JPS6273445A - Optical head - Google Patents

Abstract

PURPOSE:To ensure the reproduction of an information signal by correcting the phase difference of light beams caused on the way of the optical path from the information recording medium to a detection optical system. CONSTITUTION:A light beam L reflected in the information recording medium 62 is reflected in a mirror 58 resulting in causing a phase shift, and the beam is reflected in a beam splitter 56 having a light reflection face coated with a dielectric polylayer film by a prescribed thickness to correct the phase shift thereby correcting the phase shift until the beam reaches a polarized beam splitter 68. Thus, after the phase shift caused in reflecting the light beam reflected in the medium 62 is corrected, the information signal is reproduced.

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 aspect of the invention and its problems] There are already 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. Are known. When reproducing information from an information recording medium using such a magneto-optical effect, the information recording medium is irradiated with a light beam and the reflected light beam is detected by a photodetector, etc. 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 reflected by the information recording medium is reflected many times before reaching the detection optical system. A phase difference occurs between the S-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 P-width light component and the S-polarized light component of the light beam will be explained. As shown in FIG. 4, if the mirror 18' has a structure that utilizes total reflection that occurs at the end face of the prism, the phase change amount of the Plti light component of the light beam is θp, and the phase change amount of the S polarization component is θS9. The difference between the names is θ-θp-θ5
Then, each can be expressed as follows.

tan Op / 2 = -nJ Shoulder T 2 s
in 2 tp −l /cos ψ・・・・・・
・〈1) tanθs/2--5s ” sin7τ〒/ncos
ψ・・・・・・(2) tanθ/2 = tanθρ−θs/2−cosφ
n 2 sin 2 tJ＞τ了／n5in2ψ・・
...(3) However, n refractive index of nibism ψ: angle of incidence of the light beam on the end surface of the prism.
and ψ=45, it becomes θ-36°9 degrees. This θ = 36.9 degrees corresponds to approximately λ/9°8, so if total reflection is used as the mirror 18', there will be approximately λ/9.8 between the P polarized light component and the S polarized light component of the light beam. It can be seen that a phase shift occurs. P polarization component and S
A linearly polarized light beam containing a polarized component passes through this mirror 18.
- When the light is reflected by -, it becomes elliptically polarized light instead of completely linearly polarized light due to the above-mentioned phase shift. Therefore, such a mirror 18' exists in the detection optical path of the reproduction light for the information recording medium using the magneto-optical effect. Then, the S/N ratio of the read signal decreases due to an increase in the elliptically polarized light component.

In addition, in the case of a structure in which the mirror 18 is closed and a light reflective coating is used to reflect the light beam on the surface, the characteristics will vary depending on the material of the light reflective coating, but if 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. Further, when a multi-coated surface is used as the metal, the material has conductivity, and when light is reflected, a slight loss of the light beam occurs, and a phase shift also occurs. However, the phase shift greatly differs depending on the material and structure of the coating material. Note that the above also applies to beam splitters etc.
The same thing can be said about Habo.

However, 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 the optical head, this J:
There was a drawback that the S/N ratio of S@ detection decreased due to the phase shift occurring between the Q light component and the S polarized light component.

Purpose of the Invention The present invention has been made based on the above-mentioned circumstances, and has a very simple 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 object of the present invention is to provide an optical head that can reliably reproduce signals.

[Overview of the invention 1] In order to achieve the above object, the present invention provides 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 source that focuses the light beam generated from the light source on an information recording medium. at least one first light reflecting means for reflecting the reflected light beam; a reflective film is coated so as to correct a phase shift that occurs when the light beam is reflected by the first light reflecting means; a second light reflecting means for reflecting the light beam reflected by the first light reflecting means; an analyzer for separating the light beam reflected by the second light reflecting means into light components; The device is characterized in that it includes a photodetector that is long enough to detect the light beam separated by the analyzer.

[Embodiment of the Invention] An embodiment of the present invention will be described below 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 is obliquely incident on the light incident surface 54 of the beam splitter 56, for example, a prism body having a half mirror, the laser beam L is
The elliptical beam is converted into a circular beam within the beam splitter 56. The light beam transmitted 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 has a recording layer made of, for example, an amorphous LA bamboo alloy, and a tracking guide is formed concentrically or spirally on the surface of the recording layer.
It is formed in a convex shape. Roughly speaking, preliminary information such as track addresses and sector addresses as well as preformat signals are formed in advance on this tracking guide as concave or convex pre-pits. In the recording layer of this information recording medium 62, in a state where information is not recorded, all magnetic domains thereof are arranged in a fixed direction,
During recording, when a magnetic field is applied and the area is rapidly heated, the magnetization direction of the magnetic domain in that area 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, the light beam L is emitted according to the information to be recorded. Intensity modulated light beam L
is generated, and during erasing, a light beam l- having a constant light intensity greater than that during reproduction is generated.

During recording, a static magnetic field generated by the magnet device 64 is applied to the information recording medium 62, and when the recording light beam is traced on the tracking guide of the information recording medium 62, a specific area is rapidly heated and the magnetization direction is changed. It is reversed and information is recorded. Furthermore, during reproduction, when the tracking guide is traced by the reproduction light beam L and the convergent light beam L is irradiated onto the reversely magnetized magnetic domain region, the polarization plane of the light beam L is slightly rotated. When erasing, the magnet device fff
When the static magnetic field generated from the magnetic field 64 is applied to the information recording medium 62 and 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 changed to another region. is inverted again so that it is the same as .

The light beam reflected from the information recording medium 62 passes through the objective lens 60 and is reflected by the mirror 58, which is the first light reflecting means.
The light is reflected by the beam splitter 56, which is the second light reflecting means. A radiation beam splitter 68 which is an analyzer. The light is guided to a detection optical system including a photodetector 76 and the like. The light reflecting surface 5 of the beam splitter 56 which is the second light reflection et f=stage
6a, a reflective film is formed by coating several layers of current-carrying multilayer films so as to correct the phase shift that occurs when the light beam L is reflected by the mirror 58.

The light beam L G reflected by this beam splitter 56
, t In order to increase the ratio of the S component, a 1/2 wavelength plate 6 is used.
6, the plane of polarization is rotated approximately 45 degrees. The light beam whose polarization plane has been rotated is introduced into a polarizing beam splitter 68 as an analyzer as a parallel beam.

The polarizing beam splitter 68 has a model prism 70 bonded to a right-angle prism 69, and the bonded surface is formed as a polarizing surface 71A, and the surface of the horizontal prism 7o facing the bonded surface is formed as a reflective surface 71B. has been done.

This polarizing beam splitter 68 is made by joining six right-angle prisms to a horizontal prism 7o. is formed on the reflective surface 73. Also, this Jukyagata Pu1! The reflective surface 73 of the beam 70 is the second
As shown in the figure, there are 6 slopes 73a, 73
b and 73c (hereinafter referred to as inclined surfaces), and a boundary line 73d between the two inclined surfaces 73b and 73c.
are determined to be approximately T rows in the direction in which the tracking guide extends from 1 on the information recording medium 62 or in the direction in which the image of the tracking guide projected on a photodetector (described later) extends.

Therefore, when the parallel light beam L including the pa component and the S component is incident on the polarizing beam splitter 68, the S
The component light beam L1 is reflected by the polarizing surface 72, and the P component light beam L1- passes through the polarizing surface 72 and is reflected by the reflecting surface 73. Since the polarizing plane 72 and the reflecting surface 73 are parallel to diL and form a slight angle, the light beams L+, 1. -t- are directed in slightly different directions, and the roughly P-component light beam Lz- is directed to the respective inclined surfaces 73a, 73b, 73b,
Since the light beam L1- reflected by 73G is reflected in different directions, it is divided into three parts 1112.1-3. L4
and heads toward the condensing lens 74.

P-component and S-component light beam L1. reflected by polarizing plane 72 and reflecting surface 73. L2. 1-3 and L71 are 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 light beams L2. The first . It has second and third detection sections 77, 78, and 79, and a fourth detection section 80 having a detection area where the convergence point of the S component light beam L1 is formed. Moreover, the second and third detection sections 7
8.79 is separated in a direction parallel to the direction of the boundary ld of the reflective surface 73, and the first detection unit 77 is separated from the boundary 73d.
It is divided into two sensing regions 77a and 77b with a minute interval in a direction perpendicular to the direction of.

When the objective lens 60 is in a focused state with respect to the information recording medium 62, the S component light beam L1 reflected by the polarizing surface 72 is converged on the fourth detection section 8o, and the inclined surface 73
The light beam L2 reflected by the inclined surface 73b is directed to the first detection section 77, the light beam L3 reflected by the inclined surface 73d is directed to the second detection section 78, and the light beam L4 reflected by the inclined surface 73d is directed to the third detection section 77. 79, respectively.

A tracking error signal is generated by obtaining the difference between the signals generated from the second and third detection sections 78. A focus signal is generated by obtaining the difference between . Further, the signals from the sensing regions 77a, 77b of the first sensing section 77 and the second and third sensing sections 78, 79 are added by an adder, and the signals generated from the fourth sensing section 80 are combined with the signals generated from the fourth sensing section 80. The information signal is recovered by obtaining the difference by means of a subtractor.

The objective lens 60 is moved in the direction of its original axis in accordance with this focus signal, and the objective lens 60 is always held in a focused state with respect to the information recording medium 62. In response to the tracking error signal, the objective lens 60 is moved in the direction of its original axis. The tracking guide of the information recording medium 60 is moved in a direction perpendicular to the axis, and the tracking guide of the information recording medium 60 is tracked by the focused light beam L. 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 causes a phase shift, but the beam is energized to correct this phase shift! ? ! This phase shift is corrected by the time the light reaches the polarizing beam splitter 68 by being reflected by the beam splitter 56 having a light reflecting portion 56a coated with a film of only a predetermined layer. Therefore, in this optical head, the information recording medium 6
The information signal can be reproduced after correcting the phase shift that occurs when the light beam reflected by the light beam 2 is reflected.

Moreover, in this optical head, one photodetector 76
The information No. 1z is reproduced and the focus signal and tracking error signal are detected.

Therefore, it is very fltllt compared to conventional optical heads.
It is possible to detect each signal with the same configuration. Therefore, since the number of components of the optical head is reduced, the entire optical head becomes a pumice stone, and the access speed of this optical head can be increased, and furthermore, the cost can be reduced.

Further, in the present invention, the explanation has been made using a gold splitter as the second light reflecting member, but the light reflecting film may be formed by stacking many layers of other current-carrying multilayer films.
For example, a half prism or the like may be used, or a reflecting mirror or half mirror having exactly the same properties as the first light reflecting member may be used (#1 may also be used).

Furthermore, the first light reflecting member is not necessarily limited to just one mirror 58, and even if the structure is such that there is something else provided that serves as a light reflecting surface, such as a beam splitter or prism, It goes without saying that the same effect as in the embodiment described above can be obtained as long as the phase shift that occurs when the optical beam is reflected by the second reflecting member is corrected.

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 polarization plane 72 of the polarization beam splitter 69 may be configured to have three inclined surfaces.

1. Effects of the Invention] As explained above, the optical head of the present invention has a very rfJlll structure and corrects the phase difference of the light beam that occurs in the optical path from the information recording medium to the detection optical system. This has the advantage that it is possible to reliably reproduce 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... Second light reflecting member (beam splitter) 58
...First light beam I) 1 member (mirror) 60...Objective lens 62...Information recording medium 68...Analyzer (polarizing beam splitter) 76...
Photodetector

Claims (2)

[Claims] (1) A light source that generates a light beam; an objective lens that focuses the light beam generated from the light source onto an information recording medium; and at least one first light beam that reflects the light beam reflected by the information recording medium. a reflecting means, the light beam being directed to the first
a second light reflecting means that is coated with a reflective film to correct a phase shift that occurs when the light beam is reflected by the first light reflecting means, and that reflects the light beam reflected by the first light reflecting means; An optical head comprising: an analyzer that separates the light beam reflected by the second light reflecting means into polarized components; and a photodetector that detects the light beam separated by the analyzer. (2) The optical head according to claim 1, wherein the second light reflecting means is one of a group consisting of a beam splitter, a reflecting mirror, a half mirror, and a half prism.