JPH01149234A - Optical head - Google Patents

Abstract

PURPOSE:To erase variation in a triangle prism outgoing direction and a detecting error in a focus position detecting system and a track position detecting system at the time of changing an environmental temperature and to improve reliability by specifying the material of a triangle prism to convert the light flux shape of an outgoing light from a semiconductor laser with the refraction of light. CONSTITUTION:A triangle prism 3 is provided to convert the light flux shape of the outgoing light from a semiconductor laser 1 by the refraction of the light and the material of this triangle prism 3 is obtained to satisfy the condition of an expression I. In the expression I, a deltan/deltalambda is the wavelength dispersion of the triangle prism refracting rate and a deltalambda/deltaT is the temperature coefficient of a semiconductor laser oscillating wavelength. Thus, to the change of the environmental temperature, the fluctuation of the refracting rate in the material of the triangle prism is erased and the change of the direction of the triangle prism outgoing light is not generated. Then, the detecting error is not generated in focus error detection and track position detection and the device of the high reliability can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical head using a semiconductor laser as a light source, and more specifically, the present invention relates to an optical head using a semiconductor laser as a light source. This invention relates to an optical head that is used after being converted into a predetermined shape.

[Conventional technology]

FIG. 2 shows the main parts of the optical system of a conventional optical head disclosed in, for example, Japanese Patent Application Laid-Open No. 56-41. This converts the intensity distribution of light from a semiconductor laser by changing the intensity distribution of the light from the semiconductor laser.
A collimator lens (2) and a triangular prism (4) for correcting the intensity distribution of light from the semiconductor laser (1) are arranged in the optical path from the laser beam.

Normally, the output light from a semiconductor laser exhibits an elliptical intensity distribution. For example, as shown in Figure 3 (a), the intensity distribution at the output destination has an approximate ratio of the short axis to the long axis at the 1/e2 value. It becomes a 1:2 ellipse (5). By the way, in order to accurately record, reproduce, and erase information on an information recording medium, the light spot focused by the objective lens must be shaped into a nearly perfect circle (6), as shown in Figure (b). It is necessary to become.

In Figure 2, the emitted light from the semiconductor laser (1) enters the collimator lens (2) K, a triangular prism (4) is placed behind the collimator lens (2), and the collimator lens (2) parallelizes the light. The elliptical laser beam shown in FIG. 3(a) K is expanded only in the minor axis direction by a triangular prism (4), and converted into a perfect circular beam as shown in FIG. 3(b).

[Problem that the invention seeks to solve]

Conventional optical heads that use optical systems to change the shape of the light flux change the shape of the light flux through refraction of the triangular prism as described above, so two problems arise when the environmental temperature changes. arise. The first is that the refractive index of the material used for the triangular prism changes due to temperature changes, and the direction of the light emitted from the triangular prism changes, as shown by the broken line in Figure 2.The second is that the temperature changes. The wavelength dispersion of the triangular prism occurs when the semiconductor laser oscillation wavelength changes due to the change, and the direction of the light emitted from the triangular prism similarly changes. For this reason, when the direction of the light emitted from the triangular prism changes, there are problems such as detection errors occurring in the focal position detection optical system and track position detection system of the optical head.

This invention was made to solve the above-mentioned problems, and eliminates the fluctuation of the triangular prism output direction when the environmental temperature changes, and eliminates detection errors in the focal position detection system and track position detection system. The purpose is to obtain a highly reliable optical head.

[Means for solving problems]

In the optical head according to the present invention, the material of the triangular prism that converts the shape of the beam of light emitted from the semiconductor laser by refraction of the light satisfies the following conditions.

aT θλ aT where anlaT: Temperature coefficient of refractive index of triangular prism anlδλ: Wavelength dispersion of refractive index of triangular prism aλ/a'f: Temperature coefficient of semiconductor laser oscillation wavelength On the other hand, by eliminating variations in the refractive index of the material of the triangular prism, no change occurs in the direction of the light emitted from the triangular prism. Following the lens (2), a triangular prism (3) is arranged in the optical path from the semiconductor laser (1), and the semiconductor laser (
The diverging light flux emitted from the collimator lens (2)
) becomes a parallel beam of light, and the triangular prism (3) changes the beam shape.
3) is made of a material that does not cause changes in the direction of the luminous flux after exiting the triangular prism due to changes in environmental temperature. In order to achieve this effect, when there is a change in the environmental temperature, the oscillation wavelength of the semiconductor laser (1) and the refractive index of the material of the triangular prism (3) change, and the oscillation wavelength of the semiconductor laser (1) changes. As a result, the refractive index of the material of the triangular prism (3) changes due to the wavelength dispersion of the triangular prism (3).
AnlaT is the rate of change in the refractive index of a triangular prism due to temperature.
(°C), and the rate of change in refractive index depending on the wavelength of the incident light is an
/θλ (7°C), and the rate of change of the oscillation wavelength of the semiconductor laser (1) due to environmental temperature is θλ/eT (nm/°C). If the environmental temperature changes to T, the triangular prism in this example The refractive index variation ΔN in (3) is tM = anlaT X ΔT+δn/aλ×aλ/
aT X aT (1).

In this way, it is necessary that ΔN=0 with respect to changes in the environmental temperature.

That is, θTaλ c? T is a condition under which the direction of light emitted from the triangular prism (3) does not change with respect to temperature changes.

In addition, the following materials are available as materials that satisfy the above conditions. Normally, the oscillation wavelength of the semiconductor laser (1) increases by about 5 to 6 nm θλ when the environmental temperature rises by 20°C, so one wavelength is about 0.25 to 0.3 nm/'C.

Furthermore, according to the optical glass list of Fifroki Optical Glass Manufacturing Co., Ltd., optical glass ZK7 (refractive index n-1,50268 at a wavelength of 780 nm) has a refractive index of 760 nm to 8.
In the wavelength range of 00 nm, approximately, and the above (
2) The formula is satisfied. That is, an an
aλ δT δλ δT =6X1G-6+(-2X10-')X(0,25~0
．． 3)=IX10-6~0.

〔Effect of the invention〕

As described above, according to the present invention, a triangular prism made of a material that satisfies certain conditions is used so that the direction of light emitted from the triangular prism does not change due to fluctuations in environmental temperature, so focus error can be detected. , it is possible to obtain highly reliable track position detection without any difference in detection slope.

[Brief explanation of the drawing]

Fig. 1 is a side view of the main part of an embodiment of the present invention, Fig. 2 is a side view of the main part of a conventional optical head, and Figs. FIG. (1) Semiconductor laser, (21- Collimator lens, (3) Triangular prism. In each figure, the same reference numerals indicate the same or equivalent parts. Agent Soga Michi Teru 1.-'-゛11.7.
;; Figure 1 Figure 2 Figure 3 (a) (b)

Claims (1)

[Scope of Claims] A signal is recorded on the recording medium by condensing light emitted from a semiconductor laser onto a recording medium and detecting at least one of reflected light and transmitted light from the recording medium.
The optical head for reproducing and erasing is provided with a triangular prism that converts the shape of the beam of light emitted from the semiconductor laser by refraction of the light, and the material of the triangular prism is ∂n/∂T+∂n/∂λ× ∂λ/∂T=0 where ∂n/∂T: temperature coefficient of refractive index of triangular prism ∂n/∂λ: wavelength dispersion of refractive index of triangular prism ∂λ/∂T: temperature coefficient of semiconductor laser oscillation wavelength. An optical head characterized by satisfying the following requirements.