped optical channel and wherein the step of adjusting the ring resonator is performed by adjusting one or more of a diameter and a refractive index of the ring-shaped optical channel.

43. The method of claim 42 wherein the step of adjusting an optical path length difference between the pair of optical channels is performed by heating the Mach-Zehnder interferometer.

44. The method of claim 42 wherein the step of adjusting the ring-shaped optical channel is performed by heating the ring resonator.

45. The method of claim 42 further including the steps of

outputting an optical beam from the semiconductor laser cavity;

detecting a wavelength of the output beam;

controlling the Mach-Zehnder interferometer to maintain alignment of the broad peak of the wide tuning profile with the selected wavelength; and

controlling the ring resonator to maintain alignment of one of the sharp resonance peaks at the selected wavelength.

46. The method of claim 42 further including the step of

adjusting the gain chip, the Mach-Zehnder interferometer and the ring resonator to provide a maximum tuning range.

47. The method of claim 46 wherein the gain chip, the Mach-Zehnder interferometer and the ring resonator are each thermally-adjustable and wherein the step of adjusting the gain chip, the Mach-Zehnder interferometer and the ring resonator to provide a maximum tuning range includes the steps of:

separately determining individual thermal response characteristics of the gain chip, the Mach-Zehnder interferometer and the ring resonator;

determining thermal response interactions among the gain chip, the Mach-Zehnder interferometer and the ring resonator;

determining separate amounts of thermal energy to apply to the gain chip, the Mach-Zehnder interferometer and the ring resonator to achieve the maximum tuning range based on the individual thermal response characteristics and on the thermal response interactions; and

simultaneously applying the separate amounts of thermal energy to the gain chip, the Mach-Zehnder interferometer and the ring resonator to thereby achieve the maximum tuning range.

48. A laser multiplexer system comprising:

a plurality of lasers each operative to generate a respective laser beam; and

an optical multiplexer operative to combine the plurality of laser beams into an optic fiber for transmission; and

wherein each laser has a cavity comprised of;

a gain chip for providing radiant energy within the cavity;

an interferometric wide tuning port for generating resonances within the cavity and having at least two interferometric optical channels, with at least one of the interferometric optical channels having an adjustable length, to selectively generate resonances at selectable wavelengths, wherein the interferometric wide tuning port has a coarse tuning profile to generate a broad peak for limiting the radiant energy generated by the gain chip to a single broad peak;

a ring resonator for generating resonances within the cavity and receiving radiant energy with a single broad peak from the interferometric wide tuning port, having a ring-shaped optical channel with an adjustable diameter and at least two ring resonator channels, wherein the at least two ring resonator channels are formed sufficiently close to opposing sides of the ring-shaped optical channel to selectively permit evanescent coupling of radiant energy propagating therein at frequencies dependent upon the diameter of the ring-shaped optical channel, wherein the ring resonator has a fine tuning profile to generate a set of sharp peaks which further limit resonances within the cavity; and

wherein the interferometric tuning port aligns a wavelength of the broad peak of the coarse tuning profile at a selected wavelength and the ring resonator is aligned to a wavelength of one of the sharp peaks also at the selected wavelength so that the ring resonator may reflect light having a sharp peak at the selected wavelength through the interferometric wide tuning port and the gain chip for emission by the laser.