JP2002071910A - Optical element and device for recording and reproducing which uses the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the eccentricity of light from the center axis and to suppress fluctuation in the diameter of a beam irradiating an optical recording layer to within the allowable range. SOLUTION: The device is equipped with a light converging means to converge the light irradiating the recording layer of an optical recording medium and with a light shielding part applied in the optical recording medium side of the light converging means. A transmission hole to transmit the converged light by the light converging means is formed in the light shielding part to regulate the diameter of the light irradiating the optical information recording medium. The incident light is first converged by the light converging means and then the converged light transmits though the transmission hole and irradiates the magneto-optical recording layer of the optical recording medium. The diameter of the beam irradiating the optical recording layer of the optical recording medium is regulated by the transmission hole to determine the NA.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical element used in a recording / reproducing apparatus for recording / reproducing an information signal on / from an optical recording medium such as an optical disk, and a recording / reproducing apparatus using the same. About.

[0002]

2. Description of the Related Art In recent years, there has been proposed an optical disk apparatus which realizes high-density recording by increasing an NA by arranging an optical system on an optical recording layer side of an optical disk.

This optical disk device uses an optical element having two lenses as light converging means as disclosed in, for example, JP-A-10-123410, as an objective lens.

The above optical element is a lens on the optical disk side of the two lenses (hereinafter, the lens on the optical disk side is called a front lens, and the other lens is called a rear lens).
Is composed of a so-called hemispherical lens.

The numerical aperture NA of the optical element is determined by a stop (light transmission hole) provided before the light is emitted from the light source and enters the optical element.

In the optical element having the above structure, recording light and reproduction light are converged by the rear lens and the front lens.
Irradiates the optical recording layer of the optical disc.

[0007]

By the way, as described above, the optical element used in the conventional optical disk device is as follows.
The light converged by the rear lens and the front lens is applied to the optical recording layer of the optical disk.

The optical element is assembled so as to minimize the eccentricity of the light from the central axis due to the inclination of the optical axis and the assembly error.

On the other hand, in an optical disk system, a higher transfer rate of data is desired, and together with a focus servo and a tracking servo, a higher bandwidth of an actuator is desired, and a reduction in the weight of the actuator is required. I have.

In order to reduce the weight of the actuator, it is indispensable to reduce the size and weight of the optical element mounted on the actuator, and higher assembly accuracy for the optical element is required.

In such a situation, if a configuration is adopted in which the NA is determined by a stop (light transmission hole) provided in front, the center of the light irradiated due to an assembly error or the like is shifted from the center axis of the optical element. Even a slight deviation causes a large change in the diameter of light applied to the optical recording layer.

Accordingly, an object of the present invention is to provide an optical element configured to suppress eccentricity of light from a central axis. It is an object of the present invention to provide a recording / reproducing device that is kept within the range.

[0013]

In order to achieve the above object, an optical element according to the present invention comprises a light converging means for converging light irradiated on a recording layer of an optical recording medium, and an optical converging means for the light converging means. A light-shielding portion provided on the recording medium side, wherein the light-shielding portion is formed with a light transmission hole for transmitting the light converged by the light converging means, and a diameter of light applied to the optical information recording is adjusted. It is characterized by being regulated by this light transmitting hole.

Further, according to the manufacturing method of the present invention, a light converging means is formed on one surface of a substrate made of an optical material by dry etching, and a light shielding film serving as a light shielding portion is formed on the other surface. It is characterized by forming a light transmitting hole for transmitting the light converged by the light converging means by patterning by lithography technology.

Further, the recording / reproducing apparatus of the present invention is characterized in that the above-mentioned optical element is used in at least a part of an optical system.

In the optical element of the present invention, the incident light is first converged by the light converging means. Then, the light converged by the light converging means passes through the light transmitting hole and is irradiated on the magneto-optical recording layer of the optical recording medium.

At this time, the diameter of the light irradiated on the optical recording layer of the optical recording medium is regulated by the light transmitting holes, and the NA is determined.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an optical element to which the present invention is applied, a method for manufacturing the same, and a recording / reproducing apparatus using the same will be described with reference to the drawings.

As shown in FIG. 1, for example, as shown in FIG. 1, the optical element according to the present invention comprises a front lens 1 and a rear lens 2 having an optical axis as light converging means for converging light applied to a recording layer of an optical recording medium. They are arranged so as to match.

The front lens 1 is a so-called hemispherical lens, and the surface on the optical recording medium side is a flat surface, on which a light-shielding film 3 is formed to serve as a light-shielding portion.

Further, a light transmitting hole 4 for transmitting the light converged by the front lens 1 is formed in the light shielding film 3 so as to be substantially coincident with the optical axis of the front lens 1. The diameter of the light irradiated to the optical recording layer is
It is configured to be regulated by

Therefore, the diameter of the light irradiated on the optical recording layer of the optical recording medium is regulated by the light transmitting holes 4 and N
A will be determined.

For the purpose of preventing unnecessary reflection, it is preferable that an anti-reflection film, for example, an AR coat is formed on the light shielding film 3. In that case, it is preferable to form the antireflection film on both surfaces of the light shielding film 3.

Next, a method for manufacturing the above-mentioned optical element, particularly the front lens 1 having the light-shielding film 3 will be described.

The outline of the manufacturing process of the optical element is shown in FIGS.
As shown in FIG.

The following five steps are the main steps in the manufacturing process of the optical element. (A) arranging a material to be a mask material on a substrate; That is, when a photosensitive material is used as a mask material, a step of applying a predetermined thickness by a spin coating method or the like. (B) a step of patterning the mask material; In the case where a photosensitive material is used as the mask material, an exposure and development step. (C) a step of deforming the mask material so that the surface area of the mask material is reduced by heat treatment, and deforming the mask material into a shape having a gentle optically curved surface. (D) a step of forming a shape corresponding to the shape of the mask material on the optical material. In this example, a step of forming a shape corresponding to the shape of the mask material on the optical material by using a dry etching method. (E) forming a light-shielding film and forming a light-transmitting hole therein;

FIG. 2 shows the above step (a). First, a photosensitive material is applied on a substrate 11 made of an optical material by a spin coating method or the like, and a mask material layer 12 is formed.
To form

Next, as shown in FIG. 3, the mask material layer 12 is patterned by exposure and development to form a mask 13 corresponding to each lens.

Then, as shown in FIG. 4, heat treatment is performed to deform the mask material so that the surface area of the mask material is reduced, thereby deforming the mask 13 into a shape having an optically gentle curved surface.

Here, when an arbitrary photosensitive material is used for the mask material, a deformation phenomenon such that the surface area of the mask material is reduced by heat treatment does not necessarily occur, and an optically smooth curved surface is not necessarily obtained.

For example, when the heat treatment was conducted at a heat treatment temperature in the range of 110 to 150 ° C., when the heat treatment was performed at a temperature of 200 ° C. or more, any of the resist materials deteriorated (so-called burn-in). )
Has occurred. If the alteration occurs, the etching rate of the mask material becomes non-uniform. Therefore, when trying to obtain a shape corresponding to the shape of the mask material in the optical material, the shape may be disturbed. There is.

From the experimental results, as a condition for the mask material to be rounded by the heat treatment to obtain an optically smooth surface, the glass transition point Tg of the mask material is lower than the heat treatment temperature. . Further, when the mask is to be formed into an optical lens shape by a method such as dry etching, the mask material after the heat treatment must not be altered as described above. In addition, a condition that the temperature is such that the mask material is not deteriorated is required.

When plating is formed on a mask material and the plating is used as a mold (when forming a replica)
In, because the etching of the mask material is not performed,
Although this condition is not always necessary for the above-mentioned reason, even in the case of forming a replica, when the mask material is deteriorated by the heat treatment, the mask material surface is often roughened. ,
The temperature must not change the quality of the mask material. Is a desirable condition even when such a replica is formed.

Furthermore, if the mask is deformed while holding the substrate on which the mask is formed, the reproducibility of the process is not easy, and if the mask is deformed during the dry etching process, the process is reproduced. It is desirable that the glass transition temperature Tg of the mask material be higher than the storage temperature (room temperature) or the processing temperature (around room temperature) because the glass material becomes less easy.

Here, generally, the glass transition point Tg is a temperature at which a material is in a glassy state, that is, a temperature indicating a boundary where a material does not have a fixed structure and is capable of flowing. Considering this, it is desirable that the heat treatment temperature be a temperature higher than the glass transition point Tg with a margin. That is, in order to deform the mask material by heat treatment so as to reduce its surface area (to make the mask material flowable by heat treatment and to deform the mask material by the surface tension of the mask material), the heat treatment temperature is set to the glass transition temperature. It is desirable that the temperature is several tens degrees Celsius higher than the point Tg.

More specifically, by setting the heat treatment temperature to be higher than the glass transition point Tg by about 40 ° C. or more, the mask material can be deformed into a round shape within one hour, so that highly efficient production is performed. be able to.

Further, from the same viewpoint, the glass transition point T
In the relationship between g and the storage temperature or the processing temperature, the difference between the storage temperature or the processing temperature and the glass transition point Tg is:
The temperature may be within several tens of degrees Celsius.

As described above, after the mask 13 is deformed into a round shape, a shape corresponding to the shape of the mask 13 is formed on the optical material as shown in FIG. Specifically, a shape corresponding to the shape of the mask 13 is formed on the optical material using a dry etching method. This is the hemispherical lens 14.

In this example, a fused quartz substrate was used as the glass material of the substrate 11, a photosensitive material was applied to a thickness of about 20 μm, and a circular pattern of about 120 μm was formed by the exposure and development steps. This was deformed by a heat treatment temperature of 150 ° C., and an optical lens was manufactured by high-density plasma etching (high-speed etching by NLD plasma) using magnetic neutral discharge.

The manufactured optical lens is an optical lens having an optically smooth curved surface, an extremely small diameter optical lens having an optical lens portion having a diameter of about 120 μm, and an optical lens having a convexity of about 30 μm. It is a high NA optical lens having a part height.

Further, since the position of the manufactured optical lens where the substrate 11 and the mask 13 are in contact does not move even after the heat treatment step, the shape of the mask 13 is defined by the boundary line.

Here, since the boundary line of the mask 13 is defined by a photomask used when exposing the photosensitive material, the position of the optical lens is formed at an extremely high precision position. Further, the height of the optical lens is determined by the thickness of the mask 13.

In the optical lens manufactured as described above, since it is defined by the photomask used when exposing the photosensitive material, a multi-lens (or lens) in which a plurality of optical lenses are formed on the same substrate is used. In the case of (array), the position of the optical lens is formed at a position with high precision in both the position as a single unit and the mutual position of the lenses. Further, the manufactured optical lens can form an optical lens having a larger NA than an optical lens formed by a conventional diffusion process, and thus has a wide range of application.

Next, the optical lens is adjusted to a predetermined thickness by a polishing process, and as shown in FIG. 6, light is shielded on the surface of the substrate 11 made of an optical member on the side opposite to the curved surface. The layer 15 (metal film such as Cr) is formed.

Here, it is preferable to apply an AR coat as a stray light prevention treatment to both surfaces of the light shielding layer 15.

Next, a resist layer 16 is formed on the light-shielding layer 15 as shown in FIG. 7, and patterning corresponding to the light transmitting holes is performed. As shown in FIG. 8, the light-shielding layer 15 is removed by an etching process. Light transmission holes 17 are formed.

At this time, it is preferable to adjust the formation position of the light transmitting hole 17 with respect to the optical lens as the light converging means, for example, using a double-sided photolithography technique.

The optical element of the present invention is manufactured as described above. Such an optical element can be used for an optical pickup of a recording / reproducing apparatus for recording / reproducing on / from an optical recording medium.

FIG. 9 shows an example of the configuration of an optical pickup incorporating the above-described optical element.

In this optical pickup, the optical element is incorporated as an objective lens 21.

A linearly polarized light beam emitted from a semiconductor laser as a light source and made parallel by a collimator lens is:
The light passes through a polarizing beam splitter (PBS) 22 and a λ / 4 (quarter wavelength) plate 23 to be in a circularly polarized state.

This circularly polarized light beam is focused on the signal recording surface of the optical disk 24 via the objective lens 21 and the disk substrate 25.

The disk substrate 25 is a thin substrate having a thickness of, for example, about 0.1 mm.

The above-mentioned optical element, that is, the objective lens 21 has an NA of 0.7 to 0.7 which is formed by combining two lenses.
0.95 lens.

The light reflected by the signal recording surface returns to the original optical path, passes through the λ / 4 plate 23, and becomes linearly polarized light rotated by 90 degrees with respect to the direction of the incoming linearly polarized light.

This light beam is reflected by the polarizing beam splitter 22, passes through a focusing lens (condensing lens) 26 and a multi-lens 27, and passes through a photodetector (PD).
By 28, it is detected as an electric signal.

The multi-lens 27 is a lens whose entrance surface is a cylindrical surface (cylindrical surface) and whose exit surface is a concave surface. The multi-lens 27 imparts astigmatism to the incident light beam to enable detection of a focus error signal by a so-called astigmatism method.

The photodetector 28 is, for example, a six-element photodiode, and outputs electric signals for performing focus adjustment by the astigmatism method and tracking adjustment by the so-called three-beam method.

[0059]

As is clear from the above description, in the optical element according to the present invention, the diameter of the light irradiated on the optical recording layer of the optical recording medium is limited by the light transmitting hole. Therefore, even when the center of the light applied to the optical recording layer of the optical recording medium is deviated from the center axis of the optical element due to the inclination of the optical axis or an assembly error, the fluctuation of the diameter of the light is within an allowable range. Can be reduced.

In the optical element according to the present invention, N
The light transmission hole corresponding to A is provided on the surface of the optical lens. This light transmission hole can be formed by, for example, a metal film having a light shielding property. Such a metal film can be formed very easily and is stable to the environment. Further, since a mechanical support structure is not required, the number of parts can be reduced. Therefore, it is possible to reduce the cost and maintenance of the optical element.

Further, in the recording / reproducing apparatus according to the present invention, the diameter of the light irradiated on the optical recording layer of the optical recording medium is limited by the light transmitting hole of the optical element.
Even if the center of the light emitted from the light source is deviated from the center axis of the optical element due to the inclination of the optical axis or an assembly error, the fluctuation of the diameter of the light applied to the optical recording layer of the optical recording medium is allowed. It can be as small as the range.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of an optical element to which the present invention is applied.

FIG. 2 is a schematic diagram illustrating a step of forming an optical element and illustrating a step of forming a mask material layer on a substrate in the order of steps.

FIG. 3 is a schematic view showing a mask forming step.

FIG. 4 is a schematic view showing a step of deforming a mask by heat treatment.

FIG. 5 is a schematic view showing a lens forming step by dry etching.

FIG. 6 is a schematic view showing a light shielding layer forming step.

FIG. 7 is a schematic view showing a resist layer forming step.

FIG. 8 is a schematic view showing a light transmitting hole forming step.

FIG. 9 is a schematic diagram illustrating an example of an optical pickup using an optical element.

[Explanation of symbols]

 1 front lens, 3 light shielding film, 4 light transmission hole

Claims (10)

[Claims] 1. An optical recording medium comprising: a light converging means for converging light emitted to a recording layer of an optical recording medium; and a light shielding part provided on the optical recording medium side of the light converging means. An optical element, wherein a light transmitting hole for transmitting the light converged by the light converging means is formed, and a diameter of light applied to the optical information recording is regulated by the light transmitting hole. 2. The optical element according to claim 1, wherein at least a part of the light converging means is formed by dry etching. 3. The optical element according to claim 1, wherein the light converging means is formed on one surface of a substrate made of an optical material, and the light shielding portion is formed on the other surface. 4. The light converging means comprises a plurality of lenses arranged on an optical path of the light.
The optical element as described in the above. 5. The optical element according to claim 1, wherein anti-reflection films are formed on both surfaces of the light-shielding portion. 6. A light converging means is formed on one surface of a substrate made of an optical material by dry etching, and a light-shielding film serving as a light-shielding portion is formed on the other surface, and is patterned by a photolithography technique. A method for manufacturing an optical element, comprising: forming a light transmitting hole for transmitting light converged by a converging means. 7. The method of manufacturing an optical element according to claim 6, wherein the adjustment of the position of the light transmitting hole with respect to the light converging means is performed using a double-sided photolithography technique. 8. After a mask material corresponding to the shape of an optical lens is formed on a substrate made of an optical material, heat treatment is performed to deform the shape of the mask material so that the surface area is reduced, and the mask is formed by dry etching. 7. The method according to claim 6, wherein a light converging means having a shape corresponding to the shape is transferred to the substrate. 9. The method according to claim 8, wherein the temperature of the heat treatment is higher than the glass transition temperature of the mask material and lower than the carbonization temperature. 10. A recording / reproducing apparatus, wherein the optical element according to claim 1 is used in at least a part of an optical system.