JPS6043237A - Optical head - Google Patents

Abstract

PURPOSE:To prevent the optical axis of a reflected light beam from shifting laterally and to control the positioning of a light beam in a focus and a track direction by moving an optical element which consists of an objective lens, quarter-wavelength plate, polarization prism beam splitter, etc., in one body to move in the focus or track direction. CONSTITUTION:The light beam when made incident along an optical axis 13 is deflected at right angles by an optical path conversion prism 21, made incident on and transmitted in a polarizing prism 17, and transmitted in the quarter- wavelength plate 16 to be focused on a discoid information carrier 12 through the objective. The reflected light beam from the discoid information carrier 12 passes through the convergent objective lens 11 and is transmitted through the quarter-wavelength plate 16 to perform conversion into a light beam which is polarized linearly at right angles to the polarization of the incident light beam, and the light beam is reflected by the polarization prism beam splitter 17, a reflecting prism 15, and the optical path conversion prism 22 and projected along an optical axis 14 of reflection. Therefore, the optical axis of reflected light never shifts even when optical elements 11, 15, 16, and 17 united in the track direction are moved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical head that optically records and reproduces information, and particularly to an optical head that can perform stable focus and trunk tracking control.

Conventionally, when performing focus and track following control in this type of optical head, as shown in FIG. 1(a), the objective lens 1 is moved in the focus direction It moves to position the light beam. In other words, the light source 9 produces a single light beam, and the collimating lens 8 causes the incident light beam 3 to become parallel.
The incident light beam 3 passes through an integrated polarizing prism beam splitter 7 and a quarter-wave plate 6, is polarized by a reflection optical system 5 by 900, and is polarized by an objective lens 1 onto an information carrier 2. While the light is focused, it is reflected and detected by the photodetector 10 as a reflected beam 4. However, when the lens l is moved in the track direction y in such a configuration (lens 1'), the reflected beam 4 moves parallel to the optical axis of the incident light beam 3, and as shown in FIG. 1(b). As shown, there is a drawback that the light beam 3.degree. 4 on the photodetector 5 for detecting the track position shift shifts, making it impossible to accurately follow the track.

An object of the present invention is to provide an optical head capable of solving such a deviation of the optical axis of a reflected light beam and performing stable focus and track following control.
The gist of this is that it consists of an objective lens that focuses a light beam for recording and reproducing into a minute spot on an information medium, and a polarizing prism beam splitter that is placed between this objective lens and the light source. , a 1/4 wavelength plate disposed between the polarizing prism beam splitter and the objective lens; and a quarter-wave plate disposed between the polarizing prism beam splitter and the objective lens; A reflective optical system that emits the light beam parallel to the axis and in the same direction as the direction of incidence from the light source to the objective lens constitutes an integrated optical element, and this optical element is directed in the optical axis direction of the objective lens. and movable in a direction perpendicular to the optical axis direction of the objective lens and at an angle of 45° with respect to the reflective surface of the polarizing prism beam splitter.
It is characterized by what has been achieved.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The optical head according to the present invention will be described below with reference to the embodiments shown in the drawings.

FIG. 2 is a principle diagram showing a schematic configuration of an optical head according to the present invention. An objective lens 11 which performs recording and reproduction) and focuses a beam onto an information carrier 12 as a minute spot.
, a polarizing prism beam splitter 17 disposed between this objective lens 11 and a light source (not shown), and a polarizing prism beam splitter 17 disposed between this objective lens 11 and a light source (not shown);
1/4 wavelength plate 16 disposed between the 1/4 wavelength plate 16 and the information beam 12, the reflected light beam from the information body 12 is parallel to the light 1h11 of the objective lens 11 through the reflection of the reflective surface 17a of the polarizing prism beam splitter 17. An integrated optical element is constituted by a reflective optical system 15 that emits a light beam in the same direction as the direction of incidence of the light source (L-) on the objective lens 11. In addition, 1
3 is the optical axis of the incident light beam, and 14 is the light fi of the reflected light beam.
, :2t is an incident side optical path converting prism, 22 is an output side optical path converting prism, and the positions of both optical path converting prisms 21 and 22 are fixed even when focus and track following control is performed.

FIG. 3 is an external perspective view showing the optical head constructed as described above. The integrated optical elements 11, i5, 16, and 17 are supported by a focus actuator 23 using an electrostrictive element, and are moved in the focus direction. At the same time, it is positioned in the track direction by being supported by a housing 26 via a support member 24 and a track actuator 25 using an electrostrictive element. The optical path converting prisms 21 and 22 are in the housing 2.
The optical axis 14 of the reflected light beam does not move at all even during focus and track control, and the optical axis 14 of the reflected light beam does not move at all even during focus and track control, and the optical axis 14 of the reflected light beam is fixed at 16 and 17 with high precision due to stable focus and track detection. The structure is such that positioning is performed in the track direction using the track actuator 25 located on the opposite side of the light beam, but the lenses 15, 16 and 17, the focus actuator 23, and the support member 24 are also positioned on the incident surface without interfering with the light beam. It is supported on both sides by the actuator 25, and can prevent unnecessary vibrations such as torsional vibrations.

When a light beam having two linearly polarized planes parallel to the plane of the paper is made to enter the optical head having such a configuration along the optical axis 13, the light beam is deflected at right angles by the optical path converting prism 21 and enters the polarizing prism 17. To Penetrate. Further, the light beam passes through a quarter-wave plate 16, and the polarized light changes from linearly polarized light to circularly polarized light, and is focused onto the disk-shaped information medium 12 by the objective lens 11. The reflected light beam from the disc-shaped information carrier 12 passes through the condensing objective lens 11 to 1/4
By passing through the wavelength plate 16, the light beam is converted into a light beam having a linear polarization perpendicular to the polarization of the incident light beam, and the light beam is converted into a light beam having a linear polarization perpendicular to the polarization of the incident light beam, and the joining table surface 17a of the polarization prism beam splitter 17, the reflection prism 15 as a reflection optical system, and the optical path conversion prism 2.
2 and is emitted along the reflection optical axis 14.

Therefore, as shown in FIG. 4(a), optical elements 11, 1, 5, 16 and 1 are integrated in the track direction.
7, the optical axis of the reflected light does not shift. In other words, when the integrated optical elements 11° 15 + 16 and 17 are moved in the trunk direction by d with respect to the incident optical axis 13, the optical axis 14a of the reflected light beam entering the reflective surface 17a of the polarizing prism 17 is aligned with the objective lens 11. The light beam is moved in the track direction by 2d with respect to the optical axis 13a of the incident light beam. On the other hand, since the reflective surface 17a of the polarizing prism beam splitter 17 has moved by d in the track direction, the optical axis 13 of the incident light beam is aligned with the polarizing prism beam splitter 1.
7 is the height across the reflecting surface 17a, the optical axis center 14a of the reflected light beam is reflected by the reflecting surface 17a at a height of -ffl-1-d. Further, since the reflective surface 15a of the reflective prism 150 as a reflective optical system is also moved in parallel by d, the distance e at which the optical axis center 14b of the light beam intersects with the reflective surface 15a does not change at all.

Note that FIGS. 4(b) and 4(c) show the optical axes when the optical elements 11, 15, 16:la and 17, which are integrated in the focus direction only, are moved in the focus and trunk directions, respectively. As is clear from the above i(a), the optical axis -14 of the reflected light beam does not move at all in this case even if d.

Although the above embodiments have been described using a reflective prism as the reflective optical system 1; 5, it goes without saying that the same effect can be obtained by using a reflective mirror instead of the reflective prism.

As described above with reference to the embodiments shown in the drawings, the optical head according to the present invention includes an objective lens, a quarter-wave plate, a polarizing prism beam splitter, and a reflected light beam that passes through the reflection of the polarizing prism. By integrating a reflecting prism that is parallel to the optical axis of the objective lens and in the same direction as the incident optical axis of the objective lens, and by moving this optical element in the focus and track directions, the reflected light beam prevents lateral deviation of the optical axis of
This has the advantage that optical beam positioning control in focus and track directions can be performed stably.

[Brief explanation of drawings]

FIG. 1(a) is a principle diagram showing the schematic structure of a conventional optical head, FIG. 1(b) is a top view of its photodetector, and FIG.
The figure is a principle diagram showing a schematic configuration of an optical head according to the present invention.
FIG. 3 is a perspective view of the external appearance, and FIGS. 4(a) to (C) are diagrams illustrating the principle of the present invention. 11, 11'... Objective lens, 12... Information carrier, 15... Reflective optical system, 16... l/4 wavelength plate, 17... Polarizing prism beam subrick patent applicant
Nippon Tunshin-Tunwa Public Corporation Agent Benyashi Mitsuishi Shibu (fij 21 people) (Fig. 3 of b.

Claims (1)

[Claims] an objective lens for condensing a light beam for recording/reproduction into a minute spot on an information carrier; a polarizing prism beam splitter disposed between the objective lens and the light source; the polarizing prism beam splitter; A 1/4 wavelength plate disposed between the objective lens and the light beam reflected from the information phase body is transmitted parallel to the optical axis of the objective lens and parallel to the optical axis of the objective lens through reflection of the reflective surface of the polarizing prism beam splitter. and a reflective optical system that emits the light beam in the same direction as the direction of incidence of the light beam on the objective lens. 4 perpendicular to the polarizing prism beam splitter and with respect to the reflective surface of the polarizing prism beam splitter.
An optical head characterized in that it is configured to be movable in a 5° direction.