Thermally-assisted magnetic recording head comprising light source with photonic-band layer

A thermally-assisted magnetic recording head is provided, in which a light source having sufficiently high output power for performing thermal-assist is disposed in the element-integration surface of the substrate to achieve improved mass-productivity. The head includes: a light source having a multilayered structure including a photonic-band layer and having a light-emitting surface opposed to the element-integration surface; a diffraction optical element that converges the emitted light; a light-path changer that changes the direction of the converged light; a waveguide that propagates the direction-changed light toward the opposed-to-medium surface; and a magnetic pole that generates write field. The surface-emitting type light source includes a photonic-band layer having a periodic structure in which a light from an active region resonates, and thus emits laser light on a quite different principle from a VCSEL. Therefore, the light source can be disposed in the element-integration surface, even though having sufficiently high output power.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetic recording head used for thermally-assisted magnetic recording in which a magnetic recording medium is irradiated with light, thereby anisotropic magnetic field of the medium is lowered, thus data can be written. Further, the present invention relates to a head gimbal assembly (HGA) provided with the head, and to a magnetic recording apparatus provided with the HGA.

2. Description of the Related Art

As the recording density of a magnetic recording apparatus, as represented by a magnetic disk apparatus, becomes higher, further improvement has been required in the performance of a thin-film magnetic head and a magnetic recording medium. Especially, in the magnetic recording medium, it is necessary to decrease the size of magnetic microparticles that constitute the magnetic recording layer of the medium, and to reduce irregularity in the boundary of record bit in order to improve the recording density. However, the decrease in size of the magnetic microparticles raises a problem of degradation in thermal stability of the magnetization due to the decrease in volume. As a measure against the thermal stability problem, it may be possible to increase the magnetic anisotropy energy KUof the magnetic microparticles. However, the increase in energy KUcauses the increase in anisotropic magnetic field (coercive force) of the magnetic recording medium. As a result, the head cannot write data to the magnetic recording medium when the anisotropic magnetic field of the medium exceeds the write field limit.

Recently, as a method for solving the problem of thermal stability, so-called a thermally-assisted magnetic recording technique is proposed. In the technique, a magnetic recording medium formed of a magnetic material with a large energy KUis used so as to stabilize the magnetization, then anisotropic magnetic field of a portion of the medium, where data is to be written, is reduced by heating the portion; just after that, writing is performed by applying write field to the heated portion.

In this thermally-assisted magnetic recording technique, there has been generally used a method in which a magnetic recording medium is irradiated and thus heated with a light such as near-field light. In this case, it is important to form a very minute light spot at a desired position on the magnetic recording medium. However, from the beginning, more significant problem to be solved exists in how the light is to be supplied from a light source to the inside of a head, and specifically, where and how the light source is to be disposed.

As for the supplying of light, for example, U.S. Pat. Nos. 6,567,373 B1, 6,795,380 B2 and Japanese Patent Publication No. 2007-200475A disclose a structure in which light is guided to a desired position by using an optical fiber and a reflection means. Further, US Patent Publication No. 2006/0187564 A1 discloses a structure in which a unit having a heatsink and a laser diode is mounted on the back surface of a slider. And US Patent Publication No. 2008/0056073 A1 discloses that a structure, in which a reflection mirror is monolithically integrated into a laser diode element, is mounted on the back surface of a slider. Further, US Patent Publication No. 2005/0213436 A1 discloses a slider structure that is integrated with a semiconductor laser. And Robert E. Rottmayer et al. “Heat-Assisted Magnetic Recording” IEEE TRANSACTIONS ON MAGNETICS, Vol. 42, No. 10, p. 2417-2421 (2006) discloses a configuration in which a diffraction grating is irradiated with the light emitted from a laser unit provided within a drive apparatus.

Furthermore, US Patent Publication No. 2008/0002298 A1 and U.S. Pat. No. 5,946,281 A disclose heads in which a light source is disposed in an element-integration surface of a slider substrate. In these heads, a surface-emitting laser diode, which is easily disposed in the element-integration surface, is used as a light source, and laser light from the surface-emitting laser diode is guided to a desired position by using a diffraction grating. Conventionally, optical devices, such as a reflection mirror, an optical fiber and a laser diode, have been mounted after a polishing operation in the wafer process of the head manufacturing. On the contrary, in these heads, by forming an optical system in the wafer process and further providing the surface-emitting laser diode in the element-integration surface also in the wafer process, the construction of the optical system is completed in the stage of the wafer process, which makes this construction comparatively facilitated and simplified and allows improvement of mass-productivity.

However, the surface-emitting laser diode used in these documents is a vertical-cavity surface-emitting laser (VCSEL) that is widely used. In a magnetic recording head in which such a surface-emitting laser diode and the diffraction grating are disposed in the element-integration surface as described above, an insufficient laser output power in the surface-emitting laser diode and the degradation in function of the diffraction grating due to fluctuation of the wavelength of the laser light are likely to lead to serious problems.

First, as for the insufficient laser output power, the amount of output of near-field light, required for attaining a recording density exceeding 1 Tbits/in2in a magnetic disk apparatus for performing the thermally-assisted magnetic recording with use of near-field light, has been approximately 1 mW with a spot diameter of 40 nm or less, according to the estimation by the present inventors using simulation and the like. Moreover, the light use efficiency, which the present inventors estimated for the overall optical system in an expected head structure, has been approximately 2%. Therefore, the output power necessary for the laser diode as a light source is estimated to be 50 mW or more. However, a VCSEL generally has a short cavity length, and the output power is about several mW for general use. Therefore, it is difficult for the use of the VCSEL to meet such a high output power.

Next, as for the degradation in function of the diffraction grating due to fluctuation of the wavelength of the laser light, a diffraction grating has a function of changing a propagation direction of the light. This function is achieved by using a grating having a distance and arrangement designed based on the wavelength of incident light, and is significantly affected by the wavelength of the incident light. Here, since the laser diode mounted on a head is a device formed of a semiconductor material, its wavelength changes according to the change of surrounding temperature. Specifically, the assumed temperature in the environment where a magnetic disk apparatus is used is, for example, about −5 to 60° C. (degrees centigrade), and accordingly the wavelength may vary, for example, in the range of approximately from 5 to 10 nm. Therefore, when such a diffraction grating is used, a serious problem may occur such that the function of the diffraction grating is degraded by the wavelength fluctuation and then the laser light may not reach a desired position.

Furthermore, in a VCSEL, the size of the beam spot near the light-emitting surface is extremely small, for example, approximately 0.5 to 5.0 μm. And the divergence angle of the emitted laser light is rather large. Therefore, for example, it may become difficult to monitor the output of the light emitted from the VCSEL in order to adjust the output. Actually, for monitoring the light output of the VCSEL, a part of the laser light emitted from the VCSEL is taken out, then the part of the laser light is detected by a light detector provided also in the element-integration surface. In the case, in order to avoid greater loss in the amount of light used for the thermal assist, the part of the laser light should not be taken out by using a reflecting mirror or the like until the emitted laser light is diverged to a considerable degree. Therefore, the reflecting mirror or the like has no other choice to be provided in a position far away from the light-emitting surface of the VCSEL toward the element-integration surface. As a result, the light-path length from the VCSEL to the light detector increases, which may cause greater light loss and prevent satisfactory detection. Primarily, the considerably large divergence angle of the laser light emitted from the VCSEL has caused a difficulty in transforming the diverged laser light into a light beam with a minute spot size within the head.

SUMMARY OF THE INVENTION

Some terms used in the specification will be defined before explaining the present invention. In a layered structure or an element structure formed in the element-integration surface of a slider substrate of the magnetic recording head according to the present invention, when viewed from a standard layer or element, a substrate side is defined as “lower” side, and the opposite side as an “upper” side. Further, “X-, Y- and Z-axis directions” are indicated in some figures showing embodiments of the head according to the present invention as needed. Here, Z-axis direction indicates above-described “up-and-low” direction, and +Z side corresponds to a trailing side and −Z side to a leading side. And Y-axis direction indicates a track width direction, and X-axis direction indicates a height direction.

Further, a “side surface” of a waveguide provided within the magnetic recording head is defined as an end surface other than the end surfaces perpendicular to the direction in which light propagates within the waveguide (−X direction), out of all the end surfaces surrounding the waveguide. According to the definition, an “upper surface” and a “lower surface” are one of the “side surfaces”. The “side surface” is a surface on which the propagating light can be totally reflected within the waveguide corresponding to a core.

According to the present invention, a thermally-assisted magnetic recording head is provided, which comprises:

a light source provided in an element-integration surface of a substrate, and having a multilayered structure including a photonic-band layer having a periodic structure in which a light generated from an active region resonates, and the light source having a light-emitting surface that is a layer surface as an end surface of the multilayered structure and is opposed to the element-integration surface;

a diffraction optical element that converges a light emitted from the light-emitting surface;

a light-path changer that changes a propagation direction of the converged light;

a waveguide that propagates the light, whose propagation direction is changed by the light-path changer, toward an opposed-to-medium surface; and

a magnetic pole that generates write field from its end surface on the opposed-to-medium surface side, provided in the element-integration surface of the substrate.

The light source according to the present invention has a multilayered structure including a photonic-band layer, and thus is a laser diode of surface-emitting type that emits laser light on a quite different principle from that of a vertical-cavity surface-emitting laser (VCSEL). Therefore, the light source can be disposed in the element-integration surface of the slider substrate to achieve improvement of mass-productivity, even though the light source has a sufficiently high output power for performing thermal assist. As a result, according to the present invention, there is provided a thermally-assisted magnetic recording head in which a light source having a sufficiently high output power is disposed in the element-integration surface of the slider substrate to achieve improvement of mass-productivity.

It the thermally-assisted magnetic recording head according to the present invention, preferably further provided is a spot-size converter that converts a spot size of the light whose propagation direction is changed by the light-path changer. Here, a spot diameter of a light that is entering the spot-size converter is preferably in a range of 2-20 times larger than a spot diameter of the light that has just entered the waveguide, and is also preferably 1 μm (micrometer) or more, and is 10 μm or less. The spot-size converter plays an important role when a light source having a sufficiently large spot diameter of the emitted beam is used to obtain higher output power. The above-described diffraction optical element is preferably a binary lens. In the case, it is preferable that a two-dimensional periodic plane of the periodic structure that the photonic-band layer has and a lens plane perpendicular to an optical axis of the diffraction optical element are parallel to the element-integration surface of the substrate. Further, the light-path changer is preferably a reflecting mirror that reflects the converged light. Here, the combination of the binary lens and the reflecting mirror is an optical system that is hardly affected adversely by the change of surrounding temperature, compared with a diffraction grating. Alternatively, a prism can be used as a light-path changer.

By structuring the optical system within the head as described above, a light source having a sufficiently high output power can be disposed in the element-integration surface of the slider substrate to achieve improvement of mass-productivity: and based on that, it becomes possible to guide light efficiently into a desired position on the opposed-to-medium surface side without being hardly affected adversely by the change of surrounding temperature.

Furthermore, the thermally-assisted magnetic recording head according to the present invention preferably further comprises: a light detector that measures an output power of the light source in order to adjust the output power; and at least one detective light-path changer that directs a part of light propagating between the light-emitting surface of the light source and the diffraction optical element toward the light detector. Here, the light source provided within the head according to the present invention can emit a light that is suitable for transforming the light into a light beam with a minute spot size, or is suitable for monitoring the output power of the light, that is, the light source can emit a collimated light with a minute divergence angle. Therefore, by monitoring the light output power of the light source, it becomes possible to suppress the variation due to temperature change and further over time in the light output power, thereby there can be ensured the appropriate heating of the magnetic recording medium. Further, in the configuration including the light detector, the light source and the light detector are preferably provided on an overcoat layer formed on the element-integration surface of the substrate. Furthermore, a part of the diffraction optical element preferably acts as the detective light-path changer.

Further, in the thermally-assisted magnetic recording head according to the present invention, it is preferable that further provided in the element-integration surface of the substrate is a plasmon antenna that excites a surface plasmon by receiving the light propagating through the waveguide and generates a near-field light from its end surface on the opposed-to-medium surface side. In the case, the plasmon antenna is preferably opposed to an end portion on the opposed-to-medium surface side of the waveguide with a predetermined distance. Further in the case, the plasmon antenna preferably comprises an edge extending from a portion that is coupled with the light propagating though the waveguide in a surface plasmon mode to an near-field light generating end surface that generates the near-field light, the edge propagating the surface plasmon excited by the light.

Further, in the thermally-assisted magnetic recording head according to the present invention, the light source is preferably a photonic-crystal type surface-emitting laser diode having an output power of at least 50 mW (milliwatts). And the light emitted from the light-emitting surface of the light source preferably remains in a single mode until propagating through the waveguide, and also preferably remains in a linear polarization state until propagating through the waveguide.

According to the present invention, a head gimbal assembly (HGA) is further provided, which comprises the above-described thermally-assisted magnetic recording head and a suspension that supports the thermally-assisted magnetic recording head.

According to the present invention, a magnetic recording apparatus is further provided, which comprises: at least one HGA described above; at least one magnetic recording medium; and a recording control circuit that controls write operations that the thermally-assisted magnetic recording head performs to the at least one magnetic recording medium, the recording control circuit further including a light-emission control circuit that controls light-emission operations of the light source.

In the magnetic recording apparatus according to the present invention, the thermally-assisted magnetic recording head preferably further comprises: a light detector that measures an output power of the light source in order to adjust the output power; and at least one detective light-path changer that directs a part of light propagating between the light-emitting surface of the light source and the diffraction optical element toward the light detector, and the light-emission control circuit preferably controls the light-emission operations of the light source by using an output of the light detector. In the case, the light source and the light detector are preferably provided on an overcoat layer formed on the element-integration surface of the substrate.

Further objects and advantages of the present invention will be apparent from the following description of preferred embodiments of the invention as illustrated in the accompanying figures. In each figure, the same element as an element shown in other figure is indicated by the same reference numeral. Further, the ratio of dimensions within an element and between elements becomes arbitrary for viewability.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1shows a perspective view schematically illustrating a structure of a major part in one embodiment of a magnetic recording apparatus and a head gimbal assembly (HGA) according to the present invention. Here, in the perspective view of the HGA, a face of the HGA opposed to the surface of the magnetic recording medium is presented as the upper side.

A magnetic disk apparatus as a magnetic recording apparatus shown inFIG. 1includes: a plurality of magnetic disks10as magnetic recording media, rotating around a rotational axis of a spindle motor11; an assembly carriage device12provided with a plurality of drive arms14thereon; a head gimbal assembly (HGA)17attached on the top end portion of each drive arm14and provided with a thermally-assisted magnetic recording head21as a thin-film magnetic head; and a recording/reproducing and light-emission control circuit13for controlling write/read operations of the thermally-assisted magnetic recording head21and further for controlling the emission operation of a laser diode40that the thermally-assisted magnetic recording head21includes.

The laser diode40is a light source for emitting laser light used for thermally-assisted magnetic recording, and is provided in the element-integration surface of a slider substrate that is a base of the thermally-assisted magnetic recording head21. The laser diode40includes a photonic-band layer in which a light generated from an active layer resonates, and is, in the present embodiment, a photonic-crystal type surface-emitting laser diode. The magnetic disk10is, in the present embodiment, designed for perpendicular magnetic recording, and has a structure in which sequentially stacked on a disk substrate is: a soft-magnetic under layer; an intermediate layer; and a magnetic recording layer (perpendicular magnetization layer). The anisotropic magnetic field (coercive force) of the magnetic recording layer is set to be a sufficiently large value for stabilizing the magnetization in room temperature. The assembly carriage device12is a device for positioning the thermally-assisted magnetic recording head21above a track formed on the magnetic recording layer of the magnetic disk10, on which recording bits are aligned. In the apparatus, the drive arms14are stacked in a direction along a pivot bearing axis16and can be angularly swung around the axis16by a voice coil motor (VCM)15. The structure of the magnetic disk apparatus according to the present invention is not limited to that described above. For instance, the number of each of magnetic disks10, drive arms14, HGAs17and thermally-assisted magnetic recording heads21may be one.

Referring also toFIG. 1, a suspension20in the HGA17includes: a load beam200; a flexure201with elasticity fixed to the load beam200; and a base plate202provided on the base portion of the load beam200. Further, on the flexure201, there is provided a wiring member203that is made up of lead conductors and connection pads electrically joined to both ends of the lead conductors. The thermally-assisted magnetic recording head21is fixed to the flexure201, that is, to the top end portion of the suspension20so as to face the surface of each magnetic disk10with a predetermined spacing (flying height). Moreover, one ends of the wiring member203are electrically connected to terminal electrodes of the thermally-assisted magnetic recording head21. The structure of the suspension20is not limited to the above-described one. An IC chip for driving the head may be mounted midway on the suspension20, though not shown.

FIG. 2shows a perspective view illustrating one embodiment of thermally-assisted magnetic recording head21according to the present invention.

As shown inFIG. 2, a thermally-assisted magnetic recording head21includes: a slider substrate210formed of, for example, AlTiC (Al2O3—TiC), and having an air bearing surface (ABS)2100as an opposed-to-medium surface processed so as to provide an appropriate flying height; a head element32, a binary lens42, a reflecting mirror43, a spot-size converter44, a waveguide35and a surface plasmon antenna36, which are formed in an element-integration surface2102of the slider substrate210, the surface2102being perpendicular to the ABS2100; an overcoat layer38formed on the element-integration surface2102, so as to cover these elements; and a laser diode40disposed on the upper surface389of the overcoat layer38. The head end surface388, which is a surface of the overcoat layer38opposed to the medium, and the ABS2100constitute the whole opposed-to-medium surface of the thermally-assisted magnetic recording head21.

The head element32is constituted of a magnetoresistive (MR) element33for reading data from the magnetic disk and an electromagnetic transducer34for writing data to the magnetic disk. The laser diode40has a multilayered structure including an active layer for generating a light and a photonic-band layer having a periodic structure in which the generated light resonates. Here, the lower surface400that is a layer surface as an end surface of the multilayered structure is a light-emitting surface that emits laser light. The light-emitting surface400is opposed to the element-integration surface2102, and is, in the present embodiment, bonded on the upper surface389of the overcoat layer38.

The binary lens42is a diffraction optical element for converging the laser light emitted from the light-emitting surface400of the laser diode40. And the reflecting mirror43is a light-path changer for changing the propagation direction of the laser light converged by the binary lens42. Actually in the present embodiment, the reflecting mirror43changes the propagation of the laser light from a state in which the laser light is directed from the light-emitting surface400of the laser diode40toward the element-integration surface2102of the slider substrate210(the propagation in −Z direction) to a state in which the laser light is directed toward the head end surface388in the direction parallel to the element-integration surface2102(the propagation in −X direction). Further, the spot-size converter44is an optical element that receives the laser light the propagation direction of which is changed by the reflecting mirror43, makes the spot size of the laser light changed (smaller), then guides the laser light into the waveguide35. Further, the waveguide35is an optical path that receives the laser light, the propagation direction and spot size of which are adjusted by going through the reflecting mirror43and the spot-size converter44, and then propagates the laser light toward the head end surface388. Further, the surface plasmon antenna36is a near-field light generator that transforms the laser light (waveguide light) propagating through the waveguide35into near-field light. Here, the binary lens42, the reflecting mirror43, the spot-size converter44, the waveguide35, and the surface plasmon antenna36constitute a near-field light generating optical system within the head21.

Furthermore, the thermally-assisted magnetic recording head21includes: a pair of terminal electrodes370exposed in the upper surface of the overcoat layer38and electrically connected to the MR element33; a pair of terminal electrodes371also exposed in the upper surface of the overcoat layer38and electrically connected to the electromagnetic transducer34; and a pair of terminal electrodes410and411also exposed in the upper surface of the overcoat layer38and electrically connected to the respective electrodes of the laser diode40. These terminal electrodes370,371,410and411are electrically connected to the connection pads of the wiring member203provided on the flexure201(FIG. 1).

One ends of the MR element33, the electromagnetic transducer34, and the surface plasmon antenna36reach the head end surface388as an opposed-to-medium surface. During actual write and read operations, the thermally-assisted magnetic recording head21aerodynamically flies above the surface of the rotating magnetic disk10(FIG. 1) with a predetermined flying height. Thus, the ends of the MR element33and electromagnetic transducer34face the surface of the magnetic recording layer of the magnetic disk10with an appropriate magnetic spacing. Then, the MR element33reads data by sensing signal magnetic field from the magnetic recording layer, and the electromagnetic transducer34writes data by applying signal magnetic field to the magnetic recording layer. When writing data, laser light is emitted from the light-emitting surface400of the laser diode40disposed in the element-integration surface2102of the head21, and propagates through the waveguide35after going through the binary lens42, the reflecting mirror43and the spot-size converter44, and then the laser light (waveguide light) is coupled with the surface plasmon antenna36in a surface plasmon mode, as described in detail later. As a result, surface plasmon is excited on the surface plasmon antenna36. The surface plasmon propagates on a propagation edge provided in the surface plasmon antenna36, which will be detailed later, toward the head end surface388, which causes near-field light to be generated from the end on the head end surface388side of the surface plasmon antenna36. The generated near-field light reaches the surface of the magnetic disk, and heats a portion of the magnetic recording layer of the disk. As a result, the anisotropic magnetic field (coercive force) of the portion is decreased to a value that enables writing; thus a thermally-assisted magnetic recording can be accomplished.

Also according toFIG. 2, the slider substrate210is preferably so-called a femto slider in which the thickness TSL(in X-axis direction) is 230 μm (micrometers), the width WSLin the track width direction (Y-axis direction) is 700 μm, and the length LSL(in Z-axis direction) is 850 μm. The femto slider is generally used as a substrate for thin-film magnetic heads capable of high-density recording, and has the smallest standardized size of all the sliders currently on the market. In this case, the element-integration surface2102of the slider substrate210is a region with the area of 230 μm (TSL)×700 μm (WSL).

The laser diode40is mounted in the element-integration surface2102with such a small area, and acts as a light source for generating laser light used for the thermally-assisted magnetic recording described above. The laser diode40is, in the present embodiment, a photonic-crystal type surface-emitting laser diode, and has a multilayered structure including an active layer for generating a light and a photonic-band layer having a periodic structure in which the generated light resonates. Here, the light-emitting surface400that emits laser light of the laser diode40is a lower surface of the multilayered structure, and is opposed to the element-integration surface2102, and further is, in the present embodiment, bonded on the upper surface389of the overcoat layer38. The height TLDof the laser diode40is, for example, in the range of approximately 50 to 200 μm. And the width WLDand the length LLDof the laser diode40is, for example, in the range of approximately 50 to 200 μm. These sizes of the laser diode40represents that the laser diode40can be mounted well within the element-integration surface2102. By setting the laser diode40in the element-integration surface2102, the construction of the optical system is completed in the stage of the wafer process, which makes this construction comparatively facilitated and simplified and allows improvement of mass-productivity.

The laser diode40is preferably a photonic-crystal type surface-emitting laser diode with an output of at least 50 mW (milliwatts). This laser diode enables a sufficient and rapid heating of a portion of the magnetic recording layer. In the photonic-crystal type surface-emitting laser diode, a laser light of a single-mode having an extremely small divergence angle (for example, 1° or less) can be emitted from the light-emitting surface400. Further, the polarization of the emitted laser light can be set considerably freely; for example, a linear polarization can be realized, which is preferable for the excitation of surface plasmon explained later. Here, a single-mode means a state in which the beam spot has a circular or elliptical shape and the light intensity distribution is represented by the Gaussian distribution with single-peaked pattern. Whereas, a state in which the beam spot has a doughnut-shape or has a light intensity distribution with multi-peaked pattern is referred to as a multimode. The structure and characteristic of the laser diode40will be explained in detail later with reference toFIG. 4.

Also as shown inFIG. 2, the terminal electrode410is electrically connected, through a lead electrode4100, with a p-electrode40j(FIG. 4) formed on the light-emitting surface400that is a lower surface (bottom surface) of the laser diode40. And the terminal electrode411is electrically connected with an n-electrode40a(FIG. 4) that corresponds to an upper surface of the laser diode40. The terminal electrode411and the n-electrode40amay be connected to each other by wire-bonding as shown inFIG. 2, or by solder-ball bonding (SBB) with a solder. By electrically connecting the terminal electrodes410and411to connection pads of the wiring member203provided on the flexure201(FIG. 1), a predetermined voltage can be applied to the laser diode40through both electrodes410and411. This voltage application causes laser light to be emitted from the light-emitting surface400of the laser diode40.

Further, an electric source provided within the magnetic disk apparatus can be used for driving the laser diode40. In fact, the magnetic disk apparatus usually has an electric source with an applying voltage of, for example, approximately 2 to 5 V, which is sufficient for the laser oscillation. The laser diode40preferably has an output power of at least 50 mW as described above; even in the case that the amount of electric power consumption of the laser diode40is, for example, in the neighborhood of one hundred mW, the amount can be covered sufficiently by the electric source provided within the magnetic disk apparatus. Further, the laser diode40and terminal electrodes410and411are not limited to the above-described embodiment. For example, other configurations of the laser diode40and the terminal electrodes410and411may be possible. Further, at least one electrode of the laser diode40can electrically be connected directly with the connection pads of the wiring member203.

FIG. 3shows a cross-sectional view taken by plane A inFIG. 2, schematically illustrating the configuration of the head element32, the near-field light generating optical system, and their vicinity in the thermally-assisted magnetic recording head21.

As shown inFIG. 3, the MR element33is formed on an insulating layer380stacked on the element-integration surface2102, and includes: an MR multilayer332; and a lower shield layer330and an upper shield layer334which sandwich the MR multilayer332and an insulating layer381therebetween. The upper and lower shield layers334and330prevent the MR multilayer332from receiving external magnetic field as a noise. The MR multilayer332is a magneto-sensitive part for detecting signal magnetic field by using MR effect. The MR multilayer332may be, for example: a current-in-plane giant magnetoresistive (CIP-GMR) multilayer that utilizes CIP-GMR effect; a current-perpendicular-to-plane giant magnetoresistive (CPP-GMR) multilayer that utilizes CPP-GMR effect; or a tunnel magnetoresistive (TMR) multilayer that utilizes TMR effect. The MR multilayer332that utilizes any MR effect described above can detect signal magnetic field from the magnetic disk with high sensitivity. In the case that the MR multilayer332is a CPP-GMR multilayer or a TMR multilayer, the upper and lower shield layers334and330act as electrodes.

Referring also toFIG. 3, the electromagnetic transducer34is designed for perpendicular magnetic recording, and includes an upper yoke layer340, a main magnetic pole3400, a write coil layer343, a coil-insulating layer344, a lower yoke layer345, and a lower shield3450.

The upper yoke layer340is formed so as to cover the coil-insulating layer344, and the main magnetic pole3400is formed on an insulating layer385made of an insulating material such as Al2O3(alumina). These upper yoke layer340and main magnetic pole3400are magnetically connected with each other, and acts as a magnetic path for converging and guiding magnetic flux toward the magnetic recording layer (perpendicular magnetization layer) of the magnetic disk, the magnetic flux being excited by write current flowing through the write coil layer343. The main magnetic pole3400includes: a first main pole portion3400a(FIG. 6) reaching the head end surface388and having a small width WP(FIG. 7) in the track width direction; and a second main pole portion3400b(FIG. 6) located on the first main pole portion3400aand at the rear (+X side) of the portion3400a. The small width WPof the first main pole portion3400aenables the generation of a fine write magnetic field responding to higher recording density. The main magnetic pole3400is formed of a soft-magnetic material with a saturation magnetic flux density higher than that of the upper yoke layer340, which is, for example, an iron alloy containing Fe as a main component, such as FeNi, FeCo, FeCoNi, FeN or FeZrN. The thickness of the first main pole portion3400ais, for example, in the range of approximately 0.1 to 0.8 μm.

The write coil layer343is formed on an insulating layer3421made of an insulating material such as Al2O3(alumina), in such a way as to pass through in one turn at least between the lower yoke layer345and the upper yoke layer340, and has a spiral structure with a back contact portion3402as a center. The write coil layer343is formed of a conductive material such as Cu (copper). The write coil layer343is covered with a coil-insulating layer344that is formed of an insulating material such as a heat-cured photoresist and electrically isolates the write coil layer343from the upper yoke layer340and the write shield layer345. The write coil layer343has a monolayer structure in the present embodiment; however, may have a two or more layered structure or a helical coil shape. Further, the number of turns of the write coil layer343is not limited to that shown inFIG. 3, and may be, for example, in the range from two to seven.

The back contact portion3402has a though-hole extending in X-axis direction, and the waveguide35and insulating layers that covers the waveguide35pass through the though-hole. In the though-hole, the waveguide35is away at a predetermined distance of, for example, at least 1 μm from the inner wall of the back contact portion3402. The distance prevents the absorption of the waveguide light by the back contact portion3402.

The lower yoke layer345is formed on an insulating layer383made of an insulating material such as Al2O3(alumina), and acts as a magnetic path for the magnetic flux returning from a soft-magnetic under layer that is provided under the magnetic recording layer (perpendicular magnetization layer) of the magnetic disk10. The lower yoke layer345is formed of an soft-magnetic material, and its thickness is, for example, approximately 0.5 to 5 μm. Further, the lower shield3450is a part of the magnetic path, being connected with the lower yoke layer345and reaching the head end surface388. The lower shield3450is opposed to the main magnetic pole3400through the surface plasmon antenna36, and acts for receiving the magnetic flux spreading from the main magnetic pole3400. The lower shield3450has a width in the track width direction greatly larger than that of the main magnetic pole3400. This lower shield3450causes the magnetic field gradient between the end portion of the lower shield3450and the main pole portion3400ato become steeper. As a result, jitter of signal output becomes smaller, and therefore, error rates during read operations can be reduced. The lower shield3450is preferably formed of a material with high saturation magnetic flux density such as NiFe (Permalloy) or an iron alloy as the main magnetic pole3400is formed of.

Referring also toFIG. 3, the laser diode40is disposed within the element-integration surface2102, and is bonded on the overcoat layer38in such a way that the light-emitting surface400has a surface contact with the upper surface389of the overcoat layer38or is opposed to the upper surface389. In the present embodiment, the laser diode40is a photonic-crystal type surface-emitting laser diode, and has a multilayered structure including: an n-electrode40aas an upper surface; a p-electrode40jprovided on the light-emitting surface400; an n-clad layer40b; a p-clad layer40h; an active layer40dfor generating a light, provided between the n-clad layer40band the p-clad layer40h; and a photonic-band layer40fhaving a periodic structure in which the generated light resonates, provided between the active layer40dand the p-clad layer40h.

The photonic-band layer40fhas a periodic structure in which, in a medium40fahaving the first refractive index nF1, a plurality of optical elements40fbhaving the second refractive index nF2different from the first refractive index nF1are arranged two-dimensionally and periodically. When a predetermined voltage is applied to between the n-electrode40aand the p-electrode40j, a light is generated by the recombination of an electron and a positive hole in the active layer. In the generated lights, a light having a wavelength comparable with (nearly equal to) the period of the periodic structure of the photonic-band layer40fresonates within the layer40f. Thus, only the light with wavelength and phase specified by the resonance proceeds in the direction perpendicular to a (two-dimensional periodic) plane40fcin which the two-dimensional period of the photonic-band layer40flies (in the thickness direction: in Z-axis direction). As a result, a laser light53aof a single-mode, having a predetermined beam cross-section area and an extremely small divergence angle (an almost-collimated light) is emitted from the light-emitting surface400toward the binary lens42in −Z direction.

The binary lens42is a diffraction optical element for converging the laser light emitted from the light-emitting surface400of the laser diode40. In the present embodiment, an optical axis42cof the binary lens42is set to be parallel with Z-axis, and a lens surface420of the binary lens42perpendicular to the optical axis42cis set to be parallel with (the element-integration surface2102and) the (two-dimensional periodic) plane40fcin which the two-dimensional period of the photonic-band layer40flies. These settings enable the binary lens42to be comparatively easily formed in the element-integration surface2102of the slider substrate210by using a thin-film fine processing technique; and enable the laser diode40to be easily provided on the upper surface389of the overcoat layer38; then, the optical axis alignment between the laser diode40and the binary lens42can comparatively easily be implemented by using Z-axis as a standard. Here, the laser light emitted from the laser diode40is not directed toward a diffraction grating. Therefore, there is no need to provide the laser diode40in such a way as to be inclined from the upper surface389of the overcoat layer38for the purpose of the increase in intensity of the light propagating from the diffraction grating to the waveguide. This facilitates the setting of the laser diode40onto the upper surface389.

Further, the binary lens42can hold the capability of diffraction, even under some variation of the wavelength of the incident light. In fact, a simulation experiment was implemented, in which the binary lens42shown inFIGS. 5b1and5b2described later received the laser light with a wavelength of 955, 960, or 965 nm (nanometers). As the simulation result, the coupling efficiency, in the occasion that the laser light passed through the binary lens42and was then reflected by the reflecting mirror43; thus the spot-size converter44receives the laser light, was 30.0% in each case of the above-described wavelengths. From this result, it is understood that the binary lens42can hold its capability of diffraction as designed, even under a wavelength variation of approximately plus or minus 5 nm. For reference sake, the temperature assumed as the use environment of magnetic disk apparatuses is in the range of, for example, −5° C. to 60° C. For the temperature range, semiconductor laser is generally assumed to have a wavelength variation of, for example, approximately plus or minus 5 nm. On the other hand, generally, the diffraction capability of the diffraction grating is known to be significantly varied by the wavelength variation of, for example, approximately plus or minus 5 nm.

The reflecting mirror43is, in the present embodiment, a light-path changer for changing the propagation direction of the laser light53bconverged by the binary lens42into a laser light53cwith different propagation direction. The reflecting mirror43changes the propagation of the laser light from a state in which the laser light is directed from the light-emitting surface400of the laser diode40toward the element-integration surface2102of the slider substrate210(the propagation in −Z direction) to a state in which the laser light is directed toward the head end surface388in the direction parallel to the element-integration surface2102(the propagation in −X direction). The reflecting mirror43can be formed by stacking a layer made of a material having a high reflectance and sufficiently low transmission and absorption for the wavelength of the laser light53bon an inclined plane430having a predetermined inclination angle (45° inFIG. 3) to the element-integration surface2102. The material can be, for example, a metal such as Au, Al, Ta or, NiFe. The layer surface431of the material layer acts as a reflecting surface. Alternatively, a prism can be used as a light-path changer that changes the laser light53binto the laser light53c, instead of the reflecting mirror43. Further, according toFIG. 3, the light-path changer (reflecting mirror43) and the spot-size converter44are integrated in order to suppress unwanted reflection and scattering; however, alternatively, they may be separated as individual elements.

The laser light53creflected by the reflecting mirror43propagates through the spot-size converter44. The spot-size converter44is an optical element that makes the spot size of the laser light53cchanged (smaller), then guides the laser light53cinto the waveguide35. Further, the waveguide35is an optical path that receives the laser light, the propagation direction and spot size of which are adjusted by going through the reflecting mirror43and the spot-size converter44, and then propagates the laser light toward the head end surface388. The waveguide35extends from the rear-end surface352to the end surface350on the head end surface388side through the through-hole that is provided in the back contact portion3402and extends in X-axis direction. Furthermore, the surface plasmon antenna36is a near-field light generator that transforms the laser light (waveguide light) propagating through the waveguide35into near-field light.

As shown also inFIG. 3, a part on the head end surface388side of the waveguide35and the surface plasmon antenna36are provided between the lower shield3450(lower yoke layer345) and the main magnetic pole3400(upper yoke layer340). Further, a portion of the upper surface (side surface) of the waveguide35on the head end surface388side is opposed to a portion of the lower surface (including a propagation edge360(FIG. 6)) of the surface plasmon antenna36with a predetermined distance. The sandwiched portion between these portions constitutes a buffering portion50having a refractive index lower than that of the waveguide35. The buffering portion50acts for coupling the laser light (waveguide light) that propagates through the waveguide35with the surface plasmon antenna36in a surface plasmon mode. Here, the buffering portion50may be a portion of an insulating layer385that is a part of the overcoat layer38, or a new layer provided other than the insulating layer385. A detailed explanation of the near-field light generating optical system including the spot-size converter44, the waveguide35, the surface plasmon antenna36, and the buffering portion50will be given later with reference toFIG. 6.

Alternatively, a plasmon antenna made of a metal plate piece can be used, instead of the surface plasmon antenna36, to generate near-field light by being irradiated with the waveguide light from the waveguide35. Various other embodiments of surface plasmon antenna or plasmon antenna could be used. In any case, the laser light emitted from the laser diode40disposed in the element-integration surface2102can surely be coupled with a surface plasmon antenna or a plasmon antenna. Further, another alternative without using near-field light generators can be applied, in which the magnetic recording layer of a magnetic disk is irradiated directly with laser light emitted from the waveguide35to heat a portion of the magnetic recording layer.

Further, also as shown inFIG. 3, an inter-element shield layer39is preferably provided between the MR element33and the electromagnetic transducer34(lower yoke layer345), sandwiched by the insulating layers382and383. The inter-element shield layer39plays a role for shielding the MR element33from the magnetic field generated from the electromagnetic transducer34, and may be formed of a soft-magnetic material. Here, the insulating layers381,382,383,384,385and386constitute the overcoat layer38.

FIG. 4shows a perspective view illustrating the structure of the laser diode40. In the figure, for easy viewability of the periodic structure of the photonic-band layer40f, the layer40fand a spacer layer40gare separated from each other. Further, for easy viewability of the p-electrode40j, the light-emitting surface400, which corresponds to a bottom surface, is presented as the upper side inFIG. 3.

Referring toFIG. 4, the laser diode40includes: a n-clad layer (substrate)40bmade of, for example, n-type AlGaAs; a p-clad layer40hmade of, for example, p-type AlGaAs; an active layer40dhaving a multilayered structure of multiquantum well made of, for example, InGaAs layers and GaAs layers, and provided between the n-clad layer40band the p-clad layer40h; and a photonic-band layer40fprovided between the active layer40dand the p-clad layer40h. Further, an n-electrode40ais provided on the opposite side to the active layer40din relation to the n-clad layer40b. And a p-electrode40jis provided on the opposite side to the active layer40din relation to the p-clad layer40h, through a contact layer40imade of, for example, p-type GaAs. Further, a spacer layer40cmade of, for example, n-type GaAs is provided between the n-clad layer40band the active layer40d, and a spacer layer40emade of, for example, p-type GaAs is provided between the active layer40dand the photonic-band layer40f. Furthermore, a spacer layer40gmade of, for example, p-type GaAs is provided between the photonic-band layer40fand the p-clad layer40h.

The photonic-band layer40fhas a periodic structure in which, in a medium40fahaving the first refractive index nF1, a plurality of optical elements40fbhaving the second refractive index nF2different from the first refractive index nF1are arranged two-dimensionally and periodically. The medium40facan be formed of, for example, a semiconductor material such as p-type GaAs. And the optical elements40fbcan be vacancy openings (nF2>nF1) passing through the layer40f, which are provided in the medium40fa. Alternatively, the optical elements40fbcan be a part formed of a material that has the second refractive index nF2different from the first refractive index nF1, the part being formed of an insulating material such as Al2O3(alumina) or SiO2(silicon oxide) or a semiconductor material.

As shown also inFIG. 4, the optical elements40fbof the photonic-band layer40fhas a cross-section with circular shape, however, they may have a cross-section with a shape of ellipsoid, a polygon such as triangle, or with one of other various shapes. Further, a plurality of optical elements40fbare arranged periodically within the layer40f, and form a two-dimensional diffraction grating having square lattice the repeating unit of which is a square. The two-dimensional diffraction grating may be a lattice the repeating unit of which is, for example, another quadrangle such as a rhombus, a triangle, a hexagon or the like. By adjusting the refractive index nF2, the cross-sectional shape, and the arrangement of these optical elements40fb, there can be set and controlled the wavelength, the mode, the polarization and so on of the resonated laser light considerably freely.

In the above-described laser diode40formed of GaAs-type material, the thickness tFof the photonic-band layer40fis, for example, in the range of approximately 0.1 to 0.5 μm, and the diameter dFof the cross-section of the optical element40fbis, for example, in the range of approximately 0.05 to 0.2 μm. Further, the wavelength λLof the laser light emitted from the laser diode40is determined by the period of the two-dimensional diffraction grating that the optical elements40fbform. The period is, for example, in the range of approximately 0.1 to 0.4 μm. Alternatively, as the laser diode40, InP base, GaAs base or GaN base diodes can be utilized, and the wavelength λLmay be, for example, in the range of 375 nm (nanometers) to 1.7 μm. Therefore, the period of the two-dimensional diffraction grating of the optical elements40fbis adjusted to an appropriate value within usable wavelength-range. Further, alternatively, the photonic-band layer may be disposed between the n-clad layer40band the active layer40d, instead of between the active layer40dand the p-clad layer40h. Furthermore, an additional photonic-band layer can be provided between the n-clad layer40band the active layer40d, together with the photonic-band layer40fdisposed between the active layer40dand the p-clad layer40h.

The two-dimensional diffraction grating within the photonic-band layer40fhas a property that, when lights propagate therein in at least two different directions with the same period respectively, these lights are overlapped. That is, a light that propagates from a lattice point of the two-dimensional diffraction grating along a direction returns to the original lattice point going through a plurality of diffractions. This property is derived from a dispersion relation (photonic-band) that is energy states of the light (photon) which senses the periodic refractive-index distribution of the two-dimensional diffraction grating. Here, the overlapped lights come into a resonant state. That is, the laser diode40does not include a light resonator (cavity) having reflecting plates opposed to each other as edge-emitting type diodes have; however, the very two-dimensional diffraction grating within the photonic-band layer40ffunctions as a light resonator, that is, a wavelength selector.

Actually, by applying a predetermined voltage between the n-electrode40aand the p-electrode40jof the laser diode40, a light is generated by the recombination of an electron and a positive hole in the active layer40d. When the generated lights reach the photonic-band layer40f, a light of the generated lights, having the same wavelength as the period of the two-dimensional diffraction grating of the photonic-band layer40f, resonates within the layer40f, and its phase is specified. The light with the specified wavelength and phase propagates to the active layer40d, and expedites the inductive emission in the active layer40d. Then, the inductively-emitted light again propagates to the photonic-band layer40f. Here, the wavelength and phase of the light satisfy the conditions for wavelength and phase in the two-dimensional diffraction grating of the photonic-band layer40f. As a result, the light with a uniform wavelength and phase is amplified, and this phenomenon occurs in the region within the layers with the p-electrode40jas a center. Therefore, the light with a uniform wavelength and phase propagates in the direction perpendicular to the active layer40dand the photonic-band layer40f, and finally, is emitted as a laser beam having a predetermined cross-section from the light-emitting surface400.

As is clear from the above-described principle, the laser diode40enables the emitted light to have a larger spot size and further a higher degree of parallelization, that is, an extremely smaller divergence angle (for example, 1° or less), compared with a surface-emitting laser diode such as a VCSEL having no photonic-band layers. Further, the laser diode40can easily realize a laser light with a single-mode, based on the above-described principle. The laser light having a single-mode has a characteristic that, even when the laser light is squeezed, a laser light having a peak with a desired intensity can be obtained. Whereas, when a laser light with a multimode is squeezed, the negation of intensities occurs, and thus the loss is increased. Moreover, the laser diode40also enables emitted lights with various types of polarizations by adjusting the arrangement of the optical elements40fb.

Furthermore, the laser diode40can have a significantly high output. For example, in a VCSEL, the thickness of the active region corresponds to the cavity length; the thickness is at best in the range of, for example, approximately 2 to 10 μm. Therefore, the output of the VCSEL usually remains at several mW (milliwatts) in CW (Continuous Wave) operation. On the other hand, the laser diode40of photonic-crystal surface-emitting type enables its output to be significantly enhanced by adequately enlarging the region of existence of the light that travels between the active layer40dand the photonic-band layer40fand has a uniform wavelength and phase (the spot region of the emitted light). In fact, an experiment result has been obtained, in which the output exceeded 1000 mW. The spot diameter d (FIG. 3) of the spot region of the emitted light can be set to be, for example, in the range of 30 to 100 μm, in consideration of the incidence into the binary lens42.

FIGS. 5a1to5a3show cross-sectional views for explaining the principle of the binary lens42. In the figures, only a right half of the lens cross-section is depicted for simplicity. Further,FIGS. 5b1and5b2andFIGS. 5c1and5c2show cross-sectional views and top views illustrating the structures of different embodiments of binary lenses.

At the start, explained below is the principle of the binary lens42. First, as the cross-section shown inFIG. 5a1, prepared is a convex lens with a usual curved surface having a desired optical function. Then, as shown inFIG. 5a2, material corresponding to a length in the thickness direction of an integral multiple of wavelength λ, of the applied laser light is appropriately removed from the lens so as for the lens thickness to be reduced; thereby formed is a Fresnel lens. After that, as the cross-section shown inFIG. 5a3, a cross-section that discretely approximates the cross-section of the Fresnel lens shown inFIG. 5a2is formed by using, for example, a step structure having three layers with the unit of thickness one fourth of the wavelength λ of the laser light. Generally, in the case of setting the unit of thickness to be a length of minus n-th power of 2 times of the wavelength λ, the number of layers in the step structure is (n−1). Here, the larger the value of n is, the more the number of layers increases and the closer becomes the approximation, which can ensure an optical function closer to that of the original convex lens. However, it takes more time and effort to increase the number of layers. This optical step structure having a cross-section as shown inFIG. 5a3corresponds to a binary lens, and can fulfill an optical function comparable with that of the original convex lens having a cross-section shown inFIG. 5a1, even though having a thinner structure than the original convex lens.

The binary lens42shown inFIGS. 5b1and5b2is a multilayer pattern having a cross-section equivalent to that shown inFIG. 5a3, in which the first, the second and the third diffraction-grating layers42a,42band42care appropriately stacked, the layers being annular and parallel to the element-integration surface2102. The first, the second and the third diffraction-grating layers42a,42band42care formed of a material having a higher refractive index than that of the surrounding insulating layers550and551. For example, in the case that the wavelength λLof the laser light is 600 nm and the insulating layers550and551are formed of Al2O3(n=1.63), the first, the second and the third diffraction-grating layers42a,42band42ccan be formed of, for example, Ta2O5(n=2.16), Nb2O5(n=2.33), TiO (n=2.3-2.55) or TiO2(n=2.3-2.55). The thickness of the binary lens42at its center portion can be set to be equal to the laser-light wavelength or less. That is, because the binary lens42can be made up into a thin plate-shaped one by using a thin-film fine processing technique, the binary lens42is extremely suitable as an optical component within the thermally-assisted magnetic recording head21. Here, the binary lens42shown inFIGS. 5b1and5b2corresponds to the case that the unit of thickness is one fourth of the wavelength of the laser light, as described above. Alternatively, there can be formed a binary lens42with the unit of thickness a half, one eighth or the like of the wavelength.

The binary lens42′ shown inFIGS. 5c1and5c2is an optical system formed by combining the first lens portion421′ and the second lens portion422′. The first lens portion421′ is a multilayer pattern extending in the track width direction (Y-axis direction) within a lens plane4210′ parallel to the element-integration surface2102, and the portion421′ plays a role of converging the laser light in X-axis direction. The second lens portion422′ is a multilayer pattern extending in X-axis direction, and the portion422′ plays a role of converging the laser light in the track width direction (Y-axis direction). As just described, by combining two of, or three or more of lens portions, the laser light emitted from the laser diode40and having a spot with a large area can be converged into a laser light having a spot with a desired shape and size.

FIG. 6shows a perspective view schematically illustrating the configuration of the reflecting mirror43, the spot-size converter44, the waveguide35, the surface plasmon antenna36and the main magnetic pole3400. In the figure, the head end surface388is positioned at the left side, the surface388including positions where write field and near-field light are emitted toward the magnetic recording medium.

As shown inFIG. 6, the configuration includes the reflecting mirror43, the spot-size converter44, the waveguide35for propagating laser light53dused for generating near-field light, and the surface plasmon antenna36that has a propagation edge360as an edge on which surface plasmon excited by the laser light (waveguide light)53dpropagates. The spot-size converter44is an optical element that makes the spot size of the laser light53creflected by the reflecting mirror43changed (smaller), then guides the laser light53cinto the waveguide35. The spot-size converter44is provided on the wide-width end portion of the waveguide35on the opposite side to the head end surface388; and the lower surface of the spot-size converter44has a surface contact with the upper surface354of the waveguide35. The width WBCof the converter44in the track width direction (Y-axis direction) near the reflecting mirror43can be in the range of, for example, 1 to 5 μm, as well as the width WWG1of the waveguide35near the rear-end surface352. Further, the thickness TBC(in Z-axis direction) of the converter44can also be in the range of, for example, 1 to 5 μm. The length LBC(in X-axis direction) of the spot-size converter44can be set to be in the range of, for example, 20 to 100 μm.

As shown also inFIG. 6, the end portion of the spot-size converter44on the head end surface388side tapers toward the head end surface388. The laser light53cpropagating toward the head end surface388(in −X direction) makes the transition to the waveguide35by gradually sensing the narrower propagation region due to the above-described structure of the converter44; then the laser light53cshifts to the laser light (waveguide light)53dpropagating through the waveguide35. The waveguide35extends from the rear-end surface352to the end surface350on the head end surface388side, and the waveguide light53dpropagating through the waveguide35reaches a portion of the waveguide35opposed to the surface plasmon antenna36. Here, the spot-size converter44and the waveguide35can be integrated by using the same material.

The spot diameter of the laser light, which is converged by the binary lens42and is reflected by the reflecting mirror43and then enters the spot-size converter44, that is, the spot diameter of the laser light that has just been reflected by the mirror43is preferably 2 to 20 times larger than the spot diameter of the laser light that has just entered the waveguide35. Specifically, the spot diameter of the just-reflected laser light is preferably in the range of 1.0 to 10 μm. That is, it is preferable that the degree of the convergence of the laser light by the binary lens42is set so as to satisfy the above-described conditions, in consideration of the desired spot diameter in the waveguide35. This setting enables the laser light shifting from the converter44to the waveguide35not to turn into a multimode. Actually, the spot-size converter44plays an important role when a laser diode40having a sufficiently large spot diameter dEMof the emitted beam is provided to obtain higher output power. The spot-size converter44converts a laser light with a large spot diameter into a laser light with a smaller spot diameter, and can further guide the converted laser light to the waveguide35in such a way that the laser light holds a low loss and a single-mode.

Actually, it has been found out from an experiment that, in the case of setting the above-described conditions, for example, setting the thickness TBCof the spot-size converter44to be 5 μm and the thickness TTof the waveguide35to be 0.5 μm, the spot-size converter44converts the spot diameter of the laser light53cinto one-tenth or less of that; thus the light loss in the propagation from the converter44to the waveguide35is sufficiently suppressed, and further the shift to a multimode is avoided. Alternatively, the laser light53cfrom the reflecting mirror43could enter the waveguide35directly without using the spot-size converter44. In the case, the spot diameter d of the emitted beam is required to be limited so that the spot size of the laser light entering the waveguide35becomes sufficiently small. That is, setting the limited spot diameter d is required in order to avoid a situation that a sufficient output power cannot eventually be obtained.

The surface plasmon antenna36includes: a propagation edge360that is an edge on which surface plasmon excited by the waveguide light53dpropagates; and a near-field light generating end surface36athat reaches the head end surface388and is a destination for the propagating surface plasmon. Further, a buffering portion50is a portion sandwiched between a portion of the side surface354of the waveguide35and a portion of the lower surface362including the propagation edge360of the surface plasmon antenna36. That is, a portion of the propagation edge360is covered with the buffering portion50. The buffering portion50acts for coupling the waveguide light53dwith the surface plasmon antenna36in a surface plasmon mode. Further, the propagation edge360plays a role of propagating the surface plasmon excited by the waveguide light53dto the near-field light generating end surface36a. Here, side surfaces of the waveguide35are defined as, out of end surfaces surrounding the waveguide35, end surfaces other than the end surface350on the head end surface388side and the rear end surface352on the opposite side. These side surfaces serve as surfaces on which the propagating waveguide light53dcan be totally reflected in the waveguide35that corresponds to a core. In the present embodiment, the side surface354of the waveguide35, a portion of which is in surface contact with the buffering portion50, is the upper surface of the waveguide35. And, the buffering portion50may be a portion of the overcoat layer38(FIG. 2), or may be provided as a new layer other than the overcoat layer38.

Specifically, the waveguide light53d, which has advanced to near the buffering portion50, is involved with the optical configuration including the waveguide35with a refractive index nNG, the buffering portion50with a refractive index nBFand the surface plasmon antenna36made of a metal, and induces a surface plasmon mode on the propagation edge360of the surface plasmon antenna36. That is, the waveguide light couples with the surface plasmon antenna36in a surface plasmon mode. The induction of the surface plasmon mode becomes possible by setting the refractive index nBFof the buffering portion50to be smaller than the index n of the waveguide35(nBF<nWG). Actually, evanescent light is excited within the buffering portion50under an optical boundary condition between the waveguide35as a core and the buffering portion50. Then, the evanescent light couples with the fluctuation of electric charge excited on the metal surface (propagation edge360) of the surface plasmon antenna36, and induces the surface plasmon mode, thereby excited is surface plasmon60. To be exact, there excited is surface plasmon polariton in this system because surface plasmon as elementary excitation is coupled with an electromagnetic wave. However, the surface plasmon polariton will be hereinafter referred to as surface plasmon for short. The propagation edge360is located closest to the waveguide35on the inclined lower surface362of the surface plasmon antenna36, and is just an edge where electric field tends to converge; thus surface plasmon can easily be excited on the edge360.

In the head structure as shown inFIGS. 3 and 6, the laser light53aemitted from the light-emitting surface400of the laser diode40preferably has a linear polarization in which the oscillation direction of electric field of the laser light is X-axis direction. Further, the laser light53bresultingly have a linear polarization in which the oscillation direction of electric field of the laser light is X-axis direction, and then the laser light53cand the laser light53dpreferably have a linear polarization in which the oscillation direction of electric field of the laser light is Z-axis direction, that is, perpendicular to the layer surface of the waveguide35. The setting these polarizations enables the waveguide light53dpropagating through the waveguide35to be coupled with the surface plasmon antenna36in a surface plasmon mode.

Returning toFIG. 6, the near-field light generating end surface36aof the surface plasmon antenna36is located close to the end surface3400eof the main magnetic pole3400reaching the head end surface388. And the propagation edge360extends to the near-field light generating end surface36a. Further, in the present embodiment, a portion of the propagation edge360on the end surface36aside (on the head end surface388side) has a shape of straight line or curved line extending so as to become closer to the end surface361of the surface plasmon antenna36as going toward the near-field light generating end surface36a, the end surface361being opposite to the propagation edge360. Surface plasmon60excited on the propagation edge360propagates on the propagation edge360along the direction shown by arrows61. The propagation of the surface plasmon60can occur under the condition that the propagation edge360of the surface plasmon antenna36is covered with a buffering portion50having a refractive index nBFequal to or higher than the refractive index nINof a material layer51covering the end surface361on the opposite side to the edge360. The propagation edge360can be made rounded to prevent surface plasmon from running off from the edge360, and thus to prevent the degradation of light use efficiency. The curvature radius of the rounded edge is preferably in the range of 6.25 to 20 nm. The preferable curvature radius enables near-field light62with an intensity of electric field sufficient for realizing a satisfactory thermally-assisted magnetic recording to be generated from the near-field light generating end surface36a.

According also toFIG. 6, in the present embodiment, the surface plasmon antenna36tapers in the height direction (Z-axis direction) near the head end surface388toward the near-field light generating end surface36a. Further, the surface plasmon antenna36has, in the present embodiment, a cross-section taken by YZ plane with a triangular shape, especially, has a predetermined triangular shape in the vicinity of the head end surface388. As a result, in the present embodiment, the near-field light generating end surface36ahas a triangular shape (FIG. 7) in which one apex is the end of the propagation edge360. Thus, surface plasmon60propagating on the propagation edge360reaches the near-field light generating end surface36ahaving an apex360aas a destination of the edge360. As a result, the surface plasmon60, namely, electric field converges in the near-field light generating end surface36a. Therefore, near-field light62is emitted from the end surface36atoward the magnetic recording layer of the magnetic disk10, and reaches the surface of the magnetic disk10to heat a portion of the magnetic recording layer of the magnetic disk10. This heating reduces the anisotropic magnetic field (coercive force) of the portion to a value with which write operation can be performed. Immediately after the heating, write field63generated from the main magnetic pole3400is applied to the portion to perform write operation. Thus, the thermally-assisted magnetic recording can be achieved.

Meanwhile, in a conventional case in which a plasmon antenna provided on the end surface of a head is directly irradiated with laser light propagating through the waveguide without using a surface plasmon antenna, most of the irradiated laser light has been converted into thermal energy within the plasmon antenna. As a result, the plasmon antenna has been brought to a very high temperature, for example, 500° C. (degrees Celsius). On the contrary, in the thermally-assisted magnetic recording with the surface plasmon antenna36according to the present invention, a surface plasmon mode is utilized, and near-field light62is generated by propagating surface plasmon60toward the head end surface388. This brings the temperature at the near-field light generating end surface36ato, for example, about 100° C. during the emission of near-field light, which is greatly reduced compared to the conventional. This reduction of temperature allows the protrusion of the near-field light generating end surface36atoward the magnetic disk10to be suppressed; thereby favorable thermally-assisted magnetic recording can be achieved.

Furthermore, the length LBFof the whole buffering portion50, that is, the portion through which the waveguide35and the surface plasmon antenna36are coupled with each other in a surface plasmon mode, is preferably larger than the wavelength λLof the laser light. In this preferable case, the coupling portion has an area markedly larger than a so-called “focal region” in the case that, for example, laser light is converged on a buffering portion and a surface plasmon antenna and coupled in a surface plasmon mode. Therefore, a configuration quite different from the system including such “focal region” can be realized in the present invention; thus, very stable coupling in the surface plasmon mode can be achieved. The induction of surface plasmon mode is disclosed in, for example, Michael Hochberg, Tom Baehr-Jones, Chris Walker & Axel Scherer, “Integrated Plasmon and dielectric waveguides”, OPTICS EXPRESS Vol. 12, No. 22, pp 5481-5486 (2004), U.S. Pat. Nos. 7,330,404 B2, and 7,454,095 B2.

Referring also toFIG. 6, the waveguide35and the buffering portion50are provided on −Z side (on the leading side), that is, on the opposite side to the main magnetic pole3400in relation to the surface plasmon antenna36. As a result, the propagation edge360is also positioned on the opposite side to the main magnetic pole3400within the surface plasmon antenna36. By applying such a configuration, even when a distance between the end surface3400egenerating write field of the main magnetic pole3400and the end surface36aemitting near-field light is sufficiently small, preferably 100 nm or less, the waveguide35can be separated sufficiently apart from the main magnetic pole3400. As a result, there can be avoided a situation in which a part of the waveguide light53is absorbed into the main magnetic pole3400made of metal and the amount of light to be converted into near-field light is reduced.

Further, the waveguide35can have a constant width in the track width direction (Y-axis direction); however, as shown inFIG. 6, the waveguide35can have a portion on the head end surface388side which has a narrower width in the track width direction (Y-axis direction). The width WWG2in the track width direction (Y-axis direction) of a portion of the waveguide35near the end surface350on the head end surface388side may be, for example, in the range approximately from 0.3 to 0.7 μm. Further, the thickness T (in Z-axis direction) of the waveguide35may be, for example, in the range approximately from 0.3 to 0.7 μm, and the height (length) HWG(in X-axis direction) may be, for example, in the range approximately from 10 to 300 μm.

Further, the side surfaces of the waveguide35: the upper surface354, the lower surface353, and both the side surfaces351in the track width direction (Y-axis direction) have a surface contact with the overcoat layer38(FIG. 2), that is, the insulating layers384and385(FIG. 3), except a portion having a surface contact with the buffering portion50. Here, the waveguide35is formed of a material with a refractive index n higher than the refractive index nOCof the constituent material of the overcoat layer38, made by using, for example, a sputtering method. For example, in the case that the wavelength λLof the laser light is 600 nm and the overcoat layer38is formed of SiO2(silicon dioxide: n=1.5), the waveguide35can be formed of, for example, Al2O3(alumina: n=1.63). Further, in the case that the overcoat layer38is formed of Al2O3(n=1.63), the waveguide35can be formed of, for example, SiOXNY(n=1.7-1.85), Ta2O5(n=2.16), Nb2O5(n=2.33), TiO (n=2.3-2.55) or TiO2(n=2.3-2.55). The just-described material structure of the waveguide35enables the propagation loss of laser light53dto be reduced due to the excellent optical characteristics of the constituent material. Further, the waveguide35acting as a core can provide the total reflection in all the side surfaces of the waveguide35due to the existence of the overcoat layer38acting as a clad. As a result, more amount of laser light53dcan reach the position of the buffering portion50, which improves the propagation efficiency of the waveguide35. In the present embodiment, a portion of the propagation edge360which is not opposed to the waveguide35(buffering portion50) may be covered with a constituent material of the overcoat layer38having a refractive index nOC, for example, a portion3850of the insulating layer385.

Furthermore, alternatively, the waveguide35may have a multilayered structure of dielectric materials in which the upper a layer is, the higher becomes the refractive index n of the layer. The multilayered structure can be realized, for example, by sequentially stacking dielectric materials of SiOXNYwith the composition ratios X and Y appropriately changed. The number of stacked layers may be, for example, in the range from 8 to 12. In the case that laser light53dhas a linear polarization in Z-axis direction, the above-described structure enables the laser light53dto propagate along the course closer to the buffering portion50. In this case, by choosing the composition and layer thickness in each layer, and the number of layers of the multilayered structure, the laser light53dcan propagate through the desired positions in Z-axis direction.

The surface plasmon antenna36is preferably formed of a conductive material of, for example, a metal such as Ag, Au, pd, Pt, Rh, Ir, Ru, Cu or Al, or an alloy made of at least two of these elements, especially an alloy with Ag as a main component. Further, the surface plasmon antenna36can have a width WNFin the track width direction (Y-axis direction) of the upper surface361, the width WNFbeing sufficiently smaller than the wavelength of the laser light53d, and being in the range of, for example, approximately 10 to 100 nm. And the surface plasmon antenna36can have a thickness TNF1(in Z-axis direction) sufficiently smaller than the wavelength of the laser light53d, the thickness TNF1being in the range of, for example, approximately 10 to 100 nm. Further, the length (height) HNF(in X-axis direction) can be set to be in the range of, for example, approximately 0.8 to 6.0 μm.

The buffering portion50is formed of a dielectric material having a refractive index nBFlower than the refractive index nWGof the waveguide35. For example, when the wavelength λLof the laser light is 600 nm and the waveguide35is formed of Al2O3(alumina: n=1.63), the buffering portion50can be formed of SiO2(silicon dioxide: n=1.46). Further, when the waveguide35is formed of Ta2O5(n=2.16), the buffering portion50can be formed of SiO2(n=1.46) or Al2O3(n=1.63). In these cases, the buffering portion50can be a portion of the overcoat layer38(FIG. 2) serving as a clad made of SiO2(n=1.46) or Al2O3(n=1.63). Further, the length LBF(in X-axis direction) of the buffering portion50, namely, the length of a portion sandwiched between the side surface354of the waveguide35and the propagation edge360, is preferably in the range of 0.5 to 5 μm, and is preferably larger than the wavelength λLof the laser light53d. In this preferable case, the portion has an area markedly larger than a so-called “focal region” in the case that, for example, laser light is converged on a buffering portion50and a surface plasmon antenna36and coupled in a surface plasmon mode. As a result, the portion enables very stable coupling in a surface plasmon mode. Further, the thickness TBF(in Z-axis direction) of the buffering portion50is preferably in the range of 10 to 200 nm. These length LBFand thickness TBFof the buffering portion50are important parameters for obtaining proper excitation and propagation of surface plasmon.

Also as shown inFIG. 6, a thermal conduction layer51is preferably provided on the head end surface388side between the surface plasmon antenna36and the first main pole portion3400a. The thermal conduction layer51is formed of, for example, an insulating material such as AlN, SiC or DLC, which has higher thermal conductivity compared with that of the overcoat layer38. Providing the thermal conduction layer51allows a part of the heat generated when the surface plasmon antenna36emits near-field light to get away to the main magnetic pole3400through the thermal conduction layer51. That is, the main magnetic pole3400can be utilized as a heatsink. As a result, excessive temperature rise of the surface plasmon antenna36can be suppressed, and there can be avoided unwanted protrusion of the near-field light generating end surface36aand substantial reduction in the light use efficiency of the surface plasmon antenna36.

The thickness TTCof the thermal conduction layer51corresponds to a distance DN-P(FIG. 7) on the head end surface388between the near-field light generating end surface36aand the end surface3400eof the main magnetic pole3400, and is preferably set to be a sufficiently small value of 100 nm or less. Further, the refractive index nINof the thermal conduction layer51is set equal to or lower than the refractive index nBFof the buffering portion50that covers the propagation edge360of the surface plasmon antenna36. That is, the propagation edge360of the surface plasmon antenna36is covered with a material having a refractive index nBFequal to or higher than the refractive index nINof a material covering the end surface361opposite to the edge360. This allows surface plasmon to propagate stably on the propagation edge360.

As shown also inFIG. 6, the main magnetic pole3400includes; the first main pole portion3400ahaving the end surface3400ereaching the head end surface388; and the second main pole portion3400b, the end portion on the head end surface388side of which is stacked on and overlapped with a portion of the first main pole portion3400aon the opposite side to the head end surface388. Further, the end portion of the upper yoke layer340on the head end surface388side is stacked on and overlapped with a portion of the second main pole portion3400bon the opposite side to the head end surface388. Namely, the upper yoke layer340and the main magnetic pole3400are formed in such a way as to become closer to the near-field light generating end surface36aof the surface plasmon antenna36when going toward the head end surface388. As a result, the end surface3400eof the main magnetic pole3400can be made sufficiently close to the near-field light generating end surface36a, under the condition that the upper yoke layer340and the main magnetic pole3400are at a sufficiently large distance from the waveguide35.

FIG. 7shows a plan view illustrating the shapes of the end surfaces of the surface plasmon antenna36and the electromagnetic transducer34on the head end surface388or in its vicinity.

As shown inFIG. 7, the main magnetic pole3400(the first main pole portion3400a) and the lower shield3450of the electromagnetic transducer34reach the head end surface388. The shape of the end surface3400eof the main magnetic pole3400on the head end surface388is, for example, a rectangle, a square or a trapezoid. Here, the above-described width WPis a length of the edge along the track width direction (Y-axis direction) of the end surface3400eof the main magnetic pole3400, and provides the width of a track formed on the magnetic recording layer of the magnetic disk in the magnetically dominant recording case. The width WPis in the range of, for example, approximately 0.05 to 0.5 μm.

Moreover, on the head end surface388, the near-field light generating end surface36aof the surface plasmon antenna36is positioned close to the end surface3400eof the main magnetic pole3400, on the leading side (−Z side) of the end surface3400e, and on the trailing side (+Z side) of the lower shield3450. Here, a distance DN-Pbetween the near-field light generating end surface36aand the end surface3400eis set to be a sufficiently small value of, for example, 100 nm or less. In the thermally-assisted magnetic recording, the near-field light generating end surface36afunctions as a main heating action part, and the end surface3400efunctions as a writing action part. Therefore, by setting the distance DN-Pas described above, write field with a sufficiently large gradient can be applied to a portion of the magnetic recording layer of the magnetic disk, the portion having been sufficiently heated. This enables a stable thermally-assisted write operation to be securely achieved. Further, according to the configuration shown inFIG. 6, a distance DW-Pbetween the waveguide35and the main magnetic pole3400is made sufficiently large while the distance DN-Pis set to a minute value as described above. That is, the waveguide35can be positioned sufficiently away apart from the main magnetic pole3400. As a result, there can be avoided a situation in which a part of the laser light is absorbed into the main magnetic pole3400made of metal, and the amount of light to be converted into near-field light is reduced.

Furthermore, in the present embodiment, the near-field light generating end surface36ahas a shape of isosceles triangle on the head end surface388, which has a bottom edge361aon the trailing side (+Z side) and an apex on the leading side (−Z side) that is an end360aof the propagation edge360. The height TNF2of the near-field light generating end surface36ais preferably 30 nm or less, and is more preferably 20 nm or less. Thereby, the near-field-light emitting position on the end surface36abecomes close to the edge361aon the trailing side, that is, closer to the end surface3400eof the main magnetic pole3400. Further, the apex angle θNFof the apex360aof the isosceles triangle is preferably in the range of 60 to 130 degrees.

FIGS. 8ato8eshow schematic diagrams illustrating various embodiments regarding components of the thermally-assisted magnetic recording head according to the present invention.

In the embodiment shown inFIG. 8a, the configuration in the electromagnetic transducer including such as the upper yoke layer340, the main magnetic pole3400and the lower shield3450is the same as that shown inFIG. 3. However, there is not provided a surface plasmon antenna for generating near-field light. Instead of that, the end surface700of a waveguide70reaches the head end surface388, and the laser light generated from the laser diode40is emitted from the end surface700through the binary lens42, the reflecting mirror43, the spot-size converter44and the waveguide35. The emitted light performs the heating of the magnetic recording layer of the magnetic disk and thus the thermal assist. Utilizing this optical system enables the thermally-assisted magnetic recording with use of the surface-emitting laser diode40provided in the element-integration surface2102.

In the embodiment shown inFIG. 8b, a plasmon antenna72formed of a metal piece is added into the configuration shown inFIG. 8a. The plasmon antenna72is disposed at the end surface710of a waveguide71so as to be exposed in the head end surface388. When the end of the plasmon antenna72opposite to the exposed end surface is irradiated with the waveguide light that has propagated through the waveguide71, the plasmon antenna72emits near-field light from the exposed end surface toward the magnetic disk. The near-field light performs the heating of the magnetic recording layer of the magnetic disk and thus the thermal assist. Utilizing this optical system also enables the thermally-assisted magnetic recording with use of the surface-emitting laser diode40provided in the element-integration surface2102.

In the embodiment shown inFIG. 8c, a main magnetic pole7300and a yoke layer730are provided on the trailing side (−Z side) of the waveguide35, and a trailing shield7400and a yoke layer740are disposed on the trailing side (−Z side) of the main magnetic pole7300. That is, in the present embodiment, the positional relationship in the stacking direction (Z-axis direction) between the main magnetic pole with the yoke layer coupled to the pole and the shield with the yoke layer coupled to the shield is reverse to that of the electromagnetic transducer34shown inFIG. 3. Further, whereas the waveguide35in the embodiment shown inFIG. 3extends between both yoke layers, the waveguide75in the present embodiment is disposed on the leading side from both yoke layers. Alternatively, a surface plasmon antenna may be provided on the head end surface388side of the waveguide75as in the embodiment shown inFIG. 3, or there may be provided a plasmon antenna as in the embodiment shown inFIG. 8b. By utilizing these optical systems and electromagnetic transducers, the thermal-assisted magnetic recording can also be performed with use of the surface-emitting laser diode40provided in the element-integration surface2102.

In the embodiment shown inFIG. 8d, a prism76is provided as a light-path changer, instead of the reflecting mirror43in the near-field light generating optical system of the embodiment shown inFIG. 3. The prism76reflects totally a laser light53b′ converged by the binary lens42on the prism plane760. The totally-reflected laser light53c′ is directed toward the spot-size converter44′. The prism76is formed of a material having a larger refractive index than that of the surrounding overcoat layer38, and further, its optical condition is set in such a way that the critical angle of the reflection at the prism plane760is equal to or less than the incident angle (45° inFIG. 8d) of the laser light53b′ at the prism plane760.

In the embodiment shown inFIG. 8e, a photonic-crystal type surface-emitting laser diode77is fixed on a holder78in such a way that an n-electrode77aof the diode77is electrically connected with the holder78. The holder78is formed of a metal with high thermal conductivity such as Cu. The emitting surface770of the laser diode77is opposed to the upper surface389of the overcoat layer38with a predetermined distance (or with a surface contact to each other). Further, provided are a terminal electrode790electrically connected with a p-electrode77jpositioned on the light-emitting surface770and a terminal electrode791electrically connected with the holder78. The laser diode77can operate by applying a predetermined voltage between these terminal electrodes790and791. In the present embodiment, the holder78functions as a heatsink as well as a conduction path for applying the voltage to the laser diode77. The sufficient heat-dissipation during the operation of the laser diode77with use of the holder78enables the light-emitting operation of the laser diode77to be more stable.

Other various embodiments are possible than the embodiments shown inFIGS. 8ato8e. Actually, various types of thermally-assisted magnetic recording heads can be provided by utilizing the configuration according to the present invention, in which a laser light emitted from the light-emitting surface of a laser diode that comprises a photonic-band layer is adjusted by using a diffraction optical element and a light-path changer, and then is guided into a waveguide.

FIG. 9ashows a cross-sectional view illustrating another embodiment that includes a light detector for controlling light output power in the thermally-assisted magnetic recording head according to the present invention. AndFIG. 9bshows a schematic view illustrating an alternative of binary lens in the embodiment including a light detector for controlling light output power. Further,FIG. 9cshows a schematic view illustrating a comparative example that includes a light detector for controlling light output power.

According to the embodiment ofFIG. 9a, a near-field light generating optical system is provided in the element-integration surface2102, which includes a laser diode40, a binary lens42, and so on, as the embodiment shown inFIG. 3. Laser light83emitted from the light-emitting surface400of the laser diode40propagates through the binary lens42and so on to be used for thermal assist, also as in the embodiment shown inFIG. 3. However, in the present embodiment, a photodiode80is provided on the upper surface389of the overcoat layer38as well as the laser diode40is. The photodiode80is a light detector that measures the intensity of a light emitted from the laser diode40in order to adjust the light output power of the laser diode40. Alternatively, other optical sensors such as a photo-resistor can be used as the light detector, instead of the photodiode80.

Furthermore, a reflecting mirror81is provided as a detective light-path changer in the midway of the light-path of laser light83emitted from the light-emitting surface400. A part of the laser light83is changed in its path direction by the reflecting mirror81, and reaches a light-receiving window820of the photodiode80through a reflecting mirror82as another detective light-path changer provided down below the photodiode80. The photodiode80detects the part of the laser light83as a monitor light, measures its light intensity, and then outputs the measuring result. Alternatively, a prism can be used as a detective light-path changer, instead of the reflecting mirror81and/or the reflecting mirror82.

Generally, a laser diode is a semiconductor element; thus, the intensity of the outputted laser light varies under the change in use environment temperature, or the change in temperature due to the heat generated from the laser diode. Therefore, especially in the configuration in which a laser diode is mounted directly in the slider substrate of a head, it becomes a significant problem to hold the intensity of (near-field) light used for thermal assist constant, in response to the actual temperature during driving the head, thereby to stabilize the recording performance. As a countermeasure against the problem, in the present embodiment, the output power of the light emitted from the laser diode40is continuously measured and monitored by using the photodiode80, which enables the feedback control of the light output power. By performing the control, it becomes possible to suppress the variation due to temperature change and further over time in light output power of the laser diode40, thereby to stabilize the intensity of (near-field) light with which the magnetic recording layer of the magnetic disk is irradiated. As a result, there can be ensured the appropriate heating of the magnetic recording layer.

As shown inFIG. 9b, alternatively, a binary lens42″ can be used instead of the binary lens42and the reflecting mirror81, a part of the binary lens42″ acting as a detective light-path changer. The part87of the binary lens42″ is a reflecting mirror (or prism), and a part of the laser light emitted from the light-emitting surface400of the laser diode40can be directed toward the reflecting mirror82by being reflected at the part87. Using such a binary lens42″ can reduce the number of optical components.

Returning toFIG. 9a, the reflecting mirrors81and82can be provided, in the stacking direction (Z-axis direction), near the laser diode40and the photodiode80, respectively. Further, the reflecting mirrors81and82can be set to be as close to each other as possible within the bounds of not bringing about obstacles in fixing the laser diode40and the photodiode80onto the upper surface389. Actually, the laser light83emitted from the light-emitting surface400of the laser diode40remains an almost-collimated (almost-parallel) light with a large cross-section, from the beginning of the emission. Therefore, it becomes easy to take out a part of the laser light83immediately after the emission without significant loss of the amount of light to be used for thermal assist. As a result, the light path of monitor light from the laser diode40to the photodiode80can be made sufficiently short, which enables a reliable feedback control by detecting the monitor light with a sufficient intensity. On the contrary, as a comparative example shown inFIG. 9c, in the case of using a surface-emitting laser diode86such as a VCSEL for a light source, the size of the beam spot near the emitting point is extremely small, for example, in the range of approximately 0.5 to 5.0 μm. Therefore, a reflecting mirror85for taking out a part of the emitted laser light84has to be disposed in a position where the laser light84is diverged to a considerable degree in order not to lose a significant amount of light to be used for thermal assist. As a result, the reflecting mirror85is required to be at a considerable distance in the stacking direction (Z-axis direction) from the laser diode86. Therefore, the light path of monitor light inevitably becomes significantly long compared with the present embodiment (FIG. 9a) with use of the photonic-crystal type surface-emitting laser diode40.

InFIG. 9a, the photodiode80is positioned apart away in +Y direction from the laser diode40. However, alternatively, the photodiode80may be provided apart away in other direction from the laser diode40by disposing detective light-path changers appropriately. Further, the laser diode40and the photodiode80may be integrated as a single element, and then provided on the upper surface389of the overcoat layer38.

FIG. 10shows a block diagram illustrating the circuit structure of the recording/reproducing and light-emission control circuit13of the magnetic disk apparatus shown inFIG. 1. In the embodiment shown in this figure, the target to be controlled is the head, as shown inFIG. 9a, capable of performing the feedback adjustment for the light output power of the laser diode40.

According toFIG. 10, reference numeral90indicates a control LSI,91indicates a write gate for receiving recording data from the control LSI90,92indicates a write circuit,93indicates a ROM that stores a control table or the like for controlling the value of drive current supplied to the laser diode40,95indicates a constant current circuit for supplying sense current to the MR element33,96indicates an amplifier for amplifying the output voltage from the MR element33,97indicates a demodulator circuit for outputting reproduced data to the control LSI90,98indicates a temperature detector, and99indicates a control circuit for controlling the laser diode40, respectively.

The recording data outputted from the control LSI90is supplied to the write gate91. The write gate91supplies recording data to the write circuit92only when a recording control signal outputted from the control LSI90instructs a write operation. The write circuit92applies write current according to this recording data to the write coil layer343, and then a write operation is performed onto the magnetic disk with write field generated from the main magnetic pole3400. Further, a constant current flows from the constant current circuit95into the MR multilayer332only when the reproducing control signal outputted from the control LSI90instructs a read operation. The signal reproduced by the MR element33is amplified by the amplifier96, demodulated by the demodulator circuit97, and then, the obtained reproduced data is outputted to the control LSI90.

The laser control circuit99receives a laser ON/OFF signal and a laser power control signal, which are outputted from the control LSI90. When the laser ON/OFF signal indicates an ON operation instruction, a drive current with an oscillation threshold value or more is applied into the laser diode40. Thereby, the laser diode40emits light; then the laser light goes through the binary lens42, the reflecting mirror43and the spot-size converter44, and propagates through the waveguide35, and then couples with the surface plasmon antenna36in a surface plasmon mode. As a result, near-field light is generated from the end of the surface plasmon antenna36, and then the magnetic recording layer of the magnetic disk is irradiated and heated with the near-field light. The value of the drive current in this occasion is controlled to such a value that the laser diode40emits a laser light whose output is specified by the laser power control signal.

The control LSI90generates the laser ON/OFF signal, adjusting the timing of the signal generation according to recording/reproducing operations, and determines the value of the laser power control signal by referring the value of temperature in the magnetic recording layer of the magnetic disk or the like, which is measured by the temperature detector98, based on the control table in the ROM93. Here, the control table may include data about the relation between the drive current value and the mount of temperature increase due to thermal-assist operation in the magnetic recording layer, and data about the temperature dependence of the anisotropic magnetic field (coercive force) of the magnetic recording layer, as well as data about the temperature dependences of the oscillation threshold value and the characteristics of light output power vs. drive current. Thus, by providing the system of the laser ON/OFF signal and the laser power control signal independently from the recording/reproducing control signal system, it becomes possible to realize not only a current supply to the laser diode40linked simply with the recording operation but also more diversified current supply modes. Further, the photodiode80measures and monitors the output power of light emitted from the laser diode40, and sends the measured values to the laser control circuit99. The laser control circuit99performs the feedback adjustment with use of the measured values, and adjusts the drive current applied to the laser diode40in such a way that the laser diode40emits a laser light with an output power that is specified by the laser power control signal.

Obviously, the circuit structure of the recording/reproducing and light-emission control circuit13is not limited to that shown inFIG. 10. It is also possible to specify write and read operations by using signals other than the recording control signal and reproducing control signal.

As described above, according to the present invention, there is provided a thermally-assisted magnetic recording head in which a light source having a sufficiently high output power is disposed in the element-integration surface of the slider substrate to achieve improvement of mass-productivity. Further, it becomes possible to guide light efficiently into a desired position on the opposed-to-medium surface side by using optical elements that are hardly affected adversely by the change of surrounding temperature. Furthermore, a thermally-assisted magnetic recording head is provided, in which there is disposed, in the element-integration surface, a light source capable of emitting a light that is suitable for transforming the light into a light beam with a minute spot size, or is suitable for monitoring the output power of the light. Thus, the present invention can perform a satisfactory thermally-assisted magnetic recording, and contribute to the achievement of higher recording density, for example, exceeding 1 Tbits/in2.

All the foregoing embodiments are by way of example of the present invention only and not intended to be limiting, and many widely different alternations and modifications of the present invention may be constructed without departing from the spirit and scope of the present invention. Accordingly, the present invention is limited only as defined in the following claims and equivalents thereto.