JPH0350512A - Light source unit - Google Patents

Abstract

PURPOSE:To minimize variation in the distance between a light emission point and the principal point of a collimater lens with temperature by setting the ratio of the distance from a coupling position to the light emission point and the distance from the coupling position to the collimator lens principal point to the reciprocal of the ratio of the coefficient of heat expansion of respective holders. CONSTITUTION:When the coefficient of heat expansion of the material of the laser holder 2 is denoted as Ka and the coefficient of heat expansion of the material of a lens barrel 4 is denoted as Kb, a screw 5 is so arranged that A/B=Kb/Ka, where A is the position of the screw 5. Further, A=l/(1-Ka/Kb), where l is the focal distance of the collimator lens 3 which collimates the luminous flux from a semiconductor laser 1 into parallel luminous flux. Namely, the distance A from the light emission point of the semiconductor laser 1 to the screw 5 and the focal distance l of the collimator lens 3 are set as shown above and then the focal distance l can be held invariably constant against temperature variation. Consequently, the high-accuracy parallel luminous flux can be projected without being affected by the temperature variation.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a light source device that reduces positional deviation in the optical axis direction due to temperature between a light source and a collimator lens, and reduces errors such as focal deviation and tracking deviation. It is.

[Conventional technology]

A conventional light source device for an optical head is, for example, the one developed in U.S. Pat.
As described in Japanese Patent No. 260, changes in the distance between the collimator lens and the semiconductor laser due to temperature changes can be reduced by constructing the collimator lens holder with a material having a coefficient of thermal expansion υ higher than that of the semiconductor laser holder. has been devised.

An example of the conventional light source device described above will be described below with reference to the drawings.

FIG. 4 is a sectional view showing the configuration of a conventional light source device for an optical head. In Fig. 4, 1 indicates a semiconductor laser as a light source, 2 indicates a laser holder into which the semiconductor laser 1 is press-fitted, and 3 indicates a collimator lens that converts the diverging light beam from the semiconductor laser 1 into a parallel light beam. , 4 indicates a lens mirror to which the collimator lens 3 is fixed. A part 2a which is the contact part of the laser holder 2 with the lens barrel 4, and a part 4& which is the contact part of the lens barrel 4 with the laser holder 2.
The parts are fitted and held together. A screw 5 fixes the lens barrel 4 at a position where the light beam from the collimator lens 3 becomes a parallel light beam.

In the conventional example mentioned above, the lens barrel 4 is made of a material that has a higher thermal expansion coefficient than the laser holder 2, for example, the lens barrel 4 is made of brass and the laser holder 2 is made of iron. m has been completed. Therefore, if the screws are arranged in the position shown in Fig. 4, the distance A from the light emitting point of the semiconductor laser 1 to the screw 5'1 is longer than the distance A from the principal point of the collimator beam /, f3 to the screw 5 housing. The distance B is longer than the distance B. On the other hand, since the thermal expansion coefficient of the material of the lens barrel 4 is higher, it suppresses fluctuations in the distance @L from the light emitting point of the semiconductor radar 1 to the principal point of the collimator lens 3 due to temperature changes. becomes possible.

[Problem to be solved by the invention]

However, in the above conventional example, there is no regulation regarding the mounting position of the screw 5, and the conditions for obtaining the maximum effect (i.e., minimizing the variation in distance L due to temperature change) are unclear. If the screw is placed on the principal point of the collimator lens 3 as shown in Figure 5, the effect will be completely eliminated. [Purpose] The present invention was made in view of the problems of the prior art described above, and its purpose is to provide a light source device that makes it possible to minimize changes in the distance between the light emitting point and the principal point of the collimator lens due to temperature changes. Our goal is to provide the following.

[Means to solve the problem]

According to the present invention, the above object is achieved by fixing the light emitter and fc first
and a second holder to which a collimator lens is fixed are interconnected at a predetermined position, the second holder having a coefficient of thermal expansion as large as that of the first holder. The ratio of the distance from the connection position to the light emitting point housing and the distance from the connection position to the principal point 1 of the collimator lens is determined by the coefficient of thermal expansion of the first holder and the coefficient of thermal expansion of the second holder. This is achieved by a light source device configured so that the ratio is approximately the reciprocal of the ratio with the coefficient of thermal expansion.

〔Example〕

Hereinafter, embodiments of the present invention will be explained specifically and in detail based on the drawings. FIG. 1 is a sectional view showing a first embodiment of the light source device of the present invention. Note that the configuration of each member in FIG. 1 is the same as that of the conventional example shown in FIG. 4, and therefore a description thereof will be omitted.

In the first case, the thermal expansion coefficient of the material of the laser holder 2 is iKa, and the thermal expansion coefficient of the material of the lens barrel 4 is fit-K.
b, the position of the screw 5 is arranged so as to satisfy the following relationship. Further, the collimator lens 3 converts the beam of the semiconductor laser 1 into a parallel beam of light through the collimator lens 3.
When the focal length of is t, B becomes B = A - t (2).

As shown in equation (1), A - Ka = B-Kb Therefore, A-Ka = (A-L)Kb A●Ka = A-Kb-t-Kb KmA - Kb-A = - Kb-tA (Ka -
Kb) ” - KbItt A 1 A (1 t - Ka/Kb) From the above, set the distance A from the light emitting point of the semiconductor laser 1 to the screw 5 housing with respect to the focal length t of the collimator lens 3 as above. Then, the focal length t'6 will always remain constant against temperature changes.
can be kept constant.

For example, the focal length of the collimator lens ftt = 7.6
m, Ka=11.7 assuming that the material of the laser holder 2 is iron.
X1σA, assuming that the material of the lens barrel 4 is brass, Kb=
If it is 39.7×10 /°C, then = 10.8 cod.

2 and 3 are a sectional view and a perspective view showing a second embodiment of the light source device of the present invention.

In FIGS. 2 and 3, the laser holder 2 and the lens barrel 4 are fixed with an adhesive 11. As mentioned above, in the first embodiment, the distance from the light emitting point of the semiconductor laser 1 to the other end of the lens barrel is inevitably much longer than the pointless distance L of the collimator lens 3, and the distance between This fixing method increases the size of the light source device and does not contribute to the miniaturization required for the optical head. Therefore, in the second embodiment, the total length of the light source device is minimized by fixing the laser holder 2 and the lens barrel 4 by gluing them at their ends. [Effects of the Invention] As explained above, according to the present invention, the second holder to which the collimator lens is fixed has a larger coefficient of thermal expansion than the first holder to which the light emitter is fixed. The thermal expansion coefficient of the first holder and the ratio of the distance from the fixed part of the two to the light emitting point housing and the distance from the fixed part to the principal point of the collimator lens are determined by the coefficient of thermal expansion of the first holder and the second holder. A light source that can emit a highly accurate parallel light beam without being affected by shadows caused by temperature changes by fixing the first holder and the second holder at a position that is approximately the reciprocal of the ratio to the coefficient of thermal expansion. equipment can be provided.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a first embodiment of the light source device of the present invention, FIGS. 2 and 3 are a sectional view and a perspective view showing the second embodiment of the light source device of the present invention, and FIG. FIG. 5 is a sectional view showing a conventional example of a light source device. 1...Semiconductor laser%2...Ledeholder 3.
... Collimator lens, 4... Lens barrel, 5...
screw.

Claims (1)

[Claims] (1) In a light source device in which a first holder to which a light emitter is fixed and a second holder to which a collimator lens is fixed are interconnected at a predetermined position, the second holder is The holder is made of a material having a coefficient of thermal expansion larger than that of the holder 1, and the ratio of the distance from the connection position to the light emitting point to the distance from the connection position to the principal point of the collimator lens is
A light source device characterized in that the ratio is approximately the reciprocal of the coefficient of thermal expansion of the first holder and the coefficient of thermal expansion of the second holder.