JPH0271201A - Diffraction grating element for optical information reproducing device - Google Patents

Abstract

PURPOSE:To facilitate control among respective members and to reduce the number of parts and the production cost by irradiating a diffraction grating with the reproducing light to record interference fringes on the diffraction grating so that a specific reproducing condition is satisfied and obtaining a least circle of confusion. CONSTITUTION:Two spot light sources which emit light whose wavelengths are different from the wavelength of the light emitted from a light source for reproducing are provided, and a first spot light source is arranged in a prescribed position on the optical axis, and a second spot light source is arranged in a prescribed position on an axis which forms a prescribed angle with the optical axis, and the diffraction grating is irradiated by both spot light sources to record interference fringes. In this case, the reproducing condition satisfies an inequality I. Consequently, a part of the light transmitted through the diffraction grating element is diffracted to become astigmatic light, and a satisfactory least circle of confusion is formed in a position distance from the origin. Thus, the control among respective members is easily performed.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an optical information reproducing device such as an optical disk device or an optical measuring device, and particularly to an optical information reproducing device with an improved diffraction grating element used in the optical information reproducing device. The present invention relates to a diffraction grating element for a type information reproducing device.

[Conventional technology]

FIGS. 3(a) and 3(b) are diagrams showing a conventional optical information reproducing device.

Here, in the optical information reproducing device shown in FIG.
Objective lens 1 consisting of a wavelength plate 107 and a plurality of various lenses
09 and optical information recording medium 11 such as an optical disk.
The light is condensed and reflected on 1. The reflected laser light passes through the objective lens 109 and the quarter-wave plate 107 again and enters the PBS 105, and a portion of the laser light is reflected in the right angle direction. The reflected light passes through a cylindrical lens 113 and a concave lens 115 and reaches a six-divided photodetector 117, where the six-divided photodetector 117 detects a recording information signal, a focus error signal, and a trunking error signal.

In addition, in the optical information reproducing device having the structure shown in FIG. 2(b), part of the laser light emitted from the semiconductor laser 119 is reflected in the right angle direction by the half mirror 121, and the reflected light is further reflected. The light passes through an objective lens 123, is focused on an optical information recording medium 125 such as an optical disk, and is completely reflected. Then, the reflected laser beam passes through the objective lens 123 again, and also passes through the half mirror 121.
After passing through a concave lens 127, a four-split photodetector 129
Then, the four-division photodetector 129 detects a recording information signal,
Detects focus error signal and tracking error signal.

[Problem to be solved by the invention]

However, since the optical information reproducing device having the structure shown in FIG. 3(a) is constructed by combining a large number of lenses, the structure is complex and requires adjustment between each member, resulting in a large number of parts. There is a problem in that the number of parts increases and the manufacturing cost increases.

Furthermore, since the optical information reproducing device having the structure shown in FIG. 3(b) uses a half mirror 121,
There is a problem in that comatic aberration occurs in the astigmatic light focused on the four-split photodetector 129.

Furthermore, in both cases of FIGS. 3(a) and 3(b), there is a problem in that concave lenses 115 and 127 must be added to adjust the astigmatism position and size.

The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide a diffraction grating element for an optical information reproducing device that has a small number of parts, has a simple structure, is easy to manufacture, and does not cause coma aberration. .

[Means to solve the problem]

In order to solve the above-mentioned problems, the present invention provides a diffraction grating element for an optical information reproducing device, which includes a light source, an objective lens that focuses emitted light emitted from the light source onto an optical information recording medium, and a lens that combines the light source and the objective lens. It is arranged between the lenses at a position perpendicular to the optical axis from the light source to the objective lens, and transmits the emitted light emitted from the light source, and also transmits a part of the reflected light from the optical information recording medium. An optical information reproducing device that reproduces information on the optical information recording medium, comprising a diffraction grating that diffracts from the axis in the +1st order direction and a detector that detects the +1st order diffracted light with its circle of least confusion. In order to record interference fringes on the diffraction grating, two point light sources are provided that emit light of a wavelength different from the wavelength of light emitted from the light source during reproduction, and the first point light source is positioned on the optical axis. and the second point light source is placed at a predetermined position on an axis that makes a predetermined angle with the optical axis, and the diffraction grating is irradiated with light from both point light sources. The reproduction conditions are μ=input C/λ.

m is an arbitrary constant. RII: Distance from the first point light source to the diffraction grating during recording Ro: Distance θ from the second point light source to the diffraction grating during recording. : Angle Ro between the axis from the second point light source to the optical axis on the diffraction grating during recording and the optical axis = distance from the light source to the diffraction grating during reproduction.

[Effect]

By configuring the diffraction grating element for an optical information reproducing device as described above, it is possible to obtain a circle of minimum confusion with good astigmatism by simply arranging the objective lens and the diffraction grating element between the light source and the optical information recording medium. Therefore, the structure is simple, the adjustment between each member is easy, the number of parts is small, and the manufacturing cost can be reduced. Furthermore, since the diffraction grating element can be created by simply using light emitted from two point light sources, there is no need to create interference fringes with a complicated structure, and its manufacture is extremely easy.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail based on the drawings.

FIG. 1 is a diagram showing an optical information reproducing device using a diffraction grating element according to the present invention.

As shown in the figure, this optical information reproducing device includes a diffraction grating element 1, a semiconductor laser 3, an objective lens 5 consisting of a convex lens, and a detector 9 consisting of a 4-split photodetector or a 6-split photodetector. ing.

Further, 7 is an optical information recording medium such as an optical disk.

Here, the objective lens 5 is placed at a position facing the optical information recording medium 7.

Further, the diffraction grating element 1 is disposed between the semiconductor laser 3 and the objective lens 5, and the diffraction grating element 1 is disposed between the semiconductor laser 3 and the objective lens 5. The surfaces are arranged vertically.

Further, the detector 9 is arranged in the direction of an axis (+1st-order diffraction optical axis) that is inclined by θ with respect to the optical axis 11 from the point where the optical axis 11 intersects with the diffraction grating element 1, and the +1st-order diffraction light is and is arranged so that its surface is perpendicular to the axis.

Then, the emitted light emitted from the semiconductor laser 3 passes through the diffraction grating element 1 and is focused on the optical information recording medium 7 by the objective lens 5. The focused light is then reflected by the optical information recording medium 7, passes through the objective lens 5 again, and reaches the diffraction grating element 1. A part of the light reflected by this diffraction grating element 1 is diffracted in the +1st order direction. The light diffracted in the +1st order direction is sent to the detector 9.
The detector 9 reproduces the information on the optical information recording medium 7 into an electrical signal and detects a focus error signal and a tracking error signal.

Next, a method for creating interference fringes on the diffraction grating element 1 will be explained.

FIG. 2(a) is a diagram showing a method of recording interference fringes on the diffraction grating element 1.

As shown in the figure, the diffraction grating element 1 is arranged so that its surface is located on the X-Y plane and its origin (0° 0.0) is located at the center of the diffraction grating element 1. Then, a laser light source (first point light source) as a reference light is located at a position L2 on the second axis (optical axis) and +RR away from the diffraction grating element 1.
Place.

Also, it is located within the Y-Z plane, on an axis tilted by 00 from the Z axis with the origin as the center, and located +Ro away from the origin.
A laser light source (second point light source) as an object light is placed at . By emitting laser light from the laser light sources arranged at these Ll and L2, the diffraction grating element 1
Record the interference fringes on top.

Here, the laser light sources placed at Ll and L2 are point light sources, and the light emitted from the light sources becomes a spherical wave. Therefore, the interference fringes formed on the diffraction grating element 1 are created by the interference of two beam spherical waves. It will be done.

Also, from the above, the phase transfer function of the interference fringes of this diffraction grating element 1 is as follows: φ(x, y) = ``V''zt'') (=2nπ) However, λ0: Wavelength of light during recording n = 1 .2,3. It's as simple as...

FIG. 2(b) shows the diffraction grating element 1 prepared as described above.
When placed in the optical information reproducing device shown in Fig. 1,
3 is a diagram showing a state in which light that has been completely reflected from an optical information recording medium 7 is diffracted by the diffraction grating element 1. FIG. That is, the case where the diffraction grating element 1 is used for reproduction is shown.

As shown in the figure, when a reflected laser beam having a wavelength different from that during recording hits the diffraction grating element 1 from the -Z axis direction, the O-th new beam is located at a position L3 that is R6 away from the origin on the second axis (optical axis). The light is focused at the position of the light source 3 shown in Figure 1, and a part of the light passing through the diffraction grating element 1 is diffracted and becomes astigmatic light, and the +1st order diffracted light is Y-
A circle of least confusion is created at 4, which is located within the Z plane, on an axis with an inclination θR from the Z axis, and is located R1 away from the origin. A detector 9 is placed at this position L4, and various signals are detected.

Note that here θ. The relationship between and θ is θa=sin θ (μsinθ.) μ=(λC/λ0) However, λC: wavelength of light during reproduction λO: Wavelength of light during recording It is.

By the way, in the circle of least confusion formed at the L4 position, there are two types: one in which the light condition within the circle is uniform across the metal bodies within the circle and is good, and the other in which the light condition is uneven among the metal bodies within the circle. Some are defective due to striped patterns due to coma aberration, etc.

Therefore, the inventor of the present application focused on the fact that the various states of light within this circle of maximum confusion change depending on the value of Rc at the time of reproduction, and by changing these values, the maximum confusion It has been found that when the light condition within the circle is good, that is, the recording information signal, focus error signal, and tracking error signal can be accurately detected by the detector 9 shown in FIG.

In other words, if the distance from the diffraction grating during reproduction to the imaging point of the +1st-order diffracted light is R1, then from the imaging formula, C a =, and the imaging direction is θ, -5in-' (μsinθ0) Further, the imaging distance R1 is determined.

It was also found that in order to obtain a good circle of least confusion, the comatic aberration coefficient Cy in the Y-axis direction should at least be m'RcK*-μRc(-R*Ro).

In other words, if this reproduction condition is satisfied, a good circle of least confusion can be obtained.

Therefore, if the reproduction light is irradiated onto the diffraction grating element 1 so as to satisfy the above conditions, a good circle of least confusion can be easily obtained.

〔Effect of the invention〕

As explained in detail above, according to the diffraction grating element for an optical information reproducing device according to the present invention, good optical performance can be achieved by simply arranging the objective lens and the diffraction grating element between the light source and the optical information recording medium. A circle of least confusion of point aberration is obtained. Therefore, the structure is simple, the adjustment between each member is easy, the number of parts is small, and the manufacturing cost is low.

Furthermore, since the diffraction grating element can be created by simply using light emitted from two point light sources, there is no need to create interference fringes with a complicated structure, and its manufacture is extremely easy.

[Brief explanation of the drawing]

FIG. 1 shows an optical information reproducing device using a diffraction grating element according to the present invention, FIG. 2(a) shows a method of recording interference fringes on the diffraction grating element 1, and FIG. b) is a diagram showing a state in which the light reflected from the optical information recording medium 7 is diffracted by the diffraction grating element 1 during reproduction, and FIG.
) and (b) are diagrams showing a conventional optical information reproducing device. In the figure, 1...diffraction grating element, 3... semiconductor laser,
5... Objective lens, 7... Optical information recording medium, 9
. . . detector, 11 . . . optical axis.

Claims (1)

[Scope of Claims] A light source, an objective lens that focuses emitted light emitted from the light source onto an optical information recording medium, and an optical axis that is between the light source and the objective lens and extends from the light source toward the objective lens. a diffraction grating arranged at a position perpendicular to the light source and transmitting the emitted light emitted from the light source and diffracting a part of the reflected light from the optical information recording medium in the +1st order direction from the optical axis;
an optical information reproducing apparatus for reproducing information on the optical information recording medium, comprising a detector for detecting the +1st-order diffracted light using its circle of least confusion, and recording interference fringes on the diffraction grating. , comprising two point light sources that emit light of a wavelength different from the wavelength of light emitted from the light source during reproduction, the first point light source being disposed at a predetermined position on the optical axis, and the second point light source being disposed at a predetermined position on the optical axis. This is performed by placing a point light source at a predetermined position on an axis that makes a predetermined angle with the optical axis, and irradiating light from both point light sources to the diffraction grating, and the reproduction condition is 1.1>m^2R_OR_R/ m^2R_CR_
R-μR_C(R_R-R_O)>0.9μ=λ_C/
λ_O m is an arbitrary constant. However, R_R: Distance from the first point light source to the diffraction grating during recording R_O: Distance from the second point light source to the diffraction grating during recording θ_O: Distance from the second point light source during recording A diffraction grating element for an optical information reproducing device, characterized in that the angle R_C between the axis leading to the optical axis on the diffraction grating and the optical axis satisfies the distance from the light source to the diffraction grating during reproduction.