Laser diode array unit

A laser diode array unit for use in laser beam scanning optical apparatus and the like. The laser diode array has plural light emitting sources to be drivingly controlled independently of each other. The laser diode array is so disposed as to permit laser beams emitted from the light emitting sources to be incident to a collimator lens. On an optical axis between the laser diode array and the collimator lens is disposed a beam splitter for splitting the laser beams emitted from the light emitting sources into image light and monitor light. A magnifier lens and a photoreceptor element are arranged on the optical axis so as to allow incidence of monitor light oriented to advance in a direction perpendicular to the direction of advance of image light.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a laser diode array unit, and more 
particularly, to a laser diode array unit for use in laser beam scanning 
optical devices and the like. 
2. Description of Related Arts 
Recently, for use as a light source device in a laser beam scanning optics 
arrangement, laser diode arrays having a plurality of light emitting 
points have been receiving attention. For use with such laser diode array, 
monitoring mechanisms for monitoring the emission intensity of light 
emitting from the laser diode array itself have been proposed including 
one such that a half mirror is used to direct monitoring light onto a 
photoreceptor element as described in Japanese Patent Application 
Laid-Open No. 6-164056, and another such that an aperture having a 
polished surface is used to conduct monitoring light onto a photoreceptor 
element as described in Japanese Patent Application Laid-Open No. 
6-164070. 
The above cited arrangements are such that the mechanism for monitoring the 
intensity of light is provided outside the laser diode array package. 
Whilst, there has also been proposed an arrangement such that the 
intensity monitoring mechanism is provided within the laser diode array 
package. In such an intensity monitoring mechanism, laser beams emitted 
from individual light emitting sources are separated by means of a barrier 
so as to be prevented from overlapping, and the separated laser beams are 
separately monitored by photoreceptor elements corresponding to respective 
laser beams which are provided within the laser diode array. 
However, of these prior art intensity monitoring mechanisms, those of the 
type in which the monitoring mechanism is provided outside the laser diode 
array package are such that the light emitting sources in the laser diode 
array are spaced a small distance from each other, say, on the order of 
several tens of .mu.m, so that laser beams emitted from respective light 
emitting sources overlap one with another, which fact makes it difficult 
to separately monitor the intensity of light with respect to laser beams 
emitted from respective light emitting sources. Therefore, such monitoring 
mechanism could only monitor a total intensity of light of plural laser 
beams. 
Those of the type in which the intensity monitoring mechanism is provided 
within the laser diode array package involve a problem that the laser 
diode array itself is complex in construction and higher in cost. Another 
problem is that since the construction of the laser diode array requires 
provision of a barrier or the like, it is impracticable to reduce the 
distance between the light emitting sources. 
SUMMARY OF THE INVENTION 
The object of the present invention is to provide a laser diode array unit 
which can monitor the intensity of light separately with respect to laser 
beams emitted from individual light emitting sources. 
In order to accomplish the above object, the laser diode array unit in 
accordance with the present invention comprises a laser diode array having 
a plurality of light emitting sources which are drivingly controlled 
independently of each other; a beam split element for splitting monitor 
beams from respective laser beams emitted from the light emitting sources 
of the laser diode array; a photoreceptor element for independently 
monitoring respective intensity of light of the monitor beams; and a 
magnifier optic system for enabling the monitor beam to be condensed on 
the photoreceptor element to form a magnified image. 
According to the foregoing arrangement, part of laser beams emitted from 
the respective light emitting sources is made to serve as monitor beam by 
the beam split element. Since the monitor beam is condensed on the 
photoreceptor element by the magnifier optic system to form a magnified 
image, there can be provided a larger distance between monitor beam images 
projected onto the photoreceptor element. Therefore, the intensity of 
light from the respective light emitting sources can be separately 
monitored without involving any overlapping of monitor beam rays and in a 
stable manner. 
In the laser diode array unit of the present invention, the plurality of 
light emitting sources are synchronously driven, and the photoreceptor 
element has a split light receiving surface and outputs electric currents 
according to the intensity of light of laser beams incident to respective 
light receiving areas of the split light receiving surface. This 
arrangement permits the relative position of monitor beam and the 
photoreceptor element to be corrected to an optimum condition at all 
times, irrespective of any changes in the ambient conditions (temperature) 
of the laser diode array unit. 
In a further aspect of the present invention, the laser diode array unit 
includes a relay lens provided between the laser diode array and the 
magnifier optic system such that an intermediate image of the monitor beam 
is formed between the relay lens and the magnifier optic system. This 
arrangement makes it possible to increase the lateral magnification of the 
monitoring optics without the necessity of increasing the image side 
conjugate length of the magnifier optic system, thereby reducing the 
distance between the magnifier optic system and the photoreceptor element. 
Further, in the laser diode array unlit of the invention, the magnifier 
optic system is a retrofocus--type lens system comprising a first set of 
lenses having a negative power and a second set of lenses having a 
positive power which are arranged in a sequential order from the 
photoreceptor element side. According to this arrangement, the position of 
the fore-side principal point of the magnifier optic system on the laser 
diode array side shifts further from the magnifier optic system toward the 
laser diode array. Therefore, the lateral magnification of the magnifier 
optic system can be increased without increasing the total length of the 
magnifier optic system. In the foregoing arrangement, assuming that the 
light receiving surface of the photoreceptor element is an object surface 
and that the light emitting sources of the laser diode array is an image 
point, the lens arrangement is substantially equivalent to that of 
photographic wide-angle lenses.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Embodiments of the laser diode array unit in accordance with the present 
invention will now be described with reference to the accompanying 
drawings. In the embodiments, like parts and like portions are designated 
by like reference numerals. 
Embodiment 1 (FIGS. 1 through 3) 
As FIGS. 1 and 2 show, a laser diode array unit 1 consists essentially of a 
laser diode array 2, a beam splitter 3, a magnifier lens 4, a 
photoreceptor element 5, and a collimator lens 6. 
The laser diode array 2 includes a plurality of light emitting sources (two 
in number in the present embodiment, but of course the number may be three 
or more; the same applies in the embodiments to follow) 21, 22 adapted to 
be drivingly controlled independently of each other. The laser diode array 
2 is so disposed as to enable laser beams L radiated from the light 
emitting sources 21, 22 to become incident to the collimator lens 6. 
Disposed on an optical axis between the laser diode array 2 and the 
collimator lens 6 is a beam splitter 3 for splitting the laser beams L 
emitted from the light emitting sources 21, 22 into image light Li and 
monitor light L2. The magnifier lens 4 and the photoreceptor element 5 are 
so arranged on the optical axis as to allow the incidence of monitor light 
L2 and to advance in a direction perpendicular to the direction of advance 
of image light L1. The photoreceptor element 5 has two light receiving 
faces 5a, 5b. 
As FIG. 3 shows, image data output from CPU 10 is input to an LD drive 
circuit 11. The light emitting sources 21, 22 of the laser diode array 2 
are modulatedly (on-off) controlled independently of each other on the 
basis of image data input to the LD drive circuit 11 and radiate laser 
beams when they are on. For this purpose, the light emitting sources 21, 
22 are synchronously driven. 
The laser beams L emitted respectively from the light emitting sources 21, 
22 of the laser diode array 2 are partly reflected from a joint plane 3a 
of the beam splitter 3. The reflected beams, as monitor light L2, are 
focused through the magnifier lens 4 onto the light receiving faces 5a, 5b 
of the photoreceptor element 5. Specifically, the laser beam L emitted 
from the light emitting source 21 is projected onto the light receiving 
face 5a, and the laser beam L emitted from the light emitting source 22 is 
projected onto the light receiving face 5b. The monitoring optics system 
from the laser diode array 2 to the photoreceptor element 5 constitutes a 
magnifier system, and the laser beams L emitted respectively from the 
light emitting sources 21, 22, spaced a distance P.sub.0 from each other, 
are focused onto the photoreceptor element 5 at positions spaced a 
distance P expressed by the following relation (1): 
EQU P=.beta.P.sub.0 (1) 
where .beta. represents a lateral magnification of the monitoring optics 
system, which is preferably set to 70.times. or higher magnification. If 
.beta. is set to 70.times., the above relation (1) tells that the distance 
P between images formed on the photoreceptor element 5 can be of the order 
of 1 mm, whereas the distance between the light emitting sources 21 and 22 
is usually of the order of several tens of .mu.m. Thus, overlapping of 
monitor light L2 is prevented, and this permits the intensity of light 
from light emitting sources 21, 22 to be separately monitored in a stable 
manner. 
Whilst, remaining portions, as image light L1, of the laser beams which 
have been transmitted through the beam splitter 3 are converged by the 
collimator lens 6 in generally parallel relation, and are focused at 
minute points through a deflector and/or an optical element, not shown, so 
that they are linearly scanned over a scanning surface at a generally 
uniform rate. 
Thus, with such a simple arrangement that a magnifier lens 4 is provided 
between the beam splitter 3 and the photoreceptor element 5, the distance 
between laser beams emitted from small-spaced light emitting sources 21, 
22 can be increased on the photoreceptor element 5. This makes it possible 
to obtain a laser diode array unit 1 which can always separately monitor 
the intensity of light from the light emitting sources 21, 22. 
Embodiment 2 (FIG. 4) 
With the above described laser diode array unit 1 of Embodiment 1, the 
lateral magnification .beta. of the monitoring optic system can be made 
larger as the position of principal point of the magnifier lens 4 is set 
more upstream in the optical axis, that is, set closer to the laser diode 
array 2 along the optical path. However, the possibility of reducing the 
distance between the magnifier lens 4 and the laser diode array 2 is 
limited because of the fact that the beam splitter 3 is disposed between 
the laser diode array 2 and the magnifier lens 4, coupled with some 
limitations arising from the sizes of such functional elements as laser 
diode array 2 and magnifier lens 4, and of associated holding members. 
Therefore, in case that a laser diode array unit 1 with a larger lateral 
magnification .beta. is required, the trouble is that the length of the 
optical path from the laser diode array 2 to the photoreceptor element 5 
must be increased. 
Therefore, the present Embodiment 2 presents a laser diode array unit which 
provides a higher lateral magnification .beta. even where the length of 
optical path from the laser diode array to the photoreceptor element is 
relatively short. 
As FIG. 4 shows, a laser diode array unit 51 consists essentially of a 
laser diode array 2, a beam splitter 3, a magnifier lens 4, a 
photoreceptor element 5, a collimator lens 6, and a relay lens 52. 
The relay lens 52 is disposed between the beam splitter 3 and the magnifier 
lens 4. The relay lens 52 transmits an illuminant image of monitor light 
L2 spectro-reflected by the beam splitter 3, in a magnified size or in its 
original size. That is, the illuminant image of monitor light L2 is formed 
as an intermediate image by the relay lens 52 at a position shown by 
dotted line 53 in FIG. 4. The intermediate image is magnified by the 
magnifier lens 4 at high magnifications, and the so magnified image is 
projected onto the light receiving faces 5a, 5b. In this case, the lateral 
magnification .beta. of the monitoring optic system can be increased 
without increasing the image-side conjugate length of the magnifier lens 
4, and the distance between the magnifier lens 4 and the photoreceptor 
element 5 can be decreased. Also, by selecting any desired magnifier lens 
4, it is possible to freely set the lateral magnification .beta. and the 
conjugate distance between the intermediate image and the photoreceptor 
element 5. In this way, the laser diode array unit 51 can obtain a high 
lateral magnification .beta. even when the optical path length from the 
laser diode array 2 to the photoreceptor element 5 is rather short. 
Embodiment 3 (FIG. 5) 
Embodiment 3 presents another type of laser diode array unit in which the 
optical path length from the laser diode array to the photoreceptor 
element is rather short but which has a high lateral magnification .beta.. 
As FIG. 5 shows, a laser diode array unit 55 consists essentially of a 
laser diode array 2, a beam splitter 3, a photoreceptor element 5, a 
collimator lens 6, and a magnifier lens system 56. 
The magnifier lens system 56 is a retrofocus type lens system comprising a 
lens 56b having a negative power and a lens 56a having a positive power 
which are arranged on the optical axis in sequential order from the 
photoreceptor element 5 side. 
According to the above arrangement, the position of the foreside principal 
point of the magnifier lens system 56 shifts from the magnifier lens 
system 56 toward the laser diode array 2, and therefore, the lateral 
magnification of the magnifier lens system 56 can be increased without 
increasing the total length of the magnifier lens system 56. In the 
foregoing arrangement, assuming that the light receiving surfaces of the 
photoreceptor element 5 are object surfaces and that the illuminant 
position of the laser diode array 2 is an image point, the lens 
arrangement is substantially equivalent to that of photographic wide-angle 
lenses. 
Thus, the laser diode array unit 55 can obtain a high lateral magnification 
.beta. even when the optical path length from the laser diode array 2 to 
the photoreceptor element 5 is rather short. In FIG. 5, the position shown 
by a dotted line 57 is a pupil position at which a diaphragm may be 
provided for aberration adjustment. 
Embodiments 4, 5 and 6 (FIGS. 6 through 9) 
Embodiments 4 through 6 present laser diode array units for separating a 
laser beam transmitted through the collimator lens into image light and 
monitor light. 
As FIGS. 6 and 7 show, a laser diode array unit 60 of Embodiment 4 consists 
essentially of a laser diode array 2, a beam splitter 3, a magnifier lens 
4, a photoreceptor element 5, and a collimator lens 6. The beam splitter 3 
is disposed behind the collimator lens 6. 
Laser beams L emitted from the light emitting sources 21, 22 are converged 
generally parallel by the collimator lens 6, and thereafter, the converged 
beams are partly reflected from a joint plane 3a of the beam splitter 3. 
The reflected beams, as monitor light L2, are focused onto the light 
receiving faces 5a, 5b through the magnifier lens 4. That is, the monitor 
optic system from the laser diode array 2 to the photoreceptor element 5 
functions as a magnifier system, and the lateral magnification .beta. is 
determined by a focal length ratio of the magnifier lens 4 to the 
collimator lens 6. In this way, the distance between images of the laser 
beams emitted from small-spaced light emitting sources 21, 22 can be 
increased on the photoreceptor element 5. Thus, the laser diode array unit 
60 can prevent overlapping of monitor light L2 and constantly permits the 
intensity of light from the light emitting sources 21, 22 to be separately 
monitored. 
However, this arrangement poses one problem such that in order to increase 
the lateral magnification .beta. of the monitoring optic system of the 
laser diode array unit 60, the image side conjugate length of the 
magnifier lens 4 must be increased, which results in an increase in the 
length of light path from the laser diode array 2 to the photoreceptor 
element 5. 
In order to overcome the foregoing problem, in Embodiment 5 of the 
invention, as FIG. 8 shows, a relay lens 52 is provided between the beam 
splitter 3 and the magnifier lens 4. According to this arrangement, it is 
possible to increase the lateral magnification .beta. of the monitor optic 
system to a high power level without increasing the image side conjugate 
length of the magnifier lens 4. Thus, a laser diode array unit 65 having a 
high lateral magnification .beta. can be obtained even when the length of 
the light path from the laser diode array 2 to the photoreceptor element 5 
is rather short. For this laser diode array unit 65, the collimator lens 
6, the relay lens 52 and the magnifier lens 4 may be independently 
designed as such. This affords considerable freedom of design. 
The Embodiment 6 presents a laser diode array unit 70 incorporating a 
retrofocus type lens system which, as FIG. 9 shows, comprises a lens 56b 
having a negative power and a lens 56a having a positive power which are 
arranged on the optical axis sequentially from the photoreceptor element 5 
side. According to this arrangement, the laser diode array unit 70 can 
have a high level of lateral magnification .beta. even when the optical 
path length from the laser diode array 2 to the photoreceptor element 5 is 
rather short. 
In the Embodiments 3 through 6, though the beam emitted from the collimator 
lens 6 is a parallel beam, it is possible that the beam emitted from the 
collimator lens 6 is convergent in shape. 
Embodiment 7 (FIGS. 10 through 15) 
In laser diode array units of the foregoing Embodiments 1 through 6, there 
may occur some deviations in relative positions of the laser diode array 
2, the beam splitter 3, the magnifier lens 4, and/or collimator lens 6 due 
to some mechanical error and/or changes of ambient condition 
(temperature). For example, if the position of the laser diode array 2 
shifts several tens of .mu.m in the direction of the side-by-side 
arrangement of the light emitting sources 21, 22, spots Lb of monitor 
light L2 projected onto the light receiving faces 5a, 5b would be 
displaced by the following formula, 
EQU .beta..multidot..DELTA.L 
wherein .beta. represents a lateral magnification of monitor optic system 
and .DELTA.L represents an amount of shift of laser diode array 2. 
However, in order to increase the distance between monitor light beams on 
the photoreceptor element 5, lateral magnification .beta. is increased to 
a high power level, and this tends to produce high error sensitivity. 
Possibly, therefore, the spots Lb of monitor light L2 may straddle the 
light receiving faces 5a and 5b, or the spots of two monitor light beams 
may be projected onto the light receiving face 5a; and this may lead to 
erroneous detection of the intensity of light. 
As a countermeasure against the foregoing problem, Embodiment 7 provides 
for correction of monitoring position. 
Example 1 of Monitor Position Adjustment 
As FIG. 10 shows, the light receiving face 5b of the photoreceptor element 
5 is a light receiving surface split by a split line 31 into two parts. 
Each of the respective light receiving areas S1, S2 of the split light 
receiving surface outputs an electric current proportional to the 
intensity of light received. The light receiving face 5a is a single 
photoreceptor surface and outputs an electric current proportional to the 
intensity of incident light. 
Distance R between the center line of the light receiving face 5a and the 
split line 31 of the light receiving face 5b is set to be substantially 
equal to the value of the following formula, 
EQU Po.multidot..beta. 
wherein where .beta. represents a lateral magnification of monitor optic 
system and Po represents a distance between light emitting sources 21 and 
22. On a pedestal supporting the photoreceptor element 5 there is provided 
a parallel shifting mechanism, not shown including a rack-and-pinion held 
in mesh engagement with a gear which can be driven by a micro-stepping 
motor or the like. 
When spots Lb of monitor light L2, having a beam intensity profile as 
expressed by a curve 33 shown in FIG. 10, are projected onto the light 
receiving faces 5a, 5b, light receiving areas S1, S2 of the two-part light 
receiving face 5b output electric currents in proportion to the intensity 
of light received. If the difference between the output of the light 
receiving area S1 and the output of the light receiving area S2 is less 
than a predetermined value, it is determined that the photoreceptor 
element 5 is at its regular monitoring position, and accordingly the 
intensity of light from one of the light emitting sources is monitored by 
the output of the light receiving face 5a. The intensity of light from the 
other light emitting source is monitored by a combined total of the 
outputs of the light receiving areas S1 and S2. 
On the other hand, if the difference between the output of the light 
receiving area S1 and the output of the light receiving area S2 is more 
than the predetermined value, it is determined that the photoreceptor 
element 5 is off its regular monitoring position, and while sampling is 
made with respect to the output difference, the monitoring position of the 
photoreceptor element 5 is corrected in such a way that the pedestal 
supporting the photoreceptor element 5 is moved by a micro-stepping motor 
or the like through the parallel shifting mechanism in the direction of 
arrow a as shown in FIG. 11, that is, in a direction perpendicular to the 
split line 31 of the light receiving face 5b. When the output difference 
drops below the predetermined value, the micro-stepping motor is turned 
off, and a day run torque of the micro-stepping motor is utilized to hold 
the pedestal in position. In this condition, the intensity of light of one 
light emitting source is monitored by the output of the light receiving 
face 5a, and the intensity of light of the other light emitting source is 
monitored by a combined output of the light receiving areas S1 and S2. In 
this way, the photoreceptor element 5 can constantly receive monitor light 
L2 at its regular monitoring position without any detection error being 
caused, monitoring accuracy being thus enhanced. 
Example 2 of Monitoring Position Adjustment 
As FIG. 12 shows, the light receiving face 5b of the photoreceptor element 
5 is a light receiving surface split by two split lines 35, 36 into three 
parts. Each of respective light receiving areas S1, S2, S3 of the split 
light receiving surface outputs an electric current proportional to the 
intensity of light received. The light receiving face 5a is a single 
photoreceptor surface. Distance R between the center line of the light 
receiving face 5a and the split line 36 of the light receiving face 5b is 
set to be substantially equal to the value of the following formula, 
EQU Po.multidot..beta. 
wherein where .beta. represents a lateral magnification of monitor optic 
system and Po represents a distance between light emitting sources 21, and 
22. On a pedestal supporting the photoreceptor element 5 there is 
provided, not shown though, a parallel shifting mechanism, not shown 
including a rack-and-pinion held in mesh engagement with a gear which can 
be driven by a micro-stepping motor or the like. 
Further, as FIGS. 13 and 14 show, an optical path split element 41 (prism 
in Embodiment 7) is disposed before the photoreceptor element 5. Part of 
monitor light L2 is split off by the optical path split element 41 for use 
as position sensing light L3. Spots Lb of monitor light L2, having a beam 
intensity profile shown by a curve 44 (see FIG. 12), are projected onto 
the light receiving faces 5a, 5b, and further a spot Lb1 of position 
sensing light L3 is projected onto the light receiving face 5b. The spots 
Lb of monitor light L2 are spread wider on the light receiving faces 5a, 
5b by an optical path difference than the spots LB1 of position sensing 
light L3. This results in a decrease in error sensitivity due to an error 
of monitoring position of the photoreceptor element 5. 
In the light receiving face 5b, the spot Lb of monitor light L2 is 
projected onto the light receiving area S1, and the spot Lb1 of position 
sensing light L3 is projected onto the light receiving areas S2, S3. If 
the difference between the output of the light receiving area S2 and the 
output of the light receiving area S3 is less than a predetermined value, 
it is determined that the photoreceptor element 5 is at its regular 
monitoring position, and accordingly the intensity of light of one of the 
light emitting sources is monitored by the output of the light receiving 
face 5a, and the intensity of light of the other light emitting source is 
monitored. On the other hand, if the difference between the output of the 
light receiving area S2 and the light receiving area S3 is more than the 
predetermined value, it is determined that the photoreceptor element 5 is 
off its regular monitoring position, and accordingly the pedestal 
supporting the photoreceptor element 5 is moved by a micro-stepping motor 
through the parallel shifting mechanism in the direction of arrow a as 
shown in FIG. 14 for correcting the monitoring position of the 
photoreceptor element 5. When the output difference drops below the 
predetermined value, the micro-stepping motor is turned off, and a day run 
torque of the micro-stepping motor is utilized to hold the pedestal in 
position. In this condition, the intensity of light of one light emitting 
source is monitored by the output of the light receiving face 5a, and the 
intensity of light of the other light emitting source is monitored by the 
output of the light receiving area S1. In this way, the photoreceptor 
element 5 can constantly receive monitor light L2 at its regular 
monitoring position without any detection error being caused, monitoring 
accuracy being thus enhanced. 
Example 3 of Monitoring Position Adjustment 
As FIG. 15 shows, a transparent flat plate 45 (flat glass plate in 
Embodiment 7) is disposed before the photoreceptor element 5. On a 
pedestal supporting the transparent flat plate 45 there is provided, not 
shown though, a pivoting mechanism including a rack-and-pinion held in 
mesh engagement with a gear which can be driven by a microstepping motor 
or the like. The photoreceptor element 5 is similar to the one described 
in Example 1 of monitor position adjustment. 
When spots Lb of monitor light L2 are projected onto the light receiving 
faces 5a, 5b, currents proportional to the intensity of light received are 
output from the light receiving areas S1, S2 of the two-part light 
receiving face 5b. If the difference between the output of the light 
receiving area S1 and the output of the light receiving area S2 is less 
than a predetermined value, it is determined that the photoreceptor 
element 5 is at its regular monitoring position, and accordingly the 
intensity of light from one of the light emitting sources is monitored by 
the output of the light receiving face 5a. The intensity of light from the 
other light emitting source is monitored by a combined output of the light 
receiving areas S1 and S2. 
On the other hand, if the difference between the output of the light 
receiving area S1 and the output of the light receiving area S2 is more 
than the predetermined value, it is determined that the photoreceptor 
element 5 is off its regular monitoring position, and while sampling is 
made with respect to the output difference, the monitoring position of the 
photoreceptor element 5 is corrected in such a way that the pedestal 
supporting the transparent flat plate 45 is moved by a micro-stepping 
motor through the pivoting mechanism in the direction of arrow b as shown 
in FIG. 15, for example to a position indicated by dotted line 45', 
whereby projection positions of the spots Lb of monitor light L2 on the 
light receiving faces 5a, 5b are moved to the position indicated by dotted 
line L2' for correction. When the output difference drops below the 
predetermined value, the micro-stepping motor is turned off, and a day run 
torque of the micro-stepping motor is utilized to hold the pedestal in 
position. In this condition, the intensity of light of the one light 
emitting source is monitored by the output of the light receiving face 5a, 
and the intensity of light of other light emitting source is monitored by 
a combined output of the light receiving areas S1 and S2. 
In this way, the photoreceptor element 5 can constantly receive monitor 
light L2 at its regular monitoring position without any detection error 
being caused, monitoring accuracy being thus enhanced. 
Other Embodiments 
In the present invention, as shown in FIGS. 16 and 17, for example, an 
aperture regulating plate 100 may be disposed behind the collimator lens 6 
for regulating the shapes of spots of laser beams emitted from the laser 
diode array 2. 
For the optical path split element for splitting laser beams into image 
light and monitor light, a half mirror or the like may be used as well as 
the beam splitter. 
For purposes of monitoring position adjustment in Embodiment 7, as in 
Examples 1 and 3 of monitor position correction, all the light receiving 
faces 5a, 5b of the photoreceptor element 5 may be designed to be two-part 
light receiving surfaces as shown in FIG. 18 so that respective light 
receiving faces 5a, 5b are used for position detection or so that position 
detection is carried out only by any one light receiving face. 
Further, as FIG. 19 shows, the light receiving faces 5a, 5b may be designed 
to be four-part light receiving faces split by two split lines 31a, 31b 
extending in rectangular relation to each other, each thus defining light 
receiving areas S1, S2, S3, S4, so that position adjustment can be 
performed in directions perpendicular to split lines 31a and 31b, that is, 
in two directions perpendicular to each other. 
Further, in Example 2 of monitor position adjustment, as FIG. 20 shows, the 
light receiving faces 5a, 5b of the photoreceptor element 5 are three-part 
light receiving surfaces so that position detection can be performed at 
respective light receiving faces 5a, 5b, or so that position detection is 
carried out at one selected light receiving face only. For purposes of 
above described shifting, besides parallel shifting of the photoreceptor 
element 5 and pivotal movement of the transparent flat plate, it is also 
possible to use a method of shifting the magnifier lens 4 in a direction 
perpendicular to the split line of the light receiving surface. 
The laser diode array unit of the present invention is not limited to the 
above described embodiments, and may be modified, changed, altered, or 
varied in various ways within the scope and spirit of the appended claims.