JP2547983B2 - Optical information recording / reproducing mechanism - Google Patents

Description

The present invention relates to an optical information recording / reproducing mechanism.

[Conventional technology]

The optical information recording / reproducing mechanism is very important for realizing a higher density information recording device. However, in the past, this mechanism required a very precise structure and fine adjustment. This is because this mechanism requires focus position control in addition to tracking control, and it is required to detect a slight shift in focus position and correct it.

Specifically, in the conventional case, astigmatism method, critical angle method, declination method, knife edge method or the like has been used as a method for detecting the focal position. However, all of these methods require delicate adjustment to obtain a proper defocus signal.

Further, as a method of correcting the focal position, a precise structure for accurately and mechanically moving the optical system by the defocus signal is required.

Specific examples thereof are disclosed, for example, in JP-A-57-25.
803,58-121141,58-208945,58-220249. The basic structure is schematically shown in FIG. In the figure, 10 is a light source, 11 is a lens system, 12 is a beam splitter, 13 is a mechanism for driving the lens system 14, 15 is a recording medium, 16 is a defocus detection mechanism and defocus correction control mechanism. It shows typically. This mechanism detects defocus by 16 and corrects the defocus by moving the lens system 14 using 13 by the signal.

[Problems to be solved by the invention]

However, as described above, all of these methods require delicate adjustment to obtain an appropriate defocus signal, and a complicated and precise mechanism for mechanically moving the optical system to correct the focus position is required. Needed. In addition, there is a problem that they reduce the reliability of this mechanism.

[Means for solving problems]

In order to solve the above problems, in the present invention, an optical system is used to irradiate light to a recording medium arranged perpendicularly to the optical axis to record information, or the recording medium reflects light. In the optical information recording / reproducing mechanism that reproduces information based on the above, in the optical system, a light source section and a linear focus that collects light emitted from the light source section and extends along the optical axis are formed. Optical means, and the linear focus of the light reflected from the recording medium located on the linear focus, that is, in the linear focus forming range in the optical axis direction and passing through the optical means, It is characterized in that a light beam selecting means for selectively guiding the reflected light from the intersection with the recording medium toward the photodetector is provided.

In the present invention, as the optical means, a conical lens,
It is preferable to use a truncated cone type lens or a Fresnel type lens.

Further, as the light flux selecting means, there is a pinhole which selectively passes the reflected light toward the photodetector at the image forming position of the reflected light from the intersection of the linear focus and the recording medium. It is preferable to use the formed light shielding member.

[Operation] The basic principle of the present invention will be described with reference to FIGS. 3, 4, and 5.

FIG. 3 shows a case where a Fresnel lens is used as an example of a conical lens, a truncated cone lens, or an optical component having optical characteristics equivalent to those, which is the center of the present invention. It is assumed that this Fresnel lens is circular with a radius R, and collimates parallel light incident from the left side in the drawing at a deflection angle θ uniformly and axially symmetrically.

At this time, the intensity distribution I of the convergent light on the virtual planes separated by d ₁ and d ₂ from the lens is measured from the symmetry axis (the optical axis of the optical system for recording / reproducing information on / from the recording medium). It is given as shown in FIGS. 4 (i) and (ii), where γ is the distance.
However, FIG. 4 (i) shows the case where the distance is d ₁ and R / 2> d ₁ tan θ, and FIG. 4 (ii) shows the case where the distance is d ₂ and R> d. It is assumed that ₂ tan θ> R / 2.

As is clear from the figure, the intensities in each plane diverge at γ = 0 and have a focus. That is, this system has a linear focus on the axis of symmetry in the range of R / tan θ>d> 0.

Based on this as a basic principle, the mechanism of the present invention will be described with reference to FIG. In the figure, reference numerals 17 and 20 are point light sources, reference numerals 18 and 21 are Fresnel lenses as an example of the present invention, and reference numerals 19 and 22 are recording surfaces of media.

In FIG. 5, the light emitted from the point light source forms a linear focus on the axis of symmetry by the lens, which is the same as in the example of FIG. Here, when the recording medium is placed on this linear focus, the system is axially symmetric, so the principle of light reversal causes the light emitted from the light source to be reflected at the inner recording surface and then repositioned to the light source position. Only the light reflected at the intersection of the linear focal point and the recording surface is converged.

This means that as long as the recording surface has an intersection with the linear focus,
It holds even if the recording surface moves.

〔Example〕

Based on the above facts, the present invention will be described in more detail using examples.

FIG. 1 schematically shows an embodiment of the present invention. In the figure, numeral 1 is a light source, 2 is an optical system for shaping the light from the light source, 3 is a beam split system for separating incident and reflected light, 4 is a condenser lens system, and 5 is reflected light. In the above, a light-shielding system for shielding excess light, 6 is a conical lens which is the gist of the present invention, a truncated cone lens, or a Fresnel lens as an example of a part having optical characteristics equivalent thereto,
7 is a recording medium surface, 8 is a condenser lens system, and 9 is a photodetector.

In the figure, the light-shielding system 5 in which a pinhole is formed is arranged on the opposite side of the recording medium 7 with a Fresnel lens 6 (optical means in this example) as a light flux selecting means. Here, the pinhole of the light shielding system 5 is at the image forming position of the reflected light from the intersection of the linear focus and the recording medium 7.
In this mechanism, the light source section includes a light source 1, an optical system 2, a beam splitting system 3, and a condenser lens system 4, and the light emitted from the light source 1 passes through 2, 3, 4 and a light shielding system 5 A dot-like image is formed in the hole portion of the transparent portion (for example, a pinhole). As described above, of the light from this image, only the light reflected at the intersection of the linear focus and the recording medium surface is reflected at the recording surface and then converges again at this position. Therefore,
The light guided to the photodetector 9 through 4, 3, 8 is only the light reflected at the intersection. And, as described above, this does not depend on the position of the recording medium as long as this intersection exists.

That is, according to this mechanism, the information detected by the photodetector 9 is only the information at the intersection of the symmetry axis of the optical system and the surface of the recording medium without mechanically moving the optical system. I will say. Therefore, it is possible to realize an optical information recording / reproducing mechanism which does not require delicate adjustment of defocus detection which has been a problem in the conventional case and a precise structure for mechanically moving an optical system.

In the present case, the reproduction has been mainly described, but as shown in FIGS. 4 (i) and (ii), the light intensity distribution in the recording surface has a sharp maximum. Therefore, it is clear that this mechanism is effective even during writing.

Further, FIG. 1 is a schematic view of an embodiment of the present invention, and in other cases, for example, in addition to the Fresnel type lens shown in 6 in the figure, a conical type lens as shown in FIG. A conical lens, a combination of conical lenses, an aspherical lens, or a lens having a structure in which an additive is diffused on a substrate to change the refractive index can be considered. What is essential in each case is that a linear focal point can be formed, and other optical components can be used if it can be realized.

Further, the entire configuration shown in FIG. 1 is not limited to this example. As another example, as shown in FIG. 7, for example, the light-shielding system 30 in which a pinhole is formed is provided between the Fresnel lens 27 (optical means in this example) and another optical component (condensing lens system). 26, 29) and the like, the pinhole of the light-shielding system 30 is still at the image formation position of the reflected light from the intersection of the linear focus and the recording medium 28. Therefore, even after the light reflected by the recording medium 28 and once condensed by the Fresnel lens 27 is diverged, it is converged again by the condenser lens system 29, etc., so that the light-shielding system 30 records as a linear focus. It is possible to selectively guide only the light reflected by the intersection of the medium (the light flux is shown by the solid line arrow) to the detector 31 and block the other light (shown by the dotted line). Further, as in the embodiment shown in FIG. 8, without using a light-shielding system in which pinholes are formed, the recording medium 37 reflects and the light condensed by the Fresnel lens 36 (optical means in this example) is once diverged. Then, it is converged again by the condenser lens systems 38 and 39, and the linear focus and the recording medium are
It is also possible to select only the light reflected at the intersection with 37 (the light flux is indicated by the solid arrow) and guide it to the detector 40. At this time, other light (shown by a dotted line) passes through a position deviated from the detector 40. As described above, various configurations are possible, such as a light beam selecting unit in which a light blocking system having a pinhole is arranged in front of a photodetector, or a light beam selecting unit having a configuration that does not require such a light blocking system. is there.

〔The invention's effect〕

As described above, according to the present invention, the defocusing detection mechanism, which is required in the conventional optical recording / reproducing mechanism, is unnecessary, and the fine adjustment thereof is also unnecessary. As a result, the structure of the optical recording / reproducing mechanism becomes very simple. Further, a focus offset due to a change in the defocus detection mechanism over time or a change in the environment does not occur, and an extremely reliable optical recording and reproducing mechanism can be realized.

Furthermore, no precise mechanical drive mechanism is required for moving the optical system such as the objective lens corresponding to the displacement of the medium in the optical axis direction. As a result, the structure of the optical recording / reproducing mechanism can be made very simple and high reliability can be realized. Further, in the case of an optical disc, it becomes difficult to make an optical system such as an objective lens follow the optical disc as the rotation speed is increased. Therefore, the mechanical precision of the optical disk must be made extremely strict. However, according to the present invention, it is possible to realize a state in which the optical disc is always in focus without moving the objective lens or the like, so that the number of rotations of the optical disc can be extremely increased. As described above, according to the present invention, it is possible to realize an optical recording / reproducing mechanism which has a simple structure and is capable of supporting high performance while maintaining high reliability.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of an optical information recording / reproducing mechanism of the present invention. In the figure, the numbers 1 are a light source, 2 is a beam shaping optical system, 3 is a beam split system, and 4 is a condenser lens system.
Reference numeral 5 denotes a light-shielding system (pinhole or the like), 6 denotes a Fresnel-type lens (hereinafter referred to as a conical lens, a truncated cone-shaped lens, or an optical component having optical characteristics equivalent to those of the present invention. (Collectively referred to simply as Fresnel lens), 7 is the surface of the recording medium, 8 is the condensed light system, and 9 is
Shows a photodetector typically. FIG. 2 is a diagram schematically showing a conventional optical information recording / reproducing mechanism. In the figure, reference numerals 10 are a light source, 11 is a light beam shaping optical system, 12 is a beam split system, 13 is a drive system for mechanically moving the condensing lens system of 14, and 15 is a recording medium surface. 16
Shows a control system for detecting defocus and driving 13. FIG. 3 is a view showing a linear focus formed by taking a Fresnel lens as an example in order to explain the basic principle of the present invention. FIGS. 4 (i) and 4 (ii) are views showing in-plane light intensity distributions of the surfaces separated from the lens by distances d ₁ and d ₂ , respectively, to supplement the explanation of FIG. 5 (i) and (ii) are diagrams showing the principle of the present invention based on FIGS. 3 and 4. In the figure, numbers 17 and 20 are light sources, 18 and 21 are Fresnel lenses as an example, and 19 and 22 are recording medium surfaces. FIG. 6 is a view showing an example of a conical lens, a truncated cone lens, or an optical component having optical characteristics equivalent to those of the present invention. In the figure, (i) is a Fresnel lens, (ii) is a conical lens, (iii) is a truncated cone lens, (iv) is an example in which both sides of the lens are not flat, and (v) is a lens. Is an example in which the lens is formed by a curved surface, and (vi) is a diagram schematically showing an example in which the lens is formed by changing the refractive index by diffusion of an additive element in a flat plate. Is just an example, and it is not limited to this. FIG. 7 is a diagram showing an embodiment of the optical information recording / reproducing mechanism of the present invention. The numbers in the figure are respectively 23 for the light source, 24 for the beam shaping optical system, 25 for the beam splitting system, 26 for the condenser lens system, 27 for the Fresnel lens, 28 for the recording medium surface, and 29 for the recording medium surface. Is a condenser lens system, 30 is a light-shielding system, and 31 is a photodetector. FIG. 8 is also a diagram showing an embodiment of the optical information recording / reproducing mechanism of the present invention. In the figure, reference numerals 32 are a light source, 33 is a light beam shaping optical system, 34 is a beam splitting system, 35 is a condenser lens system, 36 is a Fresnel lens, 37 is a recording medium surface, 38 , 39
Is a condenser lens system, and 40 is a photodetector.

Claims (3)

(57) [Claims] 1. A mechanism for irradiating a recording medium arranged perpendicularly to its optical axis with an optical system to record information, or for reproducing information based on light reflected by the recording medium. The optical system includes a light source unit, an optical unit that collects light emitted from the light source unit and forms a linear focus that extends along the optical axis, and the optical unit that is located on the linear focus. Among the light reflected from the recording medium and passing through the optical means, there is provided a light beam selection means for selectively directing the reflected light from the intersection of the linear focus and the recording medium toward the photodetector. An optical information recording / reproducing mechanism characterized by the above. 2. The optical information recording / reproducing mechanism according to claim 1, wherein the optical means is a conical lens, a truncated cone lens or a Fresnel lens. 3. The luminous flux selecting means selectively guides the reflected light through an image forming position of the reflected light from an intersection of the linear focus and the recording medium toward a photodetector. The optical information recording / reproducing mechanism according to claim 1, wherein the optical information recording / reproducing mechanism is a light shielding member having a pinhole formed therein.