JPS5994254A - Optical information reader - Google Patents

Abstract

PURPOSE:To avoid the revolution of a beam splitter itself by providing a laser light source, a beam splitter, a photodetecting element, etc. at the fixed stage side and providing an objective lens and an optical system which leads the laser light to the objective lens to a mobile stage that moves in the radius direction of a disk. CONSTITUTION:If it is supposed that a mobile stage 2 revolves in response to the shift of a disk 1 toward its radius direction, it is sufficient to think about the revolution of an objective lens 14a since only said objective lens is set on the stae 2. If the lens 14a turns around a center point P by theta as shown by broken lines for convenience, the image forming position a' of the laser light on the disk 1 set by an objective lens 14a' after revolution goes away from the image forming position (a) set with no revolution by a focal distance of f1tantheta, where f1 shows the focal distance of the lens 14a (14a'). However, a beam splitter 10, a condenser lens 15 and a photodetecting element 16 are set on a fixed stage 3 and consequently have no revolution. Therefore the polarization separating surface 10a of the splitter 10 also has no revolution. Thus the reflected luminous flux 17a' sent from the surface 10a is made correctly incident to a point (b) of the element 16 as in the case where the mobile stage 2 has no revolution.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical information reading device that reads information from an optical recording disk.

FIG. 1 shows a conventional example of this type of information reading device. In the figure, 1 is a disk on which optically readable information is recorded, 2 is a movable table movable in the radial direction of this disk, and 3 is a stationary table that does not move. Fixed stand 3
A laser light source 4, a fixed mirror 6.7 for bending and reflecting the linearly polarized laser beam 5 from the laser light source, and a beam diameter enlarging lens 8 are mounted and supported on the top.

On the other hand, on the movable table 2, there is a beam splitter 10 that receives the parallel beam 9 whose diameter has been expanded by the beam diameter enlarging lens 8, a quarter wavelength plate 11, and movable mirrors 12 and 13.
A focusing actuator 14 having an objective lens 14a is mounted and supported, and a beam splitter 1
A condensing lens 15 and a light receiving element l6 that receive reflected light from zero are fixed.

In the optical information reading device having such a basic configuration, information is read out in the following manner by rotating the disk 1 and moving the movable table 2 in the radial direction of the disk 1. A linearly polarized laser beam from a laser light source enters a beam splitter 10 as a parallel beam via a fixed mirror 6.7 and a light diameter enlarging lens 8. The parallel light beam emitted from the beam splitter 10 passes through the quarter-wave plate 11 and is reflected by the focusing actuator 1.
An image is formed on the disk 1'' by the objective lens 14a of No. 4. The laser beam reflected by the information recording surface of the disk l returns along the same optical path as the incident optical path, passes through the quarter-wave plate 11 again, and reaches the beam splitter 10. The plane of polarization of the light beam that has passed through the quarter-wave plate 11 changes with respect to the light beam emitted from the laser light source 4 due to the phase change upon reflection on the disk surface and the reciprocation through the quarter-wave plate 11. Therefore, the reflected light beam incident on the beam splitter 10 is reflected at the polarization separation surface 10a of the beam splitter 10, and is reflected by the condenser lens 15.
The light reaches the light receiving element 16 through the.

Since information is written as the magnitude of reflectance in small pits arranged in a concentric or spiral track shape on the disk l, the signal of the reflected light that reaches the light receiving element 16 is an electrical digital signal or an analog signal. It will be taken out as.

In order for this information reading device to accurately read all the information on the disc l, it is essential to move the focused spot by the objective lens 14a correctly in the radial direction of the disc l. However, in the conventional device described above, the optical axis of the laser beam may shift due to mechanical errors in the moving mechanism of the moving table 2, and as a result, the light cannot be accurately received by the light receiving element 16, and the converted electrical signal may become unstable. there were.

Although various studies have been made regarding the causes of this, the inventors have discovered that this is mainly due to the slight rotation that occurs as the moving table 2 moves. That is, when the movable table 2 rotates, all the elements on the movable table 2 also rotate, but the rotation angle of the light beam reflected by the polarization separation surface 10a of the beam splitter 10 is different from that of the condenser lens 15 and the light receiving element. 16
is larger than that of the optical axis, which causes the optical axis to shift.

FIG. 2 is a diagram showing the following two relationships. In this figure, the quarter-wave plate 11 and movable mirrors 12, 13 of FIG. 1 are omitted to simplify the problem. First, consider an ideal state in which there is no error in the movement mechanism of the moving table 2 and no rotation occurs when the disk 1 is moved in the radial direction. After passing through the beam splitter 10, the parallel light beam 9 emitted from the light beam diameter enlarging lens 8 is focused on a point a on the disk l by the objective lens 14a, and is reflected. The reflected light beam 17 passes through the objective lens 14a again, is reflected by the polarization separation surface 10a of the beam splitter 10, is condensed by the condenser lens 15, and is focused on the dot of the light receiving element 16. At this time, the chief ray 18 of the reflected light beam 17 is vertically incident on the light receiving element 16 .

Next, consider the case where the moving table 2 rotates as it moves. For the sake of convenience, the rotation axis is assumed to be the center point O of the beam splitter lO, and its rotation angle is assumed to be θ. Assuming that each element after rotation is indicated by a dashed line, and a dash (°) is added to the symbol,
The parallel light beam 9 passing through the beam splitter 10' and entering the objective lens 14a' is focused on a point a' on the disk 1 because the objective lens 14a' is rotated by θ.

Point a′ is f 1tanθ (f+ is objective lens 1
4 (14°) focal length). disc 1
The light beam reflected by the beam passes through the objective lens 14a' again and enters the beam splitter 10'. Objective lens 14a'
The reflected light flux 17' reaching the beam splitter 10' from
The chief ray is almost parallel to the incident light beam 9, although there is some movement. Incidentally, the rotation angle of the polarization separation surface 10a'' of the beam splitter 10' is θ;
The rotation angle of the reflected light beam 17' reflected at 0a' is 2θ with respect to the reflected light beam 17 when the separation surface 10a' is not rotated. Therefore, the condensing point b'' on the light receiving element 16' by the condenser lens 15' is shifted from the condensing point b' when the rotation angle of the reflected light beam 17' is θ. 15゛ and the rotation angle θ of the light-receiving element 16'', the reflected luminous flux 17° is rotated by θ more than that.
Approximately f2tan (+ (f2 is the condensing L/7 lens 15 (15
Furthermore, the principal ray 1B' of the reflected light beam 17' does not enter the light receiving element 16' perpendicularly. In this way, the elements on the moving stage 2, especially the beam splitter 1
Since the rotation angle of the reflected light beam is twice as large as the rotation angle of 0, it is thought that the correct electrical output according to the reflected signal will not be generated in the light-receiving element 16, and as a result, noise and other noise will occur. .

The present invention was made based on the above analysis, and solves the above problems by mounting and supporting the beam splitter and the light receiving element on a fixed table to prevent the beam splitter from rotating itself. It is characterized by

The invention will now be described with reference to the illustrated embodiments. FIG. 3 shows an embodiment of the present invention, but the components themselves are similar to the first embodiment.
This is the same as the conventional example shown in the figure, and the same elements are given the same reference numerals.The feature of the present invention is that the beam splitter lO and the light receiving element 16 are mounted and supported on the fixed base 2 together with the laser light source. . Further, on the fixed base 2, there are installed an optical system that guides the laser light from the laser light source 4 to the beam splitter 10, that is, a fixed mirror 6.7, a beam system magnifying lens 8, and a light receiving element that receives the reflected light from the beam splitter O. 16, that is, a condensing lens 15, is similarly mounted and supported.Furthermore, a quarter-wave plate 11 is fixed to the output end of the beam splitter O.

On the other hand, a moving table 3 that moves in the radial direction of the disk 1
On the top, there is a focusing actuator 14 having an objective lens 14a, and an optical system that guides the laser beam exiting the quarter-wave plate 11 to the objective lens 14a, that is, a movable mirror 1.
Only 2.13 is supported on board.

The operation of the present information reading device having the configuration described in section 2 is not substantially different from that of the conventional device shown in FIG. can accurately read the information recorded in the

Referring to FIG. 4, let us examine the effect of rotation of the moving table 2 in the same manner as in the conventional example. In this figure, the quarter-wave plate 11 and movable mirrors 12 and 13 are omitted as in FIG. 2. Assuming that the moving table 2 rotates as the disk l moves in the radial direction, only the objective lens 14a (focusing actuator 14) is mounted on the moving table 2, so consider only the rotation of this. Bye. For convenience, it is assumed that the objective lens 14a is rotated by θ as shown by a broken line around the center point P. The imaging position a° of the laser beam on the disk l by the objective lens 14a' after rotation is fita from the imaging position a when there is no rotation.
They are separated by iθ (f+ is the focal length of the objective lens 14a (14a')). This is the same as in FIG. The reflected light beam 17' reflected by the disk l passes through the objective lens 14a', travels in the same optical path as the incident light beam 9 in the opposite direction, and enters the beam splitter 10. However, the beam splitter lO1 condenser lens 15 and the light receiving element 16 are not rotated because they are mounted on the fixed base 2, and therefore the polarization separation surface 10a of the beam splitter 10 is also not rotated. Therefore, the reflected light beam 17a° reflected by the polarization separation surface 10a correctly enters the light receiving element 16 as in the case where the moving table 2 does not rotate.

The principal ray 18' of the reflected light beam 17' also enters the light receiving element 16 perpendicularly. Therefore, even if the moving table 2 rotates,
Reading errors that occur with conventional devices are less likely to occur.

The quarter-wave plate 11 is mounted on the moving table 2.
Although it is possible to do so, it is clear that it is more advantageous to mount it on the fixed base 3 side as in the embodiment. In this type of optical information reading device, a so-called 3-beam method is also known, in which a diffraction grating is placed in front of the beam splitter 10 to split the light beam into three beams, and the tracking error is detected using the ±1st-order light. It is being The beam splitter referred to in the present invention also includes a beam splitter having this diffraction grating.

As described above, in the present invention, a laser light source, a beam splitter, a light receiving element, etc. are provided on the fixed table side, and a movable table that moves in the radial direction of the disk is provided with an objective lens and an optical system that guides the laser beam to the lens. Since the beam splitter and light receiving element remain stationary even when the moving table moves, it is possible to obtain optical information with great accuracy compared to conventional devices in which these elements move together. can. Furthermore, since the number of elements mounted on the moving table 2 is significantly reduced, the moving table can be made lighter and smaller, and the moving table driving mechanism can be simplified and the load can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of the main parts of an example of a conventional optical information reading device, Fig. 2 is an optical path diagram for explaining the problems of the conventional example shown in Fig. 1, and Fig. 3 is an embodiment of the present invention. FIG. 4 is a perspective view of a main part showing an example, and is an optical path diagram for explaining one effect of the device of the present invention. l... Optical recording disk, 2... Moving table, 3...
- Fixed stand, 4... Laser light source, 6, 7... Fixed mirror, 8... Luminous flux diameter enlarging lens, 10... Beam splitter. 11... Quarter wavelength plate, 12.13... Movable mirror, 14a... Objective lens, 15... Condensing lens 1
．． 16... Light receiving element. Patent Applicant: Asahi Optical Industry Co., Ltd. Agent: Kunio Miura 2. Hand-selling assistant'iE letter (spontaneous) 1. Display of case 1982 Patent Application No. 204800 2, name of invention Optical information reader 3, person making amendment Relationship to case Patent applicant address 2-36-9 Maeno-cho, Itabashi-ku, Tokyo Name (
052) Asahi Optical Industry Co., Ltd. Representative Toru Matsumoto 4, Agent 102 Address 5-6 Goban-cho, Chiyoda-ku, Tokyo, Japan Claims column and Detailed description of the invention column 6 of the specification, Amendment Contents (1) Amend the claims as shown in the attached sheet. (2) After "Fixed." in the first line of page 3 of the specification, "Beam splitter 10 is strictly a polarizing beam splitter, and this polarizing beam splitter 10 and the quarter-wave plate 11 Both of these constitute a beam splitter for linearly polarized laser light, but it is known in optical principles that a single half mirror can also be used as a beam splitter for linearly polarized laser light. Insert. (3) “Quarter wavelength plate 1” in the bottom line of page 10 of the circular, line 6
1 is preceded by ``As mentioned above, in terms of optical principles, the beam splitter 10 can be replaced with a single half mirror, and in this case, the quarter-wave plate 1'l is unnecessary. When using a polarizing beam splitter and a quarter wave plate as the beam splitter as in the above embodiment, this
Insert. Document stating the amended scope of patent claims (Japanese Patent Application 1982-
(No. 204800) (1) Beam split the laser beam! The irradiated laser beam is irradiated onto the optical recording disk through the objective lens, and the irradiated laser beam is moved in the radial direction of the disk, and the reflected light from the disk is guided to the light receiving element via the objective lens and beam splitter, and the laser beam is irradiated onto the optical recording disk. An optical information reading device for reading information recorded on a disc is provided with a movable base that moves in the radial direction of the disc and a fixed base that does not move, and a laser light source, the beam spree, and a light source are mounted on the fixed base. , the light receiving element and an optical system between these elements are mounted and supported, and the objective lens and an optical system that guides the laser light from the beam splitter to the objective lens are mounted and supported on the moving table. An optical information reading device characterized by: 309-

Claims (1)

[Claims] (1) A laser beam is irradiated onto an optical recording disk through a beam splitter, a quarter-wave plate, and an objective lens, and this irradiated laser beam is moved in the radial direction of the disk to reflect reflection from the disk. An optical information reading device that reads information recorded on the disk by guiding light to the light receiving element through the objective lens and the beam splitter, which includes a movable table that moves in the radial direction of the disk and a fixed table that does not move. A laser light source, the beam splitter, the light receiving element,
and an optical system between these elements is mounted and supported, and the objective lens and the optical system that guides the laser beam from the beam splitter to the objective lens are mounted and supported on the moving table. information reading device. (2. The optical information reading device according to claim 1, wherein the quarter-wave plate is mounted and supported on the fixed base side.