Vertical cavity surface emitting laser with improved mode-selectivity
View Patent ↗It is an object of the invention to provide a VCSEL having both a high beam quality or a low M 2 -factor, respectively, and a reduced mirror thickness which improves the heat dissipation due to the reduced thickness and the production cost. It is suggested to employ a Bragg-reflector in combination with a metal reflector terminating the distal side of the Bragg-reflector as seen from the laser cavity, wherein the metal reflector layer is localized at the center around the optical axis.
1. A vertical cavity surface emitting laser diode, comprising
a substrate and disposed thereon,
a first Bragg-reflector layer stack,
a second Bragg-reflector layer stack, said first and second Bragg-reflector layer stacks forming a laser cavity with an optical axis along which a laser beam is emitted in operation;
a metallic reflector layer terminating one of the Bragg-reflector layer stacks, said metallic reflector layer being localised about said optical axis and covering an area no larger than an area within which the intensity of the TEM 00 -laser mode exceeds more than one third of its maximum intensity.
2. The vertical cavity surface emitting laser diode according to claim 1 , comprising a current confinement layer having a current aperture which laterally confines the current flowing through the laser cavity, wherein said metallic reflector layer covers an area of a size which does not exceed the size of the area covered by said aperture.
3. The vertical cavity surface emitting laser diode according to claim 2 , wherein said area covered by said metallic reflector layer is at least 1/10 of the area covered by said aperture.
4. The vertical cavity surface emitting laser diode according to claim 1 , wherein the metallic reflector layer is deposited onto an insulating layer.
5. The vertical cavity surface emitting layer according to claim 4 , wherein said insulating layer is a silicon oxide layer.
6. The vertical cavity surface emitting laser diode according to claim 1 , wherein said vertical cavity surface emitting laser diode is a bottom emitting laser diode and said metallic reflector layer is disposed on the topmost Bragg-reflector layer stack deposited on said substrate.
7. The vertical cavity surface emitting laser diode according to claim 6 , in which said metallic reflection layer is circumferentially surrounded by a ring contact.
8. The vertical cavity surface emitting laser diode according to claim 1 , in which the real part of refractive index of said metallic reflector layer is lower than 0.5.
9. The vertical cavity surface emitting laser diode according to claim 1 , wherein the material of said metallic reflection layer is selected from the group consisting of gold, silver, copper, and alloys thereof.
10. The vertical cavity surface emitting laser diode according to claim 1 , wherein the coverage by said metallic reflection layer decreases gradually from the coverage at the optical axis along a direction radially outwards.
11. The vertical cavity surface emitting laser diode according to claim 1 , in which said metallic reflector layer forms at least a part of one of the electrical contacts.
12. The vertical cavity surface emitting laser diode according to claim 1 , wherein said vertical cavity surface emitting laser diode is a top emitting laser diode and said metallic reflector layer is buried underneath said first and second Bragg-reflector layer stacks.
13. The vertical cavity surface emitting laser diode according to claim 1 , wherein the Bragg-reflector layer stack terminated by said metallic reflector layer comprises at most 15 pairs of layers with alternating higher and lower refractive index.
14. The vertical cavity surface emitting laser diode according to claim 1 , further comprising an electrical contact layer contacting the Bragg-reflector layer stack terminated by said metallic reflector layer and comprising sections intersecting said metallic reflector layer.