Laser diode module

A laser diode module includes a laser diode emitting a laser beam, and a lens for collimating the laser beam. The lens is tilted with respect to an optical axis along which the laser beam is propagated.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention generally relates to laser diode modules and, more 
particularly, to a laser diode module suitably applied to a bar code 
reader in which a laser diode is used as a light source. 
2. Description of the Prior Art 
Various types of laser sources have been proposed. In the past, a He--Ne 
laser was widely used. Recently, semiconductor laser diodes have been 
proposed and applied to various fields as light sources. Such 
semiconductor laser diodes contribute to down-sizing of various devices. 
A bar code reader that optically reads a bar code uses a semiconductor 
laser diode (hereinafter, simply referred to as a laser diode). Normally, 
a laser diode is combined with optical elements such as lenses, and a 
laser diode module made up of the laser diode and the optical elements is 
provided as a light source. A light emitted from the laser diode is 
optically processed by the optical elements of the laser diode module and 
is projected onto a bar code via an optical scanning system outside of the 
laser diode module. 
The performance of the bar code reader greatly depends on the performance 
of the laser diode module. Conventionally, a complex adjustment mechanism 
is employed in the laser diode module in order to improve the performance 
thereof. For example, such an adjustment mechanism is designed to adjust 
the positions of optical elements, such as lenses. By way of another 
example, a plurality of optical elements are used to improve the 
performance of the laser diode module. 
From the above viewpoints, it is required to provide a simple laser diode 
module capable of providing good performance by a simple adjustment 
mechanism. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a simple laser diode 
module capable of providing good performance by a simple adjustment 
mechanism. 
The above object of the present invention is achieved by a laser diode 
module comprising: a laser diode emitting a laser beam; and a lens for 
collimating the laser beam, the lens being tilted with respect to an 
optical axis along which the laser beam is propagated. 
It is preferable that the laser diode module comprises a base which holds 
the laser diode; and a lens holder which holds the lens so that a tilt 
angle of the lens with respect to the optical axis can be adjusted and 
which is mounted on the base. 
It is also preferable that the laser diode module comprises a base which 
holds the laser diode and has a mounting surface; a lens holder which 
holds the lens and is slidably mounted on the mounting surface; and a 
mechanism which tilts the lens holder with respect to the mounting surface 
of the base so that the lens is tilted with respect to the optical axis. 
It is also preferable that the laser diode module comprises: a base holding 
the laser diode and having a mounting surface; a first lens holder holding 
the lens; and a second holder slidably mounted on the mounting surface of 
the base. The first lens holder has a first through hole in which the lens 
is placed. The second holder has a second hole, into which the first lens 
holder is inserted, and two third holes joined to the first through hole 
and formed on respective sides of the first through hole. The laser beam 
emitted from the laser diode is propagated through one of the two third 
holes, a part of the second hole, the lens, a remaining part of the second 
hole, and the other one of the two third holes.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In order to facilitate understanding of the present invention, a 
description will now be given, with reference to FIG. 1, of a bar code 
reader. 
Referring to FIG. 1, a bar code reader 1 is made up of a laser diode module 
2 functioning as a light source, an optical scanning system 4, a 
photodetector 9 and a processing circuit 10. A laser beam 3 emitted from 
the laser diode module 2 is oriented toward an item 6 and deflected as 
indicated by an arrow 5 by means of the optical scanning system 4, which 
comprises, for example, a polygon mirror and other mirrors. A bar code 7, 
formed on the item 6, is scanned by the deflected laser beam 3. The 
deflected laser beam 3 is reflected by the bar code 7 and the intensity 
thereof is modulated (amplitude modulation). A reflected light 8 is then 
detected by the photodetector 9, which outputs a corresponding electric 
signal to the processing circuit 10. This circuit 10 performs a 
predetermined operation on the received electric signal, and generates 
bar-code read data. 
The laser diode module 2 includes a laser diode and an optical element. 
FIG. 2 shows an optical character of a laser diode of the laser diode 
module 2. 
FIG. 2 shows a laser diode 11 used in the laser diode module 2. As shown in 
FIG. 2, the laser diode 11 has an astigmatic difference `a` normally equal 
to 10 .mu.m. In actuality, the astigmatic difference of normal laser 
diodes ranges from 5 .mu.m to 15 .mu.m. Due to the astigmatic difference, 
a far-field pattern 13 of a laser beam 12 emitted from the laser diode 11 
is of an oval shape having a long axis 14 in the vertical direction and a 
short axis 15 in the horizontal direction. 
When the laser beam 12 is focused by the lens 16, the focal point of a 
laser beam component 12.sub.V, in the vertical direction in a vertical 
plane, is defined as a vertical-direction focal point F.sub.V, and the 
focal point of a laser beam component 12.sub.H, in the horizontal 
direction in a horizontal plane, is defined as a horizontal-direction 
focal point F.sub.H. When the aforementioned astigmatic difference ranges 
within .+-.5 .mu.m, a distance `b` between the vertical-direction focal 
point F.sub.V and the horizontal-direction focal point F.sub.H ranges 
within .+-. a few tens of microns. 
When different laser diodes have different distances `b`, different bar 
code readers have different read performances. With the above in mind, 
conventional laser diode modules are equipped with an adjustment mechanism 
designed to make the difference `b` constant. Further, it is required to 
provide compact laser diode modules. 
FIG. 3 shows a conventional laser diode module 20 made up of a laser diode 
22, a collimating lens 23, a cylindrical lens 24 and a cylindrical lens 
25, these elements being arranged on an optical axis 26. The cylindrical 
lens 24 functions to converge the laser beam emitted from the laser diode 
22 in the vertical direction. The cylindrical lens 25 functions to 
converge the laser beam in the horizontal direction. The lenses 24 and 25 
are provided so that the positions thereof are independently adjusted 
along the optical axis 26. The position of the horizontal-direction focal 
point F.sub.H can be adjusted by adjusting the position of the lens 25 
along the optical axis 26. The position of the vertical-direction focal 
point F.sub.V can be adjusted by adjusting the position of the lens 24 
along the optical axis 26. 
However, the conventional laser diode shown in FIG. 3 has a disadvantage in 
that the module 20 is of a large size and is expensive due to use of the 
three lenses 23, 24 and 25. 
It is to be noted that the present invention is based on a phenomenon found 
by the inventors. A description will now be given, with reference to FIGS. 
4 and 5, of such a phenomenon. 
As shown in FIG. 4-(A) and FIG. 4-(B), the inventors attempted to tilt a 
lens 30 with respect to a horizontal axis 31. At this time, the inventors 
observed that the position P.sub.H of a beam waist of a beam 32.sub.H in 
the horizontal direction did not change, while the position P.sub.V of a 
beam waist of a beam 32.sub.V in the vertical direction changed from an 
original position P.sub.V to a position P.sub.V1 towards the lens 30. 
The inventors also found that a tilt angle .theta. of the lens 30 and the 
degree of positional variation in the beam waist from the original 
position P.sub.V have a relationship indicated by a line I in FIG. 5. It 
can be seen from FIG. 5 that the degree of positional variation in the 
beam waist position P.sub.V is increased as the tilt angle .theta. is 
increased, within a certain range. 
A description will now be given of embodiments of the present invention. It 
will be noted that the present invention has a mechanism for tilting a 
lens. 
FIGS. 6A, 6B and 6C are diagrams of a laser diode module 40 according to a 
first embodiment of the present invention. The laser diode module 40 
includes a base 41 having a first vertical portion 43c to which a laser 
diode 42 is fixed. Further, the base 41 has a lens holder mounting part 
43, which includes a horizontal lens holder mounting portion 43a and a 
second vertical portion 43b. The surfaces of the portions 43a and 43b are 
high-precision flat surfaces. 
A lens holder 44 is of a substantially L-shape, and has a vertical portion 
44a and a horizontal portion 44b. A lens 45 is fixed to the vertical 
portion 44a. A through female screw 46 is vertically formed at an end part 
of the horizontal portion 44b of the lens holder 44. An adjustment male 
screw 47 for pivoting the lens holder 44 engages the female screw 46. An 
end portion of the adjustment male screw 47 can project from the lower 
surface of the horizontal portion 44b of the lens holder 44. 
A hole 48 that is long (i.e., elongated) the horizontal direction is formed 
in a vertical wall 41a of the base 41. A male screw 49 is inserted into 
the long hole 48 and is engaged with a female screw 50 formed in a root 
portion at which the vertical portion 44a of the lens holder 44 and the 
horizontal portion 44b thereof are connected to each other. 
A leaf spring 51 presses the lens holder 44 against the lens holder 
mounting portion 43a of the base 41. 
An adjustment operation of the lens holder 44 is performed as follows. As 
shown in FIG. 6A, an optical bench 60 and a beam spot measuring instrument 
61 are used to perform the adjustment operation. At the first step of the 
adjustment operation, the base 41 and the measuring instrument 61 are 
placed on the optical bench 60 so that the distance between the laser 
diode 42 and the measuring instrument 61 is equal to a predetermined 
distance L. 
At the second step of the adjustment operation, the horizontal-direction 
focal point is adjusted as follows. The male screw 49 is turned (loosed) 
in a state in which the screw 47 does not project from the lower surface 
of the horizontal portion 44b of the lens holder 44. In other words, the 
male screw 49 is turned in a state in which the lens 45 is not tilt. An 
output signal of the measuring instrument 61 is monitored while the lens 
holder 44 is made to slide on the lens holder mounting portion 43a in a 
direction indicated by a two-headed arrow A, as shown in FIG. 6A. In this 
manner, the position of the lens holder 44, at which a minimum beam spot 
size can be obtained, is identified. Therefore, the screw 49 is secured so 
that the lens holder 44 is provisionally fixed to the base 41. 
At the third step of the adjustment operation, the vertical-direction focal 
point is adjusted as follows. The measuring instrument 61 is moved in a 
direction indicated by a single-headed arrow B, as shown in FIG. 6A. 
Thereafter, the screw 47 is turned so that it projects downwardly from the 
horizontal portion 44b of the lens holder 44. Hence, the screw 47 presses 
downwardly on the lens holder mounting portion 43a, so that the lens 
holder 44 is turned (i.e., rotated) as indicated by an arrow C shown in 
FIG. 6A. Hence, an angle .theta. between the vertical direction and the 
vertical surface of the vertical portion 44a of the lens holder 44 is 
formed. That is, the lens 45 is tilted by the angle .theta. in the 
counterclockwise direction. It will be noted that the lens 45 is tilted by 
tilting the lens holder 44 in the above-mentioned manner and hence no 
stress is exerted on the lens 45. The screw 47 is turned in order to 
determine a tilted position of the lens holder 44 at which a minimum beam 
spot size can be obtained. Then, the screw 49 is secured to fix the lens 
holder 44 to the base 41. When the third step of the adjustment operation 
is completed, the adjustment operation is completed. 
As shown in FIG. 7A, the lens holder 44 has a chamfered corner 55. At the 
third step of the adjustment operation, the lens holder 44 is caused to 
pivot about an end 56 of the chamfered corner 55 in the direction 
indicated by the arrow C. The chamfered corner 55 is formed so that the 
end 56 is located just below the female screw 50. If the chamfered portion 
55 is not formed, as shown in FIG. 7B, the position of the female screw 50 
will move greatly in the vertical direction, and the possible tilt angle 
.theta. will be limited to a narrow range due to the relation with the 
long hole 48. On the other hand, the chamfered corner 55 causes the female 
screw 50 to be moved, as shown in FIG. 7A. It will be seen from FIG. 7A 
that the position of the female screw 50 does not move greatly in the 
vertical direction. With the above structure, it is possible to cause the 
lens holder 44 to pivot about the end 56 up to approximately 10.degree. 
and to facilitate the adjustment of the vertical-direction focal point. 
The leaf spring 51 presses the lens holder 44 against the lens holder 
mounting surface 43a. Hence, the lens holder 44 can be made to pivot about 
the end 56 in the state where the end 56 is in contact with the lens 
holder mounting surface 43a of the base 41. 
Alternatively, as shown in FIG. 8, it is possible to provide the adjustment 
screw 47 so that it engages a female screw 46a formed in the base 41 and 
can project upwardly from the lens holder mounting surface 43a of the base 
41. 
A description will now be given, with reference to FIGS. 9 and 10, of a 
laser diode module 40A according to a second embodiment of the present 
invention. In FIGS. 9 and 10, parts that are the same as those shown in 
the previously described figures are given the same reference numbers. 
The laser diode module 40A shown in FIGS. 9 and 10 has a base 41A having a 
hole 71 which is formed in the vertical portion 41a of the base 41A and is 
long (i.e., elongated) in the horizontal direction A. The lens holder 44 
is rotatable in the direction indicated by the arrow C (FIG. 10). A laser 
diode holder 70 is provided so that it can slide on the lens holder 
mounting surface 43a in the direction A (FIG. 9). It will be noted that 
the base 41A shown in FIGS. 9 and 10 does not have the vertical portion 
43c of the base 41 shown in FIGS. 6A through 6C. The laser diode holder 70 
can be fixed at a desired position by means of a male screw 72, which is 
inserted into the long hole 71 and is engaged with a female screw formed 
in the laser diode holder 70. 
The horizontal-direction focal point can be adjusted so that the lens 
holder 70 is moved in the direction A. The vertical-direction focal point 
can be adjusted by means of the screw 47 in the same manner as that in the 
first embodiment of the present invention. 
A description will now be given, with reference to FIGS. 11A, 11B and 11C, 
of a laser diode module 40B according to a third embodiment of the present 
invention. In FIGS. 11A through 11C, parts that are the same as those 
shown in the previously described figures are given the same reference 
numbers. 
A lens holder 44A, to be used instead of the aforementioned lens holder 44, 
has a first vertical plate portion 81a and a second vertical portion 8lb. 
The lens holder 44A is an integrally formed member and the portions 81a 
and 81b thereof are integrally formed and are opposite to each other via a 
slit 80. The lens 45 is fixed to the first vertical plate portion 81a. The 
second vertical portion 81b has a through hole 80b extending in the 
horizontal direction and allows the laser beam, via the lens 45, to pass 
through the through hole 80b. A through female screw 84 is formed in the 
vertical portion 81b and is located above the through hole 80b. A male 
screw 82, which engages the female screw 84, passes through the slit 80 
and can come in contact with an upper portion of the vertical plate 
portion 81a. By turning the male screw 82, it gradually presses the 
vertical plate portion 81a, which is gradually bent and tilted, so that 
the lens 45 is tilted by the angle .theta.. The slit 80 makes the vertical 
plate portion 81a flexible. In this manner, the vertical-direction focal 
point can be adjusted. 
The horizontal-direction focal point can be adjusted in the same manner as 
that of the first embodiment of the present invention. That is, the lens 
holder 44A is slidable on the lens holder mounting surface 43a, and is 
fixed at a position where a minimum beam spot size can be obtained. 
FIG. 12 is a diagram of a first variation 44B of the lens holder 44A used 
in the third embodiment of the present invention. In FIG. 12, parts that 
are the same as those shown in the previously described figures are given 
the same reference numbers. A groove 90 is formed in an outer root portion 
of the vertical plate portion 81a. The groove 90 facilitate the degree of 
flexibility of the vertical plate portion 81a. 
FIG. 13 is a diagram of a second variation 44C of the lens holder 44A used 
in the third embodiment of the present invention. In FIG. 13, parts that 
are the same as those shown in the previously described figures are given 
the same reference numbers. The vertical portion 81b has a horizontal 
projection 81b' located above the slit 80. A male screw 91 vertically 
penetrates the horizontal portion 81b' and projects therefrom. A female 
screw engaging the male screw 91 is formed in the horizontal projection 
81b'. A wedge 92 is depressed by the male screw 91, so that the wedge 92 
is forced to be inserted into the slit 80. The adjustment operation can be 
performed from the upper side of the laser diode module without 
interrupting the laser beam emitted via the lens 45. 
FIG. 14 is a diagram of a third variation 44D of the lens holder 44A used 
in the third embodiment of the present invention. In FIG. 14, parts that 
are the same as those shown in the previously described figures are given 
the same reference numbers. A rod 93 having an oval cross-section is 
rotatably provided in the slit 80. By rotating the rod 93, the vertical 
plate portion 81a is bent, so that the lens 45 is tilted. 
A description will now be given, with reference to FIGS. 15A, 15B and 15C, 
of a laser diode module 40C according to a fourth embodiment of the 
present invention. In FIGS. 15A through 15C, parts that are the same as 
those shown in the previously described figures are given the same 
reference numbers. 
A lens holder 44B-1 includes the vertical projections 81a and 81b. A sloped 
portion 95 is formed on a corner of the vertical portion 81b. A leaf 
spring 96 having an end embedded in the vertical portion 41b of the base 
41 engages the sloped portion 95 of the vertical portion 81b. The leaf 
spring 96 urges the lens holder 44B-1 in a direction indicated by an arrow 
97 shown in FIG. 15B. Hence, the lens holder 44B-1 is pressed against the 
lens holder mounting surface 43a and the vertical surface 43b. After the 
positioning of the lens holder 44B-1 is completed, the lens holder 44B-1 
can be fastened to the base 41 by means of an adhesive or the like. 
FIGS. 16A and 16B are diagrams of a laser diode module 40D according to a 
fifth embodiment of the present invention. In FIGS. 16A and 16B, parts 
that are the same as those shown in the previously described figures are 
given the same reference numbers. A base 41B has a first vertical plate 
portion 101a and a second vertical portion 101b, these portions being 
spaced apart from each other via a slit 100. The lens 45 is fixed to the 
vertical portion 101a. A male screw 102 engages a female screw formed in 
the vertical portion 101b and projects therefrom. A through hole 103 is 
formed in the vertical portion 101b so that the laser beam passing through 
the lens 45 is allowed to pass. The screw 102 comes into contact with an 
upper portion of the vertical portion 101a. By turning the screw 102, the 
vertical portion 101a is bent and tilted, so that the lens 45 can be 
tilted. The laser diode 42 is held by the laser diode holder 70, also used 
in the second embodiment of the present invention. Since the screw 102 for 
the adjustment is provided in the base 41B fixed to the optical bench, it 
is easy to operate the screw 102. 
A description will now be given, with reference to FIG. 17A, 17B and 17C, 
of a laser diode module 40E according to a sixth embodiment of the present 
invention. The laser diode module 40E includes a base 111 having a first 
vertical portion 111a, a second vertical portion 111b, and a holder 
mounting surface 111c. The first and second vertical portions 111a and 
111b are provided so that these portions form a right angle. The laser 
diode 42 is fixed to the second vertical portion 111b. 
A holder 114 is mounted on the holder mounting surface 111c, and is 
slidable thereon. A leaf spring 113 fixes the holder 114 on the holder 
mounting surface 111C in a state in which the holder 114 is in contact 
with the first vertical portion 111a of the base 111. One end of the leaf, 
spring 113 is embedded in the first vertical portion 111a, and the other 
end engages an edge of the holder 114. 
The holder 114 has a large cylindrical through hole 117, and two small 
cylindrical holes 115 and 116. The holes 115 and 116 are located on 
respective sides of the through hole 117 and are connected to the through 
hole 117. The laser beam emitted from the laser diode 42 enters into the 
hole 116. The through hole 117 accommodates a lens holder 118 having a 
cylindrical shape and almost the same diameter as that of the holder 114. 
The lens holder 118 has a through hole 120, which is integrated with the 
holes 115 and 116 when the lens holder 118 is inserted into the holder 114 
and placed in position. The lens 45 is located in the through hole 120 of 
the lens holder 118. The laser beam from the hole 116 passes through the 
lens 45 and is emitted through the hole 115. A straight groove 119 is 
formed on a front surface of the lens holder 118. By turning the lens 
holder 118, when accommodated in the holder 114, by means of an instrument 
engaged with the groove 119, it is possible to tilt the lens 45 with 
respect to the laser beam emitted from the laser diode 42. Thereby, the 
vertical-direction focal point can be adjusted. The horizontal-direction 
focal point can be adjusted by moving the holder 114 in the direction A. 
A description will now be given, with reference to FIGS. 18A, 18B and 18C, 
of a first variation 40F of the laser diode module 40E according to the 
sixth embodiment of the present invention. In FIGS. 18A through 18C, parts 
that are the same as those shown in FIGS. 17A through 17C are given the 
same reference numbers. 
The laser diode module 40F shown in FIGS. 18A through 18C has a leaf spring 
126 fastened to the holder 114 by means of a male screw 127. The leaf 
spring 126 presses the lens holder 118 against the first vertical portion 
ilia of the base 111. Thereby, a deviation of the lens holder 118 and the 
lens 45 in the direction perpendicular to the optical axis of the laser 
diode 42 can be prevented. 
FIGS. 19A, 19B and 19C illustrate a second variation 40G of the laser diode 
module 40E according to the sixth embodiment of the present invention. In 
FIGS. 19A through 19C, parts that are the same as those shown in the 
previously described figures are given the same reference numbers. 
The laser diode module 40G has a holder 114A having a through hole 117A and 
the aforementioned holes 115 and 116. The lens holder 118 is inserted into 
the through hole 117A from the side of the holder 114A which is to come 
into contact with the first vertical portion 111a of the base 111. The 
diameter of the through hole 117A on the outside thereof is less than the 
diameter of the lens holder 118. Hence, a circular edge portion of the 
lens holder 118 comes into contact with an inner wall of the through hole 
117A of the holder 114A. In the state in which the holder 114A, with the 
lens holder 118 inserted therein, is placed on the holder mounting surface 
111c as shown in FIG. 19C, the leaf spring 113 presses the holder 114A 
against the first vertical portion 111a of the base 111 in such a state in 
which an end surface of the lens holder 118 opposite to the groove is in 
pressure contact with the first vertical portion 111a of the base 111. 
Hence, it is possible to deviate the lens holder 118 and the lens 45 from 
the predetermined position at which the optical axis of the laser diode 42 
matches the optical axis of the lens 45. The vertical-direction focal 
point can be adjusted by turning the lens holder 118 by means of an 
instrument. 
A description will now be given, with reference to FIGS. 20A, 20B and 20C, 
of a third variation 40H of the laser diode module 40E according to the 
sixth embodiment of the present invention. In FIGS. 20A, 20B and 20C, 
parts that are the same as those shown in the previously described figures 
are given the same reference numbers. 
The laser diode module 40H shown in Figs. 20A, 20B and 20C has a base 131 
having a hole 136 into which the lens holder 118 is inserted. A hole 132 
is joined to the hole 120 of the lens holder 118 when the lens holder 118 
is inserted into the hole 136 and placed in a position. As shown in FIG. 
20A, a hole 133 is formed in the base 131 so that it receives the laser 
beam emitted from the laser diode 42. The base 131 has a laser diode 
holder accommodating space defined by a vertical portion 131a and a laser 
diode holder mounting surface 131b. A block-shaped laser diode holder 141, 
which is slidable on the mounting surface 131b in the direction A, holds 
the laser diode 42. A leaf spring 135, having an end embedded in the 
vertical portion 131a of the base 131, engages an edge of the holder 141 
and presses it against the vertical portion 131a. The horizontal-direction 
focal point can be adjusted by moving the laser diode holder 141 in the 
direction A. The vertical-distance focal point can be adjusted by turning 
the lens holder 118. 
The present invention is not limited to the specifically described 
embodiments and variations, and other variations and modifications may be 
made without departing from the scope of the present invention.