JP2014135103A - Optically assisted magnetic head and optical coupling structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a matching method of a spot size and a waveguide mode field diameter which secures desired coupling efficiency even if positional deviation of the spot occurs in head assembling.SOLUTION: An optically assisted magnetic head has: a light source; and a waveguide having a predetermined width in a width direction orthogonal to a depth direction, receiving light from the light source on a waveguide incidence surface positioned at one end of a propagation direction orthogonal to both the width direction and the depth direction, and propagating the light to the other end of the propagation direction. The light from the light source is guided to the waveguide incidence surface without being affected by the act of light condensation or diffusion. A mode field diameter MFDx where the relative intensity of the waveguide in the width direction is exp(-2), satisfies 0.35α≤MFDx≤2.75α when a geometric mean of a spot diameter where the relative intensity of the light in the width direction is exp(-2) at an emission point of the light source and a spot diameter where the relative intensity of the light in the width direction is exp(-2) on the waveguide incidence surface is defined as α.

Description

  The present invention relates to the technology of an optically assisted magnetic head, and more particularly to the technology of an optical coupling structure used in an optically assisted magnetic head.

  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. However, although the upper limit of the magnetic field generated by the recording head is determined by the saturation magnetic flux density, the value approaches the material limit and there is a fact that a dramatic increase cannot be expected. Therefore, local recording is heated during recording to cause magnetic softening and recording is performed in a state where the coercive force is small, and then the heating is stopped and natural cooling is performed to guarantee the stability of the recorded magnetic bit. A recording method has been proposed. This recording method is called a heat-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 come into contact with each other. For this reason, heating is generally performed by irradiating a recording medium with a minute spot of laser light, and thus this method using light for heating is called an optically assisted magnetic recording method. When ultra-high density recording is performed by the optically assisted magnetic recording method, the required spot diameter is about 20 nm. However, a normal optical system has a diffraction limit, so that light cannot be condensed to that extent. Therefore, an optically assisted magnetic head using near-field light (sometimes referred to as “near-field light”) generated from an optical aperture having a size equal to or smaller than the incident light wavelength may be used.

  Examples of the optically assisted magnetic head are disclosed in Patent Document 1 and Patent Document 2.

  In the optically assisted magnetic head described in Patent Document 1, light from a light source is directly irradiated onto an optical waveguide (hereinafter simply referred to as a “waveguide”) formed on a slider to guide the optical waveguide, and the disk side waveguide is emitted. Near-field light is generated by irradiating the plasmon probe formed at the end. As a result, a disk area smaller than the diffraction limit of light is heated, and only the heated disk area is magnetically recorded.

  In the optically assisted magnetic head described in Patent Document 2, light emitted from the LD is deflected by 90 ° by a micromirror formed monolithically on a semiconductor laser (LD: Laser Diode) and irradiated onto the waveguide. Yes. By using such an LD, it is possible to place the LD horizontally on a slider, and the head can be made thinner.

  Patent Document 3 discloses a beam shaping element design method for optimizing the shape of a beam shaping element that shapes a laser beam into an arbitrary intensity distribution shape.

JP 2008-59697 A JP 2008-59645 A JP 2001-242414 A

  The waveguide formed in the optically assisted magnetic head has a thickness of several μm to 10 μm and a width of several μm to several hundred μm on the order of microns. Therefore, in order to couple light to a waveguide having such a thickness and width with high coupling efficiency, it is necessary to accurately determine the relative positions of the irradiation spot (hereinafter simply referred to as “spot”) and the waveguide. There is. Some current assembly adjustment devices can achieve a high accuracy of positioning accuracy of ± 1 μm. However, if the spot size or aberration is not matched with the waveguide mode field, there is a problem that it is difficult to ensure the coupling efficiency itself even if the adjustment can be performed without positional deviation. Furthermore, even if the adjustment is performed with an accuracy of ± 1 μm, there is a problem that when assembled with the relative position shifted, the degradation of the coupling efficiency increases and the performance varies between products. That is, it is a problem to ensure the necessary coupling efficiency even when the relative position deviation between the spot and the waveguide occurs at the time of assembling the head, and to suppress the variation of the coupling efficiency.

  In Patent Document 1, the spot diameter in the core thickness direction of the spot irradiated to the waveguide entrance surface is made larger than the core thickness, thereby suppressing the fluctuation of the incident efficiency due to the relative displacement between the spot in the core thickness direction and the waveguide. Techniques to do this are disclosed. However, this incidence efficiency indicates the ratio of the amount of irradiation light within the core thickness range, and is not the coupling efficiency to the actual waveguide, so it cannot be said that it has been studied strictly. The waveguide coupling efficiency is calculated using a superposition integral of the complex amplitude distribution function of light on the waveguide entrance surface and the amplitude distribution function of the propagation mode field of the waveguide (see Equation (6) in Patent Document 3). Furthermore, the calculation of the waveguide coupling efficiency requires superposition integration in both the core thickness direction and the core width direction, but Patent Document 1 has no description about the core width direction.

  On the other hand, in Patent Document 2, the coupling efficiency is strictly calculated by using the light field of the waveguide irradiation light and the light field of the propagation mode of the waveguide. However, there is no mention of a specific method of “matching the shape of the LD element and the waveguide in the slider (see paragraph 0048 of Patent Document 2)” or the specific size of the waveguide mode field.

  That is, an object of the present invention is to provide a method for matching a spot size and a waveguide mode field diameter in order to ensure a desired coupling efficiency even if a relative positional deviation between the spot and the waveguide occurs during head assembly. Furthermore, the present invention provides a method for suppressing the deterioration of the coupling efficiency in manufacturing by suppressing the degradation of the coupling efficiency at the time of positional deviation to a predetermined range.

但し、αは、以下の式により定義される。
［数２］

なお、「集光または拡散の作用を受けずに」という表現は、レンズ等の光学部品により、積極的に光を集光または拡散させないことを示している。
また、請求項２に記載の発明は、請求項１に記載の光アシスト磁気ヘッドであって、前記導波路入射面に対する前記光の位置ズレ量が１．５μｍ以下の範囲において、結合効率が１５％以上であることを特徴とする。
また、請求項３に記載の発明は、請求項１または請求項２に記載の光アシスト磁気ヘッドであって、前記導波路は、基板上に前記厚み方向に積層された第１のクラッド層と、コア層と、第２のクラッド層とを有することを特徴とする。
また、請求項４に記載の発明は、請求項１乃至請求項３のいずれかに記載の光アシスト磁気ヘッドであって、前記モードフィールド直径ＭＦＤｘが、前記第１の条件に代えて、以下に示す第２の条件を満たすことを特徴とする。
［数３］

また、請求項５に記載の発明は、請求項１乃至請求項４のいずれかに記載の光アシスト磁気ヘッドであって、前記光源が前記光を出射する出射面から前記導波路入射面までの空気換算距離ｚが、前記光の波長λと、前記光のスポットの前記導波路入射面における前記厚み方向の位置ズレ量Δｙと、前記光源の発光点において前記光の前記厚み方向の相対強度がｅｘｐ（−２）となるスポット半径ｗ_０ｙと、前記導波路において前記厚み方向の相対強度がｅｘｐ（−２）となるモードフィールド半径ｗ_２ｙと、前記導波路入射面上において前記スポットの位置ズレが生じていない場合の結合効率を１として、前記スポットの前記厚み方向の位置ズレに伴う相対的な結合効率を示す相対結合効率Δη_ｙと、を用いて次の条件を満たすことを特徴とする。
［数４］

但し、前記相対結合効率Δη_ｙは、第３の条件としてΔη_ｙ≧０．４を満たす。
また、請求項６に記載の発明は、請求項５に記載の光アシスト磁気ヘッドであって、前記相対結合効率Δη_ｙが、前記第３の条件に代えて、第４の条件としてΔη_ｙ≧０．５を満たすことを特徴とする。
また、請求項７に記載の発明は、請求項６に記載の光アシスト磁気ヘッドであって、前記光源と前記導波路との間に位置し、前記光源からの光が前記導波路入射面に入射するように前記光を偏向させる偏向部を設けたことを特徴とする。
また、請求項８に記載の発明は、請求項７に記載の光アシスト磁気ヘッドであって、前記偏向部は、前記光源からの光を反射させて前記導波路入射面に導く平面ミラーであることを特徴とする。
また、請求項９に記載の発明は、請求項８に記載の光アシスト磁気ヘッドであって、前記平面ミラーは、表面反射型のミラー、または内面反射型のプリズムであることを特徴とする。
また、請求項１０に記載の発明は、光源と、厚み方向（ｙ方向）と直交する幅方向（ｘ方向）に所定の幅を有し、前記幅方向及び前記厚み方向の双方に直交する伝播方向（ｚ方向）の一端に位置する導波路入射面で前記光源からの光を受け、前記伝播方向の他端に前記光を伝播させる導波路と、の光学的結合構造であって、前記光源からの光は、集光または拡散の作用を受けずに前記導波路入射面に導かれ、前記光源の発光点において前記光の前記幅方向の相対強度がｅｘｐ（−２）となるスポット半径ｗ_０ｘと、前記導波路入射面において前記光の前記幅方向の相対強度がｅｘｐ（−２）となるスポット半径ｗ_１ｘとしたとき、前記幅方向の相対強度がｅｘｐ（−２）となる前記導波路のモードフィールド直径ＭＦＤｘが、以下に示す第１の条件を満たすことを特徴とする光学的結合構造である。
［数１］

但し、αは、以下の式により定義される。
［数２］

また、請求項１１に記載の発明は、請求項１０に記載の光学的結合構造であって、前記導波路入射面に対する前記光の位置ズレ量が１．５μｍ以下の範囲において、結合効率が１５％以上であることを特徴とする。
また、請求項１２に記載の発明は、請求項１０または請求項１１に記載の光学的結合構造であって、前記導波路は、基板上に前記厚み方向に積層された第１のクラッド層と、コア層と、第２のクラッド層とを有することを特徴とする。
また、請求項１３に記載の発明は、請求項１０乃至請求項１２のいずれかに記載の光学的結合構造であって、前記モードフィールド直径ＭＦＤｘが、前記第１の条件に代えて、以下に示す第２の条件を満たすことを特徴とする。
［数３］

また、請求項１４に記載の発明は、請求項１０乃至請求項１３のいずれかに記載の光学的結合構造であって、前記光源の発光点から前記導波路入射面までの空気換算距離ｚが、前記光の波長λと、前記光のスポットの前記導波路入射面における前記厚み方向の位置ズレ量Δｙと、前記光源の発光点において前記光の前記厚み方向の相対強度がｅｘｐ（−２）となるスポット半径ｗ_０ｙと、前記導波路において前記厚み方向の相対強度がｅｘｐ（−２）となるモードフィールド半径ｗ_２ｙと、前記導波路入射面上において前記スポットの位置ズレが生じていない場合の結合効率を１として、前記スポットの前記厚み方向の位置ズレに伴う相対的な結合効率を示す相対結合効率Δη_ｙと、を用いて次の条件を満たすことを特徴とする。
［数４］

但し、前記相対結合効率Δη_ｙは、第３の条件としてΔη_ｙ≧０．４を満たす。
また、請求項１５に記載の発明は、請求項１４に記載の光学的結合構造であって、前記相対結合効率Δη_ｙが、前記第３の条件に代えて、第４の条件としてΔη_ｙ≧０．５を満たすことを特徴とする。 The invention according to claim 1 is a light source, a slider that floats and moves relative to the recording medium in response to rotation of the disk-shaped recording medium, and a thickness direction (y direction) provided on the slider. Light from the light source is incident on a waveguide entrance surface that has a predetermined width in the orthogonal width direction (x direction) and is located at one end of the propagation direction (z direction) orthogonal to both the width direction and the thickness direction. And a waveguide for propagating the light toward the recording medium located on the other end side in the propagation direction, wherein the light from the light source is condensed or diffused. The spot radius w _0x is guided to the waveguide entrance surface without being received, and the relative intensity in the width direction of the light becomes exp (−2) at the light emitting point of the light source, and the light at the waveguide entrance surface. The relative strength in the width direction is ex When the spot radius w _1x which becomes p (−2) is set, the mode field diameter MFDx of the waveguide whose relative intensity in the width direction becomes exp (−2) satisfies the following first condition. The optically assisted magnetic head, wherein the light source and the waveguide constitute an optical coupling structure.
[Equation 1]

However, (alpha) is defined by the following formula | equation.
[Equation 2]

Note that the expression “without being subjected to the action of light collection or diffusion” indicates that light is not actively collected or diffused by an optical component such as a lens.
According to a second aspect of the present invention, there is provided the optically assisted magnetic head according to the first aspect, wherein the coupling efficiency is 15 in a range where the positional deviation of the light with respect to the waveguide incident surface is 1.5 μm or less. % Or more.
The invention according to claim 3 is the optically assisted magnetic head according to claim 1 or 2, wherein the waveguide includes a first clad layer laminated on the substrate in the thickness direction. And having a core layer and a second cladding layer.
According to a fourth aspect of the present invention, there is provided the optically assisted magnetic head according to any one of the first to third aspects, wherein the mode field diameter MFDx is as follows, instead of the first condition. The second condition shown is satisfied.
[Equation 3]

The invention according to claim 5 is the optically assisted magnetic head according to any one of claims 1 to 4, wherein the light source emits the light from the exit surface to the waveguide entrance surface. The air equivalent distance z is the wavelength λ of the light, the positional deviation amount Δy of the light spot in the waveguide entrance surface in the thickness direction, and the relative intensity of the light in the thickness direction at the light emitting point of the light source. The spot radius w _0y that becomes exp (−2), the mode field radius w _2y that the relative intensity in the thickness direction becomes exp (−2) in the waveguide, and the positional deviation of the spot on the waveguide entrance surface and wherein the following condition is satisfied as a coupling efficiency in the case where there is no, using the relative binding efficiency .DELTA..eta _y showing the relative binding efficiency caused by the positional deviation of the thickness direction of the spot That.
[Equation 4]

However, the relative coupling efficiency Δη _y satisfies Δη _y ≧ 0.4 as a third condition.
The invention according to claim 6 is the optically assisted magnetic head according to claim 5, wherein the relative coupling efficiency Δη _y is set as Δη _y ≧ 4 as a fourth condition instead of the third condition. It is characterized by satisfying 0.5.
The invention according to claim 7 is the optically assisted magnetic head according to claim 6, which is located between the light source and the waveguide, and the light from the light source is incident on the waveguide entrance surface. A deflecting unit for deflecting the light so as to be incident is provided.
The invention according to claim 8 is the optically assisted magnetic head according to claim 7, wherein the deflecting unit is a plane mirror that reflects light from the light source and guides it to the waveguide entrance surface. It is characterized by that.
According to a ninth aspect of the present invention, in the optically assisted magnetic head according to the eighth aspect, the plane mirror is a surface reflection type mirror or an internal reflection type prism.
The invention described in claim 10 has a predetermined width in the width direction (x direction) orthogonal to the light source and the thickness direction (y direction), and propagation orthogonal to both the width direction and the thickness direction. An optical coupling structure with a waveguide that receives light from the light source at a waveguide entrance surface located at one end in the direction (z direction) and propagates the light to the other end in the propagation direction, the light source The light from the light is guided to the waveguide entrance surface without being subjected to condensing or diffusing action, and the spot radius w at which the relative intensity in the width direction of the light becomes exp (−2) at the light emitting point of the light source. _0x and the spot radius w _{1x at} which the relative intensity in the width direction of the light at the waveguide entrance surface becomes exp (−2), the guide at which the relative intensity in the width direction becomes exp (−2). The mode field diameter MFDx of the waveguide is An optical coupling structure, wherein the condition is satisfied.
[Equation 1]

However, (alpha) is defined by the following formula | equation.
[Equation 2]

The invention according to claim 11 is the optical coupling structure according to claim 10, wherein the coupling efficiency is 15 in a range where the amount of positional deviation of the light with respect to the waveguide entrance surface is 1.5 μm or less. % Or more.
The invention according to claim 12 is the optical coupling structure according to claim 10 or claim 11, wherein the waveguide includes a first clad layer laminated on the substrate in the thickness direction. And having a core layer and a second cladding layer.
The invention according to claim 13 is the optical coupling structure according to any one of claims 10 to 12, wherein the mode field diameter MFDx is as follows, instead of the first condition. The second condition shown is satisfied.
[Equation 3]

The invention according to claim 14 is the optical coupling structure according to any one of claims 10 to 13, wherein an air conversion distance z from a light emitting point of the light source to the waveguide incident surface is , The wavelength λ of the light, the positional deviation amount Δy in the thickness direction of the light spot on the waveguide entrance surface, and the relative intensity in the thickness direction of the light at the light emitting point of the light source exp (−2) When the spot radius w _0y becomes, the mode field radius w _2y where the relative strength in the thickness direction is exp (−2) in the waveguide, and the positional deviation of the spot does not occur on the waveguide entrance surface The following condition is satisfied using a relative coupling efficiency Δη _y indicating a relative coupling efficiency associated with a positional shift of the spot in the thickness direction, with a coupling efficiency of 1.
[Equation 4]

However, the relative coupling efficiency Δη _y satisfies Δη _y ≧ 0.4 as a third condition.
The invention according to claim 15 is the optical coupling structure according to claim 14, wherein the relative coupling efficiency Δη _y is set to Δη _y ≧ 4 as a fourth condition instead of the third condition. It is characterized by satisfying 0.5.

  According to the optical coupling structure of the present invention, it is possible to ensure the waveguide coupling efficiency of 15% or more even when the spot is shifted by about 1 μm in the width direction or the thickness direction on the waveguide entrance surface. Therefore, by applying this optical coupling structure to the optically assisted magnetic head, it is possible to reliably record information on the medium.

It is a perspective view which shows schematic structure of an information recording device. It is a schematic sectional drawing of an optically assisted magnetic head. FIG. 4 is an enlarged cross-sectional view around a plane mirror of an optically assisted magnetic head. It is a top view of a magnetic head part. It is the figure which showed the relationship between the air conversion distance from a light source, and the spot diameter of the waveguide width direction of an emitted light. It is the figure which showed the relationship between the air conversion distance from a light source, and the spot diameter of the waveguide thickness direction of an emitted light. It is the graph which showed the coupling efficiency characteristic with respect to the position shift in the waveguide width direction of the spot in the waveguide entrance plane of an emitted light. It is the graph which showed the coupling efficiency characteristic with respect to the position shift in the waveguide thickness direction of the spot in the waveguide entrance plane of an emitted light. 6 is a graph showing a coupling efficiency characteristic with respect to a mode field diameter in a waveguide width direction in Example 1. 6 is a graph showing coupling efficiency characteristics with respect to a mode field diameter in a waveguide width direction in Example 2. 10 is a graph showing coupling efficiency characteristics with respect to a mode field diameter in the waveguide width direction in Example 3. 10 is a graph showing coupling efficiency characteristics with respect to a mode field diameter in a waveguide width direction in Example 4. 10 is a graph showing coupling efficiency characteristics with respect to a mode field diameter in a waveguide width direction in Example 5. It is the graph which showed the relative coupling efficiency characteristic at the time of changing the air conversion distance in Example 6. FIG. It is the graph which showed the relative coupling efficiency characteristic at the time of changing the air conversion distance in Example 7. FIG. It is the graph which showed the relative coupling efficiency characteristic at the time of changing the air conversion distance in Example 8. FIG. 10 is a table showing a relationship between a positional deviation amount, coupling efficiency, and relative coupling efficiency in Example 9.

(Schematic configuration of information recording device)
FIG. 1 shows a schematic configuration of an optically assisted magnetic recording apparatus (for example, a hard disk apparatus, hereinafter also referred to as “information recording apparatus”) equipped with an optically assisted magnetic head. The information recording apparatus 1 includes, for example, a plurality of rotatable disks (magnetic recording media) 3 for recording, a head support portion 5, a tracking actuator 7, an optically assisted magnetic head 4, a driving device (not shown), Is provided in the housing 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 optically assisted magnetic head 4 is attached to the tip of the head support portion 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 optically assisted magnetic head 4 can move relatively while flying over the disk 3.

(Optical assist magnetic head 4)
FIG. 2A is a sectional view showing a schematic configuration example of the optically assisted magnetic head 4. The optically assisted magnetic head 4 is a minute optical recording head that uses light for information recording on the disk 3. The optically assisted magnetic head 4 includes a light source unit 50, a slider 60, and a plane mirror 40. The information recording apparatus 1 is configured to move the disk 3 in the direction of arrow C so that the optically assisted magnetic head 4 can move relative to the disk 3 while flying over the disk 3.

  The light source unit 50 has an LD. The wavelength of light emitted from the LD constituting the light source unit 50 is a wavelength from visible light to near-infrared (the wavelength band is about 0.6 μm to 2 μm, and the specific wavelength is 650 nm, 780 nm, 830 nm, 1310 nm, 1550 nm, etc.). The light source unit 50 is disposed on the upper surface 60 a of the slider 60. The light source unit 50 has an emission surface 50 a and emits light from the emission surface 50 a toward the deflection surface 40 a of the flat mirror 40. The light emitted from the light source unit 50 propagates while spreading at a predetermined radiation angle without reaching the condensing or diffusing action, and reaches the deflection surface 40 a of the flat mirror 40. Note that the expression “without being subjected to the action of light collection or diffusion” indicates that light is not actively collected or diffused by an optical component such as a lens.

  The plane mirror 40 has a deflecting surface 40 a and guides light emitted from the light source unit 50 (hereinafter, sometimes referred to as “emitted light”) to a waveguide 64 provided in the magnetic head unit 63 of the slider 60. . In the example of FIG. 2, the deflection surface 40 a reflects the light emitted from the light source unit 50 toward the waveguide incident surface 64 a of the waveguide 64. As a result, the emitted light is deflected by 90 ° and guided to the waveguide entrance surface 64 a of the waveguide 64. The flat mirror 40 does not have optical power, that is, has no light collecting function. Therefore, the light emitted from the light source unit 50 propagates while spreading at a predetermined radiation angle, is reflected by the deflecting surface 40a, and reaches the waveguide entrance surface 64a.

  As the plane mirror 40, a surface reflection type mirror as shown in FIG. 2A may be used, or an internal reflection type prism may be used instead of the surface reflection type mirror. Here, the internal reflection type prism refers to a prism that deflects incident light by internally reflecting the light incident on the prism with a reflection surface provided inside. Further, without using the flat mirror 40, for example, the light source unit 50 is arranged so that the emission surface 50a of the light source unit 50 faces the slider upper surface 60a in parallel, and the light emitted from the light source unit 50 is used as an optical component. The waveguide 64 may be directly irradiated without being interposed (that is, without being deflected).

  The slider 60 has a magnetic head part 63 at the tip. The magnetic head unit 63 includes a waveguide 64, a magnetic recording unit (not shown), and a magnetic information reproducing unit (not shown).

The waveguide 64 guides the light guided by the flat mirror 40 and emits it toward the disk 3. Although not shown, the waveguide 64 is formed by laminating a lower clad layer, a core layer, and an upper clad layer in this order along the thickness direction perpendicular to the direction in which light propagates. 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 waveguide 64 is totally reflected between the core layer and each cladding layer. The lower cladding layer corresponds to the “first cladding layer” and the upper cladding layer corresponds to the “second cladding layer”.

  Reference is now made to FIG. 2B. 2B is an enlarged cross-sectional view in which the periphery of the plane mirror 40 in FIG. 2A is enlarged. As shown in FIG. 2B, the waveguide 64 has a waveguide entrance surface 64a on the upper surface 60a of the slider 60, and a waveguide exit surface 64b on the surface opposite to the upper surface 60a (the surface facing the disk 3). Have. A plasmon probe 65 as a near-field light generating element is provided on the waveguide exit surface 64 b of the waveguide 64. The light deflected by the plane mirror 40 enters the waveguide 64 from the waveguide incident surface 64a and travels in the waveguide 64 toward the waveguide exit surface 64b. The plasmon probe 65 provided on the waveguide exit surface 64b converts the light guided by the plane mirror 40 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.

  Hereinafter, as the first embodiment and the second embodiment, an optical coupling structure for coupling the emitted light from the light source unit 50 to the waveguide 64 via the waveguide incident surface 64a will be described. In the following, the light emitted from the light exit surface 50a of the light source unit 50 (that is, the light emitted) is focused on the optical path until the light enters the waveguide entrance surface 64a of the waveguide 64, and light is emitted from the waveguide entrance surface 64a. Is the z direction, the width direction of the waveguide 64 (hereinafter sometimes referred to as “waveguide width direction”), the x direction, and the thickness direction (hereinafter sometimes referred to as “waveguide thickness direction”). Is described as the y direction. In the example of FIG. 2, the optical path from the exit surface 50a to the waveguide entrance surface 64a is deflected 90 ° at the deflection surface 40a in the middle, and the distance from the exit surface 50a to the deflection surface 40a is L1 in this optical path. The distance from the surface 40a to the waveguide entrance surface 64a is indicated by L2. That is, the distance z from the exit surface 50a to the waveguide entrance surface 64a is represented by L1 + L2. At this time, since the emitted light propagates in the air, the distance z = L1 + L2 is equal to the air equivalent distance.

(First embodiment)
The optical coupling structure according to the first embodiment will be described with reference to FIGS. 2A and 3. FIG. 3 is a view (ie, a top view of the magnetic head portion 63) of the magnetic head portion 63 as viewed from the arrow III (ie, the z direction) in FIG. 2A. FIG. 3 shows a state in which the center of the spot P of the outgoing light on the waveguide entrance surface 64a is shifted from the center of the waveguide 64 on the xy plane by Δx in the x direction and Δy in the y direction.

  The LD used in the light source unit 50 is an edge-emitting semiconductor laser, and the light emitted from the light source unit 50 has a large emission angle in the thickness direction of the active layer (that is, the z direction in FIG. 2A). Therefore, when the distance z (= L1 + L2) from the exit surface 50a of the light source unit 50 to the waveguide entrance surface 64a is about 5 μm or more, the spot irradiates the waveguide entrance surface 64a is radiated. It has an elliptical shape that is long in the y direction in proportion to the angle. Since the light is not condensed, the waveguide incident surface 64a is irradiated with a defocus component as an aberration.

  The power of the LD used in the light source unit 50 and the coupling efficiency of the emitted light with respect to the waveguide 64 are factors that determine the intensity of the near-field light emitted from the waveguide emitting surface 64b toward the disk 3. The conductive coupling efficiency is determined by the refractive index of the material used for the waveguide 64 and the diameter of the waveguide 64 (that is, the width in the x direction and the thickness in the y direction). In recent years, many high-power LDs of 100 mW or more have been mass-produced. Therefore, if there is a coupling efficiency of about 15%, it is possible to obtain near-field light necessary for recording.

  The optical coupling structure according to the present embodiment focuses on the relationship between the coupling field efficiency and the mode field diameter of the waveguide 64, in particular, the mode field diameter MDFx in the x direction (that is, the waveguide width direction) on the waveguide entrance surface 64a. doing. Here, the mode field diameter indicates the diameter of the intensity distribution of light that can propagate through the waveguide 64. Specifically, the waveguide 64 is formed by being laminated in the waveguide thickness direction (that is, the y direction) by a semiconductor process. Therefore, the formation along the y direction has a low degree of freedom because it is restricted by the time of the semiconductor process. On the other hand, since the shape and size in the waveguide width direction are determined by the shape and size of the mask to be used, the degree of freedom in design is higher than in the thickness direction (that is, the stacking direction). Therefore, in the optical coupling structure according to the present embodiment, the mode field diameter MDFx in the x direction with a high degree of design freedom is adjusted without changing the mode field diameter MFDy in the waveguide thickness direction, which is difficult to increase. As a result, the coupling efficiency is improved.

  The optical coupling structure according to the present embodiment adjusts the configuration of the waveguide 64 or the positional relationship between the light source unit 50 and the waveguide 64 with reference to the mode field diameter MFDx calculated in advance based on a predetermined condition. Thus, even if the spot misalignment occurs within a range of 1.5 μm or less, a coupling efficiency of 15% or more can be ensured. The optical coupling structure according to this embodiment will be specifically described below. In FIG. 2, the outgoing light is deflected by 90 ° by the plane mirror 40, but thereafter, the outgoing light is not deflected, and the waveguide entrance surface 64 a of the waveguide 64 extends from the light source unit 50 along the z-axis direction. In the following description, it is assumed that the emitted light is irradiated.

(Relationship between spot size and coupling efficiency)
First, the spot size of the emitted light will be described. The intensity of the light emitted from the light source unit 50 approximates a Gaussian distribution, and there is no problem even assuming a Gaussian distribution. Reference is now made to FIGS. 4A and 4B. FIG. 4A shows the relationship between the air equivalent distance z in the propagation direction from the emission surface 50a and the spot radius w _{1x in the} waveguide width direction (x direction) of the outgoing light at the air equivalent distance z. FIG. 4B shows the relationship between the air equivalent distance z in the propagation direction from the emission surface 50a and the spot radius _{w1x in the} waveguide width direction (x direction) of the emitted light at the air equivalent distance z. In FIG. 4A, w _0x indicates the spot radius in the x direction at which the relative intensity of the emitted light is exp (−2) on the emission surface 50a. In addition, w _0y in FIG. 4B indicates a spot radius in the y direction where the relative intensity of the emitted light is exp (−2) on the emission surface 50a.

但し、θ_ｘについては以下の式で表される。
［数５Ｂ］

ここで、θｈは、光源部５０の導波路幅方向（ｘ方向）の放射角（半値全角）を示しており、λは、出射光の波長を示している。また、θ_ｘ、は、出射光の相対強度がｅｘｐ（−２）となるｘ方向の半角を示している。 The spot radius w _0x of the outgoing light in the x direction on the outgoing surface 50a is calculated by the following equation.
[Formula 5A]

However, θ _x is expressed by the following equation.
[Formula 5B]

Here, θh represents the radiation angle (full width at half maximum) of the light source unit 50 in the waveguide width direction (x direction), and λ represents the wavelength of the emitted light. Θ _x represents a half angle in the x direction where the relative intensity of the emitted light is exp (−2).

但し、θ_ｙについては以下の式で表される。
［数６Ｂ］

ここで、θｖは、光源部５０の導波路厚み方向（ｙ方向）の放射角（半値全角）を示している。また、θ_ｙは、出射光の相対強度がｅｘｐ（−２）となるｙ方向の半角を示している。 The spot radius w _0y in the y direction on the exit surface 50a is calculated by the following equation.
[Formula 6A]

However, θ _y is expressed by the following equation.
[Formula 6B]

Here, θv represents the radiation angle (full width at half maximum) of the light source unit 50 in the waveguide thickness direction (y direction). Further, θ _y indicates a half angle in the y direction where the relative intensity of the emitted light is exp (−2).

［数８］

Further, the spot radii w _1x and w _{1y at} the position of the air conversion distance z along the propagation direction from the emission surface 50a are given by the following expressions based on the Gaussian propagation theory.
[Equation 7]

[Equation 8]

ここで、κ_ｘは、導波路入射面６４ａ上において、スポットの位置ズレが無い場合のｘ方向の結合効率を示しており、同様に、κ_ｙは、ｙ方向の結合効率を示している。また、Δη_ｘは、位置ズレが無い場合の値を１としたときの、位置ズレがある場合におけるｘ方向の相対結合効率を示しており、同様に、Δη_ｙは、ｙ方向の相対結合効率を示している。 Next, the coupling efficiency of the emitted light with respect to the waveguide 64 will be described on the assumption that the waveguide entrance surface 64a of the waveguide 64 is located at the air-converted distance z. Since the mode field of the waveguide 64 also approximates a Gaussian distribution, it is assumed to be a Gaussian distribution. The coupling efficiency η of the waveguide 64 is given by the following equation.
[Equation 9]

Here, κ _x indicates the coupling efficiency in the x direction when there is no positional deviation of the spot on the waveguide incident surface 64a, and similarly, κ _y indicates the coupling efficiency in the y direction. In addition, Δη _x indicates the relative coupling efficiency in the x direction when there is a positional deviation when the value when there is no positional deviation is 1. Similarly, Δη _y indicates the relative coupling efficiency in the y direction. Is shown.

ここで、ｗ_２ｘは、導波路６４のモードフィールドにおいて相対強度がｅｘｐ（−２）となるｘ方向のモードフィールド半径を示している。即ち、ｘ方向のモードフィールド直径ＭＦＤｘ＝２ｗ_２ｘとなる。 The coupling efficiency κ _x is given by the following equation.
[Equation 10]

Here, w _2x represents the mode field radius in the x direction in which the relative intensity is exp (−2) in the mode field of the waveguide 64. That is, the mode field diameter MFDx = 2w _2x in the x direction.

ここで、ｗ_２ｙは、導波路６４のモードフィールドにおいて相対強度がｅｘｐ（−２）となるｙ方向のモードフィールド半径を示している。即ち、ｙ方向のモードフィールド直径ＭＦＤｙとしたとき、ＭＦＤｙ＝２ｗ_２ｙとなる。 Similarly, the coupling efficiency κ _y is given by the following equation.
[Equation 11]

Here, w _2y indicates the mode field radius in the y direction in which the relative intensity is exp (−2) in the mode field of the waveguide 64. That is, when the mode field diameter MFDy in the y direction is MFDy = 2w _2y .

ここで、Δｘは、図３に示すように、導波路入射面６４ａ上における出射光のスポットＰの、ｘ方向のズレ量を示している。 Further, the relative coupling efficiency Δη _x is given by the following equation.
[Equation 12]

Here, Δx indicates the amount of deviation in the x direction of the spot P of the emitted light on the waveguide entrance surface 64a, as shown in FIG.

ここで、Δｙは、図３に示すように、導波路入射面６４ａ上における出射光のスポットＰの、ｙ方向のズレ量を示している。 Similarly, the relative coupling efficiency Δη _y is given by the following equation.
[Equation 13]

Here, Δy indicates the amount of deviation in the y direction of the spot P of the emitted light on the waveguide entrance surface 64a, as shown in FIG.

(Relationship between mode field diameter in the waveguide width direction and coupling efficiency)
Next, the relationship between the mode field diameter MFDx in the waveguide width direction and the coupling efficiency will be described with reference to FIGS. FIG. 5 is a graph showing the coupling efficiency characteristic with the waveguide 64 with respect to the positional deviation Δx of the spot P in the x direction. The vertical axis represents the coupling efficiency, and the horizontal axis represents the positional deviation Δx. FIG. 6 is a graph showing the coupling efficiency characteristics with respect to the waveguide 64 with respect to the positional deviation Δy in the y direction of the spot P. The vertical axis shows the coupling efficiency and the horizontal axis shows the positional deviation Δy.

The graphs of FIGS. 5 and 6 show, as Example 1, the light emitted from the LD with the wavelength λ = 0.66 μm of the emitted light, the radiation angle θh = 9 °, and θv = 16.5 °, as the air equivalent distance z. This shows a case where the waveguide incident surface 64a at the position of = 15 μm (for example, L1 = L2 = 7.5 μm in FIG. 2A) is irradiated. The mode field diameter MFDy in the waveguide thickness direction where the relative intensity is exp (−2) is 3 μm. At this time, w _2y = 0.5MFDy = 1.5 μm. In addition, the full width at half maximum θv = 16.5 ° in the above is a value that becomes 28 ° in the full angle of the relative intensity exp (−2). Also, since the main aspect ratio of LD is about 1.8 to 2, θh = 9 °. Further, for a mode field diameter (MFDy) of 3 μm in the y direction, z = 5MFDy = 15 μm. The graphs shown in FIGS. 5 and 6 show the respective characteristics when the mode field diameter MFDx in the waveguide width direction is changed in the range of 1 to 10 μm.

As is apparent from the graph shown in FIG. 5, the coupling efficiency characteristic with respect to the positional deviation Δx in the x direction varies greatly depending on the value of the mode field diameter MFDx. On the other hand, in the coupling efficiency characteristic with respect to the positional deviation Δy in the y direction shown in FIG. 4A, the value of the coupling efficiency itself varies depending on the mode field diameter MFDx, but the basic characteristic is the mode field diameter MFDx shown in Equation 13. It can be seen that it is determined by the equation of Δη _y not included. From the above, since the coupling efficiency varies greatly depending on the value of the mode field diameter MFDx, it is necessary to optimize the mode field diameter MFDx.

(Mode field diameter optimization)
Next, optimization of the mode field diameter MFDx will be described with reference to FIG. FIG. 7 is a graph showing the coupling efficiency characteristics with respect to the mode field diameter MFDx, where the vertical axis represents the coupling efficiency and the horizontal axis represents the mode field diameter MFDx. The graph of FIG. 7 shows a case where there is no positional deviation of the spot P (Δx = 0, Δy = 0) and a case where the positional deviation amount is 1.5 μm (Δx = 1.5 μm, Δy = 1.5 μm). ing. In addition to the accuracy of the position adjustment device of 1 μm, the positional shift amount of 1.5 μm is a shift amount that allows for the positional shift of the light source unit 50 due to thermal contraction of the solder and the positional shift of the flat mirror 40 due to curing shrinkage of the adhesive. is there.

即ち、αは、以下のようになる。
［数２］

ここで、２ｗ_０ｘは、光源部５０の出射面５０ａにおけるｘ方向のスポット直径である。また、２ｗ_１ｘは、導波路入射面６４ａにおけるｘ方向のスポット直径である。この式は、αが出射面５０ａにおけるスポット直径と、導波路入射面６４ａにおけるスポット直径との相乗平均となることを示している。なお、実施例１として示した条件の場合、α＝４．０μｍとなる。 As shown in FIG. 7, there is a maximum value in the graph when there is no positional deviation (Δx = 0, Δy = 0). If the mode field diameter MFDx that maximizes the coupling efficiency when there is no positional deviation is α, α is given by the following equation.
[Formula 14]

That is, α is as follows.
[Equation 2]

Here, 2w _0x is a spot diameter in the x direction on the emission surface 50a of the light source unit 50. 2w _1x is the spot diameter in the x direction on the waveguide entrance surface 64a. This equation indicates that α is the geometric mean of the spot diameter on the exit surface 50a and the spot diameter on the waveguide entrance surface 64a. In the case of the conditions shown as Example 1, α = 4.0 μm.

ｘ方向のモードフィールド直径ＭＦＤｘは、導波路６４に用いられる材料の屈折率や、導波路６４のｘ方向の幅に基づき決定される。言い換えると、数１で示した条件式に基づき算出されたモードフィールド直径ＭＦＤｘと、導波路６４に用いられる材料の屈折率とに基づき、導波路６４のｘ方向の幅を決定することで、上述した結合効率を確保することが可能となる。 When a high power LD of 100 mW or more is applied to the light source unit 50, if the coupling efficiency is 15% or more, the intensity of near-field light necessary for recording can be obtained. As shown in FIG. 5, under the conditions of Example 1, if the mode field diameter MFDx was set within the range of the conditional expression shown below, the positional deviation of the spot P occurred within the positional deviation amount of 1.5 μm or less. However, it is possible to secure a coupling efficiency of 15% or more.
[Equation 1]

The mode field diameter MFDx in the x direction is determined based on the refractive index of the material used for the waveguide 64 and the width of the waveguide 64 in the x direction. In other words, by determining the width in the x direction of the waveguide 64 based on the mode field diameter MFDx calculated based on the conditional expression shown in Equation 1 and the refractive index of the material used for the waveguide 64, It is possible to ensure the coupling efficiency.

望ましくは、０．５５α≦ＭＦＤｘ≦１．９αであり、この場合には、確実に結合効率を２０％以上確保することが可能となる。結合効率が２０％以上あれば、前述したハイパワーＬＤを光源部５０に用いた場合においても、ＬＤの出力を小さくすることができるため、装置としての消費電力を抑制することが可能となる。 Further, if the mode field diameter MFDx is set within the range of the conditional expression shown below, it is possible to ensure a coupling efficiency of approximately 20% or more.
[Equation 3]

Desirably, 0.55α ≦ MFDx ≦ 1.9α, and in this case, it is possible to reliably ensure a coupling efficiency of 20% or more. If the coupling efficiency is 20% or more, even when the above-described high power LD is used for the light source unit 50, the output of the LD can be reduced, so that the power consumption of the device can be suppressed.

  The waveguide 64 is formed by being laminated in the waveguide thickness direction (that is, the y direction) by a semiconductor process. Therefore, the formation along the y direction has a low degree of freedom because it is restricted by the time of the semiconductor process. On the other hand, in the optical coupling structure according to this embodiment, the coupling efficiency is improved by paying attention to the mode field diameter MFDx of the waveguide 64 in the waveguide width direction (that is, the x direction). Since the shape and size of the waveguide 64 in the waveguide width direction are determined by the shape and size of the mask to be used, the degree of freedom in design is higher than in the thickness direction (that is, the stacking direction). Therefore, according to the optical coupling structure according to the present embodiment, the coupling efficiency can be improved without being restricted by the time of the semiconductor process when the waveguide 64 is manufactured.

In the case of the conditions of Example 1, the spot diameter of the emitted light on the waveguide incident surface 64a is 2w _1x = 5.10 μm in the x direction and 2w _1y = 7.67 μm in the y direction. In this case, when the mode field diameter MFDx is in the range of 5.10 μm <MFDx ≦ 2.75α = 9.8 μm, (spot diameter in the x direction 2w _1x ) <(mode field diameter MFDx in the x direction). For this reason, (spot diameter)> (mode field diameter) is not necessarily required in the waveguide width direction (x direction).

  In addition, the equation (14) shown in the first embodiment can be converted into an equation of z using the relationship of the first equality equation. That is, even in the case of the invention in which the coupling efficiency is improved by adjusting the air conversion distance z, the formula of α shown in Expression 14 is satisfied, and the mode field diameter MFDx is 0.35α ≦ MFDx ≦ 2.75α. If the condition is satisfied, the invention is substantially the same as the invention.

(Example 2)
Next, as Example 2, an example in which the conditions of the wavelength λ of the emitted light and the radiation angle θv in the y direction are changed from the conditions of Example 1 will be described. In this embodiment, the wavelength λ = 0.83 μm of the emitted light, the radiation angle θh = 9 °, θv = 22 °, the mode field diameter MFDy = 3 μm in the waveguide thickness direction, and the air equivalent distance z = 15 μm. When α is calculated based on this condition, α = 4.7 μm.

  Reference is now made to FIG. FIG. 8 is a graph showing the coupling efficiency characteristics with respect to the mode field diameter MFDx in the waveguide width direction in this example, where the vertical axis represents the coupling efficiency and the horizontal axis represents the mode field diameter MFDx. As shown in FIG. 8, also in this embodiment, by setting the mode field diameter MFDx within the range of 0.35α ≦ MFDx ≦ 2.75α, the position of the spot P within the range of the positional deviation amount of 1.5 μm or less. Even if a deviation occurs, it is possible to ensure a coupling efficiency of 15% or more.

  Further, if the mode field diameter MFDx is set within the range of 0.5α ≦ MFDx ≦ 2α, it is possible to ensure a coupling efficiency of approximately 20% or more. Also in this embodiment, it is desirable that 0.55α ≦ MFDx ≦ 1.9α. In this case, it is possible to ensure the coupling efficiency of 20% or more.

(Example 3)
Next, as Example 3, an example in which the condition of the mode field diameter MFDy in the waveguide thickness direction is changed from the condition of Example 1 will be described. In this embodiment, the wavelength λ = 0.66 μm of the emitted light, the radiation angle θh = 9 °, θv = 16.5 °, the mode field diameter MFDy = 2 μm in the waveguide thickness direction, and the air equivalent distance z = 10 μm. The air conversion distance z is calculated based on the condition of z = 5MFDy as in the first embodiment. Further, the positional deviation amounts Δx and Δy of the spot position P in this embodiment are set to ½ of the mode field diameter MFDy, that is, Δx = 1 μm and Δy = 1 μm. When α is calculated based on this condition, α = 3.6 μm.

  Reference is now made to FIG. FIG. 9 is a graph showing the coupling efficiency characteristics with respect to the mode field diameter MFDx in the waveguide width direction in the present embodiment, where the vertical axis represents the coupling efficiency and the horizontal axis represents the mode field diameter MFDx. As shown in FIG. 9, also in this embodiment, by setting the mode field diameter MFDx within the range of 0.35α ≦ MFDx ≦ 2.75α, the position of the spot P within the range of the positional deviation amount of 1.0 μm or less. Even if a deviation occurs, it is possible to ensure a coupling efficiency of 15% or more. In addition, even when the positional deviation of the light source unit 50 due to the thermal contraction of the solder or the positional deviation of the flat mirror 40 due to the effective contraction of the adhesive, by adjusting the target adjustment position in consideration of these positional deviations, A position accuracy of 1 μm or less can also be handled.

  Further, if the mode field diameter MFDx is set within the range of 0.5α ≦ MFDx ≦ 2α, it is possible to ensure a coupling efficiency of 20% or more.

  Next, as Example 4 and Example 5, an example in which the condition of the air conversion distance z is changed in Example 3 will be described.

(Example 4)
First, Example 4 will be described. In this embodiment, the wavelength λ = 0.66 μm of the emitted light, the radiation angle θh = 9 °, θv = 16.5 °, the mode field diameter MFDy = 2 μm in the waveguide thickness direction, and the air equivalent distance z = 4 μm. In addition, the positional deviation amounts Δx and Δy of the spot position P in this embodiment are set to Δx = 1 μm and Δy = 1 μm. When α is calculated based on this condition, α = 3.2 μm.

  Reference is now made to FIG. FIG. 10 is a graph showing the coupling efficiency characteristics with respect to the mode field diameter MFDx in the waveguide width direction in the present embodiment, where the vertical axis indicates the coupling efficiency and the horizontal axis indicates the mode field diameter MFDx. As shown in FIG. 10, also in this embodiment, by setting the mode field diameter MFDx within the range of 0.35α ≦ MFDx ≦ 2.75α, the position of the spot P within the range of the positional deviation amount of 1.0 μm or less. Even if a deviation occurs, it is possible to ensure a coupling efficiency of 15% or more.

  Further, if the mode field diameter MFDx is set within the range of 0.5α ≦ MFDx ≦ 2α, it is possible to ensure a coupling efficiency of 20% or more.

(Example 5)
Next, Example 5 will be described. In this embodiment, the wavelength λ = 0.66 μm of the emitted light, the radiation angle θh = 9 °, θv = 16.5 °, the mode field diameter MFDy = 2 μm in the waveguide thickness direction, and the air equivalent distance z = 16 μm. In addition, the positional deviation amounts Δx and Δy of the spot position P in this embodiment are set to Δx = 1 μm and Δy = 1 μm. When α is calculated based on this condition, α = 4.1 μm.

  Reference is now made to FIG. FIG. 11 is a graph showing the coupling efficiency characteristics with respect to the mode field diameter MFDx in the waveguide width direction in the present embodiment, where the vertical axis indicates the coupling efficiency and the horizontal axis indicates the mode field diameter MFDx. As shown in FIG. 11, also in this embodiment, by setting the mode field diameter MFDx within the range of 0.35α ≦ MFDx ≦ 2.75α, the position of the spot P within the range of the positional deviation amount of 1.0 μm or less. Even if a deviation occurs, it is possible to ensure a coupling efficiency of 15% or more.

  Further, if the mode field diameter MFDx is set within the range of 0.5α ≦ MFDx ≦ 2α, it is possible to ensure a coupling efficiency of 20% or more.

  In Example 4, z / MFDy = 2, and in Example 5, z / MFDy = 8. That is, according to the optical coupling structure according to the present embodiment, when the air conversion distance z is in the range of 2MFDy ≦ z ≦ 8MFDy, even when a positional deviation of 1 μm occurs, a coupling efficiency of 15% or more can be secured. Is possible.

  As described above, in the optical coupling structure according to the present embodiment, α is calculated based on the formula shown in Expression 14, and the mode field diameter MFDx in the waveguide width direction is in the range of 0.35α ≦ MFDx ≦ 2.75α. The configuration of the waveguide 64 and the positional relationship with the light source unit 50 are adjusted so as to be set inside. As a result, even when the spot misalignment occurs within a range of 1.5 μm or less, it is possible to ensure a coupling efficiency of 15% or more.

(Second Embodiment)
Next, an optical coupling structure according to the second embodiment will be described. At the time of assembling the optically assisted magnetic head 4 described above, it is necessary to suppress fluctuations in coupling efficiency even if the spot P is misaligned in the positioning accuracy of the adjusting device. In other words, on the basis of the case where there is no positional deviation, it is necessary to ensure the relative coupling efficiency when the positional deviation occurs to a predetermined value or more. Here, the relative coupling efficiency indicates the relative coupling efficiency associated with the positional deviation of the spot P, where the coupling efficiency is 1 when there is no positional deviation of the spot P on the waveguide incident surface 64a. In general, when the positional deviation of the spot P (that is, Δx or Δy) occurs, if the relative coupling efficiency is 40% (−4 dB) or more, the variation in coupling efficiency can be adjusted by adjusting the output power of the LD. Can be absorbed. More preferably, the relative coupling efficiency is 50% (−3 dB) or more.

On the other hand, the waveguide 64 is created by a semiconductor process in the same manner as the magnetic head unit 63. In this case, the core portion of the waveguide 64 is formed by laminating a high refractive index material such as Ta ₂ O _{5 in the} waveguide thickness direction (y direction). Therefore, the thicker the waveguide 64, that is, the larger the mode field diameter MFDy in the waveguide thickness direction, the longer the lamination time. Therefore, the waveguide 64 is created so that the mode field diameter MFDy is about 1 to 5 μm. In general, the smaller the mode field diameter, the greater the degradation of coupling efficiency with respect to spot misalignment. That is, the relative coupling efficiency is low.

Therefore, the optical coupling structure according to the present embodiment focuses on the relationship between the relative coupling efficiency Δη _y in the waveguide thickness direction and the air equivalent distance z. The optical coupling structure according to the present embodiment has a relative coupling efficiency of 40% or more by adjusting the air conversion distance z without changing the mode field diameter MFDy in the waveguide thickness direction, which is difficult to increase. It can be secured. The optical coupling structure according to this embodiment will be specifically described below.

ここで、Δｙは、導波路入射面６４ａ上でｙ方向（導波路厚み方向）におけるスポットＰの位置ズレ量を示している。また、ｗ_０ｙは、出射面５０ａにおける、出射光のｙ方向のスポット半径を示している。また、ｗ_２ｙは、導波路６４のモードフィールドにおいて相対強度がｅｘｐ（−２）となるｙ方向のモードフィールド半径を示している。 By using the coupling efficiency κ _y in the waveguide thickness direction shown in [Equation 11], the equation of the relative coupling efficiency Δη _{y in} the waveguide thickness direction shown in [Equation 13] is arranged with respect to the air equivalent distance z. It becomes.
[Equation 15]

Here, Δy indicates the positional deviation amount of the spot P in the y direction (waveguide thickness direction) on the waveguide incident surface 64a. Further, w _0y indicates the spot radius in the y direction of the outgoing light on the outgoing face 50a. In addition, w _2y indicates a mode field radius in the y direction in which the relative intensity is exp (−2) in the mode field of the waveguide 64.

That is, the equation shown in [Equation 4] specifies an assumed positional deviation amount Δy for a given spot radius w _0y and mode field radius w _{2y so} that Δη _y ≧ 40%. It shows that the relative coupling efficiency Δη _y can be secured by 40% or more by adjusting the air conversion distance z.

When the relative coupling efficiency Δη _y = 40%, 2 / ln (Δη _y ) is −2.18. Therefore, the relative coupling efficiency can be ensured by 40% or more by setting the air conversion distance z so that the following conditional expression is satisfied.
[Equation 16]

When the relative coupling efficiency Δη _y = 50%, 2 / ln (Δη _y ) is −2.89. Therefore, the relative coupling efficiency can be ensured by 50% or more by setting the air conversion distance z so that the following conditional expression is satisfied.
[Equation 17]

As described above, by setting the air-converted distance z based on the following equation, it is possible to ensure a relative coupling efficiency that is equal to or greater than the value set as Δη _y .
[Equation 4]

(Example 6)
Next, an example of the second embodiment will be described. First, as Example 6, the case where the wavelength λ = 0.66 μm of emitted light, the radiation angle θh = 9 °, θv = 16.5 °, and the mode field diameter MFDy = 3 μm in the waveguide thickness direction will be described. In this embodiment, the positional deviation amounts Δx and Δy of the spot position P are set to Δx = 1.5 μm and Δy = 1.5 μm. When β ₁ and β ₂ are calculated based on this condition, β ₁ = 11.4 μm and β ₂ = 15.4 μm.

  Reference is now made to FIG. FIG. 12 is a graph showing the relative coupling efficiency characteristics when the air conversion distance z is changed in the present embodiment, where the vertical axis indicates the relative coupling efficiency and the horizontal axis indicates the air conversion distance z. FIG. 12 shows not only the case where the positional deviation Δy = 1.5 μm of the spot P occurs in the y direction at MFDy = 3 μm, but also the case where the positional deviation Δx = 1.5 μm of the spot P occurs in the x direction. Relative coupling efficiency characteristics are also shown. When the positional deviation of the spot P in the x direction occurs, the mode field diameter in the waveguide width direction is based on the conditional expression 0.35α ≦ MFDx ≦ 2.75α expressed by Equation 1 in the first embodiment. The relative coupling efficiencies are shown for MFDx values of 0.35α, α, and 2.75α (where α is a value calculated using Equation 14 for each z).

As shown in FIG. 12, by setting the z ≧ beta _1, it is possible to secure 40% or more relative binding efficiency in the case of [Delta] y = 1.5 [mu] m. In this case, even when Δx = 1.5 μm, it is possible to ensure a relative coupling efficiency of 40% or more for any mode field diameter MFDx in the range of 0.35α ≦ MFDx ≦ 2.75α. Is possible.

Further, by setting the z ≧ beta _2, it is possible to secure 50% or more of the relative binding efficiency in the case of [Delta] y = 1.5 [mu] m. In this case, even when Δx = 1.5 μm, it is possible to ensure a relative coupling efficiency of 50% or more for any mode field diameter MFDx in the range of 0.35α ≦ MFDx ≦ 2.75α. Is possible.

(Example 7)
Next, as Example 7, an example in which the conditions shown in Example 2 are applied will be described. That is, in this embodiment, the wavelength λ = 0.83 μm of the emitted light, the radiation angle θh = 9 °, θv = 22 °, and the mode field diameter MFDy = 3 μm in the waveguide thickness direction. Further, the positional deviation amounts Δx and Δy of the spot position P in the present embodiment are set to Δx = 1.5 μm and Δy = 1.5 μm. When β ₁ and β ₂ are calculated based on this condition, β ₁ = 9.2 μm and β ₂ = 12.2 μm.

  Reference is now made to FIG. FIG. 13 is a graph showing the relative coupling efficiency characteristics when the air conversion distance z is changed in the present embodiment, where the vertical axis indicates the relative coupling efficiency and the horizontal axis indicates the air conversion distance z. In FIG. 13, the mode field diameter MFDx in the waveguide width direction is set to 0.35α, α, and 2.75α (where α is a value calculated using Equation 14 for each z). Each of these also shows the relative coupling efficiency.

As shown in FIG. 13, by setting the z ≧ beta _1, it is possible to secure 40% or more relative binding efficiency in the case of [Delta] y = 1.5 [mu] m. In this case, even when Δx = 1.5 μm, it is possible to ensure a relative coupling efficiency of 40% or more for any mode field diameter MFDx in the range of 0.35α ≦ MFDx ≦ 2.75α. Is possible.

Further, by setting the z ≧ beta _2, it is possible to secure 50% or more of the relative binding efficiency in the case of [Delta] y = 1.5 [mu] m. In this case, even when Δx = 1.5 μm, it is possible to ensure a relative coupling efficiency of 50% or more for any mode field diameter MFDx in the range of 0.35α ≦ MFDx ≦ 2.75α. Is possible.

(Example 8)
Next, as an eighth embodiment, an example where the conditions shown in the third embodiment are applied will be described. That is, in this embodiment, the wavelength λ = 0.66 μm of the emitted light, the radiation angle θh = 9 °, θv = 16.5 °, and the mode field diameter MFDy = 2 μm in the waveguide thickness direction. In addition, the positional deviation amounts Δx and Δy of the spot position P in this embodiment are set to Δx = 1 μm and Δy = 1 μm. When β ₁ and β ₂ are calculated based on this condition, β ₁ = 4.3 μm and β ₂ = 6.8 μm.

  Reference is now made to FIG. FIG. 14 is a graph showing the relative coupling efficiency characteristics when the air conversion distance z is changed in the present embodiment, where the vertical axis indicates the relative coupling efficiency and the horizontal axis indicates the air conversion distance z. In FIG. 14, the mode field diameter MFDx in the waveguide width direction is 0.35α, α, and 2.75α (where α is a value calculated using [Equation 14] for each z). In each case, the relative coupling efficiency is also shown.

As shown in FIG. 14, by setting the z ≧ beta _1, it is possible to secure 40% or more relative binding efficiency in the case of [Delta] y = 1 [mu] m. In this case, even when Δx = 1 μm, it is possible to ensure a relative coupling efficiency of 40% or more for any mode field diameter MFDx in the range of 0.35α ≦ MFDx ≦ 2.75α. is there.

Further, by setting the z ≧ beta _2, it is possible to secure 50% or more of the relative binding efficiency in the case of [Delta] y = 1 [mu] m. In this case, even when Δx = 1 μm, it is possible to ensure a relative coupling efficiency of 50% or more for any mode field diameter MFDx in the range of 0.35α ≦ MFDx ≦ 2.75α. is there.

  As described above, in the optical coupling structure according to the present embodiment, the air conversion distance z is set based on the equation shown in Equation 15. As a result, if the mode field diameter MFDx in the waveguide width direction is set in the range of 0.35α ≦ MFDx ≦ 2.75α shown in Equation 1, in addition to the relative coupling efficiency against the deviation in the waveguide thickness direction, the waveguide width The relative coupling efficiency in the direction can also be ensured.

Example 9
Finally, as Example 9, the coupling efficiency and the relative coupling efficiency when the core field thickness MFDy in the waveguide thickness direction is increased by increasing the core thickness of the waveguide 64 in the waveguide thickness direction will be summarized below. In this embodiment, the wavelength λ = 0.66 μm of the emitted light, the radiation angle θh = 9 °, θv = 16.5 °, and the mode field diameter MFDy in the waveguide thickness direction = 4 μm. Further, the positional deviation amounts Δx and Δy of the spot position P in the present embodiment are set to Δx = 1.5 μm and Δy = 1.5 μm. In this case, β ₁ = 4.6 μm and β ₂ = 13.8 μm. Further, the air conversion distance z, and z = 6μm> β _1, the mode field diameter MFDx the waveguide width direction, alpha in the case of the z = 6 [mu] m, i.e., a MFDx = α = 3.3μm.

  FIG. 15 shows the coupling efficiency when there is no positional deviation and the values of the coupling efficiency and the relative coupling efficiency when Δx = 1.5 μm and Δy = 1.5 μm in this example. As shown in FIG. 15, even if a positional deviation of Δx = 1.5 μm occurs in the waveguide width direction, the coupling efficiency is 29.6% and the relative coupling efficiency is 44.2%. Even if a positional deviation of Δy = 1.5 μm occurs in the waveguide thickness direction, the coupling efficiency is 27.5% and the relative coupling efficiency is 41.0%. Thus, it can be seen that even when the spot misalignment occurs within a range of 1.5 μm or less, a coupling efficiency of 15% or more and a relative coupling efficiency of 40% or more can be secured.

In addition, the spot diameter on the waveguide entrance surface 64a in this embodiment is as follows: waveguide width direction: 2w _1x = 3.52 μm, waveguide thickness direction: 2w _1y = 3.44 μm. In this case, MFDy> 2w _1y . From this, it can be seen that according to the optical coupling structure of the present invention, MFDy <2w _1y is not necessarily required.

  As described above, the plane mirror 40 can be an internal reflection type prism. In this case, the air conversion distance z may be calculated in consideration of the refractive index of the prism. For example, the distance from the incident surface into the prism to the reflecting surface in the prism is L1 ', the distance from the reflecting surface to the exit surface outside the prism is L2', and the refractive index of the material of the prism is n. In this case, the physical distance z ′ in the prism is z ′ = L1 ′ + L2 ′. The air equivalent distance z of the distance z ′ may be calculated by z = z ′ / n = (L1 ′ + L2 ′) / n.

  As described above, according to the optical coupling structure of the present invention, a coupling efficiency of 15% or more is ensured even when the spot P is shifted by about 1 μm in the waveguide width direction or the waveguide thickness direction on the waveguide incident surface 64a. It becomes possible. Therefore, by applying this optical coupling structure to the optically assisted magnetic head 4, it is possible to reliably record information on the medium.

DESCRIPTION OF SYMBOLS 1 Information recording device 2 Housing | casing 3 Disk 4 Optical assist magnetic head 5 Head support part 6 Support shaft 7 Tracking actuator 30 Surface reflection mirror 40 Plane mirror 40a Polarization surface 50 Light source part 50a Output surface 60 Slider 60a Upper surface 63 Magnetic head part 64 Waveguide 64a Waveguide entrance surface 64b Waveguide exit surface 65 Plasmon probe

Claims (15)

A light source;
A slider that floats and moves relative to the recording medium in accordance with the rotation of the disk-shaped recording medium;
Provided on the slider, having a predetermined width in the width direction (x direction) perpendicular to the thickness direction (y direction), and at one end of the propagation direction (z direction) perpendicular to both the width direction and the thickness direction A waveguide that receives light from the light source at a waveguide entrance surface that is located and propagates the light toward the recording medium located on the other end side in the propagation direction;
An optically assisted magnetic head having
The light from the light source is guided to the waveguide entrance surface without being subjected to condensing or diffusing action,
The spot radius w _{0x at} which the relative intensity in the width direction of the light at the light emitting point of the light source becomes exp (−2), and the relative intensity in the width direction of the light at the waveguide entrance surface is exp (−2). When the spot radius w _1x becomes, the mode field diameter MFDx of the waveguide whose relative intensity in the width direction is exp (−2) satisfies the first condition shown below, and the light source and the An optically assisted magnetic head, wherein an optical coupling structure is formed with a waveguide.
[Equation 1]

However, (alpha) is defined by the following formula | equation.
[Equation 2]

  2. The optically assisted magnetic head according to claim 1, wherein the coupling efficiency is 15% or more in a range where the amount of positional deviation of the light with respect to the waveguide entrance surface is 1.5 μm or less.   3. The light according to claim 1, wherein the waveguide includes a first cladding layer, a core layer, and a second cladding layer stacked in the thickness direction on a substrate. Assist magnetic head. 4. The optically assisted magnetic head according to claim 1, wherein the mode field diameter MFDx satisfies the following second condition instead of the first condition. 5.
[Equation 3]

The air-converted distance z from the exit surface from which the light source emits the light to the waveguide entrance surface is the wavelength λ of the light and the positional deviation amount Δy of the light spot in the thickness direction at the waveguide entrance surface. And a spot radius w _0y where the relative intensity in the thickness direction of the light is exp (−2) at the light emitting point of the light source, and a mode where the relative intensity in the thickness direction is exp (−2) in the waveguide. Relative coupling showing the relative coupling efficiency associated with the positional deviation of the spot in the thickness direction, assuming that the field radius w _2y and the coupling efficiency when the spot positional deviation does not occur on the waveguide entrance surface are 1. The optically assisted magnetic head according to claim 1, wherein the following condition is satisfied using the efficiency Δη _y .
[Equation 4]

However, the relative coupling efficiency Δη _y satisfies Δη _y ≧ 0.4 as a third condition. 6. The optically assisted magnetic head according to claim 5, wherein the relative coupling efficiency Δη _y satisfies Δη _y ≧ 0.5 as a fourth condition instead of the third condition.   The deflecting unit that is located between the light source and the waveguide and deflects the light so that light from the light source enters the waveguide incident surface is provided. Optically assisted magnetic head.   8. The optically assisted magnetic head according to claim 7, wherein the deflecting unit is a plane mirror that reflects light from the light source and guides the light to the waveguide incident surface.   9. The optically assisted magnetic head according to claim 8, wherein the plane mirror is a surface reflection type mirror or an internal reflection type prism. A light source;
A waveguide entrance surface having a predetermined width in the width direction (x direction) orthogonal to the thickness direction (y direction) and positioned at one end of the propagation direction (z direction) orthogonal to both the width direction and the thickness direction A waveguide that receives the light from the light source and propagates the light to the other end in the propagation direction;
An optical coupling structure of
The light from the light source is guided to the waveguide entrance surface without being subjected to condensing or diffusing action,
The spot radius w _{0x at} which the relative intensity in the width direction of the light at the light emitting point of the light source becomes exp (−2), and the relative intensity in the width direction of the light at the waveguide entrance surface is exp (−2). When the spot radius w _1x becomes, the mode field diameter MFDx of the waveguide where the relative intensity in the width direction is exp (−2) satisfies the following first condition. Bond structure.
[Equation 1]

However, (alpha) is defined by the following formula | equation.
[Equation 2]

  11. The optical coupling structure according to claim 10, wherein the coupling efficiency is 15% or more when the amount of positional deviation of the light with respect to the waveguide entrance surface is 1.5 μm or less.   The optical waveguide according to claim 10 or 11, wherein the waveguide includes a first cladding layer, a core layer, and a second cladding layer laminated in the thickness direction on a substrate. Combined structure. The optical coupling structure according to any one of claims 10 to 12, wherein the mode field diameter MFDx satisfies the following second condition instead of the first condition.
[Equation 3]

The air-converted distance z from the light emitting point of the light source to the waveguide entrance surface is the wavelength λ of the light, the positional deviation amount Δy in the thickness direction of the light spot on the waveguide entrance surface, and the light source A spot radius w _{0y at} which the relative intensity in the thickness direction of the light is exp (−2) at the light emitting point, and a mode field radius w _{2y at} which the relative intensity in the thickness direction is exp (−2) at the waveguide. A relative coupling efficiency Δη _y indicating a relative coupling efficiency associated with a positional shift of the spot in the thickness direction, assuming that the coupling efficiency when the positional shift of the spot does not occur on the waveguide entrance surface is 1, The optical coupling structure according to claim 10, wherein the following condition is satisfied using:
[Equation 4]

However, the relative coupling efficiency Δη _y satisfies Δη _y ≧ 0.4 as a third condition. The optical coupling structure according to claim 14, wherein the relative coupling efficiency Δη _y satisfies Δη _y ≧ 0.5 as a fourth condition instead of the third condition.

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