JPH0495234A - Optical information processor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention relates to an optical information processing device that uses light to record, reproduce, and erase information on an information recording medium such as an optical disk.

(Prior art) Technology for recording and reproducing information on disk-shaped media using light has made remarkable progress in recent years, and the trend in its practical use has changed from playback-only types such as compact discs to write-once types. Currently, the focus has shifted to erasable media using phase change media and magneto-optical media. At the same time, research and development is actively being carried out to speed up access and make the devices thinner, as one of the technical goals to improve the performance and expand the range of applications for the information processing devices used in these applications. ing.

FIG. 13 shows a conventional magneto-optical disk drive device developed for such a purpose.

Here, the fixed optical system 101 includes a semiconductor laser as a light source,
It consists of a collimator lens, a signal detection system, etc., and is integrally fixed to the frame of the drive device. The light beam emitted from the fixed optical system 101 is transmitted to the galvano mirror 102.
The direction of the disc 1 is bent and directed toward the objective lens 110, and the rotation of the galvanometer mirror 102 causes the disc 1 to be
05 tracking direction. In the figure, reference numeral 103 is a linear slide motor, and the slide motor is used to seek the actuator portion of the objective lens 110 in the radial direction of the disk 105.

FIG. 14 shows the optical system after the galvanometer mirror of the drive device, and in the figure, the light flux (
(represented by the principal ray in the figure) is deflected by the reflecting surface 106 of the galvano mirror, and the bending mirror 1
After being bent into an optical path directed toward an objective lens 110 at step 09, the light is focused onto the medium surface of the optical disk 105 by the objective lens 110 and narrowed down to a predetermined light spot. As a result, information is recorded, reproduced, erased, etc. in the drive device. Record information on a predetermined information track,
In order to reproduce and erase, the objective lens 110 and the bending mirror 109 are mounted on the actuator part and constitute a movable optical system, and the information area of the disk 105 is moved from the outermost position A to the outermost position by the slide motor. The track is sought in the range up to the inner circumferential position B, and reaches the vicinity of the predetermined track. Next, due to the rotation of the galvanometer mirror, the emitted light flux from the light source changes to 107.108107'' and 1 in the figure.
The tracking operation is performed by changing the angle of incidence on the objective lens 110 such as 0g'. As a result, access to a predetermined information track is completed in cooperation with the servo circuit.

In this way, by separating the optical system into a fixed optical system and a movable optical system, and by using a galvanometer mirror to perform tracking from outside the movable optical system, the weight of the movable part of the optical head can be reduced. The seek speed has been increased. In addition, since the objective lens actuator only needs to be driven in the focus direction, the above actuator,
As a result, the entire drive device is becoming thinner.

(Problems to be Solved by the Invention) As described above, in the conventional optical information processing device, optical scanning for tracking is performed from outside the movable optical system using a galvanometer mirror, etc.
．． 108. As shown at 107° and 108°, the position of the light beam entering the objective lens deviates from the optical axis of the objective lens, and as a result, part of the light beam deviates from the transmission area of the objective lens and reaches the disk. The amount of light reflected by the disc may vary, and the position of the light beam reflected by the disk and returned may be different from that at the time of incidence, which may adversely affect the accuracy of signal detection.

In particular, fluctuations in the position of the light beam after reflection are affected by both the deflection angle of the light beam by the galvanomirror and the position of the movable optical system, so it is difficult to correct. There was a problem in that it required a lot of control.

(Object of the Invention) The present invention has been made based on the above-mentioned circumstances, and includes an optical element having a plurality of reflection or refraction surfaces arranged between a fixed optical system and a movable optical system. An object of the present invention is to provide an optical information processing device that can minimize fluctuations in the light flux reflected by an optical disk and reaching a fixed optical system by arbitrarily setting the intersection point of the light flux (intersection with the optical axis). It is something.

(Means for Solving the Problems) Therefore, the present invention provides a fixed optical system that includes a light source and a signal detection system and is fixed relative to other members, and a light beam emitted from the fixed optical system. A movable optical system having an objective lens focused on the optical disc and movable in the radial direction of the optical disc, and an optical element comprising a plurality of reflective or refractive surfaces disposed between the fixed optical system and the movable optical system. In the optical information processing device, the optical element is rotated parallel to the optical axis of the light beam incident on the optical element such that the light beam passing through the optical element intersects at one point on the extension of the optical axis of the incident light beam. Configured to be rotatable around an axis (Example) The present invention will be described in detail below with reference to illustrated examples. FIG. 1 schematically shows an optical head for a magneto-optical disk of an optical information processing device according to the present invention. A collimator lens is used to form a light beam, and 3 is a polarizing beam splitter. A part of the polarizing beam splitter also serves as a shaping prism that expands the width in the plane of the paper of the parallel light flux incident from the collimator lens. Further, 4 is a wedge prism, and the wedge prism can be rotated around the incident parallel light beam using a rotation mechanism (not shown). The wedge direction of the wedge prism 4 is included within the paper plane of FIG. 1 in a reference state to be described later. The above-mentioned light beam is deflected upward in the plane of the paper by a bending mirror 5, and an objective lens 6 corresponding to the upper side
The light is focused onto the medium surface of the optical disk 7 and narrowed down as a light spot. Note that the optical axis of the objective lens 6 is adjusted in advance so as to coincide with the optical axis (principal ray) of the light beam passing through the wedge prism 4.

The bending mirror 5 and the objective lens 6 are mounted on an objective lens actuator base (not shown), and are movable from point A to point B in the radial direction of the optical disc 7 by a seek mechanism (also not shown). The light beam reflected on the medium surface of the disk 7 follows an optical path in the reverse order of the objective lens 6, the bending mirror 5, and the wedge prism 4, and after being reflected by the polarizing beam splitter 3, the polarization plane is changed by the l/2 wavelength plate 8. After passing through an astigmatism optical system 9 consisting of a spherical lens and a symmetrical lens, the beam is split into three beams by a beam splitting surface 10 and reaches a photodetector 11. Beam splitter 10
is a composite prism in which the first beam splitting surface is a non-polarizing beam splitter and the second beam splitting surface is a polarizing beam splitter. Second and third beams having orthogonal polarization directions are generated.

Note that the focusing method in this example is an astigmatism method,
The tracking method is a one-beam push-pull method.

In the figure, 20 is a fixed optical system, and the members included therein are fixed to the main body of a drive device (not shown).

The objective lens 6 is movable in the focus direction by its actuator, and is used to perform autofocus control. However, here, the so-called auto-tracking is not performed in the objective lens section, but is performed using the wedge prism 4 as explained below.

FIG. 2 is a diagram of the wedge prism 4 viewed from the optical axis direction of the incident light beam. That is, the Z-axis is the optical axis direction, and the wedge prism 4 is rotated around the Z-axis by a rotation mechanism described later. In the figure, the position indicated by the broken line is the reference position. The direction of the fascia at this position, that is, the direction in which the wedge thickness increases, is the X-axis direction. Therefore, the light beam passing through the wedge prism 4 is deflected within the plane of the paper in Figure 1, and coincides with the optical axis of the objective lens. proceed in the direction. In Fig. 2, when the wedge prism 4 is rotated by an angle θ around the Z axis,
The refracted light ray travels in the x'z plane.

FIG. 3 is an enlarged view of the wedge prism 4 in the XZ plane, and FIG. 4 illustrates the deflection direction of the light beam due to rotation of the wedge prism 4. As shown in FIG. 3, the incident light ray 21 is refracted by the first surface of the wedge prism 4, and is refracted again by the second surface, so that it follows the P-Q-H optical path and becomes the output light ray 22. The output ray 22 intersects the extension of the input ray 21 at a point R at an angle δ. wedge prism 4
When rotates around the incident light beam 21, the output light beam 22 moves around the rotation axis without maintaining an angle δ with the rotation axis. The X, Y, and coordinates in Figure 4 are in a coordinate system perpendicular to the incident ray including point Q in Figure 3, the X1Ya coordinates are in a coordinate system with the origin at point R, and the ξη coordinate is orthogonal to the optical axis of the objective lens. do,
Represents the coordinates taken on the entrance pupil of the objective lens. As can be understood from the figure, when the wedge prism is rotated by the azimuth θ, when viewed from the optical axis side of the objective lens, the luminous flux is δ sin θ in the η direction (radial direction of the disk) and δ sin θ in the ξ direction (tangential direction). The light is deflected by 1-cos θ) and enters the objective lens. As mentioned above, θ=O
When the wedge prism is rotated by a certain angle back and forth with .degree. as a reference position, a light beam having the above-mentioned angle of view will be incident on the objective lens, thereby making it possible to perform tracking. As shown later in numerical examples, if the angle δ is appropriately selected, the movement in the ξ direction is negligibly small, and tracking in the η direction, that is, in the radial direction, is possible.

Returning to the explanation of FIG. 3 again, the deflection angle of the emitted light beam when the specifications of the wedge prism 4 are given will be specifically calculated. In the figure, the wedge angle of the wedge prism 4 is ε, the refractive index is n,
The angle of incidence of the ray on the first surface of the prism is i, and the angle of deflection is δ.
and find the position of point R.

In △QSH, tQsR=90" + i+ε, so (90°+i+ε) + (90"-i') +δ
= 1800, that is, δ=i' −i−ε, , , , , , , , , , ,
(It becomes 11.

On the other hand, at points P and Q, according to Snell's law, sin i
=nsin r, , , , , , , , , (
2) n sin (r + ε) = sin i ',,,,
,,, (3). By substituting io obtained using equations (2) and (3) into (1), δ can be determined. Next, QH=PQ sin (i - r) where the point Q' is the point where the normal to the first surface at point P intersects with the second surface. PQ' is defined as the thickness of the wedge passing through point P. Using equations (4), (5) and (2), calculate the length PR
5, that is, the position of point P with respect to point P is determined.

If point R, that is, the intersection of the deflected light rays, is placed at the front focal point of the objective lens, a so-called telecentric optical arrangement will be created, and the light reflected from the disk will return along the same optical path as the incident light, so the deflection No deflection of the light beam occurs. In the case of a separation optical system, since the objective lens moves, it is not possible to always maintain the intersection of the rays at the front focal position, but by setting the R point near the center of the movable range of the objective lens, the deflection of the rays and the objective lens can be reduced. It is possible to minimize the vignetting of the luminous flux due to

The results calculated using the above formula are shown in the table below.

Furthermore, the rotation angle θ of the wedge prism is calculated for the case where 1=45°. As mentioned before, the light flux incident on the objective lens changes in the radial direction by δsin due to the rotation of the angle θ.
Since it enters the field with an angle of view of θ, the focal length of the objective lens is set to fo = 3.5 mm, and the track pitch is 5 on the disk.
In order to perform the main task, that is, tracking of 1.6 μm×5=8 μm, fo tan(δsinθ) =0.00
8, we get θ=4.2°.

In other words, in the calculation example above, a wedge prism with a wedge angle of 2 degrees and a thickness of about 4 mm is tilted at approximately 45 degrees and rotated about ±4 degrees around the optical axis, thereby achieving tracking within a range of several tracks. Optical spot scanning is possible. By combining this with the aforementioned seek operation of the objective lens actuator, it becomes possible to access any information track.

FIG. 5 is a diagram showing a specific example of a rotation mechanism for rotating the wedge prism. In the figure, 24 is a lens barrel that holds the wedge prism 4, 25 and 26 are supporting the lens barrel 24, and a rotating shaft 2.
9 is a bearing for rotation, and 27 is a coil. FIG. 6 shows the lens barrel 24 including the coil 27 and the rotating shaft 2.
FIG. 9 is a sectional view taken from a section perpendicular to FIG. The wedge prism 27 rotates around a rotation axis 29 as indicated by an arrow in the figure due to interaction between a fixed magnet 28 provided near the coil 27 and a magnetic field generated by energizing the coil 27.

FIG. 7 is a diagram showing another example of the rotation mechanism. The housing 30 shown in the figure holds the wedge prism 4 therein, and
It rotates around a rotation axis 29 parallel to the incident light beam 21 and spaced a certain distance apart. 27 hails the coil. When the incident optical axis and the rotation axis are parallel to each other and deviate by β as in this example, the thickness PQ of the wedge described above changes with the rotation, but the amount is approximately (1-cosθ )・12 tanε
It is. Using the above numerical example of θ=4.2° and ε=2°, 4
Even if 2 = 10 mm, it is less than 1 uI11 and is so small that it can be ignored.

Another feature of this embodiment is that assembly and adjustment are easy. In addition to the small effect of the misalignment between the rotational axis and the optical axis as in the example above, the accuracy of setting the angle of incidence of the light ray on the wedge prism is also moderate. It can be seen that even if i changes in the vicinity of 45°, the deflection angle δ changes by less than 0.06° per 1°.Furthermore, the tilting of the wedge prism in the direction perpendicular to the wedge direction causes the angle fluctuation of the output light to change. The amount of parallel deviation is also 1 for a prism with a thickness of 4 mm.

The diameter is as small as about 20 μm.

Since a conventional galvanometer mirror is a single reflecting mirror, the direction of the reflected light beam is sensitively affected by angle setting errors.

Additionally, the reflective surface may move due to changes in temperature or over time, causing an offset. On the other hand, the structure of the present invention has the advantage of being easy to assemble and less likely to change over time.

FIG. 8 is a diagram for explaining the second embodiment of the present invention. In FIG. 0, 31 and 32 are both wedge prisms.
The first wedge prism 31 is fixed to the main body of the drive device (not shown) and does not move, and only the second wedge prism 32 rotates around the optical axis that enters the prism. The wedge prisms 31 and 32 are arranged so that their wedge angles are the same, their directions are opposite, and their overall inclination directions are also opposite.

This arrangement allows the incident light beam 21 and the output light beam 22 to be made parallel, which is convenient for manufacturing the optical head device. Also, although very slight, variations in the output angle caused by variations in the wavelength of the light source when a single wedge prism is used can also be canceled out by adopting such a configuration.

FIG. 9 is a schematic diagram of main parts of a third embodiment of the present invention. In the figure, 33 and 34 are wedge prisms. The wedge angles are different from each other, and the output beam 22 has a constant deviation angle with respect to the input beam. Two wedge prisms33.
34 together about a rotation axis coinciding with the input beam 21, the output beam 22 is deflected. Two surfaces, the ray entrance surface of the wedge prism 33 and the ray exit surface of the wedge prism 34, are perpendicular to the incident ray.

For this reason, when holding the wedge prism in the rotating mechanism as explained in FIG. 5 or FIG. 7, there is no need to arrange it obliquely, and there is an advantage that processing and assembly of the lens barrel is facilitated.

FIG. 10 is a schematic diagram of a main part of a fourth embodiment of the present invention.

In the figure, 35 is a parallel flat glass plate, and 36 is a wedge prism, which are simultaneously rotated around the incident light beam 21.

Although the above embodiments have been described with reference to an optical head of a separated optical system, the present invention can also be applied to a fixed optical system in which the entire optical system is integrated. In this embodiment, for example, a point R where the emitted light 22 intersects the rotation axis in a fixed optical system is used.
This is convenient for the purpose of finely adjusting the inclination of only the parallel plate glass 35 and moving the point R on the extension line of the incident light ray 21 in order to precisely match the focal position of the objective lens.

FIG. 11 is a schematic diagram of main parts of a fifth embodiment of the present invention.

In the figure, 37 and 38 are mirrors, and these two mirrors can rotate together around the incident light beam 21. In the case of a system using such a mirror, it is easier to set the deflection angle δ to be thicker than that of a wedge prism. Therefore, if the deflection angle of the light beam incident on the objective lens (δsinθ described above) is fixed. , the rotation angle θ can be made small.For example, if δ is set to 15° and the same conditions as in the calculation example of the first embodiment are applied, θ=±0.5°, and the rotation angle θ
becomes significantly smaller. As a result, it becomes possible to configure the rotation mechanism using a piezoelectric element or the like instead of the electromagnetic drive type rotation mechanism as shown in FIG. 5 or 7.

In addition, the so-called two-mirror configuration consisting of two reflective surfaces as in this example is stable against rotation or parallel movement of the entire body in directions other than the intended rotation direction, and the emitted light beam is It is well known that it is not accepted.

FIG. 12 shows a modification in which the two mirrors of the fifth embodiment are replaced with one prism 39. By integrating the prism, it becomes mechanically stronger and more stable.

(Effects of the Invention) As described in detail above, the present invention allows the intersection position (fixed point) of the deflected and scanned light beam to be set at any position on the optical axis using a simple optical element. Alternatively, it is highly effective in reducing vignetting of the light beam incident on the objective lens in the optical system of an optical head such as a fixed optical system, and in suppressing fluctuations in the light beam reflected on the disk surface and reaching the detection system. . It also has the advantage of being easy to assemble and adjust, and being less susceptible to environmental changes and deformation over time unlike conventional galvanometer mirrors.

Note that the present invention is applicable not only to optical heads but also to general scanning optical systems that scan light beams, and can exhibit the same effects as described above.

[Brief explanation of drawings]

FIG. 1 is a schematic plan view of an optical head section of an optical information processing device according to a first embodiment of the present invention, FIGS. 2 to 4 are diagrams explaining the functions of the first embodiment, and FIGS. FIG. 7 is an explanatory diagram of the rotating scanning mechanism of the first embodiment, FIGS. 8 to 11 are schematic diagrams of main parts of the second to fifth embodiments of the present invention, and FIG.
FIG. 13 is a schematic diagram of a conventional magneto-optical disk drive device, and FIG. 14 is a schematic sectional view of an optical system of the device. 1... Semiconductor laser 4... Wedge prism 6
...Objective lens 10...Fixed optical system 21.
...Incoming ray 22...Outgoing ray. Figure 1 / / / / Agent Patent Attorney Seki Yamashita Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure

Claims (3)

[Claims] (1) It has a fixed optical system that includes a light source and a signal detection system and is fixed relative to other members, and an objective lens that narrows the light beam emitted from the fixed optical system onto the optical disc, and also in the radial direction of the optical disc. an optical information processing device comprising a movable optical system that is movable between the fixed optical system and the movable optical system; The optical element is configured to be rotatable around a rotation axis parallel to the optical axis of the light flux incident on the optical element so that the light flux passing through the element intersects at one point on the extension of the optical axis of the incident light flux. An optical information processing device characterized by: (2) The optical information processing device according to claim 1, wherein the optical element is a wedge-shaped prism. (3) The above-mentioned optical element has an even number of reflective surfaces, and the reflective surfaces are arranged so that the light flux emitted from the optical element intersects the rotation axis. The optical information processing device according to item 1.