JPH04241235A - Optical system for optical disk device - Google Patents

Abstract

PURPOSE:To extend the allowable width of an angle error and to facilitate assembling work by providing a composite prism having a separation surface and a reflection surface which are parallel with each other in a specified optical path. CONSTITUTION:A laser beam is reflected on a disk and made incident on the composite prim 4. A part of the laser beam is transmitted through the separation surface 4b and condensed on a servo sensor 8 as the laser beam for detecting an error. On the other hand, a luminous flux which is reflected and goes toward the optical disk is reflected by the reflection surface 4a and the separation surface 4b which are parallel with each other, and the parallel shift amount of the luminous flux is small and the outgoing angle thereof is not changed even when the prism 4 is set at a different angle from a normal one. Since the reflected light beam to the sensor is only transmitted through the separation surface 4b, it shifts in parallel with the normal light beam. Thus, the angular deviation of the luminous flux is restrained and the allowable width of the angle error is extended.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical system for an optical disc device that converges a luminous flux emitted from a light source onto an optical disc and detects a signal by receiving reflected light from the optical disc.

0002

2. Description of the Related Art FIG. 3 shows an optical system of a conventional magneto-optical disk device. This optical system includes a light emitting system consisting of a semiconductor laser 1, a collimator lens 2, a shaping prism 3, a compound prism 4 having two half mirror surfaces 4a and 4b, a condensing lens 5, a cylindrical lens 7,
It consists of an error signal detection system consisting of a servo sensor 8, and a magnetic recording signal detection system consisting of a condenser lens 5, a λ/2 plate 9, a polarizing beam splitter 10, and data sensors 11a and 11b.

The light beam emitted by the semiconductor laser 1 passes through the half mirror surfaces 4a and 4b of the composite prism 4 and heads toward the magneto-optical disk, and the reflected light from the optical disk is reflected by each half mirror surface and is directed to the sensor. reach

0004

[Problem to be Solved by the Invention] When the positional relationship between the composite prism, the light emitting system, and each detection system is set as described above, when the composite prism 4 is in the normal position shown by the solid line in FIG. The light beam also passes through the regular position as shown by the solid line.

However, if the composite prism 4 is installed at an angle different from the normal angle as shown by the broken line in FIG. Shift parallel as shown,
The reflected light heading toward the detection system also goes in a direction different from the normal direction, as shown by the broken line. In the optical system in which the sensor and light source of FIG. 3 are replaced, the angular deviation of the composite prism appears as an angular deviation of the light beam incident on the optical disk.

[0006] As described above, when the angle of emission of the light beam toward the resensor or the optical disk changes depending on the set angle of the compound prism, even a slight difference in the set angle of the compound prism may cause the light beam to deviate from the sensor. Since it is no longer able to function as an optical system, strict precision is required for assembling the composite prism, making the assembling work complicated and the fixing method complicated.

[0007]

[Object of the Invention] The present invention has been made in view of the above-mentioned problems, and an object thereof is to provide an optical system for an optical disc device that has a wide tolerance for errors in the setting angle of a composite prism and is easy to assemble. shall be.

[0008]

[Means for Solving the Problems] In order to achieve the above object, an optical disc device according to the present invention uses a composite prism having a separating surface and a reflecting surface that are parallel to each other to receive incident light directed toward an optical disc from a light source and light from the optical disc. The light source and the light-receiving element are placed in the optical path of the reflected light heading toward the element, and the light source and the light-receiving element are placed in a position where either the incident light or the reflected light is transmitted through the separation surface, and the other is reflected by the separation surface and the reflection surface. It is characterized by what it did.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained below based on the drawings. 1 and 2 show an embodiment in which the present invention is applied to an information recording/reproducing apparatus for a magneto-optical disk.

As shown in FIG. 1, a diverging beam emitted from a semiconductor laser 1 is made into a parallel beam by a collimator lens 2, and is shaped into a circular cross-section by a shaping prism 3, with a reflecting surface 4a parallel to each other. The light enters the composite prism 4 having a separation surface 4b. The light beam incident on the composite prism 4 and directed toward the magneto-optical disk is reflected by the reflecting surface 4a and the separation surface 4b, exits in the direction indicated by the arrow in the figure, and is reflected onto the magneto-optical disk by an objective lens (not shown). Converged. In this example, the reflection surface 4a is a total reflection surface, and the separation surface 4b is a half mirror surface.

The light beam reflected by the disk enters the composite prism 4 again. A part of the reflected light passes through the separation surface 4b, is turned into convergent light by the condenser lens 5, and enters the half mirror prism 6. The light beam transmitted through the half mirror prism 6 is sent to a servo sensor 8 for error signal detection via a cylindrical lens 7 attached to one surface of the half mirror prism 6.
Focus the light upward. The servo sensor 8 has a light-receiving area divided into four parts in the shape of a square, and by calculating the output of each area, it generates a focus error signal using the astigmatism method and tracking using the push-pull method. Generates an error signal.

The light beam reflected by the half mirror prism 6 has its polarization direction rotated by 45° by a λ/2 plate 9 attached to the prism, and then passes through a polarizing beam splitter 10.
incident on . The P-polarized component of the light beam incident on the polarizing beam splitter 10 passes through the cemented surface and is focused on the first data sensor 11a, and the S-polarized component is reflected by the cemented surface and focused on the second data sensor 11b. Shine. The polarization direction of the laser beam incident on the magneto-optical disk rotates due to the magnetic Kerr effect in accordance with the magnetization direction of the disk at the position where the spot is imaged, so by rotating this by 45 degrees,
By separating the S component into S components and detecting them with separate light receiving elements, the recording signal can be read out from the difference in intensity.

Next, the influence of the placement error of the composite prism 4 will be explained. When the composite prism 4 is attached to the regular position shown by the solid line, the incident light and reflected light pass through the regular position shown by the solid line.

When the composite prism 4 is attached at an angle different from the normal angle as shown by the broken line, the light beam incident on the optical disk is transmitted to the reflecting surface 4a and the separating surface 4b which are parallel to each other.
As a result, although the light is shifted in parallel as shown by the broken line, the emission angle does not change, and the amount of shift is also small. Since the reflected light heading toward the sensor only passes through the separation surface 4b, it is only shifted parallel to the normal light beam as shown by the broken line.

[0015] In this way, by reflecting the light incident on the optical disc on two mutually parallel surfaces and transmitting the reflected light from the optical disc, it is possible to prevent the angular deviation of the composite prism from causing the angular deviation of the light beam, and The permissible range of prism installation angle error can be wider than before.

In the above example, both the reflecting surface 4a and the separating surface 4b may be half mirror surfaces, and when applied to a read-only optical disk device, the separating surface may be a polarization separating surface. There may be.

Furthermore, in the above embodiment, the incident light from the light source toward the optical disk is reflected twice and the returning light is transmitted, but conversely, the configuration is such that the incident light is transmitted and the returning light is reflected twice. You can also use it as

[0018]

[Effect] As explained above, according to the optical disc device of the present invention, even if the arrangement angle of the composite prism deviates from the design value, no angular deviation of the luminous flux occurs. The percentage of deviation is small. Therefore, the mounting accuracy of the composite prism is relaxed, and the mounting work can be facilitated. Further, even if the position of the composite prism changes due to temperature changes after installation or changes over time, the deviation of the light beam can be kept small, and the reliability of the device can be improved.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of an optical system of an optical disc device according to the invention.

2 is an enlarged view of a composite prism portion of the optical system in FIG. 1. FIG.

FIG. 3 is an explanatory diagram of an optical system of a conventional optical disc device.

4 is an enlarged view of the composite prism portion of the optical system of FIG. 3. FIG.

[Explanation of symbols]

1 Semiconductor laser 4 Composite prism 4a Reflective surface 4b Separation surface 8 Servo sensor 11a, 11b data sensor

Claims (7)

[Claims] Claim 1: A light source that generates light incident on an optical disk;
The light source and the light receiving element include a light receiving element that receives reflected light from the optical disk, and a composite prism that is provided in the optical path of the incident light and the reflected light and has a separating surface and a reflecting surface that are parallel to each other. An optical system for an optical disc device, characterized in that the optical system is disposed at a position where one of the incident light and the reflected light is transmitted through the separation surface, and the other is reflected by the separation surface and the reflection surface. 2. The optical system of an optical disc device according to claim 1, wherein the separation surface is a half mirror surface. 3. The optical system of an optical disc device according to claim 1, wherein the reflective surface is a total reflection surface. 4. A light source that generates light incident on an optical disk;
a light receiving element that receives reflected light from the optical disk; a separating surface that separates the optical path of the incident light and the reflected light; and an incident light that is provided parallel to the separating surface and is reflected by the separating surface; 1. An optical system for an optical disc device, comprising: a composite prism having a reflecting surface that reflects one of the reflected lights. 5. A light source that generates light incident on an optical disk;
a light-receiving element that receives reflected light from the optical disk; a separation surface that separates the reflected light from an incident optical path; 1. An optical system for an optical disc device, comprising: a composite prism having a guiding reflective surface. 6. A light source that generates light incident on an optical disk;
a light receiving element that receives reflected light from the optical disk; a reflective surface that reflects the incident light; and a light receiving element that is provided parallel to the reflective surface and that reflects the incident light reflected by the reflective surface and guides it to the optical disk; An optical system for an optical disc device, comprising: a composite prism having a separation surface that transmits the reflected light and guides it to the light receiving element. 7. A light source that generates light incident on an optical disk;
It has a light receiving element that receives reflected light from the optical disk, and a reflecting surface and a separating surface that are parallel to each other, and the separating surface reflects either the incident light or the reflected light and transmits the other. An optical system for an optical disc device, wherein the reflecting surface includes a composite prism that reflects the incident light and the light reflected by the separation surface among the reflected light.