JP2015034830A - Base material for optical element, optical element, optical assist magnetic recording head, and method of manufacturing optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology capable of easily obtaining an accurate optical element using a drawing method.SOLUTION: A base material for an optical element is used for manufacturing, by drawing processing, an optical element that has, as a part of the outer surface, an optical surface including an effective area satisfying optical performance. The base material for the optical element includes a first bent section. The first bent section is disposed in a part other than the curved surface corresponding to the optical surface, and is formed by the drawing processing so that the cross-sectional shape becomes a target cross-sectional shape.

Description

  The present invention relates to an optical element base material, an optical element, an optically assisted magnetic recording head having the optical element, and a method for manufacturing the optical element.

  In a magnetic recording system used for a hard disk drive (HDD), when an attempt is made to increase the recording density, the interval between magnetic bits becomes narrow, and the polarity becomes unstable due to a superparamagnetic effect or the like. For this reason, a recording medium having a high coercive force is required. However, when such a recording medium is used, a magnetic field required for recording also increases. Here, the upper limit of the magnetic field generated by the recording head is determined by the saturation magnetic flux density, but the value is approaching the material limit, and there is a fact that a dramatic increase cannot be expected. Therefore, during recording, the magnetic bit is heated locally to cause magnetic softening, recording is performed with a reduced coercive force, and then the heating is stopped and natural cooling is performed to stabilize the recorded magnetic bit. A recording method that guarantees the performance has been proposed. This method is called a “thermally assisted magnetic recording method”.

  In the heat-assisted magnetic recording method, it is desirable that the recording medium is instantaneously heated. Further, the heating mechanism and the recording medium rotating at high speed are not allowed to contact. Therefore, heating is generally performed by irradiating a recording medium with a minute spot of laser light. This method using light for heating is called an “optically assisted magnetic recording method”.

  In the optically assisted magnetic recording method, laser light from a light source is reflected by a reflection surface (optical surface) of an optical element disposed on a slider. The reflected laser light is incident on the optical waveguide formed on the slider and is irradiated on the plasmon probe formed on the output end of the optical waveguide. The plasmon probe irradiated with the laser light generates near-field light.

  Here, as a method of manufacturing an optical element such as a cylindrical lens or a prism, there is a method called a drawing method. The drawing method is a method of forming a desired optical element by stretching a base material while heating. An optical element manufactured by the drawing method has a cross section reduced to a few tenths to a hundredth of the cross section of the base material. Therefore, even when the surface accuracy of the optical surface of the base material is low, the optical surface of the optical element formed by the drawing process can obtain high surface accuracy.

International Publication No. 2002/091038 JP 2003-329817 A

  However, in the drawing method, a desired optical element may not be obtained depending on the material of the base material and the drawing conditions (drawing speed, temperature, etc.). FIG. 14 is a cross-sectional view of the base material O ′ and the optical element O. For example, when a drawing process is performed on the base material O ′, the manufactured optical element O may be deformed (expanded) so that the outer surface thereof approaches a cylinder due to surface tension during heating and stretching. That is, the outer surface of the optical element O after drawing is deformed into a convex shape instead of a flat surface. In FIG. 14, in order to facilitate understanding of the deformation of the outer surface, the cross section of the base material and the cross section of the optical element are shown in the same size (actually, the cross section of the optical element manufactured by the drawing method is , Smaller than the cross section of the base material). Alternatively, depending on the drawing conditions, the outer surface of the optical element after drawing may be deformed (contracted) into a concave shape as shown in FIG.

  Thus, in the conventional drawing method, there is a possibility that an optical element having an outer surface shape (cross-sectional shape) different from that of the base material may be manufactured (a desired optical element may not be obtained).

  Here, the optical element used for the optically assisted magnetic recording head is required to have high accuracy. Therefore, when the optical element is manufactured by the drawing method, the influence of the deformation is large. In particular, when an optical surface formed on a part of the outer surface of the base material is deformed, there is a possibility of affecting the light reflection direction and the like. If the light reflection direction changes due to deformation of the optical surface, it becomes difficult to accurately guide the laser light from the light source to the optical waveguide.

  The present invention solves the above-described problems, and an object thereof is to provide a technique capable of easily obtaining a high-precision optical element using a drawing method.

In order to solve the above problems, the optical element base material according to claim 1 is used for manufacturing an optical element having an optical surface including an effective area satisfying optical performance as a part of an outer surface by a drawing process. The base material for optical elements has a 1st bending part. The first bent portion is provided in a portion other than the curved surface corresponding to the optical surface, and is formed so that the cross-sectional shape becomes a target cross-sectional shape by a drawing process.
In order to solve the above-mentioned problem, an optical element base material according to claim 2 is the optical element base material according to claim 1, and is a cross section of a first bent portion with respect to a shape similar to a target cross-sectional shape. The shape difference D satisfies the following expression.
D = d / α
However,
d: Difference between the cross-sectional shape of the optical element obtained by drawing a base material for an optical element having a cross-sectional shape similar to the target cross-sectional shape and the target cross-sectional shape α: Reduction ratio of the base material for optical element by the drawing process In order to solve the above problems, an optical element base material described in claim 3 is the optical element base material described in claim 1 or 2, and has a second bent portion. The second bent portion is provided on a curved surface corresponding to the optical surface, and is formed so that a cross-sectional shape of the optical surface becomes a target cross-sectional shape by a drawing process.
In order to solve the above problem, the optical element base material according to claim 4 is the optical element base material according to claim 3, and the curvature radius R ′ of the second bent portion is expressed by the following equation: Meet.
R ′ = (r / r ′) R
However,
R: radius of curvature of the curved surface of the optical element base material corresponding to the optical surface r: radius of curvature of the optical surface in the target cross-sectional shape r ′: when the optical element base material having a curved surface with a constant curvature radius R is drawn Among the optical surfaces in the cross-sectional shape of the optical element obtained in the above, the radius of curvature at a predetermined position of the optical surface different from the target cross-sectional shape. 4 is obtained by subjecting the optical element base material according to any one of 4 to a drawing process and a cutting process.
In order to solve the above problem, an optically assisted magnetic recording head according to claim 6 is a slider having an optical waveguide, a light source that outputs light in a direction perpendicular to the optical waveguide, and a light reflected from the light source. And an optical element according to claim 5 for guiding light to an optical waveguide.
In order to solve the above problem, an optical element manufacturing method according to a seventh aspect includes a first bent portion forming step, a drawing process step, and a cutting step. In the first bent portion forming step, the first bent portion is formed on the outer surface of the optical element base material so that the cross-sectional shape becomes a target cross-sectional shape by a drawing process. In the drawing process, drawing is performed until the cross section of the optical element base material has a predetermined size to obtain an intermediate product. In the cutting step, a plurality of optical elements are obtained by cutting the intermediate product.
In order to solve the above problem, an optical element manufacturing method according to an eighth aspect is the optical element manufacturing method according to a seventh aspect, which includes a second bent portion forming step. In the second bent portion forming step, the second bent portion is formed on the curved surface of the optical element base material by the drawing process so that the cross-sectional shape of the optical surface becomes the target cross-sectional shape.

  In this way, considering the deformation due to the drawing process in advance, the bent portion (first bent portion, second bent portion) is provided in the optical element base material. Therefore, the optical element obtained by the drawing process has a desired shape. That is, it is possible to easily obtain a highly accurate optical element by using a drawing method.

1 is a perspective view showing an information recording apparatus according to a first embodiment. 1 is a cross-sectional view showing an optically assisted magnetic recording head according to a first embodiment. It is a perspective view which shows the optical element which concerns on 1st Embodiment. It is sectional drawing which shows the optical element which concerns on 1st Embodiment. It is a perspective view which shows the preform | base_material for optical elements which concerns on 1st Embodiment. It is sectional drawing which shows the base material for optical elements which concerns on 1st Embodiment. It is sectional drawing which shows an example of the optical element base material for optical elements, and an optical element obtained by performing a drawing process. It is a figure which shows the wire drawing apparatus which concerns on 1st Embodiment. It is a flowchart which shows the manufacturing method of the optical element which concerns on 1st Embodiment. It is sectional drawing which shows an example of the optical element base material for optical elements, and an optical element obtained by performing a drawing process. It is a perspective view which shows the base material for optical elements which concerns on 2nd Embodiment. It is sectional drawing which shows the preform | base_material for optical elements which concerns on 2nd Embodiment. It is a flowchart which shows the manufacturing method of the optical element which concerns on 2nd Embodiment. It is sectional drawing which shows an example of the optical element base material for optical elements, and an optical element obtained by performing a drawing process.

<First Embodiment>
The optical element (base material for an optical element) according to the first embodiment will be described with reference to FIGS.

[Configuration of information recording device]
As shown in FIG. 1, an optically assisted magnetic recording device (for example, a hard disk device, hereinafter sometimes referred to as “information recording device 1”) equipped with an optically assisted magnetic recording head is capable of rotating a plurality of recording sheets, for example. A disk (magnetic recording medium) 3, a head support 5, a tracking actuator 7, an optically assisted magnetic recording head 4 (hereinafter sometimes referred to as “optical head 4”), and a drive device (not shown) are provided. It is provided in the body 2. The disk 3 may be one. The head support portion 5 is provided to be rotatable in the direction of arrow A (tracking direction) with the support shaft 6 as a fulcrum. The tracking actuator 7 is attached to the head support portion 5. The optical head 4 is attached to the tip of the head support 5. A drive device (not shown) rotates the disk 3 in the direction of arrow B. The information recording apparatus 1 is configured such that the optical head 4 can move relatively while flying over the disk 3.

[Optical assisted magnetic recording head]
Next, a schematic configuration example of the optical head 4 will be described with reference to FIGS. FIG. 2 is a sectional view of the optical head 4. FIG. 3 is a perspective view of the optical element 30. FIG. 4 is a DD cross section of FIG.

  The optical head 4 is a minute optical recording head that uses light for information recording on the disk 3. The optical head 4 includes a slider 10, a light source unit 20, and an optical element 30. The information recording apparatus 1 is configured such that the disk 3 is moved in the direction of arrow C, and the optical head 4 can move relatively while flying over the disk 3. In this embodiment, the rotation direction (arrow C direction) of the disk 3 is described as the y direction, the thickness direction of the optical head 4 is described as the z direction, and the direction orthogonal to both the y direction and the z direction is described as the x direction.

(Slider)
The slider 10 is a square substrate formed of a material such as AlTiC, for example. The slider 10 has a lower surface 10a that faces the disk 3, an upper surface 10b that is located on the opposite side of the lower surface 10a in the z direction, and a side surface 10c that is located at an end in the y direction.

  A magnetic head portion 13 is formed on the slider 10. The magnetic head unit 13 includes an optical waveguide 14, a magnetic recording unit (not shown), a magnetic information reproducing unit (not shown), and an electrode (not shown). In the present embodiment, the magnetic head portion 13 is formed integrally with the slider 10, but a separate member may be attached to the side surface 10 c of the slider 10.

The optical waveguide 14 guides light from the light source unit 20 guided by the optical element 30 and forms a path for emitting the light toward the disk 3. The optical waveguide 14 has an incident end 14a and an exit end 14b. Light from the light source unit 20 is incident on the incident end 14a. The incident end 14 a is provided on the upper surface of the magnetic head unit 13 that is substantially flush with the upper surface 10 b of the slider 10. Light that has passed through the optical waveguide 14 is emitted from the emission end 14b. The emission end 14 b is provided on the lower surface of the magnetic head portion 13 that is substantially flush with the lower surface 10 a of the slider 10. The optical waveguide 14 is formed by laminating a lower clad layer, a core layer, and an upper clad layer (all not shown) in this order along the thickness direction (y direction) perpendicular to the direction in which light propagates. is there. The core layer is formed of a material (for example, Ta ₂ O ₅ ) having a higher refractive index than each cladding layer (for example, formed of SiO ₂ ). Thereby, the light guided to the optical waveguide 14 propagates toward the disk 3 while being totally reflected between the core layer and each cladding layer.

  In the vicinity of the emission end 14b of the optical waveguide 14, a plasmon probe 15 as a near-field light generating element is disposed.

  The light from the light source unit 20 guided by the optical element 30 enters the optical waveguide 14 from the incident end 14a and travels in the optical waveguide 14 toward the output end 14b. The plasmon probe 15 provided at the emission end 14 b converts the light guided by the optical element 30 into near-field light and emits it toward the disk 3.

  A magnetic recording unit (not shown) writes magnetic information to the recording portion of the disk 3. A magnetic information reproducing unit (not shown) reads magnetic information recorded on the disk 3. An electrode (not shown) is formed on the upper surface 10 b of the slider 10. The electrodes have a predetermined pattern shape and are connected to the light source unit 20 to supply driving power to the light source unit 20.

Further, the slider 10 moves relative to the disk 3 that is a magnetic recording medium while flying, but there is a possibility of contact with the disk 3 if there is a dust attached to the disk 3 or a defect in the disk 3. There is. In order to reduce the friction generated in that case, it is preferable to use a hard material having high friction resistance as the material of the slider 10. For example, a ceramic material containing Al ₂ O ₃ , AlTiC, zirconia, TiN, or the like may be used. In order to prevent friction, the surface of the slider 10 on the disk 3 side may be subjected to a surface treatment for increasing the friction resistance. For example, high hardness can be obtained by using a DLC (Diamond Like Carbon) coating.

(Light source)
The light source unit 20 includes, for example, a semiconductor laser (Laser Diode: LD). The light source unit 20 outputs light in a direction substantially orthogonal to the optical waveguide 14. The “substantially orthogonal direction” refers to a direction in which light from the light source unit 20 can enter the optical surface 32 (effective area 32a, which will be described later) of the optical element 30. The wavelength of light output from the semiconductor laser is from visible light to near-infrared wavelength (the wavelength band is about 0.6 μm to 2 μm. Specific wavelengths are 650 nm, 780 nm, 830 nm, and 1310 nm. , 1550 nm, and the like.

  As a material constituting the semiconductor laser, for example, any one of materials such as GaAs, AlGaAs, InGaAs, AlGaInP, InAlGaN, InGaN, GaN, GaInNA, GaNAsP, and AlGaNAs may be used. Then, a semiconductor laser can be manufactured by stacking layers necessary for light emission on the wafer.

  The light source unit 20 is disposed on the upper surface 10 b of the slider 10. The light source unit 20 has an emission surface 20a and a bottom surface 20b. On the emission surface 20a, an emission end 20c for emitting light from the semiconductor laser to the outside of the light source unit 20 is formed. The light source unit 20 outputs light from the emission end 20 c toward the optical element 30.

(Optical element)
The optical element 30 is an element for reflecting and condensing light from the light source unit 20 and guiding it to the incident end 14 a of the optical waveguide 14. As shown in FIG. 3, the optical element 30 is made of, for example, a rectangular member, and an optical surface 32 is formed on a part of the outer surface 31 thereof. The optical surface 32 reflects light from the light source unit 20.

  The optical element 30 is made of, for example, an optically transparent resin or glass. The optical element 30 is formed, for example, by subjecting a base material made of glass such as quartz to a drawing process and a cutting process. Details of the manufacturing method of the optical element 30 will be described later.

  In the present embodiment, the optical surface 32 is exposed to the outside. Therefore, the optical surface 32 functions as a surface reflection mirror. The optical surface 32 can be formed of a metal film such as gold or aluminum, a reflective film of a dielectric multilayer film, or the like. Since the optical surface 32 is a surface reflection mirror, the light from the light source unit 20 does not enter the optical element 30. Therefore, it is possible to reduce the light amount loss due to the light passing through the optical element 30.

  The optical surface 32 is formed in a cylindrical surface shape (a part of the cylindrical surface). As shown in FIG. 4, the optical surface 32 includes an effective area 32a that satisfies the required optical performance (for example, a function of reflecting light from the light source unit 20 in a predetermined direction) and a region 32b other than that. Has been.

  The shape of the optical surface 32 is not limited to a circle (cylinder), but may be a cylindrical surface formed of a part of an aspherical cross section such as an ellipse. Even in this case, the optical surface 32 includes an effective area 32a that satisfies the optical performance and a region 32b other than the effective area 32a.

  A part of the outer surface 31 of the optical element 30 functions as a light source side bonding surface 31a and a magnetic head unit side bonding surface 31b. The light source side bonding surface 31a is bonded to the emission surface 20a of the light source unit 20 via an adhesive or the like. The magnetic head side bonding surface 31b is bonded to the upper surface of the magnetic head portion 13 (the upper surface 10b of the slider 10) via an adhesive or the like. When the optical element 30 is bonded to the optical head 4, at least one of the light source side bonding surface 31a and the magnetic head unit side bonding surface 31b may be bonded by an adhesive or the like. The areas of the light source side bonding surface 31a and the magnetic head unit side bonding surface 31b may be the same or different (FIG. 3 and the like show examples having different areas).

  In the present embodiment, the cross-sectional shape (for example, the cross-sectional shape shown in FIG. 4) of the optical element 30 used in the optical head 4 is referred to as a “target cross-sectional shape”.

[Base materials for optical elements]
Next, the optical element base material 30 ′ will be described with reference to FIGS. 5 to 7. FIG. 5 is a perspective view of the optical element base material 30 ′. 6 is an EE cross section in FIG. FIG. 7 is a cross-sectional view showing an example of a base material M ′ having a cross-sectional shape similar to the target cross-sectional shape and an optical element M manufactured by drawing the base material M ′. The broken line in FIG. 6 shows a shape similar to the target cross-sectional shape. The broken line in FIG. 7 indicates the target cross-sectional shape. In the present embodiment, the cross-sectional shape of the optical element base material 30 ′ (base material M ′) and the cross-sectional shape of the optical element 30 (optical element M) are shown to be approximately the same size. When 30 is manufactured by a drawing method, generally, the outer shape (cross section) size of the optical element 30 (optical element M) is smaller than the outer shape (cross section) size of the optical element base material 30 ′ (base material M ′). (For example, about 1/10 to 1/100).

  The optical element base material 30 ′ is a member that is a base of the optical element 30. The optical element 30 is obtained by performing a drawing process or the like on the optical element base material 30 ′. The optical element base material 30 ′ is provided with a first bent portion 31 ′ corresponding to the outer surface 31 of the optical element 30 and a curved surface 32 ′ corresponding to the optical surface 32 of the optical element 30.

  The first bent portion 31 ′ is provided on the outer peripheral surface other than the curved surface 32 ′, and is formed so that the cross-sectional shape of the optical element 30 obtained by the drawing process becomes a target cross-sectional shape.

  Here, as shown in FIG. 7, when the drawing process is performed on the base material M ′ having a cross-sectional shape similar to the target cross-sectional shape, the surface tension generated by the heating and stretching performed during the drawing is obtained. The cross-sectional shape of the obtained optical element M expands compared to the target cross-sectional shape (in FIG. 7, the cross-sectional shape expands by the difference d with respect to the target cross-sectional shape). That is, when the base material M ′ having a cross-sectional shape similar to the target cross-sectional shape is used, there is a high possibility that the cross-sectional shape of the optical element M obtained by the drawing process does not become the target cross-sectional shape.

  Therefore, in the present embodiment, the deformation of the outer surface 31 that occurs when the optical element base material 30 ′ having a shape similar to the optical element 30 is drawn is considered in advance, and the deformation in the opposite direction to the deformation (for example, against expansion) Thus, a first bent portion 31 ′ that is contracted by that amount is formed on the optical element base material 30 ′. Therefore, the optical element 30 after the drawing process can be obtained in a desired shape. That is, the cross-sectional shape of the optical element 30 obtained when the optical element base material 30 ′ having the first bent portion 31 ′ is drawn is the target cross-sectional shape.

  For example, as shown in FIG. 6, the first bent portion 31 ′ has a concave shape that is contracted by a difference D (described later) with respect to the target cross-sectional shape in advance. By processing under the condition of drawing so that the optical element base material 30 ′ having the first bent portion 31 ′ expands, the cross-sectional shape of the optical element 30 obtained becomes equal to the target cross-sectional shape.

  The shape of the first bent portion 31 ′ can be appropriately determined in consideration of conditions such as the material of the base material, the drawing speed (speed for drawing the base material), the heating temperature, and the like.

  For example, the difference between the cross-sectional shape of the optical element M obtained when the base material M ′ is drawn under the drawing condition f and the target cross-sectional shape is d (see FIG. 7), and the optical element base material 30 ′ by the drawing process is used. The reduction rate α of The “reduction ratio” refers to the degree of contraction of the outer dimension (cross section) of the optical element with respect to the outer dimension (cross section) of the optical element base material when the optical element is manufactured by a drawing method. At this time, the difference D (see FIG. 6) in the cross-sectional shape of the first bent portion 31 ′ with respect to the shape similar to the target cross-sectional shape when the line drawing process is performed under the condition f is a value that satisfies the following equation (1) It is desirable.

[Equation 1]
D = d / α (1)

  When the reduction ratio α is in the line drawing condition f, a convex deformation (difference from the target cross-sectional shape) occurs on the outer surface 31 of the optical element 30 by d. The conversion amount of d into the size of the optical element base material 30 ′ is d / α obtained by multiplying d by the inverse 1 / α of the reduction ratio. By applying this converted amount d / α to the outer surface of the optical element base material 30 ′ in advance in the opposite direction to the deformation (convex shape) due to the drawing process, that is, as a concave deformation, the first bent portion 31 ′ is formed. The When the optical element base material 30 ′ having the first bent portion 31 ′ is drawn under the drawing condition f, the concave first bent portion 31 ′ expands. Then, the concave first bent portion 31 ′ becomes planar, that is, a target cross-sectional shape when the reduction ratio becomes α.

  Based on the calculation result of Expression (1), the optical element base material 30 ′ can be formed by denting each of the first bent portions 31 ′ by D.

  Depending on the conditions of the drawing process, the outer surface of the optical element may contract with respect to the outer surface of the base material. In this case, it is also possible to form a convex first bent portion 31 ′ on the optical element base material 30 ′. Further, the shapes of the first bent portions 31 ′ may all be the same shape or may be different shapes.

  In addition, the outer surface 31 of the optical element 30 formed by the drawing process can be formed in a plane by providing the first bent portion 31 ′ in the optical element base material 30 ′. Therefore, when a part of the outer surface 31 functions as the light source side bonding surface 31a or the magnetic head unit side bonding surface 31b, positioning of the optical element 30 with respect to the light source unit 20 or the magnetic head unit 13 is facilitated.

  The curved surface 32 ′ is a surface corresponding to the optical surface 32 of the optical element 30. The curved surface 32 ′ forms the optical surface 32 by drawing the optical element base material 30 ′. In the present embodiment, it is assumed that the curved surface 32 ′ is not deformed by the drawing process (an example in which the deformation of the curved surface 32 ′ is taken into account will be described in the second embodiment).

[Drawing device]
Next, a drawing apparatus 100 used for the drawing method will be described with reference to FIG. The drawing apparatus 100 includes rollers 101 and 102, a heating unit 103, an external dimension measuring unit 104, and a cutter 105.

  The roller 101 sends the optical element base material 30 ′ to the heating unit 103.

  The heating unit 103 includes an electric furnace 103a and a temperature adjustment unit 103b. The temperature adjustment unit 103b adjusts the temperature of the electric furnace 103a. Specifically, when the optical element base material 30 ′ is fed into the vicinity of the electric furnace 103 a by the roller 101, the temperature adjustment unit 103 b is electrically operated so as to heat more than the yield point of the material of the optical element base material 30 ′. The temperature of the furnace 103a is adjusted.

  The roller 102 stretches the optical element base material 30 ′ heated by the heating unit 103 until its outer shape (cross-sectional) dimension reaches a predetermined size (drawing process).

  The external dimension measuring unit 104 is provided between the roller 101 and the roller 102. The outer dimension measuring unit 104 measures the outer diameter of the optical element base material 30 'that has been subjected to the drawing process, and whether or not the outer dimension is a predetermined outer dimension (that is, the cross section has a predetermined size). Is determined). The external dimension measuring unit 104 includes a laser unit 104a, a light receiving unit 104b, and an analysis unit 104c. The laser unit 104a irradiates laser light to the optical element base material 30 ′ that has been subjected to the drawing process. The light receiving unit 104b receives the laser light that has passed through the optical element base material 30 '. The analysis unit 104c calculates the outer dimensions of the optical element base material 30 ′ based on the amount of light received by the light receiving unit 104b.

  The cutter 105 is provided below the roller 102, and when the outer dimension measuring unit 104 determines that the outer dimension of the optical element base material 30 ′ is a predetermined dimension, the optical element base material 30. 'Is cut into a predetermined length, and the intermediate product P is formed. A plurality of optical elements 30 can be obtained by further cutting and processing the intermediate product P (for example, chamfering the cutting surface ridge line or coating the optical surface 32).

[Method for Manufacturing Optical Element]
With reference to FIG. 9, the manufacturing method of the optical element 30 using the drawing apparatus 100 is demonstrated. FIG. 9 is a flowchart showing a manufacturing procedure of the optical element 30 according to the present embodiment.

  First, a simulation is performed based on the conditions of the drawing process, and the shape of the first bent portion 31 ′ is determined. Based on the simulation result, the optical element base material 30 'is processed to form a first bent portion 31' (S10). S10 is an example of a “first bent portion forming step”.

  The optical element base material 30 ′ processed in S <b> 10 is fed into the drawing apparatus 100. The optical element base material 30 ′ is heated and stretched by the heating unit 103 and the roller 102 of the drawing apparatus 100 (S 11).

  When the outer dimension of the stretched optical element base material 30 ′ reaches a predetermined value, the cutter 105 cuts the optical element base material 30 ′ to obtain an intermediate product P (S 12). S11 and S12 are examples of the “drawing process”.

  Then, the intermediate product P is further cut and processed (for example, chamfering of the cutting surface ridge line or coating of the optical surface 32) by a cutting device or a processing device (both not shown) to obtain a plurality of optical elements 30. (S13). S13 is an example of a “cutting step”.

[Action / Effect]
The operation and effect of this embodiment will be described.

  The optical element base material 30 ′ according to the present embodiment includes an optical surface 32 including an effective area 32 a that satisfies the optical performance (for example, reflects light from the light source unit 20 in a predetermined direction) as a part of the outer surface 31. It is used for manufacturing the optical element 30 having a drawing process. The optical element base material 30 ′ has a first bent portion 31 ′. The first bent portion 31 ′ is provided in a portion other than the curved surface 32 ′ corresponding to the optical surface 32, and is formed so that the cross-sectional shape becomes a target cross-sectional shape by a drawing process.

Further, in the optical element base material 30 ′ according to the present embodiment, the difference D in the cross-sectional shape of the first bent portion 31 ′ with respect to the shape similar to the target cross-sectional shape of the first bent portion 31 ′ is expressed by the equation (1). It is desirable to form so as to satisfy.
D = d / α (1)
However,
d: Difference between the cross-sectional shape of the optical element 30 and the target cross-sectional shape obtained when the optical element base material 30 ′ having a cross-sectional shape similar to the target cross-sectional shape is drawn. α: Optical element base material by the drawing process. 30 'reduction ratio

  The optical element 30 according to the present embodiment performs a drawing process and a cutting process on the optical element base material 30 ′ described above (including a processing process such as chamfering of a cutting surface ridge line and coating of the optical surface 32). It is obtained by doing.

  In addition, the method for manufacturing the optical element 30 according to the present embodiment includes a first bent portion forming process, a drawing process, and a cutting process. In the first bent portion forming step, the first bent portion 31 ′ is formed on the outer surface of the optical element base material 30 ′ so that the cross-sectional shape becomes the target cross-sectional shape by the drawing process. In the drawing process, drawing is performed until the cross section of the optical element base material 30 ′ has a predetermined size to obtain an intermediate product. In the cutting step, the intermediate product P is cut to obtain a plurality of optical elements 30.

  In this way, considering the deformation caused by the drawing process in advance, the first bent portion 31 ′ is provided on the outer surface of the optical element base material 30 ′, so that the cross-sectional shape of the optical element 30 obtained by the drawing process is set to the target cross section. It can be a shape. That is, the optical element 30 obtained by the drawing process can be formed into a desired shape. Therefore, it is possible to easily obtain a highly accurate optical element using the drawing method.

Second Embodiment
Next, an optical element (base material for an optical element) according to the second embodiment will be described with reference to FIGS. Note that a detailed description of the same configuration as in the first embodiment may be omitted. FIG. 10 is a cross-sectional view showing an example of a base material N ′ having a cross-sectional shape similar to the target cross-sectional shape and an optical element N manufactured by drawing the base material N ′. FIG. 11 is a perspective view of the optical element base material 30 ″. 12 is a cross-sectional view taken along line FF in FIG. FIG. 13 is a flowchart showing a manufacturing procedure of the optical element according to the present embodiment. The broken line in FIG. 10 indicates the target cross-sectional shape. The broken line in FIG. 12 shows a shape similar to the target cross-sectional shape. Also in this embodiment, the cross-sectional shape of the optical element base material and the cross-sectional shape of the optical element are shown with substantially the same size. In addition, it is assumed that the optical element obtained by drawing the optical element base material 30 ″ in the present embodiment is the same as the optical element 30 in the first embodiment.

  The first embodiment has been described assuming that the curved surface 32 ′ of the optical element base material 30 ′ is not deformed by the drawing process.

  However, depending on the drawing conditions, the curved surface of the base material may be deformed. For example, as shown in FIG. 10, when a drawing process is performed on a base material N ′ having a cross-sectional shape similar to the target cross-sectional shape, it is obtained by surface tension generated by heating and stretching performed at the time of drawing. The cross-sectional shape of the optical element N expands compared to the target cross-sectional shape. At this time, the curved surface N′b is pulled by the expansion of the outer surface N′a of the base material N ′. Therefore, the curvature radius of the optical surface Nb of the obtained optical element N increases as the portion is closer to the outer surface Na. For example, when the curvature radius of the curved surface N′b is R, the curvature radius (r ′) of the portion close to the outer surface Na and the portion far from the outer surface Na (effective) of the optical surface Nb of the optical element N obtained after the drawing process It differs from the radius of curvature (r) near the center of the area.

  Here, when the NA of the optical element (optical surface) is small, the optical element can exhibit optical performance even if the effective area formed on the optical surface is narrow. That is, even if the radius of curvature of the region other than the effective area is different from the radius of curvature in the target cross-sectional shape due to the drawing process, it is unlikely to affect the optical performance of the optical element.

  On the other hand, when the NA of the optical element (optical surface) is large, the effective area formed on the optical surface is also widely formed. Therefore, the radius of curvature in the effective area of the optical element may be different from the target radius of curvature (the radius of curvature of the effective area in the target cross-sectional shape) due to the drawing process. If the radius of curvature is different within the effective area, the optical performance of the optical element may be affected. For example, the reflection direction may change depending on the position where light from the light source unit 20 hits in the effective area. In this case, light cannot be efficiently guided to the optical waveguide 14.

  In the present embodiment, the configuration of the optical element base material 30 ″ considering the deformation of the curved surface due to the drawing process will be described.

[Base materials for optical elements]
The optical element base material 30 ″ is a member that is a base of the optical element 30. The optical element 30 is obtained by subjecting the optical element base material 30 ″ to a drawing process or the like. The optical element base material 30 ″ is provided with a first bent portion 31 ″ corresponding to the outer surface 31 of the optical element 30 and a curved surface 32 ″ corresponding to the optical surface 32 of the optical element 30.

  The first bent portion 31 ″ is provided on the outer peripheral surface other than the curved surface 32 ″, and is formed so that the cross-sectional shape of the optical element 30 obtained by the drawing process becomes a target cross-sectional shape. Since the first bent portion 31 ″ has a structure substantially similar to that of the first bent portion 31 ′, detailed description thereof is omitted. In addition, according to the shape of the curved surface 32 ″, the cross-sectional shapes of the first bent portion 31 ″ adjacent to the curved surface 32 ″ and the other first bent portions 31 ″ can be different.

The curved surface 32 ″ is a surface corresponding to the optical surface 32 of the optical element 30. In the present embodiment, the curved surface 32 ″ includes a region 32 ″ a and a second bent portion 32 ″ b.
The region 32 ″ a is a region corresponding to the vicinity of the center of the effective area 32a of the optical surface 32. The region 32 ″ a is a region that is not easily deformed (change in the radius of curvature) by the drawing process. The second bent portion 32 ″ b is a region corresponding to the region 32b of the optical surface 32 and a part (peripheral portion) of the effective area 32a adjacent to the region 32b. It is formed to have a shape. That is, the second bent portion 32 ″ b is a region that is susceptible to deformation (change in the radius of curvature) due to the drawing process.

  For example, as shown in FIG. 12, the curved surface 32 ″ is formed in advance so that the radius of curvature of the second bent portion 32 ″ b is smaller than the radius of curvature of the region 32 ″ a. By performing a drawing process under the drawing conditions such that the optical element base material 30 ″ expands, the first bent portion 31 ″ adjacent to the curved surface 32 ″ expands. Then, the second bent portion 32 ″ b is expanded by being pulled by the expanding first bent portion 31 ″, so that the cross-sectional shape of the obtained optical element 30 becomes equal to the target cross-sectional shape.

  The shape of the second bent portion 32 ″ b can be appropriately determined in consideration of conditions such as the material of the base material, the drawing speed, and the heating temperature.

  For example, a curvature radius of the curved surface 32 ″ corresponding to the optical surface 32 is R, a curvature radius of the optical surface 32 in the target cross-sectional shape is r, and a base material N ′ having a curved surface N′b with a constant curvature radius R is obtained. Of the optical surfaces in the cross-sectional shape of the optical element N obtained when the drawing process is performed, the radius of curvature at a predetermined position of the optical surface different from the target cross-sectional shape is r ′. The “predetermined position” is an arbitrary position in a part (peripheral part) of the effective area other than the effective area or adjacent to the area other than the effective area. For example, in the present embodiment, a position where the curved surface 32 ″ and the first bent portion 31 ″ are adjacent to each other is shown. At this time, it is desirable that the radius of curvature R ′ of the second bent portion 32 ″ b be a value satisfying the following formula (2).

[Equation 2]
R ′ = (r / r ′) R (1)

  The portion of the curved surface Nb close to the outer surface Na is pulled by the expansion of the outer surface N′a by the drawing process, and becomes a radius r ′ whose radius of curvature is larger than the target curvature radius r. Accordingly, by previously giving a value obtained by multiplying the curvature radius R of the curved surface 32 ″ by the reciprocal r / r ′ of the deformation radius r ′ / r of the curvature radius by the drawing process to the outer surface of the optical element base material 30 ″, A second bent portion 32 ″ b having a radius of curvature R ′ (= (r / r ′) R) is formed. As described above, if the second bent portion 32 ″ b is set in advance, the radius of curvature of the optical surface 32 after the drawing process becomes the radius of curvature r of the target cross-sectional shape. In general, since the expansion rate of the outer surface of the base material is different from the deformation rate of the radius of curvature by traction, such correction is desirable.

  Based on the calculation result of Formula (2), the base material 30 ″ for the optical element can be formed by setting the curvature radius of the second bent portion 32 ″ b to R ′.

  Depending on the conditions of the drawing process, the outer surface of the optical element may contract with respect to the outer surface of the base material. In this case, it is also possible to make the curvature radius of the second bent portion 32 ″ b larger than the curvature radius of the region 32 ″ a. Further, the shape of the second bent portion 32 ″ b may be the same shape or different shapes.

  In the case where the optical surface is a cylindrical surface composed of a part of an aspherical cross section such as an ellipse, the local radius of curvature varies depending on a predetermined position on the optical surface. In such a case, when the distance from the center position of the curvature radius R to the predetermined position on the curved surface of the base material corresponding to the vicinity of the effective area center is R ″, R ″ = (r / r ″) R may be set. Here, r ″ is obtained when the base material N ′ is drawn when the curved surface N′b of the base material N ′ (see FIG. 10) has an aspheric shape similar to the target cross-sectional shape. This is the distance from the center position of the radius of curvature r near the center of the effective area of the optical element N to the predetermined position.

[Method for Manufacturing Optical Element]
With reference to FIG. 13, the manufacturing method of the optical element 30 using the preform | base_material 30 '' for optical elements is demonstrated.

  First, a simulation is performed based on the conditions of the drawing process and the like to determine the shape of the first bent portion 31 ″. Based on the simulation result, the optical element base material 30 ″ is processed to form the first bent portion 31 ″ (S20). S20 is an example of a “first bent portion forming step”.

  Similarly, a simulation is performed based on the conditions of the drawing process, and the shape of the second bent part 32 ″ b is determined. Based on the simulation result, the optical element base material 30 ″ is processed to form the second bent portion 32 ″ b (S21). S21 is an example of a “second bent portion forming step”. It is desirable that the simulations be performed simultaneously. Moreover, S20 and S21 may be performed simultaneously.

  The optical element base material 30 ″ processed in S 20 and S 21 is sent to the drawing apparatus 100. The optical element base material 30 ″ is heated and stretched by the heating unit 103 and the roller 102 of the drawing apparatus 100 (S22).

  When the outer dimension of the stretched optical element base material 30 ″ reaches a predetermined value, the cutter 105 cuts the optical element base material 30 ″ to obtain an intermediate product P (S23). S22 and S23 are examples of the “drawing process”.

  Then, the intermediate product P is further cut and processed (for example, chamfering of the cutting surface ridge line or coating of the optical surface 32) by a cutting device or a processing device (both not shown) to obtain a plurality of optical elements 30. (S24). S24 is an example of a “cutting step”.

[Action / Effect]
The operation and effect of this embodiment will be described.

  The optical element base material 30 ″ according to the present embodiment is provided on a curved surface 32 ″ corresponding to the optical surface 32, and is formed so that the cross-sectional shape of the optical surface 32 becomes a target cross-sectional shape by a drawing process. It has 2 bending parts 32''b.

In addition, in the optical element base material 30 ″ according to the present embodiment, it is desirable that the curvature radius R ′ of the second bent portion 32 ″ b satisfies the following formula.
R ′ = (r / r ′) R
However,
R: radius of curvature of the curved surface of the optical element base material corresponding to the optical surface r: radius of curvature of the optical surface in the target cross-sectional shape r ′: when the optical element base material having a curved surface with a constant curvature radius R is drawn Curvature radius at a predetermined position of the optical surface different from the target cross-sectional shape among the optical surfaces in the cross-sectional shape of the optical element obtained in

  Moreover, in the manufacturing method of the optical element 30 according to the present embodiment, a second bent portion forming step can be provided. In the second bent portion forming step, the second bent portion 32 ″ b is formed such that the cross-sectional shape of the optical surface 32 becomes the target cross-sectional shape by the drawing process with respect to the curved surface 32 ″ of the optical element base material 30 ″. Form.

  In this way, by taking into consideration the deformation of the curved surface due to the drawing process in advance, the second bent portion 32 ″ b is provided on the curved surface 32 ″ of the optical element base material 30 ″, thereby obtaining the optical obtained by the drawing process. The cross-sectional shape of the element 30 can be more accurately set as the target cross-sectional shape. That is, the optical element 30 obtained by the drawing process can be formed into a desired shape. Therefore, it is possible to easily obtain a highly accurate optical element using the drawing method. Further, according to the configuration of the present embodiment, it is possible to easily obtain a highly accurate optical element even when the optical element (optical surface) to be manufactured has a large NA.

DESCRIPTION OF SYMBOLS 1 Information recording device 2 Housing 3 Disc 4 Optical assist magnetic recording head (optical head)
DESCRIPTION OF SYMBOLS 5 Head support part 6 Support axis 7 Tracking actuator 10 Slider 10a Lower surface 10b Upper surface 10c Upper surface 10c Side surface 13 Magnetic head part 14 Optical waveguide 14a Incidence end 14b Emission end 15 Plasmon probe 20 Light source part 20a Emission surface 20b Bottom surface 20c Emission end 30 Optical element 30 ′ Base material for optical element 31 Outer surface 31 ′ First bent portion 32 Optical surface 32a Effective area 32b Region 32 ′ Curved surface

Claims (8)

An optical element base material used for manufacturing an optical element having an optical surface including an effective area satisfying optical performance as a part of an outer surface by a drawing process,
An optical element base material comprising a first bent portion provided in a portion other than a curved surface corresponding to the optical surface and formed so that a cross-sectional shape becomes a target cross-sectional shape by a drawing process. 2. The optical element base material according to claim 1, wherein a difference D in a cross-sectional shape of the first bent portion with respect to a shape similar to a target cross-sectional shape satisfies the following expression.
D = d / α
However,
d: Difference between the cross-sectional shape of the optical element obtained by drawing a base material for an optical element having a cross-sectional shape similar to the target cross-sectional shape and the target cross-sectional shape α: Reduction ratio of the base material for optical element by the drawing process   3. The optical device according to claim 1, further comprising a second bent portion provided on a curved surface corresponding to the optical surface and formed so that a cross-sectional shape of the optical surface becomes a target cross-sectional shape by a drawing process. Element base material. 4. The optical element base material according to claim 3, wherein a curvature radius R ′ of the second bent portion satisfies the following expression. 5.
R ′ = (r / r ′) R
However,
R: radius of curvature of the curved surface of the optical element base material corresponding to the optical surface r: radius of curvature of the optical surface in the target cross-sectional shape r ′: when the optical element base material having a curved surface with a constant curvature radius R is drawn Curvature radius at a predetermined position of the optical surface different from the target cross-sectional shape among the optical surfaces in the cross-sectional shape of the optical element obtained in   An optical element obtained by subjecting the optical element base material according to claim 1 to a drawing process and a cutting process. A slider having an optical waveguide;
A light source that outputs light in a direction orthogonal to the optical waveguide;
The optical element according to claim 5, wherein the optical element reflects light from the light source and guides the light to the optical waveguide.
An optically assisted magnetic recording head. A first bent portion forming step of forming a first bent portion so that the cross-sectional shape becomes a target cross-sectional shape by a drawing process on the outer surface of the optical element base material;
Drawing until the cross section of the optical element base material has a predetermined size, to obtain an intermediate product,
A cutting step of obtaining a plurality of optical elements by cutting the intermediate product,
A method for producing an optical element, comprising:   The method further comprises a second bent portion forming step of forming a second bent portion so that a cross-sectional shape of the optical surface becomes a target cross-sectional shape by a drawing process with respect to the curved surface of the optical element base material. 8. A method for producing an optical element according to item 7.

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