Single mode vertical-cavity surface-emitting laser

1. A vertical-cavity surface-emitting laser (VCSEL) comprising:

a first reflector having a first reflectivity;

a radially-dependent mesa layer above the first reflector having a central point aligned with a central axis;

one or more metallic layers above the radially-dependent mesa layer;

a second reflector having a second reflectivity, wherein the second reflectivity is less than the first reflectivity;

a light generation region between the first and second reflectors;

an oxide layer having an aperture with an aperture diameter in a central area of the oxide layer; and

a substrate having a first surface and a second surface, wherein the first surface is coupled to the second reflector, and wherein the second surface is formed into a lens shape to act upon light emitted by the VCSEL through the substrate,

wherein the VCSEL lases in a single transverse mode,

wherein the aperture in the oxide layer has a higher refractive index than the surrounding oxide layer; the oxide layer is located at or near a null of a standing wave in the VCSEL; and a center of the oxide layer is approximately aligned with the central axis of the first reflector, the light generation region, the second reflector, and the substrate,

wherein the radially-dependent mesa layer comprises at least one of: a dielectric material, a transparent conductive oxide, a transparent conductive nitride, or a polymer,

wherein the radially-dependent mesa layer has a first thickness that is approximately a quarter of the VCSEL lasing wavelength within a first region having a first diameter around the central axis, and the radially-dependent mesa layer has a second thickness that is approximately half of the VCSEL lasing wavelength in a second region surrounding the first region,

wherein the first reflector comprises multiple pairs of semiconductor layers forming a distributed Bragg reflector, and

further wherein the first diameter of the first region is less than the aperture diameter.

2. The VCSEL of claim 1 , wherein the first reflector is a distributed Bragg reflector and comprises a first number of pairs of semiconductor layers in a central region of the first reflector and a second number of pairs of semiconductor layers in an outer region surrounding the central region, wherein the first number of pairs is greater than the second number of pairs, and further wherein the central region has a reflector diameter less than the aperture diameter, and the central portion has a higher reflectivity than the outer region surrounding the central region.

3. The VCSEL of claim 1 , wherein the first reflector has a central region and an outer region surrounding the central region, and wherein the outer region of the first reflector comprises multiple pairs of semiconductor layers forming a distributed Bragg reflector, and wherein the central region of the first reflector includes one or more elements selected from the group comprising: one or more pairs of semiconductor layers forming a distributed Bragg reflector, one or more pairs of dielectric layers forming a distributed Bragg reflector, one or more dielectric layers, a transparent conductive oxide layer, a transparent conductive nitride layer, a polymer, and one or more metallic layers, wherein a reflectivity of the central region is greater than a reflectivity of the outer region, and further wherein the central region has a reflector diameter less than the aperture diameter.

4. The VCSEL of claim 1 , further comprising a high contrast grating positioned over the central region of the first reflector, wherein the first reflector comprises multiple pairs of semiconductor layers forming a distributed Bragg reflector, and further wherein a diameter of the high contrast grating is less than the aperture diameter.

5. A method for fabricating a single transverse mode VCSEL comprising:

depositing a ring-shaped electrically conductive material on a first reflector, wherein the first reflector is coupled to a light generation region, the light generation region is further coupled to a second reflector, and the second reflector is coupled to a first surface of a substrate;

depositing a hard mask layer over the ring-shaped electrically conductive material;

removing material from the first reflector and the light generation region to form a wide mesa beneath the hard mask layer;

oxidizing a portion of a layer in the first reflector containing aluminum to create an oxide aperture; and

depositing an ohmic contact layer on the second reflector surrounding the wide mesa,

wherein an improvement comprises:

removing the hard mask layer;

depositing an oxide layer on the wide mesa;

removing portions of the oxide layer to leave a remaining oxide layer within the ring-shaped electrically conductive material, wherein at least a portion of the remaining oxide layer has a thickness that is approximately a quarter of a wavelength, and further wherein the VCSEL lases in a single transverse mode at the wavelength; and

depositing a metallic reflector layer on top of the quarter wavelength thickness of the remaining oxide layer, wherein the metallic reflector layer is anchored to the ring-shaped electrically conductive material.

6. The method of claim 5 , wherein the metallic reflector layer is a metal stack.

7. The method of claim 5 , further comprising fabricating a lens on a second surface of the substrate, wherein light emitted by the single mode VCSEL is emitted through the lens.

8. The method of claim 5 , further comprising placing a high contrast grating under the metallic reflector layer.

9. The method of claim 5 , wherein the remaining oxide layer has a first thickness that is approximately half of the wavelength in a ring shape adjacent to the ring-shaped electrically conductive material, and a second thickness that is approximately a quarter of the wavelength near a center of the ring-shaped electrically conductive material.

10. The method of claim 9 , wherein a diameter of the remaining oxide layer that has the second thickness is less than the inner diameter of the oxide aperture.