High output power injection lasers

In a heterostructure injection laser having an active layer sandwiched by a pair of intermediate index layers, a very thin low refractive index and high bandgap may be employed between at least active layer and one intermediate layer or at least contiguous with a surface of at least one intermediate layer remote from the active layer. These thin layers may be applied in various positional combinations to produce desired effects on fundamental mode guiding.

BACKGROUND OF THE INVENTION 
This invention relates generally to injection semiconductor lasers and more 
particularly to heterostructure lasers having a unique composition profile 
providing a high power, low divergence beam. 
In the past, five layer heterostructure lasers have been developed for high 
power, low beam divergence applications. One such device is disclosed by 
G.H.B. Thompson et al in the Journal of Applied Physics, Volume 47, page 
1501 (1976). In these devices, the refractive index profile of the 
semiconductive layers of the device have been provided with monotonic step 
type of index profile with the central active layer being the highest 
refractive index. Specifically, the index profile would be, 
low-intermediate-high-intermediate-low, vertically through the device. 
Such a profile allows the optical wave to spread within the device to 
create a low beam divergence. However, the laser also exhibits an increase 
in threshold because electrical carriers can be injected into the 
intermediate index layers rather than being completely confined to the 
higher index layer as is desirable. 
Low beam divergence in the far field pattern may also be provided by a 
heterostructure injection laser having a very thin active layer. However, 
in order to confine the optical wave in its propagation in such a device, 
it is necessary to provide thick cladding layers adjacent to the active 
layer with high aluminum content. For example, the active layer may be 
GaAs and the cladding layers may be relatively thick layers of GaAlAs to 
confine the optical wave. These thick high aluminum content cladding 
layers lead to high overall thermal resistance thereby reducing the amount 
of possible input power which, in turn, limits the power outputs necessary 
for many low beam divergence applications. 
OBJECT AND SUMMARY OF THE INVENTION 
The primary object of this invention is the provision of a heterostructure 
laser having a unique refractive index profile that provides a lower beam 
divergence and a higher output power with overall lower thermal resistance 
than previously known in the art. 
A heterostructure injection laser according to one embodiment of the 
present invention includes at least one cladding layer contiguous with one 
surface of the active layer of the laser and having a substantially lower 
index of refraction as compared to the active layer. The cladding layer 
has very thin cross-sectional thickness, the maximum thickness being 
sufficient to confine injection carriers to the active layer but 
permitting extension of the optical wave propagation beyond the cladding 
layer. A further layer is contiguous with the surface of the cladding 
layer remote from the active layer and having a relatively large thickness 
compared to the combined thickness of the cladding and active layers. This 
further layer is provided with an index of refraction intermediate of the 
active layer and the cladding so as to aid in guiding and confining the 
optical wave to its geometrical limit. The index of refraction of the 
further layers is chosen to be lower than the equivalent refractive index 
of the lowest fundamental mode of the guided optical wave. 
A still further layer may be contiguous with the mentioned further layer 
having an index of refraction and layer thickness chosen to permit 
confinement of the lowest order or fundamental mode of the guided optical 
wave but permit absorption therein of higher order modes. In this case the 
refractive index of the further layer need only be lower than the 
refractive index of the active layer. 
One or more of these layers, i.e., the active layer, the cladding layer, or 
the mentioned, further or still further layers may be made nonplanar to 
provide further single fundamental transverse mode control. A 
heterostructure injection laser according to another embodiment of the 
present invention has a refractive index profile that is 
intermediate-low-high-low-intermediate. The device is further 
characterized as having an active layer having a narrow bandgap and high 
refractive index sandwiched between two very thin, wide bandgap and low 
index cladding layers. This three layer structure is sandwiched between 
two comparatively thicker layers having a refractive index intermediate of 
cladding layers and the active layer. The intermediate layers may be 
provided with outer layers to provide for good mode confinement. 
The thin cladding layers are thick enough to confine injected carriers but 
are sufficiently thin to allow and overall low thermal resistance and 
thereby allowing for higher input powers and corresponding higher output 
powers. 
A heterostructure injection laser according to a further embodiment of the 
present invention has a refractive index profile that decreases in 
refractive index from the active layer to the outermost layers, which are 
contact layers and have higher index than the intermediate layers. The 
intermediate layers form what is referred to as a large optical cavity 
(LOC). A thin layer may be provided between the intermediate layers and 
the outermost layers to provide high optical loss for higher order 
transverse modes and low optical loss for the lowest order transverse 
modes, a prerequisite being that the refractive index of the outermost 
layers is greater than the equivalent refractive index of the fundamental 
mode of the guide optical wave propagating in the LOC. 
Other objects and attainments together with a fuller understanding of the 
invention will become apparent and appreciated by referring to the 
following description and claims taken in conjunction with the 
accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
In FIG. 1, the injection laser 10 is a heterostructure device comprising, 
in order, an additional or intermediate index layer 12, very thin cladding 
or confinement layer 14, active layer 16, very thin cladding or 
confinement layer 18, and an additional or an intermediate index layer 20. 
Layer 12 may be fabricated on a suitable substrate 25. Fabrication of 
these layers is best suited for MBE and CVD, as it is difficult to 
fabricate thin layers (such as layers 14, 18) of these semiconductor 
materials employing LPE techniques. However, LPE fabrication is possible 
in producing the behavior desired in the laser. 
Composition of layers 12, 14, 16, 18 and 20 may be, respectively, 
n-Ga.sub.1-x Al.sub.x A.sub.s,n-Ga.sub.1-y Al.sub.y As,p-GaAs,p-Ga.sub.1-y 
Al.sub.y As, and n-Ga.sub.1-x Al.sub.x As, where y-x. For example, 
intermediate layers 12 and 20 may be Ga.sub.0.95 Al.sub.0.05 As of proper 
conductivity type and cladding layers 14 and 18 may be Ga.sub.0.7 
Al.sub.0.3 As of proper conductivity type. Contact facilitating layer 23 
and substrate 25 may be, respectively, p-GaAs and n-GaAs. These layers 
provide a vehicle by which electrodes 22 and 24 may be applied to laser 10 
to provide for its operation. Layers 23 and 25 might be eliminated if the 
Al content provided in the intermediate index layers 12 and 20 is of low 
value, e.g., below 10% Al or if electrical contacts can be made to higher 
Al content layers. 
As is well known in the art, the conductivity types of these layers can be 
reversed. Also active layer 16 may have a low content of aluminum (Al) but 
such concentrations would be below Al concentrations of the intermediate 
layers 12 and 20. 
As well known in the art, appropriate stripe geometries or transverse mode 
confining structures may also be added to this and all other embodiments 
disclosed herein to confine the current to a specific lateral region of 
the structure and to provide a lateral waveguide along the plane of the 
p-n junction. 
Upon forward biasing with a potential applied to electrode 22 greater than 
that applied to electrode 24, carriers (holes and electrons) are injected 
into and confined within the active layer 16 by thin cladding layers 14 
and 18 and upon carrier recombination, produce radiation which provides an 
optical wave 26 which has a wide profile and spreads out into intermediate 
layers 12 and 20. 
Examples of possible layer thicknesses are shown in FIG. 1. 
Cladding layers 14 and 18 are very thin compared to intermediate layers 12 
and 20. Cladding layers 14 and 18 may be approximately 50A to 2000A thick 
and active layer 16 may be approximately 200A to 5000A thick. In general, 
the thicknesses of these cladding layers is governed by performance 
parameters. They, however, should not be so thin as to permit carriers to 
generally tunnel through the thin layer into the intermediate index layers 
12 and 20. 
The refractive index profile for laser 10 is shown in FIG. 2. Sections of 
the profile having identical numerical identification for corresponding 
layers in FIG. 1 and each section represents the effective index of 
refraction level for the corresponding layer composition. The index 
profile is intermediate-low-high-low-intermediate. The advantage to be 
obtained by this index profile is that the injected carriers are confined 
by the thin wide bandgap cladding layers 14 and 18 on either side of the 
low bandgap active layer 16 while the optical wave 26 is confined by the 
thick intermediate index layers 12 and 20. Optical confinement is provided 
mainly by the comparatively thick intermediate index layers 12 and 20 
because the low index cladding layers are designed to be too thin in 
cross-sectional thickness to confine the optical wave. Thus, the optical 
wave spreads deeply into these intermediate index layers, which are 
designed to have a slightly lower refractive index than the equivalent 
refractive index of the guided wave 26. 
Because the fundamental mode is guided within a larger optical cavity, 
i.e., the outer limits of layers 12 to 20, the optical power is spread 
across a large width which yields a low beam divergence in the far field 
pattern. The beam divergence angle may be approximately 10.degree. to 
20.degree. at one-half power points in the far field pattern. Also by 
spreading the optical power, lower power densities are incident per unit 
area on the mirrors. This permits laser operations at higher power levels 
before mirror damage occurs. 
Another advantage of this structure is that the overall thermal resistance 
of laser 10 is low. The temperature rise per watt input of power is lower 
than comparative devices known in the art, for example, 
10.degree.-15.degree. C./watt. The layers of highest thermal resistance 
are the carrier confinement layers 14 and 18. However, these layers being 
quite thin, do not provide high levels of thermal resistance. Good current 
confinement is provided since the energy barrier for injected carriers in 
active layer 16 are many times greater than the thermal temperature. The 
overall temperature rise of laser 10 is low because the overall lower 
thermal resistance is low, allowing for higher input powers and, 
consequently, larger output power levels. 
Thus, higher power output levels may be achieved without mirror damage and 
high thermal resistance while improving carrier confinement to the active 
layer of the laser. 
In order to demonstrate the behavior of this laser, a specific set of layer 
thicknesses and indices are shown schematically in FIG. 3(a). 
In this example, the laser is provided with an active region 16 composed of 
p-Ga.sub.1-z Al.sub.z As (n=3.6) with a thickness of 0.2 .mu.m is cladded 
on either side by p and n type Ga.sub.1-y Al.sub.y As whose refractive 
index is chosen to be 3.3 (z&lt;y). Outside of these high aluminum cladding 
layers, low aluminum content layers 20 and 12 are added as in the case of 
FIG. 1. The refractive index of these layers is 3.55. 
Plotted in FIG. 3(b) is the approximate dependence of the laser far field 
divergence, in degrees, as a function of the thickness of layers 14 and 
18, designated as t.sub.2. As shown, the beam divergence goes from 
approximately 33.degree. to 0.degree. as the thickness, t.sub.2, 
increases. Beyond a thickness of about 255A, the equivalent refractive 
index of the guided wave 26 becomes lower than the index of layers 12 and 
20 and the mode begins to radiate power into these particular layers. This 
will lead to a collimated (prism coupled) output beam. Such a beam may or 
may not be desirable depending on the device application. If not desired 
the mode may be fully confined by the addition of two more layers as will 
be shown subsequently in FIG. 4. 
The example presented in FIG. 3 provides some insight into the variations 
in device behavior based on layer thickness and refractive index. 
It should be mentioned that numerous other possibilities for the device 
design also exist. A wide range of layer thicknesses and indices may be 
employed and those presented in FIGS. 1 and 3 are only intended to 
indicate possible thickness and composition ranges. Also, this example is 
applicable for lasers having only one cladding layer, such as, disclosed 
in FIG. 8. 
The point is that, in the design of these lasers, one must calculate the 
equivalent refractive index of the guided wave 26, based on thicknesses 
and indices of the layers and compare it to that of layers 12 and 20 to 
determine whether a guided wave or radiating wave exists in the waveguide 
structure of the laser. From such a calculation, threshold, and near and 
far field patterns are also readily obtainable. 
In other words, the structure is designed in a manner to best prevent 
radiation losses, calculating to determine that the equivalent refractive 
index of the fundamental mode 36 is higher than the refractive index of 
intermediate layers 12 and 20. 
A further variation possible in the embodiments disclosed herein is that 
the small refractive index differences between the active layer 16 and 
layers 12 and 20 may be provided by a doping level change rather than 
actual composition changes in these layers, i.e., an Al content change. A 
still further possibility is that although the layers are shown with step 
changes in index, a graded index profile could also be employed. A still 
further variation is that asymmetric variations in layer thickness and/or 
refractive index may be employed relative to one or both layers 14 and 18, 
and these layers need not be identical in compositional and optical 
properties in the performance of their function. A still further variation 
is that although the invention is described in terms of GaAs/GaAlAs 
materials any other semiconducting materials such as In, Ga, As, P, Sb, 
Al, Pb, Sn, Se and Te can be used. 
These variations apply equally to the other structures disclosed herein 
having only one thin cladding layer. 
In FIG. 4, laser 30 is substantially identical to laser 10 of FIG. 1 except 
for the provision of additional confinement layers 32 and 34 between 
intermediate index layers 12 and 20 and contact facilitating layers 23 and 
25. These layers are provided at the outer boundaries of intermediate 
layers 12 and 20 and provide for improved optical confinement. Layers 32 
and 34 may be fabricated by growth techniques referred to previously. 
As noted in FIG. 5, the refractive index for layers 32 and 34 in the index 
profile is lower than that of intermediate layers 12 and 20. Although 
shown to be higher than the index for cladding layers 14 and 18, the index 
of layers 32 and 34 might also be lower. The difference in effective 
refractive index between layers 32 and 34 and adjacent layers 12 and 20 
should be sufficient to improve optical confinement of optical wave 26 and 
its propagation to the dimensional extent of layers 12 and 20. These outer 
layers 32 and 34 may also be made quite thin, such as, 1000A or less, in 
order to suppress higher order mode oscillations. 
The structures as shown thus far have been presented as being symmetric 
with respect to both thickness and composition on either side of the 
active layer 16 of the laser. This is not an absolute necessity since the 
device can be designed to be asymmetric in either or both thickness and 
material composition, as shown in FIGS. 6 and 7. 
In FIG. 6, laser 40 is substantially identical to laser 30 of FIG. 4 except 
that layer 32 has been omitted, making this region of the structure 
similar to laser 10 of FIG. 1. This design is, therefore, representative 
of a combination of lasers 10 and 30. 
As shown, the optical wave 36 will propagate asymmetrically relative to 
active layer 16. 
Alternatively, layer 34 may be omitted rather than layer 32. 
The heterostructure injection laser of previous embodiments may be provided 
with only one very thin cladding layer 14 or 18 rather than two such 
layers. This is illustrated in the injection laser 50 shown in FIG. 8. 
Full charge confinement to the active layer 16 is achieved, as well as 
desired waveguiding of the optical wave, in that, the wave is permitted to 
spread into intermediate layer 20. Layer 14 is provided to be thicker, 
that is, within a range of about 0.03 .mu.m to 2.0 .mu.m thick or possibly 
greater. The new guided wave profile 36 is obtained with center of wave 
propagation offset from the active layer, favoring a large amount of 
propagation in intermediate index layer 20. 
The fundamental mode profile 36 will be nonlossy, that is, guided, as long 
as the equivalent refractive index, n.sub.eq of mode 36 is greater than 
the refractive index, n.sub.20, of layer 20, as previously mentioned 
relative to injection lasers 10, 30 and 40. If index n.sub.20 is greater 
than index n.sub.eq, layer 20 will act as leaky waveguide permitting 
radiation to radiate away from the optical cavity in a manner similar to 
that illustrated in U.S. Pat. No. 4,063,189. 
The equivalent refractive index of mode 36 is a weighted average of the 
refractive indices of layers 14, 16, 18 and 20, depending on both the 
thickness and refractive index of each layer. 
FIG. 9 shows the refractive index profile for the layers 14, 16, 18, 20, 23 
and 25. Note that the active layer 16 in this structure as well as others 
to be disclosed may be p or n type Ga.sub.1-z Al.sub.z As or GaAs or other 
semiconducting laser material. 
As a specific example, the following Table I shows thickness and aluminum 
content that might be used for layers in injection laser 50. 
TABLE I 
______________________________________ 
Layer Thickness (.mu.m) 
AlAs Content 
______________________________________ 
14 2.0 p = 0.30 
16 0.3 z = 0.05 
18 0.005 y = 0.25 
20 3.0 x = 0.18 
______________________________________ 
In this example, p is greater than y. However, p may also be less than or 
equal to y. The primary condition is that the equivalent refractive index, 
n.sub.eq, of mode 36 be greater than the refractive index, n.sub.20, of 
layer 20 in order to achieve lossless waveguiding. 
Laser 50 may be optimized to allow only fundamental mode operation. As the 
fundamental mode nears cutoff, that is, as the equivalent refractive 
index, n.sub.eq, approaches the refractive index, n.sub.20, of layer 20, 
the higher order modes of the laser 50, will become lossy (unguided) and 
require greater laser gain in order to propagate in the established laser 
cavity. 
In FIG. 10, injection laser 60 is provided with a cladding layer 14 that is 
very thin, i.e., less than 0.05 .mu.m, while layer 18 is comparatively 
much thicker. Confinement layer 34 is also included to provide more stable 
waveguiding, that is, to improve optical confinement of the fundamental 
mode 36 as well as suppress the oscillation of higher order modes. Layer 
34 is fabricated to be thin enough (0.005-0.4 um) so that higher order 
modes will radiate into substrate layer 25, which is lossy. This radiation 
loss will exceed their gain and they will not be able to oscillate. Only a 
very small portion of the fundamental mode 36 will extend into this loosy 
layer. 
FIG. 11 illustrates the index profile for laser 60. The aluminum content 
and thickness of layer 34 are chosen to provide optimized mode filtering, 
i.e., permit confinement of the lowest order mode and allow absorption 
(radiation) of higher order modes into the lossy substrate layer 25. 
Optimization can be achieved for a given correlation between the aluminum 
content (represented by a change in the refractive index within the limit 
of arrow 52) of this layer and its thickness, t.sub.2. Once having the 
desired aluminum content to layer thickness, a corresponding respective 
decrease or increase in aluminum content would require a respective 
increase or decrease in the layer thickness. 
The laser structures thus far discussed have all been planar structures, 
i.e., all contiguous layers of the device are planar throughout the 
structures. However, one or more of these layers may be nonplanar toward 
achievement of fundamental transverse mode control. Nonplanar structuring 
may be achieved by employing a channeled substrate upon which the layers 
are sequentially, epitaxially deposited by growth methods, such as, liquid 
phase epitaxy (LPE), molecular beam epitaxy (MBE) and metalorganic 
chemical vapor deposition (MOCVD). In addition, other methods of 
nonplanaring such as chemical etching, ion implantation diffusion, growth 
through a mask, growth on a nonplanar substrate, can be used. FIGS. 12-16 
illustrate structures fabricated by LPE growth on a substrate channel 
while FIG. 17 illustrates a structure employing MOCVD growth. Basic 
structures are shown without conventional contacts. 
The channel substrate nonplanar (CSNP) laser 70 shown in FIG. 12 is guite 
similar in layer content to laser 50 in FIG. 8, except that the order and 
conductivity type of layers 14, 18 and 20 have been reversed. Intermediate 
aluminum content layer 20 is initially deposited on substrate 25, followed 
by epitaxial deposition of layers 18, 16, 14 and 23. Since an etched 
groove or channel 72 is present in the surface of substrate 25, both the 
active layer 16 and the heterolayers 18 and 20 are deposited via LPE 
forming nonplanar regions over the channel 72. The manner of accomplishing 
this layer nonlinearity is now well known in the art. 
Current confinement may be provided in any conventional manner. In the 
structures shown, ion or proton implanted regions 74 are provided parallel 
to the channel 72 for the length of the laser to provide a current channel 
76. 
The index profile of FIG. 9 is applicable to injection laser 70 if the 
layers designation is reversed. 
The enlarged regions 77 and 78 in layers 16 and 18 provide fundamental 
transverse mode control laterally along the plane of the p-n junction 71 
whereas the employment of thin cladding layer 18 is of high aluminum 
content contiguous with thicker intermediate layer 20 provides fundamental 
transverse mode control perpendicular to the plane of the p-n junction 71. 
The fundamental mode in the plane of the p-n junction 71 is guided at the 
thickest region 77 of the active layer 16 while higher order modes radiate 
and have high losses at the edges 73 of the channel 72 whereby lowest 
order mode operation is established and maintained. 
A typical example for aluminum content and layer thickness for laser 70 is 
shown in Table II. The channel width between edges 73 is about 5 .mu.m 
wide. 
TABLE II 
______________________________________ 
Thickness (A) 
Layer above channel 
adjacent channel 
AlAs Content 
______________________________________ 
14 p = 0.50 
16 a = 800A c = 600A z = 0.05 
18 b = 3000A d = 800A y = 0.30 
20 x = 0.12 
______________________________________ 
Laser 80 in FIG. 13 is identical to laser 70 of FIG. 12 except the 
epitaxial growth times are changed to permit layer 18 to grow until it is 
planar over channel 72. Thus, the growth of the active layer 16 will be 
planar. A typical example for aluminum content and layer thickness is 
shown in Table III. The channel width between edges 73 is, again, about 5 
.mu.m. 
TABLE III 
______________________________________ 
Thickness 
Layer above channel 
adjacent channel 
AlAs Content 
______________________________________ 
14 p = 0.050 
16 a = 1000A c = 1000A z = 0.05 
18 b = 0.7 .mu.m 
d = 100A y = 0.30 
20 x = 0.12 
______________________________________ 
In FIG. 14, laser 90 is identical to laser 70 of FIG. 12 except the 
epitaxial growth times are changed to permit all layers to be planar and 
uniform over channel 72. Thus, layer 20 is grown until this layer is 
planar before the deposition of the remaining layers. Both the active 
layer 16 and the thin cladding layer 18 are of uniform thickness, whereas 
the intermediate aluminum content layer 20 is of nonuniform thickness due 
to channel 72. 
A typical example of aluminum content and layer thickness is shown in Table 
IV. The channel width between edges 73 is about 5 .mu.m. 
TABLE IV 
______________________________________ 
Thickness 
Layer above channel 
adjacent channel 
AlAs Content 
______________________________________ 
14 p = 0.30 
16 a = 2500A z = 0.05 
18 b = 200A y = 0.30 
20 e = 1.5 .mu.m 
f = 0.2 .mu.m 
x = 0.12 
______________________________________ 
Laser 100 in FIG. 15 is identical in layer aluminum content and layer 
deposition to laser 10 in FIG. 1. However, layers 18, 16 and 14 in regions 
75, 77 and 78 are nonplanar due to growth over channel 72. Layers 18 and 
20 have been designated to possibly contain a different aluminum content 
than layers 12 and 14. However, p may equal y and m may equal x. The 
aluminum content values exemplified in laser 10 may be employed in laser 
100. Layer compositions and thicknesses are chosen to allow fundamental 
mode to be guided while higher order modes radiate due to their differing 
spatial overlap with the various layers 14, 16, 18 and 20. 
Laser 110 in FIG. 16 is identical in layer aluminum content and layer 
deposition to laser 60 in FIG. 10. However, layers 12, 14 and 16 are 
nonplanar due to growth over channel 72. Confinement layer 34 is thin 
(less than 0.4 .mu.m) in regions above edges 73 so that higher order modes 
will radiate into the substrate 25. 
These channel substrate lasers may also be grown by MOCVD and MBE. The 
configuration for laser 120 shown in FIG. 17 is laser 70 of FIG. 12 except 
that the growth process is MOCVD. In this case, the growth characteristics 
are somewhat different from those observable by LPE The layers are not 
curved or rounded about the channel 72 but take on the geometric shape of 
the channel. In any case, nonplanar variations 121 and 122 in the layers 
16 and 18, respectively, can be accomplished by MOCVD and MBE as well as 
providing spatially selectively absorbing layers to provide a laser 
structure that provides fundamental transverse mode control in directions 
both lateral and perpendicular to the p-n junction. 
Other geometric configurations can be employed to act as lateral transverse 
mode controlling mechanisms, such as multichanneled substrates, substrate 
mesas, channeled mesa substrates, buried heterostructures, or nonuniform 
thickness layers grown through masks to obtain nonplanar, nonuniform 
thickness layers to achieve a high output power, transverse mode 
controlled laser. 
In other words, the planar structures of FIGS. 1, 4, 6, 8 and 10 may be 
used with any known lateral mode controlling mechanism. 
FIGS. 18-22 show various heterostructure injection lasers employing one or 
more outer, thin optical mode control layers 137 and/or 138. These layers 
essentially perform the function of layers 32 and/or 34. 
Laser 130 in FIG. 18 is a large optical cavity (LOC) injection laser, the 
general concept of which has been disclosed by G. H. B. Thompson in the 
Journal of Applied Physics, Volume 47 at page 150, et seq. (1976) and by 
H. C. Casey Jr. et al in the Journal of Applied Physics, Volume 45, No. 1 
at page 322 et seq. In general, LOC laser 130 comprises an optical 
waveguide or cavity comprising active layer 132 and optical waveguide 
layers 133 and 134. These latter layers are bounded by cladding layers 137 
and 138. Layers 133 and 134 have low aluminum content as compared to 
layers 137 and 138, i.e., are significantly of higher refractive index 
compared to layers 137 and 138 in order to sustain and be transparent to 
optical wave propagation. Normally layers 137 and 138 are much thicker in 
thickness than shown in FIG. 18. See Thompson and Casey, supra. They are 
bounded by contact and support layers 139 and 140 and metalizations 141 
and 142. 
Thus, laser 130 differs from the general LOC injection laser by having, 
thin outer layers 137 and 138 of 1000A or less are provided to suppress 
higher order mode oscillations, such as the TE.sub.01 and TE.sub.02 modes, 
while enhancing the confinement and providing low optical loss for the 
lowest order as fundamental transverse mode, TE.sub.00. Higher order 
transverse modes will penetrate the thin low index layer and be absorbed 
(radiate) into the high refractive index layers 139 and 140 as indicated 
in FIG. 18. A not insignificant portion of the propagating high order 
modes will extend into those lossy layers 139 and 140. Their propagation 
will extinguish since their gain will not be sufficient to maintain 
continued propagation. On the other hand, the fundamental mode, TE.sub.00, 
does not extend significantly into lossy layers 139 and 140 and maintains 
propagation within the LOC as confined by the low refractive index layers 
137 and 138. 
The prerequisite here is that layers 139 and 140 must have a refractive 
index greater than the equivalent refractive index of the undesirable 
higher order transverse modes 144 of the optical waveguide. 
FIG. 19 illustrates the refractive index profile for laser 130. 
There are many alternatives relative to LOC laser structures and the 
employment of thin confinement layers 137 and/or 138. In FIG. 20, only one 
thin such confinement layer 138 is utilized in LOC laser 150. Here, the 
fundamental mode, TE.sub.00, 144 will propagate, without restriction, 
favoring such propagation a little off center from the center of active 
layer 132. Higher order modes will be extinguished by radiation into the 
lossy layers 139 and 140. A single confinement layer 137 or 138 can also 
substantially perform the desired function of extinguishing the 
propagation of higher order modes. 
Lasers 130 and 150 may be termed as double LOCs, since the optical 
waveguide bounds equally on both sides of the active layer 132. Laser 160 
in FIG. 21 and laser 170 in FIG. 22, however, are single LOCs, since the 
optical waveguide is only provided on one side of the active layer 132, 
i.e., waveguide layer 133 is not present and waveguide layer 134 will 
support optical wave propagation. 
In FIG. 21, laser 160 has one confinement layer 138. Layer 137 may be made 
of thick crossection in this configuration to provide a one sided LOC. 
FIG. 21, the confinement layer 138 is provided on the single LOC side of 
the laser 160 whereas in FIG. 22, confinement layer 137 is provided on the 
opposite side of laser 170 relative to the single LOC comprising layer 
134. 
The employment of confinement layers 137 and 138 illustrated in FIGS. 18-22 
may also be applied to channel substrate planar and nonplanar laser 
structures previously illustrated in FIGS. 12-17. 
While the invention has been described in conjunction with specific 
embodiments, it is evident that many alternatives, modifications and 
variations will be apparent to those skilled in the art in light of the 
foregoing description. Accordingly, it is intended to embrace all such 
alternatives, modifications, and variations as fall within within the 
spirit and scope of the appended claims. For example, the concept of the 
present invention in employing thin cladding layers has wide applicability 
to a variety of diode laser devices, such as, stripe geometry lasers, 
single transverse mode lasers, and distributive feedback lasers. A low 
beam divergence source is provided that has a nearly symmetrical high 
power output beam that is easily coupled into fiber optic waveguides. 
Also, other semiconducting crystalline materials, such as those containing 
In, Ga, Al, As, P, Sb, Pb, Sn and Te or other light emitting materials may 
be employed rather than GaAs:GaAlAs. 
Further, the thickness and compositions shown in the figures are intended 
to be only indicative of actual values. In practice, these thicknesses 
could be outside the suggested ranges in order to optimize a particular 
type of behavior of the device, for example, even lower beam divergences 
can be obtained by fabricating layers 14, 16 and 18 to be thinner than 
illustrated. However, this will cause the threshold of the laser to 
increase due to a lack of overlap of the optical wave with the active 
region. Thus, for each laser design, it is necessary to calculate the 
necessary compositions and thicknesses to optimize a certain performance 
parameter.