Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
1999-03-05
2001-06-26
Leung, Quyen P. (Department: 2881)
Coherent light generators
Particular active media
Semiconductor
C372S075000
Reexamination Certificate
active
06252896
ABSTRACT:
TECHNICAL FIELD
The invention relates generally to vertical-cavity surface-emitting lasers and more particularly to an optically pumped vertical-cavity surface-emitting laser.
DESCRIPTION OF THE RELATED ART
Vertical-cavity surface-emitting lasers (VCSELs) have a number of advantages over traditional edge-emitting lasers, such as low manufacturing cost, good beam quality and scalable geometries. These properties make VCSELs desirable for many applications. In particular, VCSELs that can produce long wavelength light (1300 nm-1550 nm) are of interest in optical communications.
A VCSEL may be driven by electrical current or may be optically pumped to produce the output laser light. A conventional current-injection VCSEL includes an active region that is positioned between two distributed Bragg reflectors (DBRs) that are formed on a substrate. In addition, the current-injection VCSEL includes two ohmic contacts for applying electrical current to the active region. Typically, one of the ohmic contacts is located below the substrate, while the other ohmic contact is located above the top DBR. When voltage is applied to the contacts, electrical current is injected into the active region, causing the active region to emit light. The emitted light is reflected between the two DBRs. A portion of the emitted light may propagate through the top DBR or the bottom DBR as the output laser light.
A conventional optically pumped VCSEL also includes an active region between two DBRs. However, the optically pumped VCSEL includes, or is operationally associated with, a light source. The light source may be another VCSEL or a light-emitting diode. The optically pumped VCSEL generates the output laser light by absorbing “pump light” supplied by the light source. The pump light is absorbed by the active region, which causes emission of the output laser light.
U.S. Pat. No. 5,513,204 to Jayaraman describes an optically pumped VCSEL device that includes a short-wavelength VCSEL that optically pumps a long-wavelength VCSEL that is coupled to the short-wavelength VCSEL. One embodiment of the optically pumped VCSEL device of Jayaraman is shown in FIG.
1
. In this embodiment, a VCSEL device
10
includes a short-wavelength VCSEL
12
that is formed on a GaAs substrate
14
. The short-wavelength VCSEL
12
is comprised of an active region
16
and mirrors
18
and
20
. The VCSEL device
10
also includes a long-wavelength VCSEL
22
formed on a GaAs substrate
24
. The long-wavelength VCSEL
22
is comprised of an active region
26
and mirrors
28
and
30
. The mirror
28
is made of alternating layers of GaAs and AlAs, while the mirror
30
is made of alternating layers of SiO
2
and TiO
2
. The long-wavelength VCSEL
22
is coupled to the short-wavelength VCSEL
12
by a layer
32
of adhesive material. The adhesive material may be a transparent optical adhesive material or a metallic bonding material. In an alternative embodiment, the VCSELs
12
and
22
are fusion bonded to form a monolithic structure.
In operation, the short-wavelength VCSEL
12
is initially activated to emit light
34
having a short peak wavelength. The activation of the VCSEL
12
involves injecting current into the active region
16
via ohmic contacts (not shown). The light
34
propagates through the mirror
30
of the long-wavelength VCSEL
22
and impinges upon the active region
26
. The light
34
is absorbed by the active region
26
, which gives rise to electron-hole pairs. These pairs collect in the quantum wells within the active region
26
where they recombine, producing laser light
36
having a long peak wave-length. The laser light
36
exits the VCSEL device
10
as output laser light from the mirror
28
of the long-wavelength VCSEL
22
.
A concern with the VCSEL device
10
is that a significant portion of the light
34
from the short-wavelength VCSEL
12
that was pumped to the long-wavelength VCSEL
22
will be transmitted along with the laser light
36
. Ideally, the output laser light will contain only the long-wavelength laser light
36
produced from the long-wavelength VCSEL
12
. However, when the short-wavelength light
34
reaches the active region
26
of the short-wavelength VCSEL
22
, some of the short-wavelength light
34
will not be absorbed by the active region
26
and will be transmitted through the mirror
28
. The mirror
28
can be designed to reflect the short-wavelength light
34
. However, it is inevitable that some of the short-wavelength light
34
will be transmitted through the mirror
28
along with the laser light
36
as part of the output laser light. When the VCSEL device
10
is coupled to a fiber optic cable, a filtering device may be required to selectively transmit only the long-wavelength laser light
36
from the VCSEL device
10
, which would add complexity and cost to the system that will embody the VCSEL device
10
.
Another optically pumped VCSEL device of interest is described in U.S. Pat. No. 5,754,578, which is also issued to Jayaraman. One embodiment of the optically pumped VCSEL device disclosed in this patent is illustrated in FIG.
2
. In this embodiment, a VCSEL device
38
includes a short-wavelength VCSEL
40
and a long-wavelength VCSEL
42
that are formed on a single GaAs substrate
44
. The short-wavelength VCSEL
40
is comprised of an active region
46
and mirrors
48
and
50
. The mirrors
48
and
50
are made of alternating layers of GaAs and AlGaAs. The short-wavelength VCSEL
40
includes metal contacts
52
and
54
that provide current to the activation layer
46
. In addition, the short-wavelength VCSEL
40
includes a current confining scheme which may be realized by proton implantation or by an oxidation layer
56
. The long-wavelength VCSEL
42
is comprised of an active region
58
and mirrors
60
and
62
. The mirror
62
is made of alternating layers of GaAs and AlGaAs. However, the mirror
60
can be made of a number of different materials suitable for fabricating a mirror in a VCSEL. The mirror
62
is described as being grown in the same epitaxial growth step as the short-wavelength VCSEL
40
.
The operation of the VCSEL device
38
is virtually identical to the operation of the VCSEL device
10
of FIG.
1
. Initially, current is injected into the active region
46
of the short-wavelength VCSEL
40
via the contacts
52
and
54
. The injected current drives the active region
46
such that light
63
having a short peak wavelength is emitted from the short-wavelength VCSEL
40
. The light
63
then propagates through the mirror
62
of the long-wavelength VCSEL
42
and impinges upon the active region
58
. The light
63
is absorbed by the active region
58
, which drives the active region
58
to emit laser light
64
having a long peak wavelength. The laser light
64
exits the VCSEL device
38
as output laser light from the mirror
60
of the long-wavelength VCSEL
38
.
The same concern of the VCSEL
10
of
FIG. 1
exists for the VCSEL device
38
of FIG.
2
. Namely, the output laser light from the VCSEL device
38
will contain a significant amount of the short-wavelength light
63
emitted from the short VCSEL
40
. Again, a costly filtering device may be required to filter the short-wavelength light
63
and transmit only the laser light
64
.
What is needed is an optically pumped VCSEL device that can efficiently output laser light having a long peak wavelength without a need for an external filter.
SUMMARY OF THE INVENTION
An optically pumped vertical-cavity surface-emitting laser (VCSEL) device and a method of fabricating the device utilize two separate substrates that perform a filtering operation to selectively transmit only light having a long peak wavelength that is generated by the device. The optically pumped VCSEL device is a self-pumped device that can generate the pump light to drive the device to emit output laser light having a long peak wavelength. Preferably, the output laser light has a peak wavelength between 1300 nm and 1550 nm, which is desirable for applications in the field of optical commun
Babic Dubravko I.
Bi Wayne
Corzine Scott W.
Ranganath Tirmula R.
Tan Michael R. T.
Agilent Technologie,s Inc.
Leung Quyen P.
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