REFLECTOR FOR VCSEL
A vertical cavity surface emitting laser (VCSEL) may include an active region (e.g., one or more quantum wells) and a chirped pattern reflector. The active region may be configured to be electrically pumped such that the active region generates light having a fundamental mode and a higher order mode. The chirped pattern reflector may include a first portion presenting to the active region as a first portion of an effective mirror having a concave shape and a second portion presenting to the active region as a second portion of the effective mirror having a convex shape.
1 . A vertical cavity surface emitting laser (VCSEL), comprising:
an active region configured to be electrically pumped to generate light having a fundamental mode and a higher order mode;
a first reflector disposed on a side of the active region;
a patterned reflector, disposed on another side of the active region opposite the first reflector, the patterned reflector having a structuration that varies at distances from an axis of symmetry of the VCSEL to form a plurality of concentric parts, arranged coaxially about the axis of symmetry, that each impart a phase retardation on a reflected wavefront that varies at distances from the axis of symmetry, the patterned reflector forming an effective mirror having:
a central portion, symmetrically aligned with the axis of symmetry, that presents an equivalent of a concave mirror to the fundamental mode; and
a peripheral portion, surrounding the central portion, that presents an equivalent of a convex mirror to the higher order mode.
2 . The VCSEL of claim 1 , wherein the structuration of the patterned reflector comprises at least one of a refractive index, a filling factor, an occupation factor, a spacing, a shape, a size, a thickness, or a pattern that varies at distances from an axis of symmetry.
3 . The VCSEL of claim 1 , wherein each of the concentric parts are circularly symmetric.
4 . The VCSEL of claim 1 , wherein each of the concentric parts are elliptically shaped.
5 . The VCSEL of claim 1 , wherein the structuration is deposited or etched into an epitaxial structure of the VCSEL.
6 . The VCSEL of claim 1 , wherein the structuration is patterned using lithography and etching.
7 . The VCSEL of claim 1 , wherein the patterned reflector is separated from the active region by an air gap.
8 . The VCSEL of claim 1 , wherein the patterned reflector is formed on or with a distributed Bragg reflector.
9 . The VCSEL of claim 1 , wherein the patterned reflector is an outcoupling reflector.
10 . The VCSEL of claim 1 , wherein the first reflector is a distributed Bragg reflector.
11 . The VCSEL of claim 1 , wherein the first reflector comprises a second patterned reflector.
12 . The VCSEL of claim 1 , wherein the active region comprise one or more quantum wells or one or more quantum dots.
13 . The VCSEL of claim 1 , further comprising an insulating layer, disposed between the patterned reflector and the first reflector, defining an aperture.
14 . The VCSEL of claim 13 , wherein the aperture is coaxially aligned with the axis of symmetry.
15 . The VCSEL of claim 1 , wherein the equivalent of the concave mirror presented by the central portion of the effective mirror imparts a phase retardation Φ(r) on the fundamental mode given by
Φ
(
r
)
=
2
π
λ
(
f
+
λ
2
π
Φ
Max
-
r
2
+
f
2
)
Modulo
2
π
and the equivalent of the convex mirror presented by the peripheral portion of the effective mirror imparts a phase retardation Φ(r) on the higher order mode given by
Φ
(
r
)
=
2
π
λ
(
-
f
′
+
λ
2
π
Φ
Max
-
r
2
+
f
′2
)
Modulo
2
π
where:
r represents a radius relative the axis of symmetry;
λ represents a wavelength of the fundamental mode in a vacuum;
f represents a focal length of the equivalent of the concave mirror;
f′ represents a focal length of the equivalent of the convex mirror; and
Φ Max represents a maximal phase retardation.
16 . The VCSEL of claim 15 , wherein:
the focal length f of the concave portion is equal to or greater than 5 μm and equal to or less than 20 μm; and
the focal length f′ of the convex portion is equal to or greater than 10 μm and equal to or less than 100 μm.
17 . A method of making a vertical cavity surface emitting laser (VCSEL), the method comprising:
forming a first reflector;
forming an optical cavity adjacent the first reflector, the optical cavity having an active region configured to be electrically pumped such that the active region generates light having a fundamental mode and a higher order mode; and
forming a second reflector on a side of the active region opposite the first reflector;
patterning a structuration on the second reflector to form a patterned reflector having a plurality of concentric parts, arranged coaxially about an axis of symmetry of the VCSEL, that vary at distances from the axis of symmetry and impart a phase retardation on a reflected wavefront that varies at distances from the axis of symmetry, the patterned reflector forming an effective mirror having:
a central portion, symmetrically aligned with the axis of symmetry, that presents an equivalent of a concave mirror to the fundamental mode; and
a peripheral portion, surrounding the central portion, that presents an equivalent of a convex mirror to the higher order mode.
18 . The method of claim 17 , wherein patterning the structuration comprises forming concentric parts having at least one of a refractive index, a filling factor, an occupation factor, a spacing, a shape, a size, a thickness, or a pattern that varies at distances from an axis of symmetry.
19 . The method of claim 17 , wherein each of the concentric parts are circularly symmetric.
20 . The method of claim 17 , wherein each of the concentric parts are elliptically shaped.