JP2616475B2 - Optical head device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head device used for an information input / output device for recording / reproducing or reproducing only information using light.

[0002]

2. Description of the Related Art As a technique for improving the information recording density of an optical head device, a technology using a super-resolution effect described in Japanese Patent Application No. 63-164026 is known. The super-resolution effect and a conventional optical head device using the same will be described below.

As shown in FIG. 6A, a central portion of a light beam 22 is shielded between an objective lens for condensing light emitted from the light source on an information recording medium and the light source to attenuate the light intensity. By disposing a super-resolution filter 21 that modulates the light intensity by using the light intensity distribution shown in FIG. 3B, a super-resolution effect can be generated. That is, to obtain a beam (solid line 24 in FIG. 3C) narrower than a normal beam profile (dashed line 23 in FIG. 3C) when the super-resolution filter 21 is not inserted on the information recording medium. As a result, the information recording density in the information recording medium can be increased as compared with the normal case. The central portion is referred to as a main lobe 26, and side lobes 25 having a non-negligible light intensity are generated around the main lobe 26.

FIG. 7A is a diagram showing an optical system of a conventional optical head device using the super-resolution effect. The light emitted from the light source 1 is collimated by the collimator lens 2, the vicinity of the center is shielded by the super-resolution filter 3, transmitted through the beam splitter 5, and then transmitted to the information recording medium 7 by the objective lens 6.
To obtain the above-mentioned super-resolution spot. Of the reflected light from the information recording medium 7, the light reflected by the beam splitter 5 is condensed by a re-condensing lens 8, passes through a pinhole 9, and is received by a photodetector 10.

Here, as shown in FIG. 7B, the shape of the condensed spot before passing through the pinhole 9 is the same as the super-resolution spot on the information recording medium 7 in FIG.
1 and side lobes 42. The main lobe 41 is mainly a reflected light component of the main lobe 26 on the information recording medium. The pinhole 9 provided near the focal point is used to suppress deterioration of a reproduction signal due to reflected light of the side lobe 25 on the information recording medium 7 by passing only the main lobe 41 without passing through the side lobe 42. It is. However, this main lobe 41 has
Strictly speaking, the information recording medium 7 is restricted by the aperture restriction of the objective lens 6.
The reflected light component of the upper side lobe 25 is also mixed. Therefore, the method of cutting the side lobes 42 using the above-described pinholes, slits, and the like is not enough to suppress the deterioration of the reproduction signal.

To cope with this, a countermeasure is taken in Japanese Patent Application No. 1-25982. As shown in FIG. 8, the main lobe 41 and the side lobe 42 are separately detected by a three-divided photodetector 40 having a divided light receiving surface, and the output signal of the main lobe 41 is electrically output from the output signal of the main lobe 41. By attenuating the signal and taking the difference signal, the in-phase removal of the reflected light component of the side lobe 25 on the information recording medium 7 mixed in the main lobe 41 is attempted.

In Japanese Patent Application No. 5-334561, an output signal obtained by detecting the light of the side lobe 42 reflected and shielded by the pinhole 9 and attenuating it by another photodetector, A method of subtracting from the signal of the main lobe 41 passing through 9 and detecting a reproduced signal is employed.

[0008]

As described above, in the conventional optical head device, various measures are taken to prevent the deterioration of the reproduced signal due to the wraparound of the reflected light of the side lobe on the information recording medium to the main lobe on the photodetector. Is used. However, these conventional devices have disadvantages in that a complicated circuit configuration for removing side lobes is required, and a higher detection accuracy is required as the information recording density is higher, and the device is complicated.

In a conventional optical head device that does not use the super-resolution effect, a photodetector is arranged around an objective lens to artificially increase the aperture of the objective lens in a light-receiving optical system (Japanese Patent Laid-Open No. Hei 2 (1994)). -116032) and information recording
A device in which return light from a medium is detected by an objective lens having a numerical aperture larger than the numerical aperture on the outward path (Japanese Patent Laid-Open No. 6-841).
No. 99), but their purpose is to increase the reproduced signal amplitude.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to minimize the mixing of a side lobe signal on an information recording medium into a main lobe on a photodetector with a very simple configuration. An object of the present invention is to provide an optical head device with little signal deterioration.

[0011]

An optical head device according to the present invention comprises a light source, a super-resolution generating means for generating a super-resolution spot on an information recording medium, and a light passing through the super-resolution generating means. A light-collecting optical system that collects light on the information recording medium, and a light-receiving optical system that receives light transmitted through the information recording medium,
A lens for re-imaging light from the light receiving optical system, and light detecting means for detecting a central portion of the light re-imaged by the lens, wherein the numerical aperture of the light receiving optical system is Is larger than the numerical aperture.

Specifically, the light receiving optical system is
It consists of a light receiving objective lens. A beam splitter for reflecting a side lobe component reflected from the light detecting means; a correcting light detecting means for collecting and receiving light from the beam splitter; and a light detecting means and a correcting light. The configuration includes a differential amplifier that takes a difference signal between the signals from the detection means.

[0013]

The reason that the light of the side lobe on the information recording medium mixes with the main lobe position on the photodetector and deteriorates the reproduction signal is that the information recording medium is restricted by the aperture limitation of the light receiving objective lens.
This is because a high spatial frequency component of the spot on the body is removed. The present invention makes it possible to receive light of such a high spatial frequency component by making the numerical aperture of the light receiving optical system larger than the numerical aperture of the condensing optical system, whereby the information recording medium is placed at the main lobe position. Is suppressed to a minimum. Therefore, it is only necessary to finally remove the side lobe with a pinhole, a slit, or the like and receive only the main lobe.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. In the conventional optical head device, a reflective information recording medium is used, and therefore, the objective lens is used for both light collection and light reception. On the other hand, in the present invention, a transmission type information recording medium is used and a transmission type information recording medium is used. In addition to the converging objective, a light receiving objective is provided.The numerical aperture is made larger than that of the converging objective, and the main beam of the light to be re-condensed on the photodetector. This suppresses the mixing of side lobe light into the lobe.

FIG. 1 is a diagram showing an optical system of a first embodiment of the optical head device according to the present invention. In the figure, light emitted from a light source 1 is collimated by a collimating lens 2, modulated by a super-resolution filter 3 for generating a super-resolution spot, and collected on an information recording medium 7. The spot diameter of this condensed spot becomes smaller than that without the super-resolution filter 3 due to the super-resolution effect, but at the same time, side lobes are generated.

The light receiving objective lens 4b is connected to the information recording medium 7
Receives light that has been modulated by the upper pit and transmitted,
Make parallel light. In the present invention, the numerical aperture of the light receiving objective lens 4b is larger than the numerical aperture of the light collecting objective lens 4a. This parallel light is condensed by the re-condensing lens 11 and
Only the center is transmitted by the pinhole 9 arranged at the focal position. This transmitted light is received by the photodetector 10 to obtain an information reproduction signal. Even at this focal position, a side lobe 42 is generated in the condensed spot. Therefore, the pinhole 9 shields the side lobe 42 and allows only the main lobe 41 to pass therethrough.

FIG. 2A is a graph showing the light intensity distribution on the information recording medium. The laser light source has a wavelength of 0.78 μm, the focal length is 3 mm, and the focusing objective lens has a numerical aperture of 0.45. This is a calculation example in the case of using a light-shielding band super-resolution filter with a width of 0.9 mm that narrows the beam diameter by 30% as a filter for generating a resolution spot. FIGS. 2B and 2C show light intensity distributions obtained by extracting only side lobes from the condensed spot and forming an image on the photodetector.

FIG. 2B shows a case where the numerical aperture of the objective lens for light reception is the same as that of the objective lens for light collection, that is, the objective lens for light reception and the objective lens for light collection are shared, as in a conventional optical head device. Is shown. In this case, the light distribution of the side lobe on the information recording medium appears at the main lobe position,
This causes the reproduction signal to deteriorate. The reason for this is
This is because a high spatial frequency component of a spot on the optical disk is removed by limiting the aperture of the light receiving objective lens.

On the other hand, FIG. 2C shows the light intensity distribution when the numerical aperture of the objective lens for light reception is made larger than that on the incident side according to the present invention. In this case, almost the same shape as the light intensity distribution on the information recording medium is restored on the photodetector, and almost no light from side lobes on the information recording medium is mixed at the main lobe position. If the main lobe in which the side lobe light is not mixed is received by a pinhole, a slit, or the like, the wraparound from the side lobe on the information recording medium is eliminated, so that the deterioration of the reproduction signal can be suppressed.

FIG. 3 shows an optical system according to a second embodiment of the present invention. In the present embodiment, a configuration for detecting a reproduced signal from a difference signal between a side lobe component and a main lobe component is added to the first embodiment. In FIG.
The side lobe component reflected by the pinhole 9 is reflected by the beam splitter 17, collected by the refocusing lens 12, and received by the photodetector 14. The signal received by the photodetector 14 is attenuated by the attenuator 15 and the photodetector 10
Is input to the differential amplifier 16 together with the output signal received at
The reproduction signal is detected by taking the difference signal. Thus, the signal from the photodetector 10 is output to the correction photodetector 1
4, and the deterioration of the information reproduction signal is further suppressed.

FIG. 4 is a diagram showing an optical system according to a third embodiment of the present invention. In the present embodiment, a configuration in which light is received by a three-division photodetector 40 instead of the pinhole 9 and the photodetector 10 in the first embodiment is shown. In this case, the reproduction signal is detected by attenuating the signal from the side lobe and obtaining the difference signal from the signal from the main lobe, thereby realizing advanced signal detection.

FIG. 5 is a diagram showing an optical system according to a fourth embodiment of the present invention. In this embodiment, the lenses 18a, 18
b is used. In this case, it may be combined with the infinite system lens used in the first embodiment.

Although the present invention has been described with reference to the preferred embodiments, the present invention is not necessarily limited to the above-described embodiments, and various improvements and modifications can be made based on the claims. For example, as the super-resolution filter used in the present invention, any of a light intensity modulation type using a light-shielding plate that blocks light, a prism that separates light into an optical path, and the like, and a phase modulation type that modulates the phase of light are used. The shape may be any one-dimensional, circular or annular two-dimensional shape. In the embodiment, only the primary component is shown as the side lobe of the super-resolution spot, but a higher-order side lobe may be present. As an information recording medium,
It can be applied to media with pits that modulate phase, pits that modulate light intensity, and pits that modulate the inclination of the plane of polarization of light . Specifically, compact discs, phase change media for recording and reproduction, and magneto-optical media And the like.

[0024]

As described above, according to the present invention, the deterioration of the information reproduction signal can be suppressed to a minimum by setting the numerical aperture of the light receiving optical system larger than the numerical aperture of the condensing optical system. As the difference in the numerical aperture is increased, the mixing ratio to the main lobe is reduced, and the deterioration of the reproduced signal can be further suppressed.

[Brief description of the drawings]

FIG. 1 is a diagram showing an optical system of a first embodiment of an optical head device according to the present invention.

2A is a diagram showing a light intensity distribution on an information recording medium, and FIGS. 2B and 2C are diagrams showing light intensity distributions obtained by extracting only side lobes and forming an image on a photodetector. ,
(B) is based on the conventional example, and (c) is based on the present invention.

FIG. 3 is a diagram showing an optical system of a second embodiment of the optical head device according to the present invention.

FIG. 4 is a diagram showing an optical system of a third embodiment of the optical head device according to the present invention.

FIG. 5 is a diagram showing an optical system of a fourth embodiment of the optical head device according to the present invention.

6A and 6B are diagrams for explaining a super-resolution effect, and FIG.
Is a diagram showing the positional relationship between the super-resolution filter and the light beam,
(B) is a diagram showing the light intensity distribution, and (c) is a diagram showing the light intensity distribution on the information recording medium.

7A and 7B are diagrams for explaining a conventional super-resolution optical head device, wherein FIG. 7A is a diagram illustrating an optical system thereof, and FIG. 7B is a diagram illustrating a light intensity distribution on a photodetector.

FIG. 8 is a diagram showing a three-division photodetector used in a conventional super-resolution optical head device.

[Explanation of symbols]

 Reference Signs List 1 light source 2 collimating lens 3, 21 super-resolution filter 4a, 4b, 6, 18a, 18b objective lens 5, 17 beam splitter 7 information recording medium 8, 11, 12 re-focusing lens 9 pinhole 10, 14 photodetector Reference Signs List 15 attenuator 16 differential amplifier 22 light beam 23 normal beam profile 24 beam profile of super-resolution spot 26, 41 main lobe 25, 42 side lobe 40 three-segment photodetector

Claims (5)

(57) [Claims] A light source; a super-resolution generating means for generating a super-resolution spot on the information recording medium; and a light condensing means for condensing light passing through the super-resolution generating means on the information recording medium. An optical system, a light receiving optical system for receiving light transmitted through the information recording medium, a lens for re-imaging light from the light receiving optical system, and detecting a central portion of the light re-imaged by the lens An optical head device comprising light detecting means, wherein a numerical aperture of the light receiving optical system is larger than a numerical aperture of the light collecting optical system. 2. The optical head device according to claim 1, wherein said light receiving optical system comprises a light receiving objective lens. 3. A beam splitter for reflecting a side lobe component reflected from the light detecting means, a correction light detecting means for condensing and receiving light from the beam splitter, and the light detecting means. 3. The optical head device according to claim 1, further comprising a differential amplifier for obtaining a difference signal between the signals from the correction light detection means. 4. The optical head device according to claim 1, wherein said light detecting means is a three-division light detector. 5. The optical head device according to claim 1, wherein an infinite system lens and / or a finite system lens is used as the lens of the condensing optical system and / or the light receiving optical system.