High performance vertically emitting lasers
A semiconductor laser that has a reflective surface. The reflective surface redirects the light of an edge emitting laser diode to emit from the top or bottom surface of the diode. The laser may include a gain layer and a feedback layer located within a semiconductive die. The gain and feedback layers generate a laser beam that travels parallel to the surface of the die. The reflective surface reflects the laser beam 90 degrees so that the beam emits the die from the top or bottom surface. The reflective surface can be formed by etching a vicinally oriented III-V semiconductive die so that the reflective surface extends along a (111)A crystalline plane of the die.
1. Field of the Invention
The subject matter disclosed generally relates to the field of semiconductor lasers.
2. Background Information
Semiconductor lasers are used in a variety of system applications. For example, semiconductor lasers are used as a light source in fiber optic communication systems. Laser diodes emit a laser beam from either the edge of the diode die or the surface of the die. Commercially available surface emitting dies contain a vertical cavity and are commonly referred to as Vertical Cavity Surface Emitting Lasers (VCSELs).
Because edge emitting diodes emit the beam from the edge of the semiconductive die, each die must be cut from the wafer before being tested. Conversely, VCSELs, being surface emitting, can be tested in wafer form. Testing at the wafer level reduces the cost associated with testing the laser diodes.
Unfortunately, VCSELs emit a relatively low power laser beam. Consequently, the use of VCSELs has been limited to short optical links. Additionally, most commercially available VCSELs emit light at 850 nanometers (nm). Fiber optic cables strongly disperse and absorb 850 nm light. Edge emitting diodes can generate light at 1310 or 1550 nm which are less affected by absorption and dispersion within a fiber cable.
There have been attempts to integrate internal mirrors within an edge emitting laser diode so that the laser beam emits from the top surface of the diode. For example, ion-beam milling processes have been used to form inclined reflective mirrors within an edge emitting diode. Ion-milling is a relatively inaccurate process that produces rough reflective surfaces. Consequently, such an approach does not have a commercial application.
BRIEF SUMMARY OF THE INVENTIONA semiconductor laser diode that includes a gain layer and a diffraction grating feedback layer within a semiconductive die. The semiconductive die also includes a reflective surface located along a (111)A cystalline plane of the die. The reflective surface reflects a laser beam generated within the semiconductive die so that the beam is emitted from a surface of the die.
BRIEF DESCRIPTION OF THE DRAWINGS
Disclosed is a semiconductor laser that has an inclined reflective surface. The reflective surface redirects the light of an edge emitting laser diode to emit from a surface of the laser diode. The laser includes a gain layer and a diffraction grating feedback layer located within a semiconductive die. The gain and feedback layers generate a laser beam that travels parallel to the surface of the die. The reflective surface reflects the laser beam 90 degrees so that the beam emits the die from the top or bottom surface. The reflective surface can be formed by etching a vicinally oriented III-V semiconductive die so that the reflecting surface extends along a (111)A crystalline plane of the die.
Referring to the drawings more particularly by reference numbers,
As shown in
The diffraction grating feedback layer 26, which is composed of a semiconductor alloy differing in refractive index from the P-type layer 30, is corrugated with a period satisfying the Bragg condition for the desired frequency of oscillation. Layer 26 may extend along the entire length of the laser, in which case it forms a distributed feedback laser, or it may extend over part of the length, in which case it forms a distributed Bragg reflector laser.
The reflective element 16 may include a reflective surface 38 that can reflect the laser through an exit facet 40 in the top surface 22 of the die 12. The facet 40 may have an anti-reflection coating. The reflective surface 38 is formed at a 45 degree angle relative to the top surface 22. The 45 degree angle will deflect the laser beam 90 degrees so that the laser exits the die 12 perpendicular to the top surface 22.
The semiconductive die 12 can be epitaxially grown on an indium-phosphide, gallium-arsenide or other III-V semiconducting substrate. The (111)A crystalline plane of these and other III-V semiconductors are more thermodynamically stable than planes of different direction. Consequently, chemically etching such materials leaves an exposed surface along the (111)A crystalline plane.
As shown in
The result is a repeatable process to form a 45 degree reflective surface within the die. Additionally, the etching process creates a relatively smooth reflective surface 38.
Typically, a large number of individual laser dice 12 will be fabricated in parallel on a single wafer, which is then cut into individual lasers.
While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention not be limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art. In particular, an essentially equivalent laser could be made if the conductivity types of P-doped and N-doped layers are reversed, if the positions of active layer 28 and distributed feedback layers 26 are reversed, or if the inclination of deflection mirror 38 is reversed so that the beam exits through the substrate rather than the surface.
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17. A method for forming a reflective surface in a semiconductor laser, comprising:
- forming a first surface in a semiconductor wafer; and,
- etching the first surface such that a thermodynamically stable crystalline plane of the semiconductor wafer is exposed as a reflective surface.
18. The method of claim 17, wherein the first surface is 9.7 degrees from a (100) plane of the semiconductor wafer.
19. The method of claim 18, wherein the thermodynamically stable crystalline plane is a (111) plane.
20. The method of claim 17, wherein the thermodynamically stable crystalline plane is oriented at an angle of 45 degrees relative to the first surface.
Type: Application
Filed: May 16, 2005
Publication Date: Sep 29, 2005
Inventor: Jeffrey Ungar (Valley Village, CA)
Application Number: 11/130,535