JPH087874B2 - Optical information reproducing device - Google Patents

Description

The present invention relates to an optical information reproducing apparatus, and more particularly to an image forming optical system having an optical axis in a direction inclined with respect to a normal line direction of an information recording surface of an information recording carrier. Thus, the present invention relates to an optical information reproducing apparatus for reproducing information by forming an image on the information recording surface on a photodetector.

[Prior Art] In recent years, there has been a growing demand for improvement in information recording density, and an optical information recording / reproducing system has come to be used in order to meet this demand. In the optical information recording / reproducing system, since the size of the irradiation spot formed when light is irradiated by using the optical system can be recorded as a unit of information, the recording density is extremely high, and the recording / reproducing means is used for the record carrier. Since recording and reproduction are performed without contact, there is an advantage that there is no wear deterioration of the record carrier and the recording and reproduction means.

The record carrier used in the optical information recording / reproducing system as described above includes a disc-shaped carrier, a pad-shaped carrier, a tape-shaped carrier and the like. Called card) is excellent,
It is expected that the range of use will expand more and more in the future.

Such an optical card is of a type capable of repetitive recording, reproduction and erasing in which information is recorded depending on the direction of magnetization, and additional recording and reproduction in which information is recorded by, for example, a pit row pattern. There are a type and a type in which only information can be reproduced, for example, information is recorded depending on the magnitude of the light reflectance, and they are used in a form that makes the best use of their respective characteristics.

When a large number of cards in which the same information is recorded are manufactured, a read-only optical card (hereinafter referred to as an optical ROM card), which has a high signal-to-noise ratio and is easy to manufacture and which can only be reproduced, is preferably used. .

The optical ROM card is manufactured, for example, as follows.
That is, for example, a vapor deposition film made of a low-reflectance metal such as Te is formed on a plastic substrate having a thickness of several hundreds of μm, and a mask corresponding to a recording information pattern is placed on the vapor deposition film.
A high-reflectance metal such as Cu is vapor-deposited on the metal layer, and a thickness of several hundred μm is formed on the low-reflectance metal film and the patterned high-reflectance metal film.
A protective film is formed by laminating about m of an optically transparent plastic film.

FIG. 7 is a block diagram of an optical head unit in the conventional reproducing apparatus used for reproducing the recorded information on the optical ROM card as described above.

In FIG. 7, reference numeral 2 denotes an optical ROM card, which has a substrate 2a, an information recording surface 2b and a transparent protective layer 2c.

Reference numeral 4 denotes an illumination light source, which is, for example, an LED or a semiconductor laser. Reference numeral 6 denotes a condenser lens that constitutes the illumination optical system, and 6a is its optical axis. The optical axis is an optical ROM
It is inclined by an angle θ with respect to the normal 12 of the information recording surface 2b of the card 2.

8 is a photodetector, which is, for example, a CCD line sensor. Reference numeral 10 is an image forming lens that constitutes an image forming optical system, and 10a is its optical axis. The optical axis is inclined by an angle θ with respect to the normal line 12 of the information recording surface 2b of the optical ROM card 2. The optical axis 10a and the optical axis 6a of the condenser lens 6
Are symmetrical with respect to the direction of the information recording surface normal 12 of the optical ROM card 2.

Illumination light emitted from the light source 4 is focused by an illumination optical system, passes through the protective layer 2c of the optical ROM card 2, and illuminates a predetermined area of the information recording surface 2b. A predetermined area of the illuminated information recording surface 2b is imaged on the photodetector 8 by the imaging optical system.

On the information recording surface 2b of the optical ROM card 2, a suitable number of recording bits as information units are arranged in the B direction to form an information track, and a suitable number of the information tracks are arranged in the A direction to form a band. Then, an appropriate number of the bands are arranged in the B direction to form the entire information recording area.

In the photodetector 8, light receiving elements are arranged in a line in the B direction, and at least one entire information track on the information recording surface of the optical ROM card 2 is imaged on the detector. At the time of reproducing information, the information tracks in a desired band are sequentially imaged on the photodetector 8 while the optical ROM card 2 is continuously or intermittently moved in the A direction by a driving means (not shown) to read the information. Done. When reproducing information in another band, the optical ROM card 2 is driven by a driving means (not shown).
Is moved in the B direction by a predetermined distance, and then information is read while moving in the A direction in the same manner as described above.

[Problems to be Solved by the Invention] According to the information reproducing apparatus as described above, the optical axis of the illumination optical system is set to the direction of the normal line of the information recording surface 2b of the optical ROM card 2 and the light flux reflected in the direction. There is an advantage in that the amount of illumination light can be effectively used as compared with an information reproducing apparatus of a type in which the image is divided by a half mirror or the like to form an image on a photodetector. In particular, when reproducing the optical ROM card as described above, since a predetermined area having a certain size of the information recording surface is simultaneously imaged on the photodetector by the imaging optical system to read the information, the amount of illumination light is changed. Improving utilization efficiency is extremely important.

However, in such an information reproducing apparatus, when reproducing the optical ROM card as described above, the transparent protective layer on the information recording surface is optically formed as a parallel plate obliquely arranged with respect to the optical system. As a result, astigmatism occurs during image formation, which makes the depth of focus extremely shallow, which makes focusing control difficult and the resolution is likely to decrease.

Letting Δp be the astigmatic difference when the light emission angle i (corresponding to θ in FIG. 7) on a parallel plate having a thickness of d and a refractive index of n ′, the following relational expression holds.

Δp = d (1-cos ² i / cos ² i ′) / n′cosi ′ ...
(1) sini = n′sini ′ (2) Therefore, for example, in the optical ROM card 2, the transparent protective layer 2c has a thickness d of 400 μm and the protective layer has a refractive index n ′ of 1.6.
When the angle θ in the figure is 30 °, i ′ is 18.2 ° and the astigmatic difference Δp is about 44 μm.

In the reproducing apparatus of the optical ROM card, the movement of the information recording surface 2b in the optical axis direction at the time of card transportation is taken into consideration as about 100 μm, but it is a considerable astigmatic difference compared to this size. Therefore, the influence on the depth of focus is great, and the focus control becomes difficult, so that the reliability of information reproduction decreases.

Therefore, the present invention solves the above-mentioned problems of the prior art, and relates to the information recording surface of an optical information recording carrier having a transparent layer on the information recording surface, the information recording surface of the information recording surface on the transparent layer side. In an optical information reproducing apparatus for reproducing information by forming an image on the information recording surface on a photodetector by an image forming optical system having an optical axis in a direction inclined with respect to the normal direction, the astigmatism caused by the transparent layer. The objective is to improve reliability of information reproduction by reducing aberrations and improving imaging performance.

[Means for Solving the Problems] According to the present invention, in order to achieve the above-mentioned object, the transparent layer of the optical information recording carrier of the optical information recording carrier having a transparent layer on the information recording surface is provided. In an optical information reproducing apparatus for reproducing information by forming an image on the information recording surface on a photodetector by an imaging optical system having an optical axis in a direction inclined with respect to the normal direction of the information recording surface on the side, An optical element for correcting astigmatism caused by the transparent layer of the record carrier is provided in either one of the image forming optical system and the record carrier and between the image forming optical system and the photodetector. An optical information reproducing device is provided, which is arranged in a divergent light beam or a focused light beam.

[Examples] Specific examples of the present invention will be described below with reference to the drawings.

FIGS. 1 (a) and 1 (b) are views showing the essential parts of a first embodiment of an optical information reproducing apparatus according to the present invention. In this embodiment, an optical ROM card is used as the optical information recording carrier.

In FIG. 1, 2 is an optical ROM card, which has a substrate 2a, an information recording surface 2b, and a transparent protective layer 2c. 8
Is a photodetector, 10 is an imaging lens that constitutes an imaging optical system, and 10a is its optical axis. The optical axis is inclined by an angle θ with respect to the normal line 12 of the information recording surface 2b of the optical ROM card 2. These are the same as in FIG. 7 above.

In this embodiment, the imaging lens 10 and the photodetector 8 are used.
A transparent parallel flat plate 14 is arranged between and. The parallel plate is in the direction orthogonal to the direction in which the information recording surface 2b is inclined with respect to the optical axis 10a of the imaging lens 1 (that is, in the xz plane) (that is, in the yz plane). It is arranged to be inclined with respect to. That is, the transparent parallel plate 14 is the optical axis of the imaging lens 10.
Information recording surface with respect to the optical axis 10a of the imaging lens when viewed in the direction of 10a
In the direction orthogonal to the direction in which 2b is tilted, the imaging lens optical axis
It is placed at an angle to 10a.

In FIG. 1, the z-axis is the direction of the optical axis 10a of the imaging lens 10, and the x-axis is the optical axis and the information recording surface 2 of the optical ROM card 2.
In the plane formed by the normal line of b, it is a direction orthogonal to the z axis, and the y axis is a direction orthogonal to both the x axis and the z axis.

On the information recording surface 2b, the information track is formed in the y direction, and the arrangement direction of the light receiving elements of the photodetector 8 is also the y direction. One information track 16 at a predetermined position is imaged on the photodetector 8 and information is read out.

In the present embodiment, the predetermined area of the information recording surface 2b of the optical ROM card 2 is illuminated in the same manner as in FIG.

In this embodiment, as described above, with respect to the optical axis 10a of the imaging lens 10 (that is, when viewed in the direction of the optical axis 10), the tilt direction of the information recording surface 2b of the optical ROM card 2 and the tilt of the parallel plate 14 are described. Since the directions are orthogonal to each other, the astigmatism caused by the transparent protective layer 2c of the optical ROM card 2 is corrected.

If the vertical magnification of the imaging lens 10 is α and the horizontal magnification is β,
Since the astigmatic difference Δp generated by the transparent protective layer 2c is magnified α times on the photodetector 8 side, the photodetector 8 by the protective layer 8c.
The astigmatic difference Δp ′ on the side is expressed by the following equation.

^{Δp '= αΔp = -β 2 Δp} ··· (3) may be corrected this astigmatism in the parallel plate 14, the characteristics of the above formula (1) may be determined by (2).
For example, in order to correct the astigmatic difference Δp = 44 μm in the above-described specific example, assuming that β = 5, Δp ′ = − 1.1 mm is obtained from the above equation (3), and this astigmatic difference is corrected. If the refractive index n'of the correcting parallel plate 14 is 1.6 and the inclination angle i of the parallel plate is 45 °, then i'is 26.2 ° from the above formula (2), and therefore the above formula (2) From 1), d becomes about 4.2 mm. That is, if the parallel plate 14 having a refractive index of 1.6 and a thickness of 4.2 mm is inclined at an angle of 45 °, the astigmatism caused by the transparent protective layer 2c can be canceled.

According to the present embodiment, the depth of focus of the image forming system is deepened, the resolving power is greatly improved, and therefore the reliability of information reproduction is improved.

As is clear from the above equations (1) and (2), the correction amount increases as the angle formed by the surface normal of the parallel plate 14 and the optical axis 10a increases, and the refractive index of the parallel plate 14 increases. The larger the correction amount is, the larger the correction amount is. Therefore, the thickness of the parallel plate 14 can be reduced. For example, if the angle i is 60 ° in the above embodiment, the thickness d may be about 2.3 mm.

Further, the correction amount can be adjusted by adjusting the inclination angle of the parallel flat plate 14, and the final adjustment can be performed by adjusting the inclination when the device is assembled and adjusted. Furthermore, optical RO
When there is a difference in the thickness and the refractive index of the protective layer 2c depending on the type of the M card 2, the type of the card is discriminated and the tilt angle of the parallel plate 14 is automatically set according to the type. It is also possible to correct the point aberration.

In this embodiment, the position of the parallel plate 14 on the optical axis 10a may be anywhere between the imaging lens 10 and the photodetector 8.

By disposing the parallel plate 14, the image forming position moves in the y direction, and the amount of movement Δy is expressed by the following equation.

Δy = dcosi (tani−tani ′) (4) For example, Δy is about 1.5 mm and about 1.2 mm in the above-mentioned specific example, which is particularly important if it is taken into consideration when designing the optical system. It doesn't matter.

2 (a), (b), and (c) are diagrams showing the essential parts of a second embodiment of the optical information reproducing apparatus according to the present invention. FIG. 2 (a) is a perspective view, and FIGS. 2 (b) and 2 (c) are views similar to FIGS. 1 (a) and 1 (b), respectively. However, in FIG. 2 (b), it is shown partially expanded.

This embodiment differs from the first embodiment only in that a rear surface mirror 18 having a reflecting surface on the back surface of the transparent parallel plate is used instead of the transparent parallel plate as an element for correcting astigmatism. In this embodiment, as shown in FIG. 2 (c), since the light beam passes through the parallel plate of the rear surface mirror 18 twice, it has a thickness half that of the parallel plate of the first embodiment. Therefore, the same effect can be obtained, and the device can be made lighter.

In this embodiment, since the image forming light beam is bent by the back mirror 18, there is also an effect that the optical head can be made thin. From this point as well, it is possible to make the optical head smaller, lighter and thinner overall. There are advantages.

FIG. 3 is a diagram showing the essential parts of a third embodiment of the optical information reproducing apparatus according to the present invention.

This embodiment differs from the first embodiment only in that the wedge prism 20 is used as an element for correcting astigmatism. The prism is arranged so that the surface normal of the effective surface is in the xz plane, so that the light flux passing through the prism 20 is deflected only in the xz plane.

The refractive index of the prism 20 is n ', the thickness of the prism on the optical axis 10a is d, and the astigmatic difference caused by the prism is Δp'.
Then, the following relational expression holds.

Δp ′ = d (1-cos ² i ₂ / cos ² i ₂ ′) / n ′ + p ₁ (1-cos ² i ₁ · cos ² i ₂ / cos ² i ₁ · cos ² i ₂ ′ ...
(5) sini ₁ = n'sini ₁ '... (6) n'sini ₂ = sini ₂ ' ... (7) where p ₁ is the image formation point and prism without prism 20
_I is the exit angle of the prism and i ₂ ′ is its entrance angle. The apex angle σ and the deviation angle ε of the prism are given by the following equations.

σ = i ₂ ′ + i ₁ (8) ε = (i ₂ + i ′) (9) In this embodiment, the prism 20 is arranged at the minimum deviation angle position. In this case, i ₂ = i ₁ ′ and i ₂ = i ₁ , so that the astigmatic difference Δp = 44 μm of the specific example of the first embodiment.
To compensate for _{the, n '= 1.6, i 1} = i 2 = 30 °, d = 8.7 m
The prism 20 having the characteristics of m, σ = 36.4 ° and ε = 23.6 ° may be arranged.

FIG. 4 is a diagram showing the essential parts of a fourth embodiment of the optical information reproducing apparatus according to the present invention.

This embodiment differs from the third embodiment in that the exit angle i ₁ of the light beam from the prism 20 is 0 °. Therefore, i ₁ ′ is also 0 °.

In this embodiment, in order to correct the astigmatic difference Δp = 44 μm of the specific example of the first embodiment, n ′ = 1.6, p ₁ = 1m
The prism 20 having the characteristics of m, i ₂ = 30 °, d = 7.1 mm, σ = 18.2 °, ε = 11.8 ° may be arranged.

FIG. 5 is a diagram showing the essential parts of a fifth embodiment of the optical information reproducing apparatus according to the present invention.

In this embodiment, the prism 20 transmits the image-forming light flux to the optical ROM card 2
It is different from the third and fourth embodiments in that the light is emitted in a direction parallel to the surface of the.

In this embodiment, in order to correct the astigmatic difference Δp = 44 μm of the specific example of the first embodiment, n ′ = 1.6, p ₁ = 20 m
m, i ₁ = 68 °, i ₂ '= 60.3 °, d = 7.7mm, σ = 68.3 °'
The prism 20 having the characteristic of ε = 60 ° may be arranged.

In this embodiment, the prism 20 converts the image-forming light beam into a light beam.
Since it is bent in a direction parallel to the surface of the ROM card 2, the optical head can be made thinner.

In the present invention, the astigmatism correction optical element in the first embodiment and the third to fifth embodiments may be used also as the light receiving window which constitutes the package of the photodetector. That is, in general, the photodetector is often used in the form of a package provided with a glass plate serving as a light receiving window in parallel with the front surface of the photodetector, and instead of the glass plate, the parallel plate 14 of the above embodiment is used. And the prism 20 is used.

FIG. 6 is a sectional view showing an embodiment of the package of the photodetector as described above. In FIG. 6, reference numeral 22 denotes a package main body, in which the photodetector 8 is fixedly arranged, and the prism 20 is attached to the photodetector 8 as a light receiving window in a predetermined positional relationship. There is. The parallel plate 14 may be used instead of the prism. In particular, the fourth
In the case of the fourth embodiment as shown in the drawing, it is convenient that the prism 20 is simply attached instead of the glass plate of the conventional package.

By integrating the photodetector package and the astigmatism correction optical element in this manner, assembly and adjustment are facilitated, and low cost and mass productivity are improved.

Although a parallel plate, a back surface mirror and a prism are shown as the astigmatism correction optical element in the above-mentioned embodiments, other suitable optical elements may be used as the astigmatism correction optical element in the present invention. .

Further, in the present invention, a plurality of different and / or the same type of astigmatism correction optical elements may be used in combination as the astigmatism correction optical element.

Further, in the present invention, the astigmatism correction optical element does not necessarily have to be arranged between the image forming lens 10 and the photodetector 8 as in the above-mentioned embodiment, and the optical information recording carrier and the image forming lens are not necessarily arranged. You may arrange in between. However, when the information recording surface 2b is enlarged and imaged on the photodetector 8, the imaging lens 10
Since the optical path length between the photodetector 8 and the photodetector 8 is longer, there is more space for installing the optical element, and the optical element can be easily installed.
Also, since astigmatism with an astigmatic difference of several tens of μm is corrected, it is preferable to dispose an optical element for correction on the magnifying side, that is, the photodetector side because the accuracy of the element and its arrangement becomes gentler. Cheap.

Furthermore, it goes without saying that the present invention is equally effective regardless of the direction of the information track of the information record carrier with respect to the direction of the optical axis of the imaging optical system.

In the above embodiment, the case where the optical information recording carrier is an optical ROM card is shown, but the present invention is the same when the optical information recording carrier is another optical card, an optical disk, an optical tape or the like. Can be applied to.

[Advantages of the Invention] According to the present invention as described above, astigmatism caused by the transparent layer on the surface of the information recording carrier can be reduced to improve the imaging performance, thus enhancing the reliability of information reproduction. Is possible. Further, according to the present invention, since the depth of focus can be increased by reducing the astigmatism, the accuracy of the optical information record carrier with respect to warpage and undulation, and the accuracy of the record carrier holding mechanism and the transport mechanism are alleviated. In addition, the accuracy of focusing control can be relaxed, and thus the cost of the optical information record carrier and its reproducing apparatus can be reduced.

[Brief description of drawings]

FIGS. 1 (a) and 1 (b) are views showing a main part of an optical information reproducing apparatus according to the present invention. 2 (a), (b) and (c) are views showing the main part of the optical information reproducing apparatus according to the present invention. 3, FIG. 4 and FIG. 5 are views showing the essential parts of the optical information reproducing apparatus according to the present invention. FIG. 6 is a sectional view showing the package of the photodetector. FIG. 7 is a block diagram of an optical head unit in a conventional reproducing apparatus used for reproducing recorded information on an optical ROM card. 2: Optical ROM card, 2a: Substrate, 2b: Information recording surface, 2c: Transparent protective layer, 4: Light source, 6: Condenser lens, 8: Photodetector, 10: Imaging lens, 10a: Optical axis, 14: Transparent parallel plate 16: Information track, 18: Rear surface mirror, 20: Prism, 22: Package.

Claims (5)

[Claims] 1. An optical information recording carrier having a transparent layer on the information recording surface, the optical recording medium having an optical axis in a direction inclined with respect to the normal line direction of the information recording surface on the transparent layer side with respect to the information recording surface. In an optical information reproducing apparatus for reproducing information by forming an image on the information recording surface on a photodetector by an image optical system, an optical element for correcting astigmatism generated by the transparent layer of the record carrier is provided with the above-mentioned structure. The optical information is arranged in either a divergent light beam or a focused light beam between the image optical system and the record carrier and between the image forming optical system and the photodetector. Playback device. 2. An astigmatism correction optical element is arranged in a direction orthogonal to a direction in which the information recording surface is inclined with respect to the optical axis of the imaging optical system when viewed in the direction of the optical axis of the imaging optical system. The optical information reproducing apparatus according to claim 1, wherein the optical information reproducing apparatus is a transparent parallel plate that is arranged to be inclined with respect to the optical axis of the image forming optical system. 3. An astigmatism correction optical element is arranged in a direction orthogonal to a direction in which the information recording surface is inclined with respect to the optical axis of the imaging optical system when viewed in the direction of the optical axis of the imaging optical system. A rear-view mirror arranged at an angle with respect to the optical axis of the imaging optical system,
The optical information reproducing device according to claim 1. 4. An astigmatism correction optical element in a direction orthogonal to a direction in which the information recording surface is inclined with respect to the optical axis of the imaging optical system when viewed in the direction of the optical axis of the imaging optical system. The optical information reproducing device according to claim 1, wherein the optical information reproducing device is a wedge type prism having a light deflecting action. 5. The optical information reproducing apparatus according to claim 1, wherein the astigmatism correction optical element is integrated with a photodetector package.