Semiconductor laser
A semiconductor laser includes an active region including an active layer, and a diffraction grating and a phase shift which determine an oscillation wavelength, and a distributed reflector region including a light guide layer and a refection diffraction grating. The distributed reflector region has an effective diffraction grating period which varies along a direction of a cavity.
1. A semiconductor laser, comprising:
a distributed feedback laser region including an active layer, and a diffraction grating and a phase shift which determine a single oscillation wavelength and provided over or under the active layer, the distributed feedback laser region being a current injection region; and
a distributed reflector region including a passive waveguide core layer jointed to an end face of the active layer and a reflection diffraction grating provided over or under the passive waveguide core layer and continuing to the diffraction grating, the distributed reflector region being a no-current injection region; and wherein
the diffraction grating in the distributed feedback laser region has a fixed period;
the distributed reflector region has an effective diffraction grating period which varies along a direction of a cavity; and
the effective diffraction grating period of the distributed reflector region becomes longer as a distance from the distributed feedback laser region increases over the entire region.
2. The semiconductor laser as claimed in claim 1 , wherein a current injection electrode is provided only in the distributed feedback laser region.
3. The semiconductor laser as claimed in claim 1 , wherein, in the distributed reflector region, the reflection diffraction grating has a period which varies along the direction of the cavity.
4. The semiconductor laser as claimed in claim 1 , wherein the distributed reflector region has an optical path length which varies along the direction of the cavity.
5. The semiconductor laser as claimed in claim 4 , wherein the distributed reflector region is curved along the direction of the cavity.
6. The semiconductor laser as claimed in claim 5 , wherein, in the distributed reflector region, a tangential angle of the passive waveguide core layer increases as a distance from the distributed feedback laser region increases.
7. The semiconductor laser as claimed in claim 4 , wherein, in the distributed reflector region, the passive waveguide core layer has an equivalent refractive index which varies along the direction of the cavity.
8. The semiconductor laser as claimed in claim 7 , wherein, in the distributed reflector region, the equivalent refractive index of the passive waveguide core layer increases as a distance from the distributed feedback laser region increases.
9. The semiconductor laser as claimed in claim 7 , wherein, in the distributed reflector region, the passive waveguide core layer has a width which varies along the direction of the cavity.
10. The semiconductor laser as claimed in claim 1 , wherein the distributed reflector region has the reflection diffraction grating which has a fixed period and an optical path length which varies along the direction of the cavity.
11. The semiconductor laser as claimed in claim 1 , wherein, in the distributed reflector region, the effective diffraction grating period is equal to or longer than a period of the diffraction grating of the distributed feedback laser region at a position at which the distributed reflector region contacts with the distributed feedback laser region.
12. The semiconductor laser as claimed in claim 1 , wherein, in the distributed reflector region, the effective diffraction grating period is equal to or shorter than a period of the diffraction grating of the distributed feedback laser region at a position at which the distributed reflector region contacts with the distributed feedback laser region.
13. The semiconductor laser as claimed in claim 1 , wherein the distributed reflector region is provided on one end side of the distributed feedback laser region.
14. The semiconductor laser as claimed in claim 1 , wherein the distributed reflector region is provided on both end sides of the distributed feedback laser region in such a manner as to sandwich the distributed feedback laser region.
15. The semiconductor laser as claimed in claim 14 , wherein one of the distributed reflector regions on both end sides of the distributed feedback laser region has a length in the direction of the cavity which is shorter than that of the other one of the distributed reflector regions.
16. The semiconductor laser as claimed in claim 1 , wherein the diffraction grating of the distributed feedback laser region and the reflection diffraction grating of the distributed reflector region have an equal coupling coefficient.
17. The semiconductor laser as claimed in claim 1 , wherein the distributed reflector region is provided on both end sides of the distributed feedback laser region in such a manner as to sandwich the distributed feedback laser region and further has anti-reflection coatings provided on both end faces thereof.
18. The semiconductor laser as claimed in claim 1 , wherein the phase shift is a λ/4 phase shift provided on the diffraction grating.