JPS6273446A - Optical head - Google Patents

Abstract

PURPOSE:To ensure the reproduction of an information signal by providing a phase correction element correcting a phase shift caused when a light beam is reflected in a light reflection means. CONSTITUTION:A light beam L reflected in an information recording medium 62 is reflected in a mirror 58 being a light reflection means and a beam splitter 56 to cause a phase shift, and since a phase correction element 84 correcting the phase shift is provided between the beam splitter 56 being the light reflection means and a polarized beam splitter 68 being an optical analyzer, the phase shift is corrected until the beam reaches the splitter 68. Thus, the phase shift caused when the light beam reflected in the medium 62 is reflected is corrected to reproduce the information signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an optical head in an information recording/reproducing apparatus that records, reproduces, and erases information on an erasable information storage medium using focused light.

[Technical Prelude to the Invention and its Problems] There are already known devices that optically record, reproduce, and erase information on an information recording medium using magneto-optical effects such as the Kerr effect or the Faraday effect. ing. When reproducing information from an information recording medium using such a magneto-optical effect, a light beam is irradiated onto the information recording medium, and the reflected light beam is detected using a photodetector or the like. The information is reproduced using the Kerr effect and the like described above.

However, in devices that utilize such magneto-optical effects, the light beam that is reflected off the information recording medium must be reflected many times before reaching the detection optical system. A phase difference occurs between the P-polarized light component and the S-polarized light component.

For example, taking the mirror 18' shown in FIG. 4 as an example, the phase difference that occurs between the pH light component and the S-polarized light component of the light beam will be explained. As shown in FIG. 4, when the mirror 18' has a structure that utilizes total internal reflection that occurs at the end face of a prism, the phase change of the light beam P (l) is θp, and the phase change of the S polarization component is θp. If the difference between θS1 and both is θ=θρ−θS, each is expressed as follows.

taIlθp/2--n n"Sin" (4-1/c
osψ...(1)...(2) tanθ/2 = tanθρ-θs/2=...
...(3) However, the refractive index ψ of n nibism is the incident angle of the light beam to the end surface of the prism. Here, in equation (3), n -1,5 is the refractive index of the glass.
If we also substitute ψ-45, we get θ-36°91. This θ-36.9 degrees corresponds to approximately λ/9°8, so if total reflection is used as the mirror 18', approximately λ, 7
It can be seen that a phase shift of 9.8 has occurred. Pva
When a linearly polarized light beam containing an optical component and an S-polarized light component is reflected by this mirror 18', it becomes elliptically polarized light rather than completely linearly polarized light due to the above-mentioned phase shift, so information using the magneto-optical effect is generated. If such a mirror 18' is present in the detection optical path of the reproduction light with respect to the recording medium, the S/N ratio of the read signal will decrease due to an increase in the elliptically polarized light component.

In addition, in the case of a structure in which a light reflective coating is used as the mirror 18' and the light beam is reflected on the surface, the characteristics will differ depending on the material of the light reflective coating, but when a metal such as aluminum or chromium is used as the light reflective coating material, These metals themselves have electrical conductivity, and some loss of the light beam occurs when light is reflected. Therefore, a phase shift occurs in the light beam. Furthermore, when a multi-coated surface is used as a metal, the coating material has conductivity and some loss of the light beam occurs when light is reflected.
Similarly, a phase shift occurs. However, the phase shift darkness varies greatly depending on the material and layer structure of the coating material. Incidentally, the above-mentioned matters are also applicable to beam splitters and the like.

That is, in the conventional optical head, when the Kerr rotation angle from the information recording medium 22 is detected by the signal detection system provided in this optical head, there is a difference between the P polarization component and the 81 light component of the light beam. There is a drawback that the S/N ratio of signal detection decreases due to the phase shift that occurs.

1. Purpose of the Invention] The present invention has been made based on the above-mentioned circumstances, and has a very accurate structure that corrects the phase difference of the light beam that occurs in the optical path from the information recording medium to the detection optical system. (The purpose is to provide an optical head that can reliably reproduce words.

[Summary of the Invention 1] In order to achieve the above object, the present invention includes a light source that generates a light beam, an objective lens that focuses the light beam generated from the light source on an information recording medium, and a light beam that is reflected by the information recording medium. at least one light reflection means for reflecting the light beam reflected by the light reflection means; a phase correction element for correcting a phase shift that occurs when the light beam is reflected by the light reflection means; and a phase correction element for polarizing the light beam that has passed through the phase correction element. It is characterized by comprising an analyzer that separates the light beam into components, and a photodetector that detects the light beam separated by the analyzer.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows an optical head according to an embodiment of the present invention.

In this optical head, a semiconductor laser 5 as a light source is used.
The elliptical light beam L from 0 is passed through the collimator lens 5
2, the beam is converted into a parallel beam by the beam splitter 56.
The light enters the light incident surface 54 from an oblique direction. Since the elliptical light beam L is obliquely incident on the beam splitter 56, for example, the light incident surface 54 of a prism body having a half mirror, this laser beam L is
The elliptical beam is converted into a circular beam within the beam splitter 56. The light beam L passes through the beam splitter 56
is reflected by the mirror 58 and introduced into the objective lens 60, and is focused onto the information recording medium 62 by the objective lens 60.

This information recording medium 62 is made of, for example, an amorphous magnetic alloy. It has a layer, and a concentric or spiral running guide is formed on the surface thereof in a concave or convex shape. Furthermore, preliminary information such as a track address and a sector address, that is, a preformat signal, is formed in advance on this tracking guide as concave or convex pre-pits. The reason for this information recording medium 62 is that when no information is recorded, all of its magnetic domains are arranged in a fixed direction, and during recording, when a magnetic field is applied and rapidly heated, the magnetization direction of the 11 magnetic domains changes. is reversed.

The semiconductor laser 50 is driven by a drive circuit (not shown). During reproduction, the semiconductor laser 50 generates a light beam L having a constant light intensity, and during recording, a light beam L having a constant light intensity is generated.
A light beam L whose light intensity is modulated according to the information to be recorded is generated, and during erasing (J), a light beam L having a constant light intensity greater than that during reproduction is generated.

During recording, static information generated from the magnet device 64 is recorded as information &! When the tracking guide of the information recording medium 62 is traced by the recording light beam L applied to the recording medium 62, a specific area is rapidly heated, the magnetization direction is reversed, and information is recorded. Also, during playback, the light beam L for playback is
When a convergent light beam L is irradiated onto a magnetic domain region which has been reversely magnetized by tracing a tracking guide, the polarization plane of the light beam L is slightly rotated. When erasing, the magnet device 64
A static magnetic field generated from the information recording medium 62 is applied to the information recording medium 62,
When the erasing light beam L is irradiated onto a specific region whose magnetization direction has been reversed, this region is gently heated and the magnetization direction is reversed again so that it becomes the same as the other regions.

The light beam reflected from the information recording medium 62 passes through the objective lens 60, is reflected by a mirror 58 which is a light reflecting means, is introduced into a beam splitter 56, and is reflected within the beam splitter 56 which is a light reflecting means. The reflected light beam L is reduced by 1/2 to increase the proportion of S component.
The light passes through the wave plate 66 and the plane of polarization is rotated by approximately 45 degrees.

The light beam L whose polarization plane has been rotated is guided to the phase correction element 84.

The phase correction element 84 is a wave plate made of crystal or calcite. By cutting this crystal or calcite to a predetermined thickness dimension, it becomes a predetermined wavelength plate and changes the P polarization component and the S polarization component of the light beam L. It changes the phase of two polarized light components.

That is, the phase correction element 84 measures in advance the phase shift caused by the light beam L reflected from the information recording medium 62 being reflected by the light reflecting member, and corrects this phase shift. The phase shift of the light beam L is corrected by determining the thickness of the light beam L and passing it through this phase correction element 84 as a predetermined wavelength plate.

For example, the light beam reflected by the mirror 18' described above has a phase shift of λ/9.8, but in this case, the phase correction element 84 is a λ/9°8 plate, and this phase correction element By passing the light beam through 84, the phase shift of the light beam caused by being reflected by the mirror 18 is corrected.

The light beam that passes through this phase correction element 84 and whose phase shift has been corrected is guided to the polarization beam splitter 68.

This polarizing beam splitter 68 has a model prism 70 bonded to a right-angle prism 69, and the bonded surface forms a polarizing surface 72, and the surface of the model prism 70 facing the bonded surface forms a reflective surface 73. It is formed.

Moreover, as shown in FIG. 2, the reflecting surfaces 73 of this model prism 70 are three surfaces 73a, 73b, and 73b, which are inclined to each other.
73c (hereinafter referred to as an inclined surface), and the boundary line 73d between the two inclined surfaces 73b and 73c is in the direction in which the tracking guide of the information recording medium 62 extends, or in the direction of the tracking guide projected on a photodetector to be described later. It is set to be approximately parallel to the direction in which the image extends.

Therefore, when a parallel light beam (-) containing a P component and an S component is input to this polarizing beam splitter 68, the S component light beam L1 is reflected by the polarizing plane 72, and the P component light beam L1 is reflected by the polarizing plane 72,
The component light beam Lm − passes through the polarization plane 72 and becomes
It is reflected at 73. Since the polarization plane 72 and the reflection plane 73 are non-parallel and form a slight angle, the P component and the S
The light beams L1 and Ll- of the components are directed in slightly opposite directions, and the light beams 1' of the P component are directed toward the respective inclined surfaces 73a and 73 of the reflective surface 73, as shown in FIG.
The light beam Lt'' reflected by 73C is divided into three parts ML2, L3 .
The light is directed toward the condenser lens 74.

P-component and S-component light beams Lt, L2 . L3. Ll is condensed by a condensing lens 74 and converged onto a photodetector 76 .

This photodetector 76 is connected to the objective lens 6 as shown in FIG.
3 when 0 is in focus with respect to the information recording medium 62.
Two P-component optical terms L2. The first . Second and third detection units 77.78°79 and S component light beam L
The fourth detection unit 80 has a detection area in which one convergence point is formed. Moreover, the second. fl and the third detection section 78,79 are separated in a direction parallel to the direction of the boundary line d of the reflective surface 73, and the first detection section 11i1s77 is separated in a direction perpendicular to the direction of the boundary line 7311. It is divided into two sensing regions 77a and 77b with a small interval therebetween.

When the objective lens 60 is in focus with respect to the information recording medium 62, the light beam Ls of the S component reflected by the polarization plane 72 is converged on the fourth detection unit 80, and the inclined plane 7
The light beam L2 reflected by 3a is directed to the first detection section 77, and the light beam L3 reflected by the inclined surface 73b is directed to the second detection section 78.
The light beam L4 reflected on the roughly inclined surface 73d is
They are respectively converged on the detection section 79 of.

A tracking error signal is generated by subtracting the difference between the signals generated from the second and third sensing sections 78. The difference between (q
A focus signal is generated by this. moreover,
The signals from the sensing areas 77a, 77b, li of the first sensing section 77 and the second and third sensing sections 78, 79 are added by an adder, and the difference with the signal generated from the fourth sensing section 80 is calculated. The information signal is reproduced by multiplying by 1 by a subtracter.

The objective lens 60 is moved in the direction of its round axis in accordance with this focus signal, and the objective lens 6o is always maintained in a focused state with respect to the information recording medium 62, and the objective lens 60 is moved in accordance with the tracking 1 signal. , is moved in a direction perpendicular to the optical axis, and the tracking guide of the information recording medium 60 is accurately tracked by the focused light beam. As a result, recorded information is reproduced from the information recording medium 62. Similarly, when recording, information is written accurately, and when erasing, recorded information is reliably erased.

In the optical head described above, the information recording medium 62
The light beam reflected by the mirror 58 is a light reflecting means.
&3 A phase shift occurs due to reflection by the beam splitter 56, and the phase correction element 84 that compensates for this phase shift is used to compensate for the phase shift between the beam splitter 56, which is a light reflecting means, and the polarizing beam splitter 68, which is an analyzer. Since the light is provided between the light beam and the light beam, this phase shift is corrected by passing through the phase correction element 84 and before reaching the polarization beam splitter 68. Therefore, in this optical head, the information signal can be reproduced after correcting the one-bit phase shift when the light beam reflected by the information recording medium 62 is reflected.

In addition, in this optical head, one light detection 176
The information signal is reproduced and the focus signal and tracking error signal are detected.

Therefore, each signal can be detected with a much simpler configuration than conventional optical heads. Therefore, since the number of component parts of the optical head is reduced, the overall weight of the optical head is reduced, the access speed of this optical head can be increased, and furthermore, the cost can be reduced.

In addition, in this optical head, the reflecting surface 73 of the model prism 70 formed in the polarizing beam splitter
Although the explanation was given using a model with two sloped surfaces,
The present invention is not necessarily limited to this, and the configuration may be such that the polarization planes 72 of the six polarization beam splitters are provided with three inclined surfaces.

[Effects of the Invention] As explained above, the optical head according to the present invention has extremely 1! It has the effect of correcting the phase difference of the light beam that occurs during the optical path from the information recording medium to the detection optical system, and reliably reproducing the information signal.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of an optical head showing an embodiment of the present invention, FIG. 2 is a schematic configuration diagram showing a reflective surface of an analyzer of the optical head shown in FIG. 1, and FIG. FIG. 4 is a schematic diagram showing the configuration of the photodetector of the optical head shown in the figure, and FIG. 4 is a schematic diagram showing the state of reflection of a light beam placed on a mirror. 50... Light source (semiconductor laser) 56... Light reflecting member (beam split) 58...
Light reflecting member (mirror) 60...Objective lens 62...Information recording medium 68...Analyzer (light beam splitter) 76...
Photodetector 84...phase correction element

Claims (1)

[Scope of Claims] A light source that generates a light beam; an objective lens that focuses the light beam generated from the light source on an information recording medium; and at least one light beam that reflects the light beam reflected by the information recording medium. a reflecting means; a phase correction element for correcting a phase shift that occurs when the light beam is reflected by the light reflecting means; an analyzer for separating the light beam that has passed through the phase correction element into polarization components; An optical head comprising: a photodetector that detects a light beam separated by photons.