JP2000182267A - Optical recording/reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical recording/reproducing device having a high utilization rate of light from a light source and having a constitution of being minimized in an optical recording/reproducing device utilizing a triple beams method as a tracking error detecting method. SOLUTION: A dittraction grating is formed on a surface 14a on the one side, a surface 14b on the other side is formed in a convex spherical face, and an optical element of multiple functions to make diverging light from the light source pass through is provided. Spherical aberration generated in the forward passage from the light source 1 just prior to a objective lens 6 is corrected by a combination of the convex spherical face of the optical device 14 of multiple functions and a curved surface formed on a lens 4A provided between a beam splittor 3 and the objective lens 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording / reproducing apparatus for recording or reproducing using a laser beam, and more particularly to an optical recording / reproducing apparatus using a three-beam method as a tracking error detecting method.

[0002]

2. Description of the Related Art FIG. 5A is a configuration diagram of an optical system as an example of a conventional optical recording / reproducing apparatus. The configuration of this optical system will be described together with the operation. Divergent light emitted from the light source 1 passes through the diffraction grating 2, passes through the beam splitter 3, goes straight, is converted into parallel light by the collimator lens 4, and The light is raised upward, becomes convergent light by the objective lens 6, and is condensed on the information recording surface 8 of the optical recording medium 7. Thereafter, the information light reflected on the information recording surface 8 returns to the objective lens 6 and the mirror 5, is converged by the collimator lens 4, is reflected by the beam splitter 3, passes through the anamorphic lens 9, and then passes through the photodetector. 10 and is converted into an electric signal. A part of the light beam traveling from the light source 1 to the optical recording medium 7 is reflected by the beam splitter 3 and
Is detected by the photodetector 11 for output control.

The use efficiency of light emitted from the light source 1 in the collimator lens 4, that is, the coupling efficiency is 3
It is sufficient that the collimator lens has a numerical aperture on the light source side (NA: Numerical Apertu).
This is achieved by setting re) to about 0.1 to 0.2.

The anamorphic lens 9 is a compound lens having a cylindrical surface on the entrance side and a concave surface on the exit side. When the light passes through the cylindrical surface, astigmatism is generated. Used for This focus error detection method is called an astigmatism method, and is generally widely known. The concave surface on the emission side of the anamorphic lens 9 is moved along the optical axis such that the light flux converged toward the photodetector 10 has an optimal profile on the light receiving surface inside the photodetector 10. It is provided for the purpose of moving and adjusting in the direction.

In the optical recording / reproducing apparatus, a three-beam method is used as a tracking error detection method. FIGS. 5B and 5C illustrate the principle of the three-beam method in the optical recording medium 7 having a high reflectivity in which pits are formed as signal components. In FIG. 5B, reference numeral 30 denotes a pit on the optical recording medium 7, S denotes a main spot, S ′ and S ″ denote spots before and after the main spot S, and as shown in FIG. S and spots S 'before and after these,
When the reflected light of S ″ reaches the photodetector 10, an electric signal is generated in each of the corresponding photodetectors 10a, 10b and 10c, and the signal from the photodetector 10a corresponding to the main spot S is a reproduction signal. RF, and the difference between the output signals of the photodetectors 10b and 10c due to the front and rear spots S 'and S "is taken by a differential amplifier 31 as a tracking control signal T, which is controlled to always be 0. Can be used to apply tracking servo.

A diffraction grating 2 is used to generate the three beams that become the spots S, S ', and S ". Of the light that is diffracted and separated when transmitted through the diffraction grating 2, it is transmitted without being diffracted. The 0th-order diffracted light, the diffracted + 1st-order diffracted light and the -1st-order diffracted light form three beams.

[0007] Incidentally, as the optical recording medium 7, the phase change system or the magneto-optical recording system which is currently the mainstream as a system which can be additionally written or rewritten is used. Among these, in the case of the phase change recording method, heating and gradual cooling at erasing power cause crystallization (increase in reflectivity), and heating and quenching at higher recording power result in amorphous (low reflectivity). A recording medium 7 having an information recording surface 8 is irradiated with laser light with different intensities to perform recording while changing the temperature at the position where the condensed spot hits.

On the other hand, in magneto-optical recording, for example, when overwriting by magnetic field modulation, a high-intensity laser spot is irradiated while applying a magnetic field to the perpendicular magnetization film as the information recording layer to locally reach the vicinity of the Curie point. Recording is performed by increasing the temperature, lowering the coercive force of the medium, and magnetizing the medium in the direction of the applied magnetic field. Reproduction is performed using the magnetic Kerr effect in which the polarization direction of the irradiated light beam is rotated according to the direction of magnetization.

Therefore, in an optical recording / reproducing apparatus capable of performing recording in both phase change recording and magneto-optical recording, the information recording surface (layer) 8 needs to be instantaneously heated to a temperature of several hundred degrees to reproduce. 5mW more than 10 times that of a dedicated optical regenerator
It is required that a light beam having an intensity of １５15 mW can be irradiated. In order to irradiate a light beam with such an intensity, it is a matter of course to use a light source 1 capable of producing a large output, but in addition, the amount of light taken in by the light source 1, that is, the NA of the light source 1 side, Is taken.

FIG. 6 shows an example of an optical system capable of recording and reproducing data by increasing the NA on the light source 1 side. The optical system shown in FIG. 6 has a coupling lens 13 made of a convex lens interposed between the light source 1 and the diffraction grating 2 in order to increase the utilization efficiency of the divergent light emitted from the light source 1. By thus providing the coupling lens 13 and increasing the NA on the light source 1 side from about 0.3 to about 0.5, the coupling efficiency can be increased to 60% or more.

[0011]

However, when a coupling lens 13 is added to increase the efficiency of using the divergent light from the light source 1 as in the optical recording / reproducing apparatus, the space for inserting the coupling lens 13 is limited. Since it is necessary, the size of the apparatus becomes larger than that of a reproduction-only apparatus that does not use the coupling lens 13.

The present invention has been made in view of the above-mentioned problems of the prior art,
It is an object of the present invention to provide an optical recording / reproducing apparatus having a configuration in which utilization efficiency of light from a light source is high and which can be downsized.

[0013]

An optical recording / reproducing apparatus according to claim 1 is an optical recording / reproducing apparatus using a three-beam method as a tracking error detecting method, wherein a light source and a diffraction grating are formed on one surface. The other surface is formed of a convex spherical surface, a multifunctional optical element that transmits divergent light from the light source, light from the multifunctional optical element, and a beam splitter that separates reflected light from the optical recording medium, An objective lens that converges light that has passed through the beam splitter on a recording surface on an optical recording medium, and a lens provided between the beam splitter and the objective lens, on an outward path from the light source to immediately before the objective lens. The resulting spherical aberration has been corrected by a combination of a convex spherical surface of the multifunctional optical element and a curved surface formed on a lens provided between the beam splitter and the objective lens. The features.

As described above, by providing the multifunctional optical element having the diffraction grating and the convex spherical surface, the installation space of the element can be reduced, the size can be reduced, and the light condensing function of the multifunctional optical element can be used for the light source. Usage efficiency increases.

According to a second aspect of the present invention, in the first aspect, the lens provided between the beam splitter and the objective lens is a collimator lens.

An optical recording / reproducing apparatus according to claim 3 is an optical recording / reproducing apparatus using a three-beam method as a tracking error detecting method, wherein a light source and a diffraction grating are formed on one surface and the other surface is convex. A multi-functional optical element formed of a spherical surface and transmitting divergent light from the light source, a light from the multi-functional optical element, a beam splitter for separating reflected light from an optical recording medium, and passing through the beam splitter. An objective lens for converging light on a recording surface of the optical recording medium, wherein a spherical aberration occurring in a forward path from the light source to immediately before the objective lens is formed on the convex spherical surface of the multifunctional optical element and the objective lens. It is characterized by being corrected by a combination with a curved surface.

As described above, by correcting the spherical aberration occurring in the entire forward optical system including the multifunctional optical element by the combination of the convex spherical surface of the multifunctional optical element and the curved surface of the objective lens, the beam splitter and the objective lens can be used. Correction of spherical aberration by the lens during the period becomes unnecessary.

[0018]

FIG. 1A is a block diagram showing an embodiment of an optical recording / reproducing apparatus according to the present invention. FIG.
In (A), 1 is a semiconductor laser provided as a light source,
Reference numeral 14 denotes a multifunctional optical element having a function of obtaining three beams from the divergent light emitted from the light source 1 and reducing the degree of divergence of the light from the light source 1. The multifunctional optical element 14 is the same as that shown in FIG.
As shown in the plan view of (B), the side view of FIG. 1 (C), and the rear view of FIG. 1 (D), the surface 14a on the light source 1 side has a diffraction grating composed of a plurality of parallel grooves. Is formed as a convex spherical surface.

By providing a convex spherical surface 14b on the emission side of the multifunctional optical element 14, the NA on the light source side is set to about 0.3 to 0.5. Further, the multifunctional optical element 14
Is mounted on a holder rotatable in a plane perpendicular to the optical axis so that both axes of rotation coincide with each other. By rotating the optical recording / reproducing apparatus during assembly adjustment, the optical recording medium 7 is
In the information recording surface 8, the arrangement of the three beams with respect to the track (the inclination of the three beams with respect to the track) is optimized.

Reference numeral 3 denotes a beam splitter which transmits a light beam emitted from the multifunctional optical element 14 toward the optical recording medium 7 and reflects reflected light from the optical recording medium 7 toward the photodetector 10. It is. 4A is a collimator lens interposed between the objective lens 5 and the beam splitter 3. The collimator lens 4A has a function of converting light emitted from the beam splitter 3 into parallel light.

The collimator lens 4A corrects spherical aberration occurring in the entire forward optical system from the light source 1 to immediately before the objective lens 6 by a combination of the convex spherical surface 14b of the multifunctional optical element 14 and the curved surface of the collimator lens 4A. Select the shape of the curved surface and the glass type. In some cases, by forming the collimator lens 4A as a meniscus lens (illustrated as a plano-convex lens in the figure), it is possible to reduce spherical aberration to a size that causes no practical problem.

Reference numeral 5 denotes a rising mirror for reflecting the light beam from the collimator lens 4A so that the light beam enters the optical recording medium 7 via the objective lens 6 at a right angle. Reference numeral 9 denotes an anamorphic lens whose entrance side is a cylindrical side,
This is a composite lens having a concave output side. The light reflected by the beam splitter 3 generates astigmatism when transmitting through the cylindrical surface, and the astigmatism is used for detecting a focus error. The concave surface on the emission side of the anamorphic lens 9 is moved along the optical axis such that the light flux converged toward the photodetector 10 has an optimal profile on the light receiving surface inside the photodetector 10. It is provided for the purpose of adjusting the convergence position by moving in the direction.

This optical recording / reproducing apparatus has a multifunctional optical element 1
4 has a function as a diffraction grating and a function to reduce the degree of divergence of divergent light. As can be seen from comparison with FIG. 6, the number of parts is reduced, and the optical recording / reproducing apparatus is downsized. Is done. Further, as will be described later, the convex spherical surface 14b of the multifunctional optical element 14 can be manufactured at a low cost because it is manufactured by polishing with high accuracy and high yield. Further, the spherical aberration occurring in the entire forward optical system is caused by the multifunctional optical element 14.
Is corrected by the combination of the convex spherical surface and the curved surface of the collimator lens 4A, so that there is no operational problem.

FIG. 2 is a view showing an example of a manufacturing process of the multifunctional optical element 14. As shown in FIG. 2A, an optical glass flat plate 20 is prepared, and one side thereof is shown in FIG. A resist 21 is applied as shown, and thereafter, as shown in FIG. 2C, the resist-coated surface is covered with a mask 22 having an exposed portion formed in a linear shape. After that, exposure and cleaning are performed.
As shown in (D), the resist 21 is left on the surface in parallel lines at a constant pitch. Then, as shown in FIG.
A thin film 23 for forming a diffraction grating such as a silicon dioxide film is formed on the surface on which the resist 21 is formed by vapor deposition or the like. Then, as shown in FIG. 2F, the optical glass flat plate 20 in which the thin film 23 is left in a parallel line shape on one surface is obtained by removing the resist. afterwards,
As shown in FIG. 2G, the optical glass flat plate 20 is cut along vertical and horizontal cutting lines 24 and 25 to obtain a plurality of square chips. Then, as shown in FIG. 2 (H), each chip is polished into a circle, then the convex spherical surface 14b is polished, the outer diameter is finished by centering, and an anti-reflection coating is applied. If the convex spherical surface 14b is formed by such polishing,
An inexpensive multifunctional optical element 14 can be manufactured with a higher yield than when a diffraction grating surface and a convex spherical surface are formed by molding.

FIG. 3 is a block diagram showing another embodiment of the optical recording / reproducing apparatus according to the present invention. In this example, since the collimator lens 4A is not provided, a finite optical system in which light incident on the objective lens 6A does not become parallel light is configured. The objective lens 6A is an objective lens for a finite optical system. In this configuration, the spherical aberration generated in the entire forward optical system including the multifunctional optical element 14 is corrected by a combination of the convex spherical surface 14b of the multifunctional optical element 14 and the curved surface formed on the objective lens 6A. And

In this embodiment, there is an advantage that the collimator lens 4A can be omitted, and further downsizing is promoted. Also in FIG. 3, the light source side NA of the multi-function optical element 14 is set to 0.3 to 0.5 in the same manner as described above. Also, the configuration of the anamorphic lens 9 is as described above.

FIG. 4A shows another embodiment of the present invention. In this embodiment, as in the case of FIG.
By not having the collimator lens 4A, a finite optical system is formed in which light incident on the objective lens 6A does not become parallel light. The objective lens 6A is an objective lens for a finite optical system. In this configuration, the spherical aberration generated in the entire forward optical system including the multifunctional optical element 14 is corrected by a combination of the convex spherical surface 14b of the multifunctional optical element 14 and the curved surface formed on the objective lens 6A. And

In the embodiment of FIG. 4A, FIG.
Unlike the case of FIG. 3 and the anamorphic lens 9, unlike a lens having a cylindrical surface and a concave surface opposed to each other, a cylindrical lens 9A having only a cylindrical surface is used, and non-uniformity generated when transmitting through the cylindrical surface is used. An astigmatism method using astigmatism is used.

In the optical recording / reproducing apparatus shown in FIG. 4A, the assembly is adjusted so that the light flux converging toward the photodetector 10 has an optimum profile on the light receiving surface of the photodetector 10. Focus adjustment is performed by moving the multifunctional optical element 14 in a direction along the optical axis. Therefore, the multifunctional optical element 14 is rotated for adjusting three beams,
It is mounted on a holder that can move in two directions for focus adjustment.

FIG. 4B is a diagram showing a combination structure of the light source 1 and the multifunctional optical element 14 which are unitized for such rotation for three-beam adjustment and focus adjustment. In FIG. 4B, the multifunctional optical element 14 is
The light source 1 and the multifunctional optical element 14 are mounted on a cylindrical holder 15 that can rotate in a plane perpendicular to the optical axis 17 so that the centers of the rotation axes of the light source 1 and the multifunctional optical element 14 coincide with each other. Holder 15
Is mounted on a housing (not shown) having a cylindrical hole or V-shaped groove formed with a predetermined accuracy.
Holder 1 provided with light source 1 and multifunctional optical element 14
Reference numeral 5 denotes that the tilt of the three beams in the information recording surface 8 of the optical recording medium 7 with respect to the track is optimized by rotating the knob 16 provided on the holder 15 around the axis of the holder 15. You.

[0031]

According to the first and second aspects of the present invention, the surface of the diffraction grating for generating three beams, which has no function in the past, is made into a convex spherical surface, so that the number of coupling lenses in the optical recording / reproducing apparatus is reduced. be able to. For this reason, the installation space is reduced, and the size of the optical recording / reproducing apparatus can be reduced. Further, the multifunctional optical element can be easily and inexpensively manufactured by combining the manufacturing steps of the diffraction grating and the lens, and as a result, an inexpensive and small optical recording / reproducing apparatus with a small number of parts is provided. can do. In addition, the spherical aberration generated in the entire forward optical system including the multifunctional optical element is corrected by a lens provided between the beam splitter and the objective lens to such an extent that there is no substantial influence.

According to the third aspect, the spherical aberration generated on the outward path from the light source to immediately before the objective lens is corrected by a combination of the curved surface of the multifunctional optical element and the curved surface formed on the objective lens. This eliminates the need for a collimator lens and the like, and further promotes downsizing of the optical recording / reproducing apparatus.

[Brief description of the drawings]

FIG. 1A is a configuration diagram showing an embodiment of an optical recording / reproducing apparatus according to the present invention, and FIGS. 1B, 1C, and 1D are a plan view and a side view of the multifunctional optical element, respectively. It is a rear view.

FIG. 2 is a process chart showing an example of a manufacturing process of the multifunctional optical element of the present embodiment.

FIG. 3 is a configuration diagram showing another embodiment of the optical recording / reproducing apparatus according to the present invention.

4A is a configuration diagram showing another embodiment of the optical recording / reproducing apparatus according to the present invention, and FIG. 4B is a side view showing a combination structure of the light source and the multifunctional optical element of FIG.

FIG. 5A is a configuration diagram showing an example of a conventional optical recording / reproducing apparatus, FIG. 5B is a plan view showing a relationship between pits and a light spot for explaining a tracking error detection method by a three-beam method, and FIG. () Is a diagram showing a tracking error detection circuit.

FIG. 6 is a configuration diagram showing another example of a conventional optical recording / reproducing apparatus.

[Explanation of symbols]

1: light source, 3: beam splitter, 4A: collimator lens, 5: rising mirror, 6, 6A: objective lens, 7:
Optical recording medium, 8: information recording surface, 9: anamorphic lens, 9A: cylindrical lens, 10: photodetector, 1
1: photodetector, 14: multifunctional optical element, 14a: diffraction grating forming surface, 14b: convex spherical surface, 15: holder, 16: knob, 17: optical axis, 20: optical glass plate, 21: resist, 22: Mask, 23: thin film, 24, 25: cutting line

Claims (3)

[Claims] An optical recording / reproducing apparatus using a three-beam method as a tracking error detection method, comprising: a light source; a diffraction grating formed on one surface; a convex surface on the other surface; A multifunctional optical element that transmits divergent light, a beam splitter that separates light from the multifunctional optical element and light reflected from an optical recording medium, and a light passing through the beam splitter on a recording surface of the optical recording medium. An objective lens that converges to the objective lens, and a lens provided between the beam splitter and the objective lens. The spherical aberration that occurs on the outward path from the light source to immediately before the objective lens is defined as a convex spherical surface of the multifunctional optical element. An optical recording / reproducing apparatus wherein the correction is performed by a combination of a curved surface formed on a lens provided between the beam splitter and the objective lens. 2. The optical recording / reproducing apparatus according to claim 1, wherein a lens provided between the beam splitter and the objective lens is a collimator lens. 3. An optical recording / reproducing apparatus using a three-beam method as a tracking error detection method, comprising: a light source; a diffraction grating formed on one surface; and a convex surface on the other surface. A multifunctional optical element that transmits divergent light, a beam splitter that separates light from the multifunctional optical element and light reflected from an optical recording medium, and a light passing through the beam splitter on a recording surface of the optical recording medium. An objective lens that converges to the objective lens, wherein the spherical aberration occurring on the outward path from the light source to immediately before the objective lens is corrected by a combination of a convex spherical surface of the multifunctional optical element and a curved surface formed on the objective lens. An optical recording / reproducing apparatus characterized by the above-mentioned.