Laser having tapered region
Various designs of semiconductor lasers may comprise a waveguide having a front region that is configured to support a plurality of transverse laser cavity modes and a rear region that support only one transverse laser cavity mode. These front and rear regions may be disposed between front and rear reflectors and may provide optical gain. Some such designs may be useful for providing higher power single mode semiconductor lasers.
1. A semiconductor laser comprising:
a waveguide comprising:
(i) a first waveguide region extending in a longitudinal direction between first and second ends of said first waveguide region and having a width extending in a lateral direction, said width of said first waveguide region being configured such that said first waveguide region supports a single bound transverse mode; and
(ii) a second waveguide region extending in a longitudinal direction between first and second ends of said second waveguide region and having a width extending in a lateral direction; and
first and second optical reflectors, said first and second waveguide regions disposed between said first and second optical reflectors, said first optical reflector closer to said first end of said first waveguide region than said second end of said first waveguide region, said second optical reflector closer to said second end of said second waveguide region than said first end of said second waveguide region, said first and second optical reflectors disposed with respect to each other to form a laser cavity therebetween;
wherein the width of said second waveguide region at said second end of said second waveguide region is larger than the width at said first end of said second waveguide region;
wherein at least a portion of said second waveguide region comprises a semiconductor gain material configured to provide optical gain for light propagating within said laser cavity;
wherein at least the first optical reflector comprises a distributed Bragg reflector (DBR) and is formed from a material different from the semiconductor gain material; and
wherein said second waveguide region is configured to support a plurality of bound transverse modes, and the laser cavity sustains and outputs a single transverse mode.
2. The laser of claim 1 , wherein the width of said second waveguide region is configured such that said second waveguide region supports multiple bound transverse modes.
3. The laser of claim 2 , wherein the width of said second waveguide region along the entire longitudinal direction is equal to or greater than a maximum width of said first waveguide region.
4. The laser of claim 1 , wherein the width of said first region is in a range from 1 to 20 microns.
5. The laser of claim 2 , wherein the width of said second region is in a range from 10 and 500 microns.
6. The laser of claim 2 , wherein the width of the second waveguide region increases progressively from said first end to said second end.
7. The laser of claim 1 , wherein the width of the first waveguide region increases progressively from said first end to said second end.
8. The laser of claim 1 , wherein said first optical reflector or said second optical reflector comprises a comb mirror.
9. The laser of claim 1 , wherein one or both first optical reflector and said second optical reflector comprise a narrow band reflector.
10. The laser of claim 1 , wherein one or both said first optical reflector and said second optical reflector comprise a passive element.
11. The laser of claim 1 , wherein one or both said first optical reflector and said second optical reflector are configured to provide gain.
12. The laser of claim 1 , further comprising an electrode disposed with respect to said first optical reflector to apply an electric signal thereto to tune said first optical reflector.
13. The laser of claim 1 , further comprising an electrode disposed with respect to said second optical reflector to apply an electric signal thereto to tune said second optical reflector.
14. The laser of claim 1 , wherein said waveguide further comprises a tunable phase section having an index of refraction that can be adjusted to increase or decrease the optical path length in said section of said waveguide.
15. The laser of claim 1 , further comprising an optical amplifier at said second end of said second waveguide region.
16. The laser of claim 1 , wherein said first waveguide region and said first optical reflector are configured to reflect only one bound transverse mode.
17. The laser of claim 1 , wherein said second waveguide region is configured to provide optical gain to a plurality of bound transverse modes.
18. The laser of claim 1 , wherein said first waveguide region is configured to increase loss of bound transverse modes higher than a fundamental mode.
19. The laser of claim 1 , wherein the laser comprises a Y branch laser, and wherein the first and the second waveguide regions are included in at least one branch of the Y branch laser.
20. The laser of claim 1 , wherein a first portion of the first waveguide region and a second portion of the second waveguide region are configured to provide optical gain for light propagating within said laser cavity and the first portion and the second portion are configured to be activated separately using separate electric contacts.
21. The laser of claim 1 , wherein the single transverse mode output by the laser cavity is a fundamental mode.
22. The laser of claim 1 , wherein the width of the second optical reflector is equal to the width the second waveguide region at the second end.
23. The laser of claim 6 , wherein the second width of the second waveguide region increases in a manner that substantially decouples propagation of a bound transverse mode from propagation of other bound transverse modes of the second plurality of bound transverse modes.
24. The laser of claim 23 , wherein the width of the second waveguide region increases nonlinearly.
25. The laser of claim 1 , wherein the first waveguide region is formed from a material different from the semiconductor gain material, and is not configured to provide gain for light propagating within said laser cavity.
26. The laser of claim 1 , wherein the combination of said first waveguide region and said first reflector are configured to preferentially support lasing of only a single transverse mode in the laser cavity.
27. The laser of claim 1 , wherein the second optical reflector is formed from a material different from the semiconductor gain material.
28. The laser of claim 9 , wherein the second optical reflector comprises a Distributed Bragg Reflectors (DBR).
29. The laser of claim 1 , wherein said width of the first waveguide region is substantially the same at the first and the second ends of said first waveguide region.