JPS6028044A - Optical information reader - Google Patents

Abstract

PURPOSE:To facilitate reproduction of signals by using an off-axis grating lens to produce a difference between the optical axis of the light incident on said grating lens from a light source and the optical axis of the light which is reflected from an information recording surface and transmitted through the grating lens. CONSTITUTION:The light beams 21 delivered from a light source 20 are turned into parallel luminous fluxes 24 through a collimating off-axis grating lens 23 and then made incident to a focusing off-axis grating lens 26. The primary diffracted light 27 forms a focal point 30 on an information recording surface 29, and the reflected light including information is sent again to the lens 26. While the zero-order transmitted light 31 goes back just as the transmitted light with an optical axis different from that of the flux 24. Then a focusing error, signal, a tracking error signal and a record information signal are detected out of the reflected light including the light 31 through a grating lens 32 for astigmatic optic and a photodetecting part including a 4-split photodiode 33. In such simple constitution, the signal can be easily reproduced.

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention relates to an information reading method for optically reproducing information formed as pits on a disc-shaped optical recording medium such as a video disc or a digital audio disc. This relates to the configuration of the optical system (hereinafter referred to as an optical head) of the device.

[Prior art and its problems]

The configuration of the most typical conventional optical head will be explained with reference to FIG.

For example, a light beam emitted from a light source (1) consisting of a semiconductor laser is collected by a collimating lens (2) to form a parallel beam, and the plane of polarization is a polarizing beam sinter (3).
) is made to travel as a P wave, and the quarter-wave plate (4) rotates the plane of polarization by 45 degrees to converge: y l: t
5) as the incident light.

In addition, when the reflected light from the disk (6) passes through the quarter-wave plate again, the plane of polarization is rotated by 45 degrees, and it eventually enters the polarizing column beam splitter (3) as an S wave, so that the semiconductor laser illumination The reflected light is guided in a direction perpendicular to the light beam.

Furthermore, this reflected light is transmitted to a photodetector (8) via a beam conversion optical system (7) composed of a cylindrical lens, a knife, etc.
), a focus error signal, a tracking error signal, one image or an audio signal can be obtained.

The above is the main configuration of the conventional example, and the most important component of the optical system is the converging lens (5).

In order to narrow down the light beam of the semiconductor laser (1) to a diameter of about 1 μm on the surface of the disk (6), it is necessary to reduce the aberration shadow # of the converging lens (5) as much as possible. Uses synthetic lenses.

In addition, the incident light to the converging lens (5) is made incident along the optical axis of the lens, and the converging lens (5)
) are perpendicular to each other, so the reflected light containing information on the disc surface returns along the optical axis of the re-string. In other words, some means must be used to extract the reproduced signal. Since it is safe to separate the reflected light, conventionally, the polarizing beam splitter (3) and the quarter-wave plate (4) are used to completely separate the reflected light as described above.

However, as mentioned above, the conventional optical head has a very large number of parts, and each optical part is required to have very high precision.

This is because, for example, the converging lens r5) is a composite lens, consisting of a lens group with several lenses arranged below the optical axis, and is incorporated into an optical information reading device to track the movement of an optical recording medium. It must be small and lightweight (
It is also clear from the fact that it is particularly difficult to assemble lenses with apertures of several millimeters by aligning their optical axes with high precision.

Furthermore, how to separate the incident light and the reflected light on the optical recording medium, that is, the polarization property of the light source (1) made of, for example, a semiconductor laser! 1. In the combination of a polarizing beam splitter and a quarter-wave plate, it is not only necessary that the polarization of both optical components be well-customized, but also that the polarization of both optical components be adjusted to the polarization plane of the semiconductor laser. This poses the difficulty of having to match and assemble with high precision.

[Purpose of the invention]

The present invention has been made in consideration of the above-mentioned problems, and is an optical head that reduces the number of component parts of an optical head and easily optically reproduces a signal from information formed as bits on an optical information recording medium. The purpose of the present invention is to provide an information reading device.

[Summary of the invention]

The present invention includes a light source, at least one off-axis gelating lens for converging a light beam emitted from the light source onto an information recording surface, and an information recording surface obtained by converging the light beam on the information recording surface. To provide an optical information reading device, which comprises an optical system that detects reflected light containing information of be.

Next, the ophaxis gelating lens, which is the main feature of the present invention, will be explained.

In general, a grating lens optically belongs to a type of diffraction grating.

This crating lens has a concentric diffraction grating pattern (10)' carved at irregular intervals as shown in FIG. 2, for example, on the surface of a glass substrate.

The A-A' sectional view inside this grating lens is shown in the third figure.
The function of this lens and the light beam separation function used in the present invention will be explained with reference to the drawings.

When a parallel beam of light is incident obliquely on the grating lens substrate (11), each beam is diffracted by the diffraction grating (12) and the grating interval changes, so the diffracted light is not diffracted in a uniform direction. It does not become a parallel beam of light.

In this case, for example, the wavelength of the incident light is λ, the grating interval is d2, and the angle between the normal to the diffraction grating surface and the incident light is θ.

Then, the angle θ between the first-order diffracted light, which becomes the convergent light, and the normal changes by θ-thickness-5 in'''-' (λ/d-sin θ1).

Also, the deflection angle δ−〇, 10, of the incident light is the lattice, the child spacing d
The smaller the light beam becomes, the larger the light beam B becomes, and the light beam B changes its traveling direction more greatly than the light beam B shown in FIG.

- Concerning the convergence of the order diffracted light, it can be converged to one convergence point (13) by appropriately arranging the grating interval d.

By converging the parallel light beam to the point 't1' in this way, the grating lens performs the same function as a convex lens, and the convergence point (13) 't- is called the focal point of the grating lens.

vertically incident on the grating lens substrate (11),
That is, a lens having the property of converging parallel light beams of θ, -0 to a single point is called an inline grating lens.

In addition, as shown in Figure 3, the grating lens substrate (1
1) A lens that has the property of converging a parallel beam of light at a certain angle to θ, .about.0 is called an ophaxis gelating lens and is used in the present invention.

The characteristics of such a grating lens will be explained in more detail. When a light beam is emitted from the focal point (13) to the grating lens substrate (11), it goes through the process opposite to the above explanation and becomes a parallel beam of light, but in the case of a normal convex lens, the light beam that enters the lens aperture passes through the glass. If reflection on surfaces or absorption within the glass is ignored, almost all incident light rays become parallel light rays.

However, in the case of a grating lens, according to the diffraction efficiency of the diffraction grating (12) as described above, some percentage of the incident light beam is 1
It has the characteristic that it becomes a parallel luminous flux as the next bright light, and the remaining incident light rays pass through the diffraction grating (12) as they are, becoming zero-order transmitted light or higher-order diffracted light and being diffused.

In the present invention, this feature is utilized to converge the original beam from the light source onto the optical information recording surface and simultaneously separate the information-containing reflected light from the disk surface.

〔Effect of the invention〕

The ophaxis gelating lens in the present invention is
Since it is basically a diffraction grating, a converging lens can be realized with a single substrate, eliminating the need for conventional lens assembly.

This reduces the number of parts of the converging lens, making it easy to make it smaller and lighter.

Furthermore, conventionally, it required complicated assembly and adjustment to separate the reflected light containing pit information, but in the present invention, the reflected light containing pit information is received by the optical axis of the incident light from the light source and the light receiving section. Since the optical axes of the two are made different in advance, bit information can be easily obtained.

In addition, in the present invention, polarization is applied to However, unlike the conventional method, the degree of separation does not change (and bit information can be obtained stably).

[Embodiments of the invention]

A first embodiment of the present invention will be described below with reference to FIGS. 4 to 46. First, FIG. 4 shows a structural diagram of the first embodiment. That is, the original beam (21) from a light source (20) consisting of, for example, a semiconductor laser with a constant output power is transmitted through an off-axis gelating lens for collimation formed on a part of the first glass substrate (22). Collected in (23),
A parallel light beam (24) forms an angle of, for example, 30° with respect to the normal direction of the first glass substrate (22) surface, and a converging ophthalmoscope formed on a part of the second glass substrate (25) The light enters the rating lens (26).

The first-order diffracted light (27) of this parallel light beam (24) by the ophaxis gelating lens (26) focuses (30) on the optical information recording surface (29) in the optical information recording medium (28).

In this case, the ophthalmic gelating lens (26) is formed so that the optical axis of the primary cutting edge (27) is perpendicular to the optical information recording surface (29).

The reflected light of the first-order diffracted light (27) containing the information of the bit placed at the focal point (30) goes again to the ophaxis gelating lens (27) for convergence, but the zero-order transmitted light of this reflected light (31) simply travels backward as transmitted light, i.e. the ophaxis gelating lens (26) for convergence.
It has an optical axis that is different from the optical axis of the parallel light beam (24) that is the incident light on the.

Therefore, the light beam (21) or parallel light (24) from the light source (20) can be separated from the zero-order transmitted light (31) containing bit information from the optical information recording surface (29).

The reflected light consisting of the zero-order transmitted light (31) thus obtained is used to form a crating lens (32) for astigmatic optics, for example, on a part of the first glass substrate (22).
) and a focus error signal by a light receiving optical system consisting of, for example, a four-part photodiode (33).

Detect tracking error signal and recording information signal.

In this case, when the pit row on the optical recording surface (29) is exactly located at the focal point (30) of the ophaxis gelating lens for convergence, the focus error signal and tracking error signal are in a state of zero output. It is necessary to adjust the system, especially the position of the quadrant photodiode.

In this example, the optical system (7) is composed of grating lenses having concentric diffraction grating patterns at irregular intervals, but the optical system is composed of grating lenses having concentric diffraction grating patterns at irregular intervals. It is sufficient if the converging lens facing the medium (28) is an ophaxis gelating lens.

Next, the above-mentioned ophaxis gelating lens (23
) and (26), grating lens for astigmatic optics (32) t-, will be explained with reference to FIGS. 5 and 6 showing the diffraction grating patterns of each grating lens.

In general, grating lenses are manufactured using microfabrication techniques such as lithography, electron beam lithography, etc. on transparent substrates such as quartz glass, crystal, acrylic, and polycarbonate that have a small coefficient of thermal expansion. A curved diffraction grating is formed with a grating spacing of approximately

In this first embodiment, first, as shown in FIG. 5, an ophaxis gelating lens (23) for collimating and a grating lens (32) for astigmatism are mounted on a first glass substrate (22). is formed.

In addition, as shown in FIG. 6, a second glass group: 1ij (2
5) An ophaxis gelating lens (26) for convergence is formed on the top.

These first and second glass substrates (22) and (25)
is fixed to the main body (34) of the optical information reading device shown in FIG. 4 with adhesive or the like.

Further, the light source (20) is fixed to the focal position lid of the ophaxis gelating lens (23) for collimation.

Here, the above-mentioned ophthalmology gelating lens (26) for convergence will be explained in detail with reference to FIG.

FIG. 7 shows a cross-sectional view of a case where a converging ophaxis gelating lens (26) and an optical information recording medium (28) are placed facing each other in parallel.

In this case, the ophaxis gelating lens (26)
A parallel light beam (24) is incident on the glass substrate (25) on which K is formed at an angle of, for example, θ, -30° to the normal direction of the surface on which the ophaxis gelating lens (26) is formed.

This parallel light beam (24) is converged by the ophaxis gelating lens (26) K so that the optical axis of the first-order diffracted light (27) is perpendicular to the optical information recording surface (29) K. (29) Focus on the upper bit (30
).

In this case, the ophaxis gelating lens (26)
When the numerical aperture of is equivalent to N, A-0.5, the wavelength is λ-
Minimum grating spacing for 800nm light beam is 0.8μ
It is expressed as about m.

In addition, the parallel light beam (24) incident on the off-axis gelating lens (26) partially passes through this off-axis gelating lens (26) as first zero-order transmitted light, but the parallel light beam (24) ) are converged on the focal point (30) as first-order diffracted light.

Note that in this case, the first zero-order transmitted light is a parallel light beam having an incident angle of, for example, 30 degrees with respect to the normal direction of the ophaxis gelating lens (26) forming surface.
The light also enters the optical information recording surface (29) at an angle of 30° with respect to the normal direction of the optical information recording surface (29).

Furthermore, the reflected light of the first-order diffracted light containing bit information is directed toward the ophaxis gelating lens (26), and some of it becomes the first-order diffracted light and travels in the opposite direction along the optical path from which it came.
1 is a glass substrate (25) as the second zero-order transmitted light (31).
) passes through and emanates.

In this case, the optical axis of the second zero-order transmitted light (31) is different from the optical axis of the first-order diffracted light or zero-order transmitted light of the ophaxis gelating lens due to the reflected light of the first zero-order transmitted light. It will be different.

Furthermore, the optical axes of the parallel light beam (24) of the light beam from the light source, which is the incident light, and the second zero-order transmitted light (31), which is the reflected light, have an angle of 30@ in this case, so they cannot overlap. do not have.

Therefore, by providing a photodiode or the like that receives the second zero-order transmitted light (31) at a certain distance from the ophaxis gelating lens (26), it is possible to avoid being affected by the incident light (24) (from the information recording medium). bit information can be separated.

Next, first and second modifications of the first embodiment described above will be explained with reference to FIGS. 8 and 9.

In the first modification, as shown in Fig. 8, the focusing off-axis gelating lens (41) has removed the diffraction grating in the center of the off-axis gelating lens (26) in Fig. 7. It has become a thing.

Ofaxis gelating lens like this (41)
The embossment can be produced, for example, by a holographic method.The embossment can be produced by exposing the center once in a circular or rectangular shape and then forming a hologram.

If the parallel light beam (24) is made to enter the t''off-axis gelating lens (41), the light beam that has reached the central portion (42) will be lost, but the light beam that has reached the diffraction grating pattern in the peripheral portion will be lost. The focal point (30
).

Therefore, the reflected light (43) from the optical information recording surface (29) placed at the focal point (30) is directed toward the ophthalmoscope gelating lens (41) and is directed mainly toward the center (42).
The parallel light beam (
24) and is separated from the incident light and guided to the light receiving optical system.

Note that the reflected light (43) is scattered light from bits on the optical information recording surface (29), which is obtained by making the optical axis of the convergent light perpendicular to the optical information recording surface (29).

Furthermore, as shown in FIG. 9, in the second modification, the converging ophaxis gelating lens (26) in the first embodiment is optically converted into a parallel light beam (50)' which is incident perpendicularly. This is replaced with an ophaxis gelating lens (51) that converges on the information recording surface (29), and the convergent light (52) on this optical information recording surface (29)
) is configured so that the optical axis of the parallel light beam (50) converges at a predetermined angle with respect to the parallel light beam (50).

In this way, the convergent light (51) incident with the original axis at a predetermined angle with respect to the normal direction of the optical information recording surface (29) illuminates the bit obliquely, so that the reflected light from the bit (
53) diverges to the opposite side from the convergent light (51).

The reflected light (53) containing the hit information is transmitted through the parallel plane glass substrate (25) without a pattern around the diffraction pattern of the ophaxis gelating lens (51) and guided to the light receiving section. Eyebrows.

That is, the optical axis of the reflected light (53) is different from the optical axis of the convergent light (51) and also different from the parallel light beam (50).

Therefore, reflected light (53)! Parallel light flux (50
) and can be separated.

Next, the relationship between the numerical apertures N and A of various offaxis gelating lenses and the angle of incidence of the original beam with respect to the normal direction of the offaxis gelating lens forming surface will be explained with reference to FIGS. 10 to 13. do.

When the optical axis of the converged light of the original beam by the ophaxis gelating lens is perpendicular to the optical information recording surface,
That is, in a case as shown in FIG. 7 in the first embodiment described above, or in a case as in FIG. 8 shown in the first modification of the first embodiment, the incident light to the off-axis gelating lens The optical axis of the ophthalmoscope must be incident at a predetermined angle with respect to the normal direction of the surface on which the ophaxis gelating lens is formed.

This is to prevent the focal point of the convergent light and the irradiation part of the zero-order transmitted light from overlapping, and to prevent the reflected light of the zero-order transmitted light from affecting the reflected light of the convergent light. Therefore, this is to improve the S/N ratio at the light receiving section.

In Fig. 1θ, the off-axis gelating lens (6
Optical formula 1a for convergent light (62) and zero-order transmitted light (63) when the incident light on 0) is parallel light flux (61)
A schematic diagram of the irradiation situation on the information recording surface (64) is shown.

In this case, if the angle between the convergent light (62) and the bisector of this maximum convergence angle is 01, and the angle between this bisector and the parallel beam (61) is 04, then 2 of the maximum convergence angle of the next transmitted light (63) and convergent light (62)
Since the angle formed with the direction of the equisector is θ, the convergent light (6
In order to prevent the focal point (65) of 2) from overlapping the irradiation part of the zero-order transmitted light (63), θ4>θ.

The following conditions are necessary.

The relationship θ4>θ is sin θ, )N,A. In Fig. 11, the light beam (66) in which the incident light to the offshoot gelating lens (60) diverges
The case is shown below.

In this case, the angle between the convergent light (67) and the bisector of this maximum convergence angle is θa, and the maximum angle between this bisector and the diverging light beam (66) is 06, and the minimum If the angle is θ, then θma〈θ6, so 0〉θ
, that is, sin θ, )N, A.

Next, unlike the cases shown in FIGS. 10 and 11, if the optical axis of the convergent light of the original beam by the off-axis gelating lens is not perpendicular to the optical information recording surface, that is, the 12th
The cases shown in Figure and @13 will be explained.

Figure 12 shows off-off xis gelating lens (60
) is a parallel light beam (68).

In this case, if the angle between the convergent light (69) and the bisector of this maximum convergence angle is θ, and the angle between this bisector and the parallel beam (68) is 09, then θ,〉
It is sufficient if it is θ6, that is, sin θ. ) N, A.

t fc,'AZ In Figure 13, the light beam incident on the off-axis gelating lens (60) diverges into a luminous flux (70
).

In the case of %
If the minimum angle is θ, i then θ, 2<θ11, which is 25, so θ1. It is good if 〉θ, 0 (i.e., sin θ1! ＞
N, A.

As described above, in the cases shown in Figs. 10 to 13), by satisfying the respective conditions, the focus of the convergent light and the irradiation part of the zero-order transmitted light can be prevented from overlapping. ,
It is possible to detect reflected light containing bits of convergent light information with good S/N.

Further, a second embodiment of the present invention is shown in FIGS. 14 and 15.
This will be explained with reference to the figures.

Since the grating lens is a diffraction grating, it is possible to simply superimpose two different diffraction grating patterns on the same plane.

This can be achieved, for example, by double exposure of a hologram or double writing of electron beam lithography.

A single grating having a complex pattern synthesized in this way combines the functions of each lens before synthesis.

FIG. 14 shows an optical information reading device of the present invention constructed using the above-described synthetic grating lens.

A composite grating lens is a combination of the converging ophaxis gelating lens pattern, which converges a beam of light that diverges from one point, and the grating lens pattern for astigmatic optics shown in Figures 4 and 5. It is made up of patterns.

This composite pattern is as shown in FIG.

In FIG. 14, the light beam (80) diverging from the semiconductor laser (20) is focused on the optical information recording surface (29) using the convergence effect of the composite grating lens (81). -Reflected light containing connection bit information (82)
goes to the synthetic grating lens (81) again, but this time it uses the astigmatism optical effect to produce a four-part photodiode (33) located in a different direction from the semiconductor laser (20).
).

In this second embodiment, the number of parts can be further simplified, and it can be made smaller and lighter, with easy assembly and adjustment.

[Brief explanation of the drawing]

FIG. 1 shows a conventional example, FIGS. 2 and 3 show an ophaxis gelating lens used in the present invention, and FIGS. 4 to 13 show a first embodiment of the present invention. , FIG. 14, and FIG. 15 are diagrams showing a second embodiment of the present invention. 20...Light source, 21...Light beam, 22.25...
・Glass substrate, 24,50,61.68...Parallel light beam, 26.41951.60,81...Offaxis gelating lens, 27,52,62,67°69.
71... Convergent light, 28... Optical information recording medium, 2
9.64...Optical j blue line recording surface, 30.65...
Focus, 31, 43, 53, 82... Repulsion light, 32...
- Grating lens for astigmatism optics, 33... Light receiving section, 34... Optical information reading device main body, 63...
・Zero-order transmitted light, 80...Divergent light flux, 81...Synthetic grating lens. Representative Patent Attorney: Kensuke Chika (and 1 other person) Figure 1 Figure 4 Figure 6 Figure 7 Figure 8 Figure 9 Figure 14 Figure 12 Figure 1a

Claims (4)

[Claims] (1) A light source, at least one off-axis gelating lens for converging a light beam from the light source onto the optical information recording surface, and converging the light beam onto the optical information recording surface. an optical system that detects reflected light containing information from the optical information recording surface, an optical axis of a light beam incident on the ophaxis gelating lens from the light source side, and the optical information recording surface; An optical information reading device characterized in that optical axes of light reflected from the ophthalmoscope and transmitted through the ophaxis gelating lens are different from each other. (2) The optical system according to claim 1, wherein the light converged onto the optical information recording surface is first-order diffracted light of the incident light in the ophaxis gelating lens. Information reading device. (3) The light reflected from the optical information recording surface and transmitted through the off-axis gelating lens is zero-order transmitted light in the off-axis gelating lens. The optical information reading device described in Section 1. (4) The convergence part of the light beam on the optical information recording surface is configured to irradiate the zero-order transmitted light of the light beam that has entered the ophaxis gelating lens from the light source side onto the optical information recording surface. 2. The optical information reading device according to claim 1, wherein the optical information reading device is located at a position different from that of the optical information reading device.