Semiconductor laser device and optical disc apparatus provided with the semiclonductor laser device

A semiconductor laser device includes: a substrate serving as a heat sink; a thermal buffer plate disposed on the surface of the substrate; a first semiconductor laser chip having first and second main surfaces and including a first light emitting point in the vicinity of the first main surface, the first semiconductor laser chip being disposed on the surface of the thermal buffer plate at the second main surface; spaced apart thermal conductors disposed on the first main surface of the first semiconductor laser chip spaced from the first light emitting point with the first light emitting point between them; a second semiconductor laser chip having third and fourth main surfaces and including a second light emitting point in the vicinity of the third main surface, the second semiconductor laser chip being disposed on the thermal conductors at the third main surface so that the light radiation direction of the second semiconductor laser chip is parallel to the light radiation direction of the first semiconductor laser chip, wherein the second light emitting point is opposed to and close to the first emitting point. Even when the environmental temperature changes, the expansion and contraction of the interval between the light emitting points is smaller than in prior art structures.

FIELD OF THE INVENTION 
The present invention relates to a semiconductor laser device that has less 
variation in the interval between light emitting points due to thermal 
deformation in a multi-point light emitting laser diode having light 
emitting points arranged in close proximity to each other, and an optical 
disc apparatus provided with the semiconductor laser device. 
BACKGROUND OF THE INVENTION 
As a method for realizing high performance of an optical disc apparatus, 
signal processing of recording pits formed on a track on a disc is 
simultaneously performed, in parallel, for a plurality of tracks, and the 
processing speed is increased. In order to realize the same, development 
of an LD chip including a plurality of light emitting points which are 
separated from each other by separating grooves and independently driven 
in a single LD chip is advancing. 
In addition, in order to realize a system in which immediately after a 
signal is recorded, the signal is reproduced and error checking is 
performed, it is necessary to constitute a two-point array in which a 
recording laser diode and a reproduction laser diode are arranged at two 
points in a line and they are controlled independently. 
Conventionally, an LD chip provided with a linear array of multiple light 
emitting points with an interval of 50-100 .mu.m on a same semiconductor 
substrate has been reported. In this system, however, Joule heat generated 
at an LD is conducted to an adjacent LD via the semiconductor substrate, 
whereby the light output is reduced, which phenomenon is called thermal 
crosstalk. 
A solution to this problem is described, for example, in an article of 
"Hybrid laser array with closely spaced dual beams" in 35-th Applied 
Physics of Japan and Related Societies Meeting (1988 spring) Lecture 
Prescript pp. 898, 30p-ZQ-3. 
This laser array with closely spaced dual beams has a structure in which 
two LD chips each having a single light emitting point are disposed on 
individual substrates functioning as a cooler and arranged with the light 
emitting points close to each other, in order to prevent thermal 
crosstalk. 
FIG. 13 is a perspective view of this prior art laser array with closely 
spaced dual beams. 
In FIG. 13, reference numeral 1 designates a stem. A high output laser 
diode (hereinafter referred to as high output LD) block for recording 2 is 
disposed on the stem 1. A high output LD submount 3 is mounted on the high 
output LD block 2. A high output LD chip 4 is mounted on the high output 
LD submount 3. A high output LD feeding wire 5 is connected to an 
electrode on the surface of the high output LD chip 4. Reference numeral 6 
designates a light emitting point of the high output LD. A low noise LD 
block for reproduction 7 is disposed on the stem 1. A low noise LD 
submount 8 is mounted on the low noise LD block for reproduction 7. A low 
noise LD feeding wire 10 is connected to an electrode on the surface of 
the low noise LD chip 9. Reference numeral 11 designates a light emitting 
point of the low noise LD. Reference numeral 12 designates a lead. 
In the laser array with closely spaced dual beams constructed as described 
above, the high output LD chip 4 and the low noise LD chip 9 are 
separately fixed to the high output LD block 2 and the low noise LD block 
7 via the high output LD submount 3 and the low noise LD submount 8, 
respectively, and the LD chips 4 and 9 are fixed to the stem 1 by the high 
output LD block 2 and the low noise LD block 7, respectively, so that the 
light emitting point 6 of the single high output LD and the light emitting 
point 11 of the single low noise LD are opposed to each other with an 
interval of about 20 .mu.m. Accordingly, the light emitting point 6 of the 
high output LD and the light emitting point 11 of the low noise LD can be 
spatially separated, thereby producing an advantage that thermal 
interference is not likely to occur. 
In the laser array with closely spaced dual beams constructed as described 
above, when the temperature variation of the environment in which the LD 
array is employed is small, the above-described construction is thought to 
be sufficient. However, when the temperature variation of the environment 
is larger, the stem 1, the high output LD block 2, and the low noise LD 
block 7 change thermally and the interval between the light emitting point 
6 of the high output LD and the light emitting point 11 of the low noise 
LD varies. For example, when the LD array is applied to an optical disc 
apparatus, the interval between the two light emitting points expands and 
contracts and, the deviation of the LD array from the optical system in 
the optical disc apparatus cannot be adjusted sufficiently only by the 
positional adjustment using the parallel movement of a semiconductor laser 
device to which the LD array is mounted. This presents preferable 
recording and reproduction. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a semiconductor laser 
device having less variation in the interval between the light emitting 
points due to the variation of the environmental temperature. 
It is another object of the present invention to provide an optical disc 
apparatus that can perform preferable recording and reproduction even when 
it is affected significantly by variation of the environmental temperature 
by using the above-described semiconductor device. 
Other objects and advantages of the present invention will become apparent 
from the detailed description given hereinafter; it should be understood, 
however, that the detailed description and specific embodiment are given 
by way of illustration only, since various changes and modifications 
within the scope of the invention will become apparent to those skilled in 
the art from this detailed description. 
According to a first aspect of the present invention, a semiconductor laser 
device includes: a substrate serving as a cooler; a thermal buffer plate 
disposed on the surface of the substrate; a first semiconductor laser chip 
having first and second main surfaces which includes a first light 
emitting point in the vicinity of the first main surface and is disposed 
on the surface of the thermal buffer plate via the second main surface; 
thermal conductors disposed on the first main surface of the first 
semiconductor laser chip with an interval from the first light emitting 
point so as to put the first light emitting point between them; a second 
semiconductor laser chip having third and fourth main surfaces which 
includes a second light emitting point in the vicinity of the third main 
surface and is disposed on the surface of the thermal conductor via the 
third main surface so that the light radiation direction of the laser chip 
is in parallel with the light radiation direction of the first 
semiconductor laser chip, wherein the second light emitting point is 
opposed to and close to the first light emitting point. Therefore, even 
when the environmental temperature changes, the expansion and contraction 
of the interval between the light emitting points can be reduced. 
According to a second aspect of the present invention, in the 
above-described semiconductor laser device, first main electrodes are 
disposed on the first main surface of the first semiconductor laser chip 
and on the third main surface of the second semiconductor laser chip, 
respectively, via the thermal conductors comprising electrical conductors. 
Therefore, the first main electrodes of the first semiconductor laser chip 
and the second semiconductor laser chip are electrically connected with 
each other via the thermal conductors. 
According to a third aspect of the present invention, in the 
above-described semiconductor laser device, a step is provided on one or 
both of the first main surface of the first semiconductor laser chip and 
the third main surface of the second semiconductor laser chip in the 
vicinity of the light emitting point, and the interval between the first 
main surface of the first semiconductor laser chip and the third main 
surface of the second semiconductor laser chip via the step is shorter 
than the height of the thermal conductor. Therefore, with keeping the 
height of the thermal conductor to a large value, the interval between the 
light emitting points can be reduced. 
According to a fourth aspect of the present invention, in the 
above-described semiconductor laser device, a step is provided on one or 
both of the first main surface of the first semiconductor laser chip and 
the third main surface of the second semiconductor laser chip in the 
vicinity of the light emitting point, and the interval between the first 
main surface of the first semiconductor laser chip and the third main 
surface of the second semiconductor laser chip via the step is longer than 
the height of the thermal conductor. Therefore, with keeping the interval 
between the light emitting points at a required value, the height of the 
thermal conductor can be reduced. 
According to a fifth aspect of the present invention, in the 
above-described semiconductor laser device, steps are provided at a 
portion of the first main surface of the first semiconductor laser chip 
and at a portion of the third main surface of the second semiconductor 
laser chip respectively so that the both steps are mutually engaged with 
each other, and the first light emitting point and the second light 
emitting point are arranged so that the steps are served as positioning 
means for opposing the first and second light emitting points with each 
other. Therefore, the first light emitting point and the second light 
emitting point can be opposed to each other with high precision. 
According to a sixth aspect of the present invention, in the 
above-described semiconductor laser device, the steps of the first 
semiconductor laser chip and the second semiconductor laser chip 
respectively have a concave part or a convex part which are mutually 
engaged with each other, the light emitting points of the respective 
semiconductor laser chips are respectively disposed at the concave part 
and the convex part, insulating films are disposed at side surfaces of the 
convex part of the semiconductor laser chip having the convex part and at 
a portion other than the convex part of the first main surface or the 
third main surface, first main electrodes are disposed on the first main 
surface or the third main surface of the convex part and the insulating 
films, and thermal conductors are disposed on the first main electrodes on 
the insulating films. Therefore, the width of the concave part or convex 
part can be made wide. 
According to a seventh aspect of the present invention, in the 
above-described semiconductor laser device, a plurality of first and 
second light emitting points are respectively disposed along the first 
main surface and the third main surface by using electrical separating 
means, and first main electrodes are individually provided on the 
respective first main surface or the respective third main surface 
corresponding to the respective light emitting points. Therefore, a 
plurality of light emitting points can be arranged in a row. 
According to an eighth aspect of the present invention, an optical disc 
apparatus is provided with the above-described semiconductor laser device. 
Therefore, an optical disc apparatus which is not affected by the 
environmental temperature is obtained.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A description is given of a semiconductor laser device according to the 
present invention and an optical disc apparatus provided with the 
semiconductor laser device. 
FIG. 1 is a perspective view illustrating an optical system for a 
generalized optical disc apparatus. In FIG. 1, reference numeral 21 
designates an optical disc. Numeral 22 designates a transparent disc 
substrate. Numeral 23 designates a recording film. Numeral 24 designates a 
recorded pit. Numeral 25 designates a semiconductor laser. Numeral 26 
designates a collimating lens. Numeral 27 designates a beam splitter. 
Numeral 28 designates a mirror. Numeral 29 designates an objective lens. 
Numeral 30 designates an optical detector. 
In FIG. 1, a recording film 23 of an opto-magnetic material as a recording 
material is formed on the transparent disc substrate 22. While recording 
information, employing the semiconductor laser 25 which is a high output 
LD, the laser beam output from the semiconductor laser 25 is made parallel 
by the collimating lens 26, passes through the beam splitter 27 and the 
mirror 28, and is focused by the objective lens 29, thereby forming the 
recording pit 24 on the recording film 23. While reproducing the recorded 
information, employing a low noise LD, the laser beam emitted from the low 
noise LD passes through the collimating lens 26, the beam splitter 27, and 
the mirror 28, and further the objective lens 29, and scans the track on 
the recording film 23 where the recording pit 24 is formed, and the 
brightness and darkness of the reflected laser beam is sent as a signal 
through the objective lens 29, the mirror 28, and the beam splitter 27 to 
the optical detector 30, to be read out. 
FIG. 2 is an exploded perspective view illustrating a general construction 
of a semiconductor laser device. In FIG. 2, reference numeral 41 
designates a stem. Numeral 42 designates a laser array. Numeral 43 
designates a monitor photodiode array. Numeral 44 designates a lead. 
Numeral 45 designates a cap. Numeral 46 designates a glass window. Numeral 
47 designates an LD. 
To the laser array 42 adhered to the stem 41, electric power is supplied 
from the lead 44, and the laser beam is emitted from the LD 47 as shown by 
the solid arrow. The laser beam is also emitted from the LD 47 in the 
direction reverse to the solid arrow and, this laser beam is received by 
the monitor photodiode 43 and the output laser beam is emitted from the LD 
47 while monitoring the light emission amount. The output laser beam is 
emitted through the glass window 46 of the cap 45 which protects the laser 
array 42 mounted to the stem 41. The inside of the cap 45 is normally 
filled with nitrogen. 
Embodiment 1. 
FIG. 3 is a plan view illustrating a semiconductor laser array according to 
a first embodiment of the present invention. As an example of the 
semiconductor laser array, a hybrid laser array with closely spaced dual 
beams is described. In addition, this hybrid laser array with closely 
spaced dual beams corresponds to a portion of the laser array 42 of the 
above-described semiconductor laser shown in FIG. 2. 
In FIG. 3, reference numeral 50 designates a silver block functioning as a 
cooler. Numeral 51 designates a plated Au film on the surface of the 
silver block 50. Numeral 52 designates a submount comprising SiC as a 
thermal buffer plate disposed on the silver block 50. Numeral 53 
designates a plated Sn film plated on the upper and lower surface of the 
submount 52. Numeral 54 designates a high output LD for recording as a 
first semiconductor laser chip. Numeral 55 designates a PN junction 
interface of the high output LD 54. Numeral 56 designates a P side 
electrode of the high output LD. Numeral 57 designates an N side electrode 
of the high output LD. Numeral 58 designates a light emitting point of the 
high output LD as a first light emitting point. Numeral 59 designates a 
low noise LD for reproduction as a second semiconductor laser chip. 
Numeral 60 designates a PN junction interface of the low noise LD. Numeral 
61 designates an N side electrode of the low noise LD. Numeral 62 
designates a P side electrode of the low noise LD. Numeral 63 designates a 
light emitting point of the low noise LD as a second light emitting point. 
Numeral 64 designates a plated Au film. Numeral 65 designates a plated Sn 
film. A heat conductive connecting leg 106 as a thermal conductor is 
constituted by the plated Au film 64 and the plated Sn film 65. Numeral 66 
designates a minus side lead wire common for the high output LD and the 
low noise LD. Numeral 67 designates a plus side lead wire of the high 
output LD. Numeral 68 designates a plus side lead wire of the low noise 
LD. The electrodes of the LD comprise Au based alloy and gold is plated on 
the surface thereof. 
To the silver block 50 having the plated Au film 51, the submount 52 having 
the plated Sn film 53 is adhered via AuSn alloy comprising the plated Au 
film 51 and the plated Sn film 53 which are pressure-welded. This submount 
52 is provided for relaxing the thermal stress that is generated by the 
difference in the thermal expansion coefficients of the materials of the 
silver submount 50 and the high output LD. The P side electrode 56 of the 
high output LD 54 is adhered to the plated Sn film 53 of the submount 52. 
The high output LD 54 and the low noise LD 59 are chips several hundreds of 
microns square. One PN junction interface 55 is close to the N side 
electrode 57 of the high output LD 54 and the light emitting point 58 of 
the high output LD is in this PN junction interface 55. The plated Sn film 
65 is formed on the N side electrode 57 in a predetermined configuration 
including two parts with the light emitting point 58 of the high output LD 
54 between them. The thickness of the plated Sn film 65 is normally on the 
order of several submicrons. 
Also in the low noise LD 59, the PN junction interface 60 is close to the N 
side electrode 61 and the light emitting point 63 of the low noise LD is 
provided in this PN junction interface 60. The low noise LD 59 is disposed 
such that the N side electrode 61 is opposite the N side electrode 57 of 
the high output LD 54 and the light emitting point 63 of the low noise LD 
59 is opposite the light emitting point 58 of the high output LD 54 with 
the N side electrode 61 and the N side electrode 57 between the light 
emitting points. Then, the high output LD 54 and the low noise LD 59 are 
disposed such that the plated Sn film 65 provided on the N side electrode 
57 of the high output LD 54 and the plated Au film 64 3-5 .mu.m thick 
formed on the N side electrode 61 of the low noise LD 59 before chip 
separation are in contact with each other. This plated Au film 64 and the 
plated Sn film 65 are alloyed when they are adhered with pressure during 
the fabrication process, thereby forming an AuSn alloy film and jointed to 
each other. The plated Au film 64 and the plated Sn film 65 junctioned by 
this AuSn alloy film become a heat conductive connecting leg 106 as a 
thermal conductor. 
In addition, since the heat conductive connecting leg 106 comprises an 
electrical conductor, the N side electrode 57 of the high output LD 54 and 
the N side electrode 61 of the low noise LD 59 to create the same voltage, 
and these N side electrodes can be connected to the minus side lead wire 
66 via a common terminal, resulting in shorter lead wires. 
At the plus side, a plus side lead wire 67 of the high output LD is 
connected to the P side electrode 56 of the high output LD 54 and a plus 
side lead wire 68 of the low noise LD is connected to the P side electrode 
62 of the low noise LD, whereby the high output LD 54 and the low noise LD 
59 can be driven independently from each other. 
A description is given of the operation. 
When predetermined voltages are applied to the high output LD 54 and the 
low noise LD 59, respectively, and the LDs are driven, the light emitting 
points serve as heat sources which generate heat. Then, the heat generated 
at the light emitting point 58 of the high output LD 54 flows into the 
silver block 50 serving as a heatsink block via the submount 52 of SiC 
having a relatively good thermal conductivity, raising the temperature of 
the high output LD 54, thereby dissipating the heat to the outside and 
increasing the temperature of the silver block 50. 
On the other hand, the heat generated at the light emitting point 63 of the 
low noise LD 59 flows into the high output LD 54 via the heat conductive 
connecting leg 106 connected by the AuSn alloy film, raising the 
temperature of the low noise LD 59, and heat, flows into the silver block 
50 via the high output LD 54 and the submount 52. 
When the LDs are driven, the light emitting point 58 of the high output LD 
54 and the light emitting point 63 of the low noise LD 59 are opposed to 
each other with a space between them, whereby there arises less amount of 
thermal interference and no thermal crosstalk. 
However, since the expansion and contraction of the space between the light 
emitting point 58 of the high output LD 54 and the light emitting point 63 
of the low noise LD 59 while the LDs are driven corresponds to the thermal 
deformation of the heat conductive connecting leg 106, the plated Au film 
64 is typically 3-5 .mu.m thick and is at most several tens of .mu.m, 
whereby the change in the spacing between the light emitting points is 
quite small even if it is summed with the plated Sn film 65. 
On the other hand, as to thermal deformation due to a change in the 
environmental temperature, two kinds of thermal deformation should be 
considered. 
The first one is a change in the interval between the light emitting points 
(hereinafter referred to as light emitting point interval) due to a change 
in the environmental temperature. Since it is thought that the change 
itself in the environmental temperature in the vicinity of the heat 
conductive connecting leg 106 is approximately equal to or less than the 
temperature change due to the thermal output power of the light emitting 
point, the variation in the light emitting point due to a change in the 
environmental temperature is thought to be approximately equal to or less 
than the variation in the light emitting point interval due to the thermal 
output power of the light emitting point, which is not so large. 
The second thermal is due to a change in the environmental temperature of 
the silver block 50 and the submount 52. This thermal deformation may also 
include the stem 41 of FIG. 2 and this thermal deformation becomes 
considerably large because the sizes of the silver block 50 and the 
submount 52 become fairly large relative to the height of the conductive 
connecting leg 106. However, since this deformation produces parallel 
movement while maintaining the same light emitting point interval, the 
deviation of the parallel movement can be corrected easily by controlling 
the setting position of the semiconductor laser while using a 
semiconductor laser, for example, by the tracking mechanism in an optical 
disk apparatus. 
While in the first embodiment, the submount 52 comprises an insulator, the 
submount 52 may comprise a conductor and an insulator may be inserted 
between the submount 52 and the silver block 50 or the silver block 50 may 
comprise an insulator with good heat conductivity. 
In addition, in the first embodiment the high output LD 54 is adhered to 
the submount 52 and the low noise LD 59 is adhered thereto via heat 
conductive connecting leg 106 comprising the plated Au film 64 and the 
plated Sn film 65, the low noise LD 59 may be adhered to the submount 52 
and the high output LD 54 may be adhered to the low noise LD 59 via this 
heat conductive connecting leg 106. 
A description is given of a method of fabricating a semiconductor laser 
device according to the first embodiment. 
FIGS. 4 to 6 are cross-sectional views of the laser array 42 in respective 
process steps in the method of fabricating the semiconductor laser device 
according to the first embodiment. FIG. 7 is a perspective view 
illustrating a semiconductor laser in a process of mounting the laser 
array 42 according to the first embodiment of the invention. 
First of all, as shown in FIG. 4, prepared constituents before the mounting 
process are the silver block 50 on which the plated Au film 51 is formed, 
the submount 52 on which the plated Sn film 53 is formed, the high output 
LD 54 in which the P side electrode 56 and the N side electrode 57 are 
formed on the surfaces and the plated Sn film 65 is formed on the surface 
of the N side electrode 57 so as to put the light emitting point 58 
between them, and the low noise LD 59 in which the P side electrode 62 and 
the N side electrode 61 are formed on the surfaces and the plated Au film 
64 is formed on the surface of the N side electrode 61 so as to put the 
light emitting point 63 between them. The submount 52, the high output LD 
54, and the low noise LD 59 are successively laminated. The high output LD 
54 and the low output LD 59 are laminated with the light emitting point 58 
and the light emitting point 63 opposed to each other via respective N 
side electrodes and with the plated Au film 64 placed on the plated Sn 
film 65. 
Next, a weight is applied to the constituents of the laminated laser array 
in the direction of the arrow shown in FIG. 5 while heating the same at a 
temperature from 300.degree. to 400.degree. C., and the AuSn alloying is 
performed between the silver block 50 and the submount 52, between the 
submount 52 and the P side electrode 56 of the high output LD 54, and 
between the plated Sn film 65 and the plated Au film 64 to adhere them 
with each other. 
Next, as shown in FIG. 6, the plus side lead wire 68 is wire-bonded to the 
P side electrode 62 of the low noise LD 59, the plus side lead wire 67 is 
wire-bonded to the P side electrode 56 of the high output LD 54, and the 
minus side lead wire 66 is wire-bonded between the N side electrode 57 of 
the high output LD 54 and the plated Au film 51 of the silver block 50, 
thereby completing a laser array 42. 
Next, as shown in FIG. 7, the laser array 42 is mounted on the stem 41 and 
is connected to the lead 44. Further, though not shown in the figure, a 
cap is attached filled with nitrogen, and sealed, thereby completing a 
semiconductor laser. 
Embodiment 2. 
FIG. 8 is a plan view illustrating a laser array according to a second 
embodiment of the present invention. In FIG. 8, the high output LD 54 and 
the low noise LD 59 have convex steps 101 and 102 at the sides of the N 
side electrode 57 and the N side electrode 61, respectively. At the step 
101 and the step 102, the PN junction interface 55 and the PN junction 
interface 60, and the light emitting point 58 and the light emitting point 
63 are respectively provided, the light emitting point 58 and the light 
emitting point 63 are arranged close to each other, and the interval 
between the surfaces of the N side electrodes at this step smaller than 
the height of the heat conductive connecting leg 106 comprising the plated 
Au film 64 and the plated Sn film 65. The SiO.sub.2 films 69 are formed on 
the N side electrode 57 of the high output LD 54 and the N side electrode 
61 of the low noise LD 59 except for the vicinity of the light emitting 
point 58 and the light emitting point 63 in order to prevent 
short-circuiting between the P side electrode 56 and the N side electrode 
57 and between the P side electrode 62 and the N side electrode 61. 
The submount 52 is disposed on the silver block 50 as in the first 
embodiment. In addition, the P side electrode 56 of the high output LD is 
connected to the plus side lead wire 67 of the high output LD which is not 
shown in the figure. 
While maintaining the light emitting point interval that is required for 
the laser array 42, the height of the heat conductive connecting leg 106 
can be made high, for example, 10 .mu.m-several tens of .mu.m, or more, 
and high precision control can be easily achieved in the formation of the 
plated Au film 64 and the plated Sn film 65, and the light emitting point 
interval can be secured with high precision. Consequently, the yield of 
the product can be increased. 
In addition, relative to a case where there is no step, since the portions 
where the N side electrode 57 of the high output LD 54 and the N side 
electrode 61 of the low noise LD 59 are opposed to each other is only in 
the vicinity of the light emitting points, the precision that is required 
for the degree of parallelization between the surface of the N side 
electrode 57 of the high output LD 54 and the surface of the N side 
electrode 61 of the low noise LD 59 is relaxed, whereby the distance 
between a N side electrodes can be narrowed and the laser array having a 
small light emitting point interval can be made. The laser array having a 
small light emitting interval can avoid the spherical surface astigmatism 
of a lens used in a semiconductor laser. 
In this embodiment, although both of the high output LD 54 and the low 
noise LD 59 include raised, i.e., portions, only one of the LDs may be 
provided with a convex part with the same effects as described above. 
Embodiment 3. 
FIG. 9 is a plan view illustrating a laser array according to a third 
embodiment of the present invention. In FIG. 9, the low noise LD 59 has a 
concave step 103 at the side of the N side electrode 61. In the vicinity 
of the N side electrode 61 in the step 103, the light emitting point 63 is 
provided. 
The submount 52 is disposed on the silver block 50 as in the first 
embodiment. Further, the P side electrode 56 of the high output LD is 
connected with the plus side lead wire 67 of the high output LD which is 
not shown in the figure. 
By such a construction, securing the interval between the light emitting 
point 58 and the light emitting point 63 at a required dimension, the heat 
conductive connecting leg 106 can be formed with the height of the plated 
Au film 64 being extremely thin. 
Since one of the factors affecting the light emitting point interval is 
thermal deformation of the heat conductive connecting leg 106 in the 
height direction, by reducing the height of the plated Au film 64 in order 
to reduce the height of the heat conductive connecting leg 106, the 
thermal deformation of the heat conductive connecting leg 106 can be 
reduced and the thermal deformation of the light emitting point interval 
can be reduced. 
In addition, in the fabricating process of the laser array 42, if the 
plated Au film 64 is made thin during plating, variations in the height 
due to plastic deformation of the plated Au film 64, which is relatively 
weak, when the laser array device is heat-welded can be reduced. 
In other words, the surface of the chip itself and the plated Sn film 65 
are finished at a high processing precision, and they are unlikely to be 
deformed because they comprise a material of sufficient hardness. 
Therefore, since the variations in the height of the plated Au film 64 due 
to the applied pressure when the film is heat-welded determine the 
dimensional precision of the light emitting point interval, by making the 
plated Au film 64 as thin as the surface waviness or surface roughness, 
for example, 1 .mu.m or less, variations in the height due to plastic 
deformation can be reduced, whereby unstable dimensional precision of the 
light emitting point interval in the heat-welding process can be avoided. 
While in the third embodiment a concave part is provided at one of the LDs, 
concave parts may be provided at the both of the LDs with the same effects 
as described above. 
Embodiment 4. 
FIG. 10 is a plan view illustrating a laser array according to a fourth 
embodiment of the present invention. In FIG. 10, at the side of the N side 
electrode 57 of the high output LD 54, a convex step 104 is provided, and 
at the side of the N side electrode 61 of the low noise LD 59, a concave 
step 105 is provided. The PN junction interface 55 is provided at the step 
104 and the PN junction interface 60, the light emitting point 58 and the 
light emitting point 63 are all provided in the vicinity of the step 106. 
The portion of the high output LD 54 at the side of the N side electrode 
57 of the high output LD 54 is formed via the SiO.sub.2 film 69 except for 
the vicinity of the light emitting point 58 in order to avoid 
short-circuiting with the P side electrode 56. Accordingly, the SiO.sub.2 
film 69 is also formed at the side wall of the step 104. 
The N side electrode 57 in the vicinity of the light emitting point 58 and 
the N side electrode 57 provided on the SiO.sub.2 film 69 in the vicinity 
of the heat conductive connecting leg 106 are electrically connected with 
each other, though not shown in FIG. 10. 
The step 104 and the step 105 are engaged with each other, and when the 
high output LD 54 and the low noise LD 59 are moved relatively in the 
transverse direction, the sidewall of the convex step 104 and the side 
wall of the concave step 105 contact each other. 
The submount 52 is disposed on the silver block 50 as in the first 
embodiment. In addition, the P side electrode 56 of the high output LD is 
connected with a plus side lead wire 67 of the high output LD that is not 
shown in the figure. 
By adopting such a structure, if the distance between the light emitting 
point 58 of the high output LD 54 and the sidewall of the convex step 104 
coincides with the distance between the light emitting point 63 of the low 
noise LD 59 and the sidewall of the concave step 105, when the parts are 
laminated in fabricating the laser array 42, positioning is performed by 
contacting the sidewall of the convex step 104 and the sidewall of the 
concave step 105, whereby the light emitting point 58 and the light 
emitting point 63 can be opposed to each other correctly via the 
respective N side electrodes, and a laser array having a high positional 
precision of the light emitting point can be obtained in a simple process. 
While in the fourth embodiment, the convex step 104 is provided at the side 
of the N side electrode 57 of the high output LD 54 and the concave step 
105 is provided at the side of the N side electrode 61 of the low noise LD 
59, the concave step may be provided at the side of the N side electrode 
57 of the high output LD 54 and the convex step may be provided at the 
side of the N side electrode 61 of the low noise LD 59. 
While in the fourth embodiment the convex part and the concave part are 
combined, the steps of the step-like configuration may be combined with 
the same effect as described above. 
In addition, the interval between the N side electrode 57 of the convex 
step 104 and the N side electrode 61 of the concave step 105 may be made 
different from the height of the heat conductive connecting leg 106, with 
the same effects as in the second and third embodiments. 
Where the convex part and the concave part are combined, a silicon dioxide 
film is formed at the side of the N side electrode of the high output LD 
except for the vicinity of the light emitting point to prevent 
short-circuiting with the P side electrode. In any of cases where convex 
parts are provided at both the high output and the low noise LD, where a 
convex part is provided only at one of the LDs, where concave parts are 
provided at both the high output LD and the low output LD, and where a 
concave part is provided only at one of the LDs, a silicon dioxide film 
may be provided except for the vicinity of the light emitting point, with 
the effect of preventing short-circuiting between the N side electrode and 
the P side electrode as in the present embodiment. 
Embodiment 5. 
FIG. 11 is a partial perspective view illustrating a laser array according 
to a fifth embodiment of the present invention. FIG. 12 is a plan view 
illustrating a laser array viewed along the arrow A of FIG. 11. 
The laser array according to the fifth embodiment includes laser chips each 
having a plurality of light emitting points opposed to each other. A 
device in which the laser chips have two light emitting points each will 
be described. 
In FIG. 12, numeral 71 designates a high output LD, numeral 72 designates 
an N side common electrode of the high output LD 71, and numeral 73 
designates a first light emitting point of the high output LD 71. Numeral 
74 designates a first P side electrode of the high output LD 71, numeral 
75 designates a second light emitting point of the high output LD 71, and 
numeral 76 designates a second P side electrode of the high output LD 71. 
Numeral 77 designates a separating groove as a means for electrically 
separating the laser at the side of the first light emitting point 73 from 
the laser at the side of the second light emitting point 75. Numeral 81 
designates a low noise LD, numeral 82 designates an N side common 
electrode of the low noise LD 81, and numeral 83 designates a first light 
emitting point of the low noise LD 81. Numeral 84 designates a first P 
side electrode of the low noise LD 81, numeral 85 designates a second 
light emitting point of the low noise LD 81, and numeral 86 designates a 
second P side electrode of the low noise LD 81. Numeral 87 designates a 
separating groove as a means for electrically separating the laser at the 
side of the first light emitting point 83 from the laser at the side of 
the second light emitting point 85. Numeral 88 designates a minus side 
lead wire connecting the N side common electrode 72 of the high output LD 
71 and the N side common electrode 82 of the low noise LD 81. In FIG. 11, 
numeral 89 designates a plus side lead wire for applying a plus voltage to 
the second light emitting point 85 of the low noise LD 81 and, although 
not shown in FIG. 11, this plus side lead wire 89 applies a plus voltage 
to the second P side electrode 86 of the low noise LD 81 through the P 
side electrode 86 which is disposed on the high output LD 71 via the 
SiO.sub.2 film 69 and the heat conductive connecting leg 106 comprising 
the plated Sn film 65 and the plated Au film 64. 
In FIG. 11, numeral 90 designates a plus side lead wire for applying a plus 
voltage to the second P side electrode 76 of the high output LD 71, and 
this is connected to the second P side electrode 76 shown in FIG. 12. 
Numeral 91 designates a plus side lead wire for applying a plus voltage to 
the first P side electrode 74 of the high output LD 71, and this is 
connected to the second P side electrode 74 shown in FIG. 12. 
In FIG. 11, numeral 92 designates a plus side lead wire for applying a plus 
voltage to the first light emitting point 83 of the low noise LD 81. The 
plus side lead wire 92 applies a voltage to the first P side electrode 84 
of the low noise LD 81 through the first P side electrode 84 disposed on 
the high output LD 71 via the SiO.sub.2 film 69 and the heat conductive 
connecting leg 106, which is only shown in FIG. 12. In FIG. 12, numeral 93 
designates a PN junction interface of the high output LD 71, numeral 94 
designates a PN junction interface of the low noise LD 81, numeral 104 
designates a convex step provided at the side of the P side electrode 74 
and the P side electrode 76 of the high output LD 71, and numeral 105 
designates a concave step provided at the side of the P side electrode 84 
and the P side electrode 86 of the low noise LD 81. 
The separating grooves 77 and 87 are formed in the same chip and having 
depths exceeding the depths of the respective PN junction interfaces from 
the chip surface for electrical separation of the driving the lasers. 
Except for such configurational separation, an insulator may be provided 
between the lasers. 
The submount 52 may be disposed on the silver block 50 as in the first 
embodiment. 
When a minus voltage is applied to the N side common electrode 72 of the 
high output LD 71 and the N side common electrode 82 of the low noise LD 
81 by the minus side lead wire 88 and a predetermined plus voltage is 
applied to the first P side electrode 74 and the second P side electrode 
76 of the high output LD 71 and also to the first P side electrode 84 and 
the second P side electrode 86 of the low noise LD 81, respectively, the 
lasers corresponding to the respective P side electrodes independently 
oscillate to emit light. 
The heat generated at the light emitting point flows into the silver block 
50 as in the first embodiment and is dispersed from this silver block 50. 
By this construction, a multi-point linear array with closely spaced dual 
beams that has less thermal crosstalk and is unlikely to be affected in 
its light emitting point interval by thermal influences is formed in a 
simple construction. 
In addition, the step 104 and the step 105 are positioned such that the 
sidewall of the convex step 104 and the sidewall of the concave step 105 
are in contact with each other as in the fourth embodiment, whereby the 
light emitting point 73 and the light emitting point 83 can be precisely 
opposed to each other and a laser array having a high positional precision 
of the light emitting point can be obtained in a simple process. 
Further, the interval between the P side electrode at the side of the 
convex step 104 and the P side electrode at the side of the concave step 
105 can be made different from the height of the heat conductive 
connecting leg 106, with the same effects as in the second and the third 
embodiments. 
In addition, in the fifth embodiment, a convex step is provided at the side 
of the N side electrode of the high output LD and a concave step is 
provided at the side of the low noise LD. Where convex parts are provided 
at both of the high output LD and the low noise LD, where a convex part is 
provided only at one of the LDs, where concave parts are provided at both 
of the high output LD and the low noise LD, and where a concave part is 
provided only at one of the LDs, a plurality of light emitting points may 
be provided in the respective laser chips that are arranged close to each 
other, with the same effects as in the above-described embodiment. 
Embodiment 6. 
The laser array with closely spaced dual beams described in the first to 
fifth embodiments can be used as a semiconductor laser of the optical disc 
apparatus. 
In the optical disc apparatus according to the sixth embodiment, the 
interval between the light emitting point of the high output LD for 
recording and the light emitting point of the low noise LD for reproducing 
are not so greatly influenced by the environmental temperature. 
Accordingly, even when the environmental temperature changes a lot when 
recording and reproduction are performed at the same time, the light 
emitting point interval of the semiconductor laser does not change and the 
light emitting points move in parallel with each other. Therefore, it is 
possible to construct an optical disc apparatus that can prevent a 
malfunction during the recording and reproduction by controlling the 
position of the semiconductor laser device using a trucking mechanism.