JPH11177123A - Manufacturing method of optical element for optical pickup - Google Patents

Abstract

[PROBLEMS] For an optical pickup, a microlens (objective lens and solid immersion lens) having an arbitrary refractive index can be integrally formed on a flat substrate with high positional accuracy by a simple manufacturing method. Provided is a method for manufacturing an optical element. The present invention provides an objective lens having a function of condensing collimated light, and a substrate having a refractive index higher than that of a substrate which is disposed closer to a recording medium than the objective lens and whose optical axis coincides with the objective lens. High solid immersion lens 4
Wherein at least one set of an objective lens and a solid immersion lens is formed on one substrate 2, wherein concave curved surfaces 2 a and 2 b are formed on both surfaces of the substrate 2. Then, lenses 3 and 4 having a higher refractive index than the substrate and conforming to the concave surfaces were arranged on the two concave surfaces, and the lenses and the substrate were fixed with a resin material 5 and flattened by etching or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an optical disk device,
The present invention relates to a method of manufacturing an optical element for an optical pickup used in an optical pickup device used for recording information on an optical memory (recording medium) or reproducing information from the recorded optical memory in an optical card device, an optical tape device, and the like.

[0002]

2. Description of the Related Art As a method of manufacturing (manufacturing) an optical element such as a microlens, for example, JP-A-6-194502 (convex microlens array and manufacturing method thereof) and JP-A-6-208006 (long focal length) Convex microlens array), JP-A-7-181303 (a method of manufacturing a biconvex microlens array), and JP-A-7-19890
No. 6 (Various biconvex materials with various microlens shapes)
Devices and manufacturing methods) have been filed. Further, regarding concave lenses, JP-A-7-244206, JP-A-7-248403, and JP-A-8-29601.
Has been filed. Since these are manufactured using a semiconductor manufacturing process, a large number of lenses having a free shape can be manufactured. Examples of the method described here include a method of applying a resist twice, a method of forming a convex curved surface and using it as a mold, and transferring and curing the ultraviolet curable material. Japanese Patent Application Laid-Open No. Hei 5-173003 claims that dry etching is performed after directly forming a convex or concave surface on a photoresist using scattered light or a diffuser. However, in this patent application, no particular flattening is performed. Further, Japanese Unexamined Patent Publication No.
300902, JP-A-7-281007,
JP-A-8-171003, JP-A-8-17929
No. 9 discloses an invention aimed at using a liquid crystal display by forming a flat microlens array by filling a material having a high refractive index after forming a concave curved surface on a substrate. Here, the concave curved surface is formed by wet etching.

On the other hand, FIG. 6 shows a configuration example of a conventional optical memory optical pickup. This optical pickup is a semiconductor laser (hereinafter, referred to as LD) that emits linearly polarized laser light.
11, a collimator lens 12, a polarization beam splitter 13, a quarter-wave plate 14, an objective lens 15, a condenser lens 17, and a photodiode (hereinafter referred to as PD) 18. The linearly polarized light parallel to the plane of the light emitted from the LD 11 is collimated by the collimator lens 12. Next, this light passes through an optical isolator composed of a polarizing beam splitter 13 and a quarter-wave plate 14 and changes from linearly polarized light to circularly polarized light. The objective lens 15 forms a minute spot on a recording surface 16 a of a recording medium 16. It is collected. When the light is reflected by the recording surface 16a, the direction of rotation of the circularly polarized light changes. When the circularly polarized light is returned to the parallel light by the objective lens 15 and passes through the quarter-wave plate 14, the light becomes perpendicular to the paper. Further, the light is reflected by the polarization beam splitter 13, travels toward the PD 18, is collected by the condenser lens 17, and is incident on the PD 18. Although there are actually optical components for focus detection and track detection in addition to the illustrated optical components, they are omitted here.

In the optical pickup having the above structure, the spot size can be obtained only up to the wavelength of light due to the diffraction limit of light. The spot size can be expressed as follows. w∝λ / sin θ ′ (1) where θ ′ is the exit angle of the objective lens 15 and the NA of the lens.
(Numerical aperture) has a relationship of NA = sin θ ′. λ
Is the wavelength of the light source.

Therefore, a method of increasing the effective NA by using a configuration in which another hemispherical lens (solid immersion lens) is inserted between the objective lens 15 and the recording medium 16 as in a liquid immersion method of a microscope has been proposed. Introduced by Kino and others at the university. This is because, as shown in FIG. 7A, by bringing the solid immersion lens 19 close to the recording medium 16 below the wavelength, the spot size focused on the end face of the lens 19 is proportional to the reciprocal of the refractive index of the lens. It is a thing that utilizes. Here, assuming that the refractive index of the lens 19 is n, the spot size is as follows. w′∝λ / nsinθ ′ (2) Further, the shape of the solid immersion lens is shown in FIG.
In the case of a super hemispherical lens 20 as shown in (b), since the Snell's law is applied on the surface of the solid immersion lens, the spot size can be further reduced as follows. w'∝λ / n ² sinθ '(3)

However, in this configuration, the distance between the recording surface of the recording medium 16 and the solid immersion lens 20 is 100
It must be close to the order of nm and below the wavelength of light.
Therefore, a flying head as shown in FIG. 8 has been proposed (US Pat. No. 5,497,359 or BD, Terris, HJ Mamin, and DR).
ugar, "Near field optical data strage", Appl.Phys.Le
tt., 68, No. 2, 141, 1996). In this head, a solid immersion lens 23 (refractive index = 1.83) is provided on the slider 22 by bonding, and an objective lens 21 (NA = 0.5) is placed at an interval from the lens 23. With this configuration, a light source having a wavelength of 830 nm is used for 360 n.
m spot size is obtained.

Other examples using solid immersion lenses are disclosed in Japanese Patent Application Laid-Open No. Hei 8-212579 (correction of spherical aberration caused by variations in recording medium thickness and lens thickness) and Japanese Patent Application Laid-Open No. Hei 8-221772 (correction of spherical aberration). Reduction) and JP-A-8-221790 (reduction of coma aberration). In these patent applications, unlike the above, the head does not float, and the solid immersion lens and the objective lens are not integrated but separated.

[0008]

The optical element manufactured by the present invention comprises two types of microlenses, an objective lens and a solid immersion lens, as described above. These lenses are provided one by one on both sides of one substrate. This lens is configured to be convex toward the inside of the substrate. This configuration is adopted from the viewpoint of aerodynamic consideration for stacking elements such as light sources or for floating the elements. Therefore, the method of manufacturing this lens includes
A method for forming a concave curved surface on a substrate is employed. Several methods have been proposed for this method. As described above, in the method of manufacturing a flat microlens of a type in which a high refractive index material is embedded, the concave surface is formed by wet etching. There is also a method of manufacturing a lens in which a refractive index distribution is provided in a substrate. However, it is difficult to produce a lens by selecting an arbitrary refractive index material using either technique.

The present invention has been made in view of the above circumstances, and is intended for an optical pickup in which a microlens having an arbitrary refractive index can be integrally formed on a flat substrate with high positional accuracy by a simple manufacturing method. An object is to provide a method for manufacturing an optical element.

[0010]

To achieve the above object, according to the first aspect of the present invention, an objective lens having a function of condensing collimated light is provided at a position closer to a recording medium than the objective lens. A light having a solid immersion lens having a higher refractive index than a substrate disposed and having an optical axis coincident with the objective lens, wherein at least one set of the objective lens and the solid immersion lens is formed on one substrate. In the method for manufacturing an optical element for pickup, a concave curved surface is formed on both surfaces of the substrate, a lens having a refractive index higher than that of the substrate is arranged on the two concave curved surfaces, and the lens is formed of a resin material. After fixing the substrate, it was flattened.

According to the second aspect of the present invention, the objective lens has a function of condensing the collimated light, and is refracted by the substrate which is disposed closer to the recording medium than the objective lens and whose optical axis coincides with the objective lens. A method for manufacturing an optical element for an optical pickup, comprising: a solid immersion lens having a high efficiency; and at least one set of an objective lens and a solid immersion lens formed on a single substrate. V-grooves were formed, and a lens having a refractive index higher than that of the substrate and in contact with the V-groove was arranged in these two V-grooves. The lens and the substrate were fixed with a resin material and then flattened.

According to the third aspect of the present invention, the objective lens having a function of condensing the collimated light and the substrate disposed closer to the recording medium than the objective lens and refracted by the substrate whose optical axis coincides with the objective lens. A method for manufacturing an optical element for an optical pickup, comprising: a solid immersion lens having a high efficiency; and at least one set of an objective lens and a solid immersion lens formed on a single substrate. A mold capable of forming a concave curved surface is produced, a resin is filled in the mold to prepare a substrate, and a lens having a refractive index higher than that of the substrate is arranged on the concave curved surface of the substrate, and the resin is formed. After fixing this lens and the substrate with the material, it was flattened.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows an example of an optical element for an optical pickup manufactured by the present invention. The optical element 1 for an optical pickup includes an objective lens 3 for converging collimated light on an upper portion of a substrate 2. In addition, the thickness of the substrate is a length at which the objective lens 3 collects light. Further, a hemispherical solid immersion lens 4 is provided below the substrate 2. The shape of the objective lens 3 may be spherical or aspherical in consideration of aberration and high NA.
Further, the shape of the solid immersion lens 4 may be a hemisphere or a super hemisphere.

Next, the operation of the optical element 1 will be described. Although not shown, the collimated light emitted from the light source and coming from above the substrate 2 via the collimator lens or the like becomes light converged by the objective lens 3 and is collected on the bottom surface of the solid immersion lens 4. In this configuration, since a spot is formed in the solid immersion lens 4, the wavelength of the light in the solid immersion lens 4 is multiplied by the reciprocal of the refractive index of the substrate 2, and is expressed by the above equation (2). The spot size is as follows.

The substrate 2 on which the objective lens 3 and the solid immersion lens 4 are formed is used as an optical element 1 for an optical pickup in a recording / reproducing section of an optical memory. At this time, the optical element 1 is provided with an actuator, a light source, and a light receiving unit (not shown) that can move to a target pit. Although the lower part of the figure is patterned so that the optical element 1 itself can float at a desired floating amount, the floating amount may be controlled using an actuator. Further, the distance between the optical element 1 and the recording surface of the recording medium may be maintained by a method other than floating.

FIG. 2 shows an example of an optical pickup optical element 1 'in an array. In this example, there are three sets of the objective lens 3 and the solid immersion lens 4. With this configuration, three spots are simultaneously formed. Although not shown, a light source, a collimator lens, and the like are provided above the substrate, and collimated light comes from above the substrate 2. The light source may be an array of light sources corresponding to the lens array on the substrate 2 or a single light source that irradiates the entire lens array. If the light source is in the form of an array, it can be driven independently, so that recording, reproduction, and erasing can be performed separately. In addition, if a single light source is used, reproduction can be simultaneously read from three places. The present invention provides a method for manufacturing an optical element for an optical pickup as shown in FIG. 1 or FIG. 2, and specific examples will be described below.

(Embodiment 1) An embodiment of the present invention is shown in FIG. FIG. 3 shows a manufacturing process of an optical element in which the objective lens 3 is provided integrally on the upper surface of the substrate 2 and the solid immersion lens 4 is provided integrally on the lower surface of the substrate 2. The shape of the objective lens 3 may be spherical or aspherical in consideration of aberration and high NA. Further, the shape of the solid immersion lens 4 may be a hemisphere or a super hemisphere.

First, concave curved surfaces 2a and 2b are formed on the upper and lower surfaces of the substrate 2 as shown in FIG. This concave surface 2a,
The diameter and depth of 2b are set to the size according to the size of the objective lens 3 and the solid immersion lens 4 to be manufactured. Furthermore, the minimum spot size in this optical system is
Is the length obtained at the bottom of The concave curved surfaces 2a and 2b are formed by, for example, patterning the resist with a mask having a thermal deformation or diffusion effect after patterning with a resist, and forming the concave curved surfaces by dry etching.

Subsequently, as shown in FIG.
The objective lens 3 and the solid immersion lens 4 that match the shape of the curved surface are installed on a and 2b. Also, if it is desired to reduce the spot size, the larger the refractive index is from Equations (2) and (3), the smaller the spot size can be. Therefore, the solid immersion lens 4 is made of a material having a refractive index larger than that of the substrate 2. You can choose For example, as a substrate, BK7 (refractive index 1.511 at a wavelength of 768.2 nm) is used.
5 (from a scientific chronological table)), and LaF2 (refractive index 1.73 at a wavelength of 768.2 nm) was used as a material for each of the lenses 3 and 4.
35 (from a scientific chronology)) or SFS1 (wavelength 768.
A refractive index of 1.8927 at 2 nm (from scientific chronology) is used. In FIG. 3B, each lens is biconvex (or spherical), but may be uniconvex (or hemispherical).

Next, as shown in FIG.
Is coated on the upper and lower surfaces of the substrate 2 to fix the lenses 3 and 4 and the substrate 2. As the resin material 5, a material having a refractive index substantially equal to or lower than that of the substrate 2 is selected.
As the resin material 5, a material having an ultraviolet curing effect or a thermosetting effect is selected. The thickness of the resin material 5 is adjusted so that the lenses 3 and 4 are etched and flattened in a later step.
To a thickness that covers At this time, if the concave curved surface does not match the lens curved surface, the lenses 3 and 4 may be arranged and fixed after filling the concave curved surface with a small amount of resin material.

Next, as shown in FIG. 3D, dry etching is performed as a flattening means for removing unnecessary resin. Specifically, reactive ion etching (RIE),
Etching is performed by electron cyclotron resonance etching (ECR), ion beam etching, plasma etching, or the like. The gas used for dry etching can be selected depending on each material. For example, when the material is glass, C
F ₄ and CHF ₃ can be used, and in the case of resin, O ₂ , CF ₄ and CH ₄ can be used. Further, in order to adjust the etching rate and the selectivity, N ₂ , O ₂ , A
A gas such as r may be mixed. The etching here is performed under the condition that the etching rates of the resin material and the lens material become equal. The amount of etching may be such that the resin material 5 is left or the substrate 2 is etched, and the etching may be performed in a desired amount. Further, the etching may be wet etching. Further, polishing can be used as a means for flattening. Thus, the objective lens 3 and the solid immersion lens 4 as shown in FIG.
Are formed on the substrate 2 and are flattened to complete an optical element for an optical pickup.

(Embodiment 2) Next, a second embodiment of the present invention will be described. In this embodiment, as shown in FIG. 4, V-grooves 2c and 2d are formed on the upper and lower surfaces of the substrate 2 at positions where the objective lens and the solid immersion lens are installed. In the above-described embodiment of the first aspect, the surface is concave, but in the embodiment of the second aspect, the surface is formed as a V-shaped groove. The V grooves 2c and 2d are formed by etching or machining. In particular, when silicon is used as the substrate, the V groove can be easily formed by anisotropic wet etching. The substrate 2 has a V-groove 2c,
The manufacturing process of the optical element after manufacturing 2d is performed in the same manner as the method described in the first embodiment (FIGS. 3 (b) to 3 (e)), and the description is omitted here. There is also a method of forming a V-groove on one of the upper and lower surfaces of the substrate and forming a concave curved surface on the other surface. This can be arbitrarily determined according to the size of the lens to be manufactured.

(Embodiment 3) Next, a third embodiment will be described. FIG. 5 shows a state in which the objective lens 3 is
1 shows a manufacturing process of an optical element in which a solid immersion lens 4 is provided on a lower surface of a substrate. In this embodiment, a substrate is manufactured by casting a resin in advance and hardening the resin. FIG. 5A shows a mold 6 used for manufacturing an optical element. The mold 6 has a convex curved surface 6a and a concave curved surface 6b for an objective lens and a solid immersion lens. In this example, the convex curved surface 6a is for an objective lens, and the concave curved surface 6b is for a solid immersion lens. The mold 6 is manufactured by machining. The mold 6 is composed of several parts so that the cured element can be peeled off.

Next, as shown in FIG. 5B, a spherical lens serving as the solid immersion lens 4 is arranged on the concave curved surface 6b of the mold 6. Subsequently, as shown in FIG. 5C, the mold 6 is filled with a resin 7 serving as a substrate. As the resin 7, an ultraviolet curable resin or a thermosetting resin is used in the same manner as the resin material described in the first embodiment. Therefore, the material of the mold 6 is selected to be transparent or resistant to ultraviolet rays depending on the type of the resin 7. When the resin 7 has hardened in this way, the mold 6 and the resin 7 are separated, and a substrate formed of the resin 7 (hereinafter, referred to as a resin substrate 7) is taken out. Further, as shown in FIG. 5D, the objective lens 3 is arranged on a concave curved surface formed on the upper surface of the resin substrate 7. The objective lens 3 may be biconvex or uniconvex. Next, as shown in FIG. 5E, a resin material 8 is coated so as to cover the lenses 3 and 4, and the lenses 3 and 4 and the resin substrate 7 are fixed. As the resin material 8, the resin used in FIG. 5C may be used, or another resin may be used. In addition, the amount of the resin material 8 to be coated only needs to cover the lenses 3 and 4.

Subsequently, as shown in FIG. 5F, dry etching is performed on both surfaces of the resin substrate 7 as a flattening means for removing unnecessary resin material 8. Specifically, etching is performed by a reactive ion etching method (RIE), an electron cyclotron resonance etching method (ECR), an ion beam etching method, a plasma etching method, or the like. The gas used for dry etching can be selected according to each material. For example, when the material is glass, CF ₄ , CHF ₃ or the like can be used, and when the material is resin, O ₂ , CF ₄ , CH ₄ or the like can be used. Further, in order to adjust the etching rate and the selectivity, a gas such as N ₂ , O ₂ , or Ar can be mixed into the etching gas. The etching here is performed under the condition that the etching rates of the resin material and the lens material become equal. The etching amount may be a desired amount.
Further, the etching may be wet etching.
Further, polishing can be used as a means for flattening. In this way, an optical element for an optical pickup in which a set of the objective lens 3 and the solid immersion lens 4 as shown in FIG.

[0026]

As described above, in the method of manufacturing an optical element for an optical pickup according to the first aspect, an objective lens and a solid immersion lens are prepared in advance, and these lenses are embedded in a substrate. Can be used. Since the two lenses are arranged on the concave curved surfaces formed on both surfaces of the substrate, the lenses can be aligned with high accuracy.

In the method for manufacturing an optical element for an optical pickup according to the second aspect, since an objective lens and a solid immersion lens are prepared in advance and these lenses are embedded in a substrate, a lens having an arbitrary refractive index or shape can be used. Can be used. Since the two lenses are arranged in the V-grooves formed on both sides of the substrate, the lenses can be aligned with high accuracy.

In the method of manufacturing an optical element for an optical pickup according to the third aspect, since an objective lens and a solid immersion lens are prepared in advance and these lenses are embedded in a substrate, a lens having an arbitrary refractive index or shape can be used. Can be used. Since the lenses are arranged on the concave curved surface formed in the mold or on the concave curved surface of the substrate molded in the mold, the lenses can be aligned with high accuracy. Further, since the element is manufactured by resin molding using a mold, a large number of elements can be manufactured.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of an optical element for an optical pickup manufactured by the present invention.

FIG. 2 is a perspective view showing another example of the optical element for an optical pickup manufactured by the present invention.

FIG. 3 is an explanatory view of a manufacturing process of the optical element for an optical pickup according to the first embodiment of the present invention.

FIG. 4 is a sectional view of a substrate according to an embodiment of the present invention.

FIG. 5 is an explanatory view of a manufacturing process of an optical element for an optical pickup according to an embodiment of the present invention.

FIG. 6 is a diagram showing a configuration example of a conventional optical memory optical pickup.

FIG. 7 is an explanatory view of the prior art, showing an example in which a hemispherical or hyperhemispherical solid immersion lens is inserted between an objective lens of an optical pickup and a recording medium.

FIG. 8 is an explanatory view of the prior art, showing an example in which a flying head provided with a solid immersion lens between an objective lens of an optical pickup and a recording medium is arranged.

[Explanation of symbols]

 1, 1 ': optical element for optical pickup 2: substrate 2a, 2b: concave surface 2c, 2d: V groove 3: objective lens 4: solid immersion lens 5, 8: resin material 6: mold 6a: convex surface 6b: concave Curved surface 7: Resin (resin substrate)

Claims (3)

[Claims] 1. An objective lens having a function of condensing collimated light, and a solid immersion lens arranged at a position closer to a recording medium than the objective lens and having a higher refractive index than a substrate whose optical axis coincides with the objective lens. Having at least one set of an objective lens and a solid immersion lens.
A method for manufacturing an optical element for an optical pickup, comprising: forming at least one pair on one substrate, forming concave surfaces on both surfaces of the substrate, and forming the concave surfaces having a higher refractive index than the substrate on the two concave surfaces. A method for manufacturing an optical element for an optical pickup, comprising: arranging a lens having a shape conforming to a curved surface, fixing the lens and a substrate with a resin material, and flattening the lens. 2. An objective lens having a function of condensing collimated light, and a solid immersion lens arranged at a position closer to a recording medium than the objective lens and having a higher refractive index than a substrate whose optical axis coincides with the objective lens. Having at least one set of an objective lens and a solid immersion lens.
In a method of manufacturing an optical element for an optical pickup, wherein at least one set is formed on one substrate, V-grooves are formed on both surfaces of the substrate, and the two V-grooves have a higher refractive index than that of the substrate. A method for manufacturing an optical element for an optical pickup, comprising: arranging a lens having a shape in contact with a groove, fixing the lens and a substrate with a resin material, and flattening the lens. 3. An objective lens having a function of condensing collimated light, and a solid immersion lens disposed at a position closer to a recording medium than the objective lens and having a higher refractive index than a substrate whose optical axis coincides with the objective lens. Having at least one set of an objective lens and a solid immersion lens.
In a method for manufacturing an optical element for an optical pickup, wherein at least one set is formed on a single substrate, a mold is formed which can form a concave curved surface on both surfaces of the substrate, and the mold is filled with a resin. An optical pickup characterized in that a lens having a refractive index higher than that of the substrate and having a shape conforming to the concave surface is arranged on the concave surface of the substrate, the lens and the substrate are fixed with a resin material, and then flattened. Of manufacturing optical element for use.