JPH0443328B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a recording/reproducing optical head used when writing or reading certain information to or from a recording medium.

Prior Art The main part of a conventional recording and reproducing device that writes information to and reads information from a rotating disk-shaped recording medium (hereinafter simply referred to as a disk) is described in the third section.
As shown in the figure. In the same figure, the recording/reproducing device is a disk motor 2 for rotating a disk 1.
and an optical head 3 for recording or reproducing data on the disk 1.
The components include a semiconductor laser 4 which is a light source, a collimator lens 5 which converts the parallel light into parallel light, an objective lens 6 which forms an image of the parallel light onto the disk 1, a light receiving element 7 which receives reflected light from the disk 1, and a disk 1.
It has a beam splitter 8 for returning reflected light from the light to the light receiving element 7, a lens 9 for focusing the light on the light receiving element 7, and the like. A detailed structure between the collimator lens 5 and the semiconductor laser 4 in this optical head 3 is shown in FIG.

The collimator lens 5 is held by a collimator lens holder 11, and the semiconductor laser 4 is held by a semiconductor laser holder 13. This semiconductor laser holder 13 has a mounting surface 13A facing the collimator lens 5, and a screw 1 is attached to the end of the collimator lens holder 11.
2, and this mounting surface 13A
A semiconductor laser 4 is directly attached to. By controlling the dimensions A ¹ , A ² , and A ³ shown in FIG. 2 to a predetermined dimensional accuracy, the distance between the light emitting point B of the semiconductor laser 4 and the collimator lens 5 is controlled to a predetermined value. are doing.

Problem to be Solved by the Invention However, in such a configuration, when a temperature change occurs, the light emitting point of the semiconductor laser 4 and the collimator lens 5
Since the distance from the collimator lens changes, it is necessary to increase the focal length of the collimator lens in consideration of compensation for temperature changes. At this time, if the NA of the collimator lens is made small in order to downsize the device, the loss of light quantity will increase, requiring greater power from the semiconductor laser, which will shorten the life of the semiconductor laser. In addition, to reduce light loss,
There was a problem in that if the NA was increased, the outer diameter of the lens would become larger, resulting in an increase in the size of the device.

The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide an optical head that has less light loss, can be made smaller in size, and is less affected by changes in ambient temperature. With the goal.

Means for Solving the Problems In order to achieve the above object, the present invention includes a semiconductor laser, a collimator lens for converting laser light from the semiconductor laser into parallel light, and a collimator lens holder for holding the collimator lens. , a semiconductor laser holder fixed to one end of the collimator lens holder and having a mounting surface on the side facing the collimator lens, and an intermediate member attached to the mounting surface of the semiconductor laser holder and having the semiconductor laser attached thereto. However, the thermal expansion coefficient of the intermediate member is selected to be larger than that of the semiconductor laser holder.

Effects The present invention has the above configuration so that the direction of distance change caused by temperature change between the semiconductor laser and the collimator lens is opposite to the direction of thickness change caused by temperature change of the intermediate member. Become a relationship. In other words, the amount of change in the thickness of the intermediate member acts to reduce the amount of change in the distance between the semiconductor laser and the collimator lens. As a result, even when ambient temperature changes occur, the amount of change in the distance between the semiconductor laser and the collimator lens can be reduced compared to the conventional method, and the effect of temperature changes on the optical head can be reduced. can.

Embodiments Hereinafter, embodiments of the drawings will be described in detail. FIG. 1 is a sectional view showing the main parts of an optical head according to an embodiment of the present invention. In the figure, parts having the same configuration as the conventional example are given the same numbers as in the conventional example. The collimator lens 5 is held in a collimator lens holder 11 having a structure similar to the conventional one. On the other hand, the semiconductor laser holder 13 holding the semiconductor laser 4 has a mounting surface 13A facing the collimator lens 5.
It is attached to the end of 1 with a screw 12,
A semiconductor laser 4 is attached to this attachment surface 13A via an intermediate member 14. This intermediate member 1
4 is made of a material having a larger coefficient of thermal expansion than the material (for example, aluminum) forming the semiconductor laser holder 13 and the collimator lens holder 11, and the coefficient of thermal expansion and thickness A ⁴ of the material are the same as those of the collimator lens 5 and the mounting surface 13A. The holders 11 and 13 between them thermally expand to move the semiconductor laser 4 into the collimator lens 5.
The semiconductor laser 4 is selected so that when it is moved away from the collimator lens 5, it also thermally expands and moves the semiconductor laser 4 in a direction closer to the collimator lens 5, so that the light emitting point B does not move much. As the material for the intermediate member 14, plastics such as astal resin are preferred because they have a large coefficient of thermal expansion.

Regarding the optical head configured as above,
The effect will be explained below.

The dimensions A ¹ , A ² , A ³ , A ⁴ shown in FIG. The distance is a predetermined dimension. However, A ¹ : Distance from the collimator lens mounting position to the semiconductor laser holder mounting position.

A ² : Distance from the semiconductor laser holder mounting position to the semiconductor laser mounting position.

A ³ : Distance from the semiconductor laser mounting position to the semiconductor laser light emitting point B.

A ⁴ : Thickness of intermediate member 14.

In this state, when the temperature rises during use, the distance between the collimator lens 5 and the mounting surface 13A of the semiconductor laser holder 13 increases due to thermal expansion of the semiconductor laser holder 13 and the collimator lens holder 11. At the same time, the intermediate member 14 and the outer cylinder of the semiconductor laser 4 also expand thermally, so that the mounting surface 13A and the light emitting point B
The distance between the two increases. Therefore, these cancel each other out, and the distance between the light emitting point B of the semiconductor laser and the collimator lens 5 is kept almost constant.

This will be explained in more detail using numerical values.
Now, the intermediate member 14 is made of acetal resin (thickness A ⁴ =
1.8 mm), the change ΔL in the distance between the light emitting point B of the semiconductor laser 4 and the collimator lens 5 caused by the temperature change Δt is determined. From Figure 1,
ΔL is expressed as follows.

ΔL=ΔA ¹ +ΔA ² −ΔA ³ −ΔA ⁴ The linear expansion coefficients of aluminum, copper, and acetal resin are as follows.

Aluminum: α ^AL = 23.9×10 ^-6 Copper: α ^CU = 17.1×10 ^-6 Acetal resin: α ^D = 84.5×10 ^-6 Therefore, ΔA ¹ = Δt・α ^AL・A ¹ ΔA ² = Δt・α ^AL・A ² ΔA ³ = Δt・α ^CU・A ³ ΔA ⁴ = Δt・α ^D・A ^4Here , A ¹ = 4 mm, A ² = 3.8 mm, A ³ = 2.2 mm,
If A ⁴ = 1.8 mm and Δt = 40°C, ΔL = -0.2 μm.

Furthermore, in order to show the effect of implementing the present invention, a comparison will be made with the amount of change in distance in a conventional optical head. In the conventional optical head, the change ΔL' in the distance between the light emitting point B of the semiconductor laser 4 and the collimator lens 5 is, as described above, ΔL'=ΔA ¹ +ΔA' ² −ΔA ³ On the other hand, when the present invention is adopted, the change ΔL' is as follows. Semiconductor laser 4
The change ΔL in the distance between the light emitting point B and the collimator lens 5 is ΔL=ΔA ¹ +ΔA ² −ΔA ³ −ΔA ⁴ .

For comparison, subtracting ΔL from ΔL′ gives ΔL′−ΔL=(ΔA ¹ +ΔA′ ² −ΔA ³ ) −(ΔA ¹ +ΔA ² −ΔA ³ −ΔA ⁴ )=ΔA′ 2 −ΔA ² +ΔA ⁴ = Δt・αAL・A′ ² −Δ t・αAL・A ² +Δt・αD・A ⁴ = Δt {αAL(A′ ² −A ² )+αD・A ⁴ } Here, A ² −A′2 = A ⁴ , and by substituting this into the above equation, ΔL' - ΔL = Δt・A ⁴ (αD - αAL) In other words, if αD > αAL, ΔL' - ΔL is a positive value, and the conventional optical head It is less affected by temperature changes compared to

Effects of the Invention As is clear from the above description, the present invention has a configuration in which a semiconductor laser is held in a semiconductor laser holder having a mounting surface facing the collimator lens via an intermediate member having a large coefficient of thermal expansion. The amount of change in the thickness of the intermediate member acts to reduce the amount of change in the distance between the semiconductor laser and the collimator lens. As a result, the amount of change in the distance between the semiconductor laser and the collimator lens can be reduced compared to conventional optical heads.
The influence of the optical head on temperature changes can be reduced without employing a collimator lens with a large focal length.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view of the main parts of an optical head showing an embodiment of the present invention, FIG. 2 is a schematic sectional view of the main parts of a conventional optical head, and FIG. 3 is a device incorporating the same optical head. FIG. 1... Disc, 2... Disc motor, 3...
...Optical head, 4... Semiconductor laser, 5... Collimator lens, 10... Semiconductor laser holder, 1
DESCRIPTION OF SYMBOLS 1... Collimator lens holder, 13... Semiconductor laser holder, 13A... Mounting surface, 14... Intermediate member, B... Light emitting point.

Claims (1)

[Claims] 1 A semiconductor laser, a collimator lens for converting laser light from this semiconductor laser into parallel light, a collimator lens holder that holds this collimator lens, and a collimator lens holder that is fixed to one end of this collimator lens holder and has a surface facing the collimator lens. a semiconductor laser holder having a mounting surface on a side thereof; and an intermediate member that is attached to the mounting surface of the semiconductor laser holder and has the semiconductor laser attached thereto, and the thermal expansion coefficient of the intermediate member is determined by the thermal expansion coefficient of the semiconductor laser holder An optical head characterized in that the coefficient is selected to be larger than the coefficient.