JPH01196742A - Optical recording and reproducing device - Google Patents

Abstract

PURPOSE:To prevent the change of a light spot position on an information recording medium with a simple element constitution by using two refracting prisms whose constants are so selected that the variation of the final projection angle of parallel beams is about zero even in case of the change of wavelength. CONSTITUTION:The divergent light outputted from a semiconductor laser 1 is converted to parallel beams having an elliptic section by a collimator lens 2 and is made incident on a first refracting prism 5. The projected light refracted in this prism 5 is made incident on a second refracting prism 6 and is refracted, and the projected light having an approximately circular section is outputted from the exit end face perpendicularly and is formed as a light spot on an information recording medium by an objective lens. Refractive indexes, vertical angles, angles of incidence and exit, and values of refractive index change to wavelength change of both prisms are so selected that the projection angle from the prism 6 is about zero even in case of the change of wavelength in the laser 1, thereby always stably performing recording, reproducing, and erasing.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical recording/reproducing device that can be used in any system including an optical device for recording or reproducing information.

Conventional Technology The modern era is called the information age, and the technology development of high-density, large-capacity memory, which forms the core of this age, is actively being carried out.

In addition to the above-mentioned high density and large capacity, the capabilities required of memory include high reliability and high speed access, and optical disk memory is attracting the most attention as a device that satisfies all of these requirements. An optical disk memory is a device that optically records information on a recording medium, and recently, a lot of research has been conducted on magneto-optical disks that can also erase recorded information.

Semiconductor lasers are mainly used as light sources for optical disk memories.

FIG. 2 shows a far-field image of a semiconductor laser and divergent light from the semiconductor laser. In FIG. 2, 1 is a semiconductor laser.

The semiconductor laser 1 emits light differently in a direction parallel to and perpendicular to the laser chip bonding surface.

That is, the far-field image of the light emitted from the semiconductor laser 1 is elliptical. If the light from this semiconductor laser 1 is focused using a normal optical system, the shape of the light spot will also become an ellipse. In order to avoid this problem, in the playback-only optical system for optical digital audio discs, a collimating lens with a small numerical aperture (N) is used, that is, only the central part of the elliptical beam of the semiconductor laser 1 is used, and the other By discarding the portion, a circular light spot is obtained on the disk. However, in a recording/reproducing optical system using the semiconductor laser 1, the above-described method is disadvantageous because the optical power usage efficiency becomes low. Therefore, conventionally, the following spherical method has been used.

These conventional examples are commonly used and described in general optical system books.

Hereinafter, a conventional optical recording/reproducing apparatus as described above will be explained with reference to the drawings.

FIG. 3 shows an example of a conventional optical recording/reproducing device. In FIG. 3, 1 is a semiconductor laser, 2 is a collimating lens, 3 is a mirror, and 4 is a refractive prism.

FIG. 3 is a sectional view taken along arrow P in FIG. 2, that is, a side parallel to the semiconductor laser chip bonding direction.

The operation of an example of the conventional optical recording/reproducing apparatus configured as described above will be explained below.

The light from the semiconductor laser 1 is made into a parallel beam by the collimating lens 2, but the cross-sectional shape of the beam here is an ellipse. (Mu human cross section) This parallel beam is reflected by the mirror 3 and enters the refracting prism 4. The refraction prism 4 has a triangular prism shape, and expands by refracting only the side parallel to the semiconductor laser chip bonding direction from the collimating lens 2, converting it into a substantially circular beam. (Cross section B-B
However, in the conventional configuration shown in FIG. 4, when the output of the semiconductor laser 1 changes and the wavelength of the diverging beam changes, the initial optical path P (refracting prism 4 Output angle θ
β2=o) changes to the optical path Q (outgoing angle θβ'2).

This change in the output angle is caused by a light spot (not shown above) formed on the information recording medium by the parallel beam entering the objective lens.
This has caused a problem in that stable recording, erasing, and reproducing cannot be achieved because of positional fluctuations.

This change in the output angle will be described in detail. For example, in the refractive prism 4, refractive index nβ: 1.51° apex angle β-6
9°, incident angle θβ1=51.13°, exit angle θβ2=0
°, refractive index change with wavelength change Dβ=-1,5x1
o /nm, and the tilt angle γ=29.
6° and the incident angle θm = 29.6°, the output of the semiconductor laser 1 changes and the wavelength changes Δλ = 10 nm.
Suppose that occurs. At this time, the output angle of the refracting prism 4 changes to θβ'2=0.008°, and the amount of change is not approximately zero, causing the above-mentioned problem.

In view of the above-mentioned problems, the present invention provides an optical recording and reproducing device that has a simple element configuration with selected constants, has a function of converting into a substantially circular beam, and can reduce the amount of change in the emission angle to substantially zero. be.

Means for Solving the Problems In order to achieve this object, the optical recording/reproducing device of the present invention has an expansion of half-maximum full-angle θ1 in the horizontal direction and half-maximum full-angle θ (\θ/) in the vertical direction. A semiconductor laser that outputs a diverging beam having a υ angle and an anisotropic intensity distribution with respect to the optical axis, a collimating lens that converts the diverging beam into a parallel beam, and an element having two surfaces parallel to the vertical direction, A first refractive prism (refractive index nα, apex angle α, incidence angle 1.output angle 2.change in refractive index with respect to wavelength change Da) on which a parallel beam is incident and refracted twice; An element having an entrance end face and an exit end face, in which the light emitted from the first refraction prism enters and is refracted, and the exit end face is perpendicular to the refracted light beam as the second refraction prism (refractive index nβ , Vertical angle Vertical angle β Incident incident angle 1. Output angle θβ 2. Change in refractive index with respect to wavelength change Dβ), and an objective lens into which the emitted light from the second refraction prism enters and forms a light spot on the information recording medium. As the output of the semiconductor laser changes and the wavelength of the diverging beam changes, the emission angle of the first refracting prism changes to θα′2.
The incident angle to the second refracting prism changes to 71 according to θβ′1, and the exit angle of the second refracting prism changes to θ
The refractive index nct+ and the apex angle α of the first refractive prism are set so that the amount of change θβ2−θβ; in the exit angle of the second refractive prism becomes approximately zero when the output angle changes to β′2.

Incident angle θ, 1. Output angle θ (g7+refractive index change with respect to wavelength change), refractive index nβ of the second refractive prism.

Vertical angle β, incident angle θβ1. Output angle θβ2. The configuration is such that the refractive index change Dβ with respect to the wavelength change is selected.

Effect: With this configuration, a parallel beam with an elliptical cross section passes through a collimating lens and is converted into a parallel beam with an approximately circular cross section through two refracting prisms, and the output of the semiconductor laser changes. Therefore, even if the wavelength of the diverging beam changes, the amount of change in the final exit angle is approximately zero,
Stable recording, reproduction, and erasing can be achieved without causing any change in the position of the light spot on the information recording medium.

EXAMPLE An example of the present invention will be described below with reference to the drawings. FIG. 1 shows an optical recording/reproducing apparatus according to an embodiment of the present invention. FIG. 1 is a sectional view taken along arrow P in FIG. 2, that is, a side parallel to the semiconductor laser chip bonding direction. In FIG. 1, 1 is a semiconductor laser, 2 is a collimating lens, 6 is a first refracting prism, and 6 is a second refracting prism B.

The operation of the optical recording/reproducing apparatus configured as described above will be explained below. The diverging light from the semiconductor laser 1 is made into a parallel beam by the collimating lens 2, but the cross-sectional shape of the beam here is an ellipse. (Moo human cross section) This parallel beam enters the first surface of the refracting prism Muro with an apex angle α at an incident angle θ41, is refracted at a refraction angle θ43, and is refracted at the second surface.
It is incident on the surface at an incident angle of 0.4 and is reflected. The reflected beam from the second surface enters the first surface again at an incident angle of θ45 and exits at an angle of 0.
．． 2, it is refracted and emitted. The beam emitted from the refracting prism 5 enters the refracting prism B6 at an incident angle θβ1, and the beam is refracted at a refracting angle θβ1.
5, and perpendicular to the output end face (incident angle θβ4=o
, the light is emitted at an emission angle θβ2=o). (In the above figure, the optical path P is indicated by the dotted chain line.) In this optical path P, by refracting only the side parallel to the chip bonding direction of the semiconductor laser 1 from the collimating lens 2, the elliptical section parallel beam (cross section person-person) is refracted. Enlarged, almost circular cross-section parallel beam (cross section B-B)
is being converted to .

When the output of the semiconductor laser 1 changes and the wavelength of the diverging beam changes, the optical path P changes to an optical path Q shown by a broken line in the figure (output angle θβ of the refractive prism B6). As mentioned in the conventional example in Fig. 3, the amount of change in the final exit angle θβ2−θβ
5 becomes a problem, but here the refractive prism 5. The constants of the refracting prism B6 are selected as follows.

For example, in a refractive prism, the refractive index is n.

=1.67, apex angle α=12.7°, incident angle θct1:6
7.6°, incident angle θ, 2 = 8.2°, refractive index change with respect to wavelength change = -3.9X10 /nm, refractive index nβ = 1.51 in refractive prism B6.
.

Vertex angle β = 55.6°, incident angle θβ, = 58.8°,
Output angle θβ2=0°・Refractive index change Dβ with respect to wavelength change
Suppose that a wavelength change Δλ==10 nm occurs in the semiconductor laser 1 when the wavelength is −1.8×10 /nm.

At this time, the amount of change in the exit angle of the refracting prism 5 is θ
. 2-θ, '2 = o, 011°, but the amount of change in the exit angle of the refracting prism B6, which is the final exit angle, is θβ2
-θβ'2--3 X 10 , which is approximately zero.

As described above, according to this embodiment, two refracting prisms B are used, and even if the final emission angle of the parallel beam passing through both prisms changes in wavelength, the amount of change is approximately zero.
By selecting the constants of both prisms, it has the function of converting a parallel beam with an elliptical cross section into a parallel beam with a substantially circular cross section with a simple element configuration, and the amount of change in the final output angle is approximately zero, that is,
No positional change of the light spot occurs on the information recording medium.

Stable recording, playback, and erasing can be achieved.

Effects of the Invention The present invention provides a semiconductor laser that is a light source and outputs diverging light with different divergence angles in the horizontal and vertical directions on a cemented surface, a collimating lens that converts this diverging light into parallel light, and a cemented surface of the semiconductor laser. a first refracting prism having two surfaces parallel to the vertical direction, into which parallel light is incident, refracted twice and emitted; and an entrance end surface and an exit end surface parallel to the vertical direction of the cemented surface;
Outgoing light from the first refraction prism enters and is refracted,
A semiconductor device comprising: a second refraction prism whose output end face is perpendicular to the refracted light beam; and an objective lens through which light emitted from the second refraction prism enters to form a light spot on an information recording medium. The first... The refractive index, apex angle, and incidence angle of the second refractive prism,
Output angle.

By selecting the right angle for the refractive index change relative to the wavelength change, it has the function of converting a parallel beam with an elliptical cross section from a collimating lens into a parallel beam with an approximately circular cross section with a simple element configuration, and the final output angle is approximately zero. In other words, stable recording and recording without causing any change in the position of the light spot on the information recording medium
This makes it possible to achieve an excellent optical recording and reproducing device that can realize reproduction and erasing.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an optical recording/reproducing device according to an embodiment of the present invention, FIG. 2 is a perspective view showing a semiconductor laser and a far-field image of divergent light from the semiconductor laser, and FIG. 3 is a conventional optical recording/reproducing device. 1 is a schematic diagram showing a type recording/reproducing device. 1... Semiconductor laser, 2... Collimating lens, 3... Mirror, 4, 6.6...
...Refraction prism. Name of agent Patent attorney Toshio Nakao and one other person (C
) 1- Semiconductor laser Fig. 2/- One-step beauty (Main laser 2- Cosome lens

Claims (1)

[Claims] A semiconductor laser that outputs a diverging beam having a divergence angle of full angle at half maximum θ_1 in the horizontal direction and full angle at half maximum θ_⊥ (≠θ_1) in the vertical direction on the bonded surface and whose intensity distribution is anisotropic with respect to the optical axis; a collimating lens that converts the beam into a parallel beam, and a first refractive prism (refractive index n_α, apex angle α, incidence Angle θ_α_1,
Output angle θ_α_2, refractive index change D_α with respect to wavelength change
), the element has an entrance end face and an exit end face that are parallel to the vertical direction, the light emitted from the first refracting prism is incident and refracted, and the exit end face is perpendicular to the refracted light beam. second refractive prism (refractive index n_β, apex angle β
, an incident angle θ_β_1, an exit angle θ_β_2, a refractive index change D_β) with respect to a wavelength change, and an objective lens into which the emitted light from the second refraction prism enters and forms a light spot on the information recording medium, By changing the output of the semiconductor laser and changing the wavelength of the diverging beam,
The output angle of the first refraction prism changes to θ_α′_2, the incident angle to the second refraction prism changes to θ_β′_1 according to θ_α′_2, and the angle of incidence on the second refraction prism changes to θ_β′_1 according to θ_β′_1. The refractive index of the first refraction prism is set such that when the output angle of the refraction prism changes to θ_β'_2, the amount of change in the output angle of the second refraction prism θ_β_2 - θ_β'_2 becomes approximately zero. n_α, vertical angle α, incident angle θ_
α_1, exit angle θ_α_2, refractive index change D_α with respect to wavelength change, refractive index n_β of the second refraction prism,
An optical recording/reproducing device characterized in that an apex angle β, an incident angle θ_β_1, an exit angle θ_β_2, and a refractive index change D_β with respect to a wavelength change are selected.