JPS59144055A - Optical head - Google Patents

Abstract

PURPOSE:To reduce the length of an optical head in the optical axis direction of an objective by shifting together the objective, the semiconductor laser of a light source and an optical system including a photodetector. CONSTITUTION:An optical head contains a semiconductor laser 21 which forms a light source, a polarized beam splitter 22, a 1/4 wavelength plate 24, a rectangular prism 25, an objective 26, a photodetector 28 which detects the laser light reflected by the splitter 22, etc. in one body. Such an optical system is shifted toward the optical axis of the lens 26 as well as in the direction rectangular to said optical axis for purposes of focusing and tracking respectively. Therefore it is possible to reduce the size of the objective 26 as well as the distance between the objective 26 and the prism 25 in comparison with the case where only the objective 26 is shifted. As a result, the length of the optical head can be reduced in the optical axis direction of the objective 26.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical head used in an optical disk reproducing device or the like.

Background Art and Problems Optical heads used in optical disc playback devices can be roughly divided into two types: those from a semiconductor laser, in which the laser beam enters the objective lens without bending its path midway; There is a type in which the laser beam is bent at a right angle by a right-angle prism or mirror midway through, and then enters the objective lens. The former type has a large length along the rotational axis of the disc, which prevents flattening of the disc playback device, but the latter type has a large length along the rotational axis of the disc. The disc playback device can be made flat.

Figures 1 and Ω are examples of the latter type of conventional optical head, in which laser light from a semiconductor laser is transmitted through a polarized beam splitter I and collimated through a collimator lens.
3, the diverging light is converted into parallel light, enters the right angle prism/S via the wavelength plate/cluster, its path is bent at right angles, is focused by the objective lens/B, and is irradiated onto the disk/.

The laser beam reflected by the disk / passes through the objective lens / B and enters the right-angle prism / S, and its path is bent at right angles. The beam is reflected by the beam splitter 2, the path of which is bent at a right angle, and reaches the photodetector 77 via the cylindrical lens 77, where it is converted into an electrical signal. The objective lens/A is the optical axis direction for focus control and tracking control in the rotational axis direction of the disk (vertical direction in Figure 1) and the radial direction of the disk (left and right in Figure 1) perpendicular to this direction. direction).

However, this conventional optical head converts the diverging light of the semiconductor laser into parallel light using the collimator lens /3, and converts only the objective lens /3 into the disk /
Since focus control and tracking control are performed by moving the disk in the direction of the rotation axis and in the radial direction, there is a problem that the length of the disk in the direction of the rotation axis cannot be made sufficiently small.

That is, as is clear from FIG. 1, the length of the conventional optical head in the direction of the rotational axis of the disk is determined by the thickness of the objective lens A, the height of the right angle prism S, and the objective lens A.
,! = [This is the sum of the distances of the square prisms/S, but for focus control, the objective lens/B is the right angle prism/S and other optical components in the direction of the disk/'s rotation axis (vertical direction in Figure 1) To prevent the objective lens/B from colliding with the right-angle prism/S when it is moved, the distance between the objective lens/B and the right-angle prism/S must be at least 2cm.

Mata, like this, the working distance of the objective lens/O is 2Wr.
m or more, even if the objective lens is moved in the radial direction (horizontal direction in Figure 1) of the disk relative to other optical components such as the right-angle prism for tracking control, the right-angle prism remains / Right angle prism / 3 to prevent the parallel beam passing through the left side from deviating from the field of view of the objective lens /
It is necessary to set the diameter of the beam incident on the VC to about S, (3) Therefore, the height of the rectangular prism/S needs to be greater than or equal to grmn. Furthermore, the thickness of the objective lens/B is usually 3 trrm or more. Therefore, the length of the entire head in the direction of the rotational axis of the disk is /3. ! ;Become more than concerned.

Purpose of the Invention The present invention provides an optical head of a type in which a laser source from a semiconductor laser is bent at a right angle by a right-angle prism or mirror midway and enters an objective lens. In other words, in the case of disc playback, the length of the disc in the rotational axis direction can be made smaller.

Summary of the Invention In the present invention, instead of using a collimator lens to convert the diverging light from a semiconductor laser into fully parallel light and then focusing it on an objective lens, the spherical wave from the semiconductor laser is directly transmitted to a disk, etc. It focuses light onto the object to be irradiated, and for this purpose an objective lens with a finite magnification is used. At the same time, in the book (plus invention), semiconductor laser, polarizing beam splitter-2
Right angle prism or mirror, objective lens.

All optical components such as photodetectors are housed in seven lens barrels, and the entire head is moved by a two-axis drive device in the direction of the optical axis of the objective lens and in a direction perpendicular to this for focus control and tracking control. Do it like this.

Embodiment Figures 3 to S show an example of the optical head of the present invention together with an example of a two-axis drive device, which serves as an objective lens with a finite magnification to converge a spherical wave diverging from one point to another point. This is a case where a hologram having a lens action that converts into a spherical wave is used.

That is, the optical head 20 is a semiconductor laser 2/.

Polarizing beam splitter 2, 2, wave plate, 211. i
[Kakupu +) Dam 2. ! ; + objective lens λ with finite magnification;
It consists of a cylindrical lens 27 and a photodetector 2g, and a hologram having a lens action that converts a spherical wave that diverges from one point into a spherical wave that converges at another point is used as the objective lens a. The laser beam transmitted through the polarizing beam splitter 22,
It enters the right angle prism 2 left through the wave plate 2'l'fr, and its path is bent at right angles.
The laser beam that is focused by the objective lens 2A and irradiated onto the disk/, and reflected by the disk/, is reflected by the objective lens Ω
The beam enters the right-angle prism 2 to the left through the cylindrical lens 27, is bent at a right angle, passes through the 7-wave plate 21I, is reflected by the polarizing beam splitter 22, and is further bent at a right angle, and passes through the cylindrical lens 27. The light reaches the photodetector 2g and is converted into an electrical signal.

As shown in FIG. 6, the hologram used as such an objective lens 2B includes an auxiliary hologram 32 on the optical path of the objective lens 3/ and a hologram made of dichromate gelatin or the like to be used as the objective lens λB. It is possible to create a convergent spherical wave with a numerical aperture of sinθl by an auxiliary hologram 3λ placed on the thin film 2a′ and a diverging spherical wave with a numerical aperture of sinθl by the objective lens 3/ on the thin film λa′. can. That is, according to this, the thin film 2a is an objective lens having a lens action that converts a spherical wave with a numerical aperture of sinθl that diverges from the point F/ into a spherical wave with a numerical aperture of sinθl that converges on the point F2. It becomes a hologram used as a hologram. Note that the auxiliary hologram 32 is the seventh
As shown in the figure, a thin film 32a'x, which is to become an auxiliary hologram 32, is arranged on the optical path of the objective lens 33, and a plane wave and a diverging spherical wave with a numerical aperture of sin θ/ by the objective lens 33 are caused to interfere on the entire thin film 32a. can be made.

This optical head 20 is housed in a chamber formed by a short rectangular cylinder part O and a plate part 4/ that covers the T end side thereof.
Each optical component is attached to the cylinder part tIO or the plate part ll/. However, the objective lens 2B is fitted into a window hole formed in the plate part G/, and is exposed to the outside of the room. Plate l
l/ semiconductor laser 2/, polarized + beam splitter 2
Legs lI2 and g3 are integrally formed at both ends of the 2 and 7 wavelength plate 2'l and the left side of the right angle prism 2 in the arrangement direction, and coils lIb and lI7 for focus control are attached to the leg parts gλ and 4t3. Can be installed respectively. In addition, the cylindrical portion lIO
A coil ring 9 for tracking control is attached to the center of one side in the arrangement direction of the polarizing beam splitter 2λ, cylindrical lens λ7, photodetector 2g. On the other hand, 8-shaped yokes 54 and &5 are attached to the legs 32 and S3 of the U-shaped board S/, respectively, and magnets S and S7 are attached to the legs on both sides of the yokes SII and 55.
are attached respectively to the legs S2 and S of the substrate S/
3, a magnetic circuit for focus control is formed.

In addition, an 8-shaped yoke Sg is attached to the center of the board S/, magnets 13-9 are attached to the legs on both sides of the yoke Sg, and a magnetic circuit for tracking control is attached to the center of the board S/. is formed. Then, the cylindrical part O is connected to the substrate 3.
The coil t/ for focus control is inserted between the legs S2 and the left 3 magnetic circuits for focus control, and the coil t/ for focus control is inserted into the gap between the respective magnetic circuits.
A coil 4t9 for tracking control is inserted into the gap of the magnetic circuit for tracking control in the center of the substrate S/,
The cylindrical part G0 is connected to the yokes 54 and 5 by the dampers Otsuko and Otsu3. t and thus supported on the left/left of the substrate.

Therefore, the entire optical head 20, together with the cylindrical portion lIO, coil ring O, l17 and lI9, etc., is connected to the optical axis of the objective lens 2O for focus control with respect to the substrate S/, yoke, tlI, 55, left g, etc. The direction of the rotational axis of the disk / (in the direction perpendicular to the plane of the paper in Fig. 3, that is, the vertical direction in Figs. 9 and S), and the direction of the rotation axis of the disk / perpendicular to this direction for tracking control. It is moved in the radial direction (in the vertical direction in FIG. 3, ie, in the direction perpendicular to the plane of the paper in FIGS. 9 and S).

As the finite magnification objective lens 2A, a normal glass lens may be used instead of the above-mentioned hologram. In this case as well, the optical head and the two-axis drive device are shown in FIGS.
The configuration may be similar to the example shown in the figure.

In the examples shown in FIGS. 3 to S, the laser beam from the semiconductor laser 2/ is transmitted through the polarizing beam splitter 22,
In this case, the laser beam reflected by the disk is reflected by the polarizing beam splitter 22, but conversely, the laser beam from the semiconductor laser is reflected by the polarizing beam splitter, and the laser beam reflected by the disk becomes polarized. The light may be transmitted through a beam splitter.

Further, a mirror may be used instead of the left side of the right angle prism 2.

Effects of the Invention According to the present invention, an objective lens with a finite magnification is used to focus the entire spherical wave from a semiconductor laser directly onto an irradiated object such as a disk, and the semiconductor laser,
Polarizing beam splitter - 1 right angle prism or mirror,
All optical components such as the objective lens and photodetector are moved together in the direction of the optical axis of the objective lens and in the direction orthogonal to this for focus control and tracking control, so the optical axis of the objective lens of the optical head is The length in the direction, that is, in the case of disc reproduction, the length in the direction of the rotation axis of the disc can be made smaller. That is, according to the present invention,
The beam incident on the right-angle prism or mirror is a spherical wave, and the objective lens Ω is not moved in a direction perpendicular to its optical axis independently with respect to other optical components, and the beam is incident on the objective lens Ω. Since there is no need to increase the diameter of the beam to be used, the height of the right-angle prism 2 or mirror can be set to approximately 3 tan, and the objective lens 2 can be adjusted independently from other optical components. Since it is not moved in the optical axis direction, the objective lens λ and the right-angle prism 2!
;'! With fC, the distance between the mirrors can be reduced to almost zero, and even when a normal glass lens is used as the objective lens λ, the length of the entire head in the optical axis direction of the objective lens Ω is significantly smaller than that of the conventional one. It can be made as short as the length of the throat. In particular, when a hologram is used as the objective lens λB, the main surface of the lens coincides with the film surface of the hologram, so the working distance can be long compared to the aperture, and the diameter of the beam incident on the objective lens λB can be reduced. Therefore, the height of the right angle prism 2S or mirror should be 3~3! Since the thickness of the objective lens 2 can be approximately Wm, and the thickness of the objective lens 2 is also approximately Ω■, the length of the objective lens λ of the entire head in the optical axis direction is smaller than that of the conventional one. Screams can also be made shorter.

[Brief explanation of the drawing]

Figures 1 and Ω show an example of a conventional optical head. Figure 1 is a side view, Figure Ω is a plan view, and Figures 3 to S are two examples of the optical head of the present invention. It is shown together with an example of a shaft drive device, and Fig. 3 is a partially cutaway plan view;
FIG. 9 is a sectional view taken along the line IV--IV, FIG. S is a side view, and FIGS. 4 and 7 are views for explaining how to make a hologram. In the figure, 1 and 2/ are semiconductor lasers, λΩ is a polarizing beam splitter, 1 and 2S are right-angle prisms, and 2 is an objective lens 1.
, 2g is a photodetector. (/2) Figure 1 Figure 2 Procedural amendment 1. Display of the case Showa Sg Year Patent Application No. 20327 2, Title of the invention Optical head 3, Person making the amendment Relationship to the case Patent applicant address 7-33 Otsu-chome, Kitashinyo-ku, Tokyo Parts Name (, 27) Sony Corporation Representative Norio Ohga6, Number of inventions to be increased due to amendment None7, Subject of amendment Column of Claims of Specification and Detailed Description of Invention Column8, Contents of Amendment (1) Amend the claims as shown in the attached sheet. (2) In the specification, the phrase "horizontal direction" on page 3, line 15, is corrected to "perpendicular to the page." The above claims include a semiconductor laser, a beam splitter that transmits or reflects laser light from the semiconductor laser, an optical component that bends the path of the laser light via the beam splitter at right angles, and a An objective lens with a finite magnification that focuses the laser beam, and a laser beam that enters the objective lens from the opposite direction, whose path is bent at a right angle by the optical component, is reflected by the beam splitter, or is transmitted through the beam splitter. and a photodetector for detecting light, the semiconductor laser as described above. An optical head in which a beam splinter, an optical component, an objective lens, and a photodetector are moved together in the optical axis direction of the objective lens and in a direction perpendicular thereto.

Claims (1)

[Claims] A semiconductor laser, a polarizing beam splitter that transmits or reflects the laser beam from the semiconductor laser, an optical component that bends the path of the laser beam through the polarizing beam splitter at right angles, and a laser beam that passes through the optical component. an objective lens with a finite magnification that focuses the laser beam, and a laser beam that enters the objective lens from the opposite direction, whose path is bent at right angles by the optical component, and is reflected by the polarizing beam splitter or transmitted through the polarizing beam splitter. a photodetector that detects light, and the semiconductor laser, the polarizing beam splitter 2 optical component, the objective lens, and the photodetector are moved together in the optical axis direction of the objective lens and in a direction perpendicular thereto. Optical head made like this.