Surface-emitting semiconductor laser device in which an edge-emitting laser is integrated with a diffractive lens, and a method for making the device
View Patent ↗A surface-emitting semiconductor laser device is provided that includes an edge-emitting laser integrated in a semiconductor material with various reflectors and a diffractive lens. The edge-emitting laser has a first section comprising an active MQW region, a second section comprising a passive region and a third section comprising a semi-insulating or un-doped semiconductor bulk layer. This configuration ensures that the injection current will pass through all of the layers of the active region, thereby preventing the occurrence of optical losses due to un-injected areas of the MQW active region. In addition, the inclusion of the passive region ensures that there is no current passing through the interface between the active MQW region and the regrown semiconductor bulk layer. The latter feature improves performance and device reliability.
1. A surface-emitting semiconductor laser device comprising:
a semiconductor substrate having an upper surface and a lower surface;
a plurality of semiconductor layers disposed on the upper surface of the semiconductor substrate, said plurality of semiconductor layers including an upper most layer, a lowermost layer and one or more layers in between the uppermost and lowermost layers;
an edge-emitting laser formed in one or more of said plurality of semiconductor layers, the laser having an active multiple quantum well (MQW) region having a first end and a second end and a passive region having a first end and a second end, the second end of the active MQW region joining the first end of the passive region, the laser having a rear facet corresponding to the first end of the active MQW region and a front facet corresponding to the second end of the passive region, wherein if the laser is activated, laser light produced in the active MQW region propagates along an optical axis of the laser that is substantially parallel to the upper and lower surfaces of the substrate through the active MQW region, out of the second end of the active MQW region, into the first end of the passive region, through the passive region, and out of the front facet of the laser, the laser light diverging as it propagates out of the front facet;
an upper reflector disposed on or near the uppermost layer of said plurality of semiconductor layers above the front facet of the laser;
an angled side reflector disposed on an angled side facet formed in one or more of said plurality of semiconductor layers;
a lower reflector disposed on or near the lower surface of the semiconductor substrate; and
a diffractive lens disposed in at least the uppermost layer of said one or more semiconductor layers, and wherein the laser, the angled side reflector, the upper reflector, the lower reflector, and the diffractive lens are oriented in relation to one another such that a first portion of the laser light propagating out of the front facet impinges directly upon the upper reflector and is reflected thereby onto the angled side reflector and such that a second portion of the laser light propagating out of the front facet impinges directly upon the angled side reflector, wherein the angled side reflector reflects the impinging first and second portions of laser light onto the lower reflector, and wherein the lower reflector reflects the first and second portions of laser light through the diffractive lens, the diffractive lens directing the laser light in a direction that is substantially normal to the upper surface of the substrate.
2. The surface-emitting semiconductor laser device of claim 1 , wherein the active MQW region and the passive region have first and second photoluminescence peaks, respectively, the second photoluminescence peak being lower than the first photoluminescence peak.
3. The surface-emitting semiconductor laser device of claim 2 , wherein the passive region comprises MQW layers.
4. The surface-emitting semiconductor laser device of claim 2 , wherein the passive region comprises a bulk quaternary layer.
5. The surface-emitting semiconductor laser device of claim 1 , wherein the edge-emitting laser comprises a ridge structure.
6. The surface-emitting semiconductor laser device of claim 5 , wherein the ridge structure extends parallel to the optical axis of the laser from at least the first end of the active MQW region past the second and first ends of the active and passive MQW regions, respectively.
7. The surface-emitting semiconductor laser device of claim 1 , wherein the edge-emitting laser is a fabry-Perot (F-P) laser.
8. The surface-emitting semiconductor laser device of claim 1 , wherein the edge-emitting laser comprises a buried diffractive grating formed in one or more of said plurality of semiconductor layers.
9. The surface-emitting semiconductor laser device of claim 1 , wherein the edge-emitting laser is a distributed feedback (DFB) laser.
10. The surface-emitting semiconductor laser device of claim 1 , wherein the edge-emitting laser is an electro-absorption modulator laser (EML).
11. The surface-emitting semiconductor laser device of claim 1 , wherein the lower reflector is a metal contact layer disposed on the lower surface of the substrate.