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

• US 20020085609A1
• Filed: 01/02/2001
• Published: 07/04/2002
• Est. Priority Date: 01/02/2001
• Status: Active Grant

• Current Assignee: Spectrasensors, Inc. (Endress+Hauser AG)
• Original Assignee: Tunable Photonics
• Inventors: May, Randy Dean, Ksendzov, Alexander
• Granted Patent: US 6,690,687 B2
• Time in Patent Office: Days
• US Class Current: 372/94
• 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;

an interferometric wide tuning port; and

a ring resonator mirror.

2. A semiconductor laser having a cavity comprised of:

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

wide tuning means for limiting resonance within the cavity based on a wide tuning profile having a broad peak; and

fine tuning means for further limiting resonance within the cavity to within a set of sharp resonance peaks;

with

the wide tuning means 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.

3. The semiconductor laser of claim 2 wherein the means for providing radiant energy and gain is a gain chip.

4. The semiconductor laser of claim 3 wherein the gain chip is formed on a III/IV material chip.

5. The semiconductor laser of claim 2 wherein the wide tuning means is a Mach-Zehnder interferometer.

6. The semiconductor laser of claim 5 wherein the Mach-Zehnder interferometer comprises:

an input optical channel;

a splitter for splitting the input optical channel into a pair of optical channels of differing lengths; and

a combining section for combining the pair of optical channels into a single output channel.

7. The semiconductor laser of claim 6 further including means for controlling the wide tuning means to adjust an optical path length difference between the pair of optical channels of the Mach-Zehnder interferometer so as to maintain alignment of the broad peak of the wide tuning profile with the selected wavelength.

8. The semiconductor laser of claim 7 wherein the means for adjusting an optical path length difference includes a heating element.

9. The semiconductor laser of claim 5 wherein the Mach-Zehnder interferometer is formed on a separate planar wave guide chip.

10. The semiconductor laser of claim 2 wherein the fine tuning means is a ring resonator mirror.

11. The semiconductor laser of claim 10 wherein the ring resonator mirror comprises:

an input optical channel;

a splitter for splitting the input optical into a pair of channels; and

a ring-shaped optical channel;

with

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.

12. The semiconductor laser of claim 11 further including means for controlling the fine tuning means includes means to adjust the ring-shaped optical channel so as to maintain alignment of one of the sharp peaks at the selected wavelength.

13. The semiconductor laser of claim 12 wherein the means for adjusting resonance frequencies of the ring-shaped optical channel includes a heating element.

14. The semiconductor laser of claim 10 wherein the ring resonator mirror is formed using planar wave guides.

16. The method of claim 15 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.

17. The method of claim 16 wherein the step of adjusting an optical path length difference between the pair of optical channels is performed by heating the Mach-Zehnder interferometer.

18. The method of claim 15 wherein the ring resonator includes a ring-shaped optical channel and wherein the step of adjusting the ring resonator mirror is performed by adjusting one or more of a diameter and a refractive index of the ring-shaped optical channel.

19. The method of claim 18 wherein the step of adjusting the ring-shaped optical channel is performed by heating the ring resonator mirror.

20. The method of claim 15 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.

21. The method of claim 15 further including the step of

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

22. The method of claim 21 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.

15. A method for operating a semiconductor laser having 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; 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.