Thermally-assisted magnetic recording head having optimal reflecting position inside waveguide

A thermally assisted magnetic head including a slider and a light source-unit. The slider includes a slider substrate and a magnetic head part. The light source-unit includes a laser diode and a sub-mount. The magnetic head part includes a medium-opposing surface, a light source-opposing surface and a waveguide which guides laser light from the light source-opposing surface to the medium-opposing surface. The thermally assisted magnetic head includes an optimal-structure which the following optimizing conditional expression, concerning an inlet-optical path length L1 of an inlet-interval of the waveguide, and an outlet-optical path length L2 of an outlet-interval, is satisfied, m1×L1=L2 (m1 is a natural number).

BACKGROUND

Field of the Invention

The present invention relates to a thermally assisted magnetic head recording data on a magnetic recording medium by thermally assisted magnetic recording using near-field light, a head gimbal assembly and a hard disk drive each having the thermally assisted magnetic head.

Related Background Art

In recent years, as magnetic disk drives have been increasing their recording densities, thin-film magnetic heads recording data on a magnetic recording media have been required to further improve their performances. As the thin-film magnetic heads, those of composite type having a structure in which a reproducing head having a magnetoresistive device (hereinafter, referred to also as an “MR device”) for read and a recording head having an electromagnetic coil device for write are laminated have been conventionally in wide use. In a magnetic disk drive, the thin-film magnetic head is provided on a slider which very slightly floats from the magnetic recording medium.

Incidentally, the magnetic disk drive records data by magnetizing magnetic fine particles on the magnetic recording medium using the recording head. In order to increase the recording density of the magnetic recording medium, it is effective to make the magnetic fine particles smaller.

When the magnetic fine particles are made smaller, however, there arises a problem that the magnetization thereof becomes unstable with respect to heat as the particles reduce in volume, thereby increasing the possibility that the data recorded on the magnetic recording medium is lost. To solve the problem, it is effective to increase the magnetic energy of the magnetic fine particles to thereby enhance the stability of magnetization. When the magnetic energy of the magnetic fine particles is increased, however, there arises another problem that the coercive force (difficulty in reversing magnetization) of the magnetic recording medium increases to deteriorate the data recording performance.

To solve such problems, a method called thermally assisted magnetic recording has been conventionally proposed. When recording data on a magnetic recording medium having a large coercive force, the thin-film magnetic head employing the thermally assisted magnetic recording (hereinafter, referred to as a “thermally assisted magnetic head”) records data while instantaneously heating and thereby increasing the temperature of a portion of the magnetic recording medium where data will be recorded.

Since the magnetic fine particles decrease in coercive force when the temperature is increased, instantaneous heating makes it possible to record data even on the magnetic recording medium having a high coercive force at room temperature. The portion of the magnetic recording medium where the data has been recorded is decreased in temperature after the recording of data and thereby increases in coercive force. Therefore, by using the thermally assisted magnetic head, it becomes possible to make the magnetic fine particles finer as well as stabilize recording in the magnetic disk drive.

On the other hand, near-field light is used as means for heating the magnetic recording medium in the conventional thermally assisted magnetic head. When light enters an opening smaller than the wavelength of light, the light slightly seeps from the opening and locally exists near the opening. The light locally existing near the opening is called near-field light. The near-field light is confined in a region much smaller than that of a spot light obtained by collecting light using a lens, so that use of the near-field light makes it possible to heat only a limited extremely small recording region of the magnetic recording medium. A conventional technology concerning the thermally assisted magnetic recording is disclosed in, for example, US 2012-0155232 (also called patent document 1).

By the way, in the thermally assisted magnetic head, because the recording head is formed on the slider, the structure, which laser light for generating the near-field light is guided to the medium-opposing surface of the slider, is important. The following structure is conventionally known as the structure.

The structure which the light source is provided on the surface of the slider (for example, US2015-0364899 (also called patent document 2), US2011-0205661 (also called patent document 3), US2015-154988 (also called patent document 4), US 2015-0380035 (also called patent document 5), JP2012-084216 (also called patent document 6)).

SUMMARY OF THE INVENTION

There is a following problem in the thermally assisted magnetic head, having the above-described conventional structure. The problem is caused by optical feedback of a laser diode.

When laser light is emitted from the laser diode as the light source, part of laser light is reflected on the surface of the slider (inlet of the waveguide), after that, the reflected light returns to the laser diode as optical feedback.

Besides, laser light is also reflected not only on the inlet of the waveguide but also on the parts (also referred to as laser light reflecting parts) such as the inside of the waveguide, a near-field light generating element (element for generating near-field light) and the surface of the recording medium or the like. The reflected laser light returns to the laser diode as optical feedback, in all these cases.

In this case, standing wave conditions collapse by mixing optical feedback, in the laser diode, unstable action, which is called “mode hopping”, which oscillation wavelength change suddenly, is caused. Thereby, optical power of the laser diode become unstable. Then, a recording characteristic of the thermally assisted magnetic head becomes unstable.

If reflectance (reflection rate), of the respective laser light reflecting parts, is lowered, thereby optical feedback is lowered. In this case, the part, which influences largest on the mode hopping, is the near-field light generating element. Therefore, it is preferable that reflectance of the near-field light generating element is lowered.

However, because the near-field light generating element is formed with metal, lowering the reflectance is limited.

On this point, because the waveguide is formed with dielectric, it is possible that reflectance is lowered, only on the inlet or inside of the waveguide. However, it is extremely difficult for the reflected light to become 0.

On the other hand, when the reflecting-position of the laser light is shifted, it brings shifting an interference pattern of laser light. Therefore, if the reflecting-position, of laser light in inside of the waveguide, is shifted, wavelength dependence of optical feedback change, thereby there is a possibility that unstableness of optical power is lowered.

However, the effective suggestion, concerning the optimal reflecting-position in inside of the waveguide, is not conventionally known, on the viewpoint that unstableness of optical power caused by the mode-hopping is lowered.

Hence the present invention is made to solve the above problem, and it is an object to provide a thermally assisted magnetic head, that the reflecting-position in inside of the waveguide is set up to the most suitable position so that the unstableness of optical power caused by the mode-hopping is lowered, the head gimbal assembly and the hard disk drive having the thermally assisted magnetic head.

To solve the above problem, the present invention is a thermally assisted magnetic head including: a slider; and a light source-unit joined to the slider, the slider includes a slider substrate and a magnetic head part formed on the slider substrate, the light source-unit includes a laser diode and a sub-mount which the laser diode is joined; the magnetic head part includes a medium-opposing surface opposing a magnetic recording medium, a light source-opposing surface arranged rear side of the medium-opposing surface and a waveguide which guides laser light, output from the laser diode, from the light source-opposing surface to the medium-opposing surface, the thermally assisted magnetic head includes an optimal-structure which the following optimizing conditional expression, concerning an inlet-optical path length L1of an inlet-interval of the waveguide from the light source-opposing surface to a reflecting-position of the laser light, and an outlet-optical path length L2of an outlet-interval from the reflecting-position to the medium-opposing surface, is satisfied.
m1×L1=L2 (m1isanatural number)

Further, the present invention provides a thermally assisted magnetic head including: a slider; and a light source-unit joined to the slider, the slider includes a slider substrate and a magnetic head part formed on the slider substrate, the light source-unit includes a laser diode and a sub-mount which the laser diode is joined; the magnetic head part includes a medium-opposing surface opposing a magnetic recording medium, a light source-opposing surface arranged rear side of the medium-opposing surface and a waveguide which guides laser light, output from the laser diode, from the light source-opposing surface to the medium-opposing surface, the thermally assisted magnetic head includes an optimal-structure which the following optimizing conditional expression, concerning an inlet-optical path length L1of an inlet-interval of the waveguide from the light source-opposing surface to a reflecting-position of the laser light, and a light-source optical path length L3of an internal waveguide of the laser diode, is satisfied.
m2×L1=L3 (m2isanatural number)

Further, the present invention provides a thermally assisted magnetic head including: a slider; and a light source-unit joined to the slider, the slider includes a slider substrate and a magnetic head part formed on the slider substrate, the light source-unit includes a laser diode and a sub-mount which the laser diode is joined; the magnetic head part includes a medium-opposing surface opposing a magnetic recording medium, a light source-opposing surface arranged rear side of the medium-opposing surface and a waveguide which guides laser light, output from the laser diode, from the light source-opposing surface to the medium-opposing surface, the thermally assisted magnetic head includes an optimal-structure which the following optimizing conditional expression, concerning a light-source optical path length L3of an internal waveguide of the laser diode and a waveguide-optical path length L4of all interval along length direction of the waveguide, is satisfied.
m3×L4=L3 (m3isanatural number)

Further, the present invention provides a thermally assisted magnetic head including: a slider; and a light source-unit joined to the slider, the slider includes a slider substrate and a magnetic head part formed on the slider substrate, the light source-unit includes a laser diode and a sub-mount which the laser diode is joined; the magnetic head part includes a medium-opposing surface opposing a magnetic recording medium, a light source-opposing surface arranged rear side of the medium-opposing surface and a waveguide which guides laser light, output from the laser diode, from the light source-opposing surface to the medium-opposing surface, the thermally assisted magnetic head includes an optimal-structure which at least any two of the following the first, second, third optimizing conditional expressions, concerning an inlet-optical path length L1of an inlet-interval of the waveguide from the light source-opposing surface to a reflecting-position of the laser light, an outlet-optical path length L2of an outlet-interval from the reflecting-position to the medium-opposing surface, a light-source optical path length L3of an internal waveguide of the laser diode and a waveguide-optical path length L4of all interval along length direction of the waveguide, are satisfied.
m1×L1=L2 (m1isanatural number)  first optimizing conditional expression
m2×L1=L3 (m2isanatural number)  second optimizing conditional expression
m3×L4=L3 (m3isanatural number)  third optimizing conditional expression

Further, it is possible that the waveguide includes a first dielectric member arranged the light source-opposing surface side and a second dielectric member arranged the medium-opposing surface side, and the boundary part, between the first dielectric member and the second dielectric member, is defined as the reflecting-position.

Further, the present invention provides a head gimbal assembly including a thermally assisted magnetic head, the thermally assisted magnetic head including: a slider; and a light source-unit joined to the slider, the slider includes a slider substrate and a magnetic head part formed on the slider substrate, the light source-unit includes a laser diode and a sub-mount which the laser diode is joined; the magnetic head part includes a medium-opposing surface opposing a magnetic recording medium, a light source-opposing surface arranged rear side of the medium-opposing surface and a waveguide which guides laser light, output from the laser diode, from the light source-opposing surface to the medium-opposing surface, the thermally assisted magnetic head includes an optimal-structure which the following optimizing conditional expression, concerning an inlet-optical path length L1of an inlet-interval of the waveguide from the light source-opposing surface to a reflecting-position of the laser light, and an outlet-optical path length L2of an outlet-interval from the reflecting-position to the medium-opposing surface, is satisfied.
m1×L1=L2 (m1isanatural number)

Further, the present invention provides a head gimbal assembly including a thermally assisted magnetic head, the thermally assisted magnetic head including: a slider; and a light source-unit joined to the slider, the slider includes a slider substrate and a magnetic head part formed on the slider substrate, the light source-unit includes a laser diode and a sub-mount which the laser diode is joined; the magnetic head part includes a medium-opposing surface opposing a magnetic recording medium, a light source-opposing surface arranged rear side of the medium-opposing surface and a waveguide which guides laser light, output from the laser diode, from the light source-opposing surface to the medium-opposing surface, the thermally assisted magnetic head includes an optimal-structure which the following optimizing conditional expression, concerning an inlet-optical path length L1of an inlet-interval of the waveguide from the light source-opposing surface to a reflecting-position of the laser light, and a light-source optical path length L3of an internal waveguide of the laser diode, is satisfied.
m2×L1=L3 (m2isanatural number)

Further, the present invention provides a head gimbal assembly including a thermally assisted magnetic head, the thermally assisted magnetic head including: a slider; and a light source-unit joined to the slider, the slider includes a slider substrate and a magnetic head part formed on the slider substrate, the light source-unit includes a laser diode and a sub-mount which the laser diode is joined; the magnetic head part includes a medium-opposing surface opposing a magnetic recording medium, a light source-opposing surface arranged rear side of the medium-opposing surface and a waveguide which guides laser light, output from the laser diode, from the light source-opposing surface to the medium-opposing surface, the thermally assisted magnetic head includes an optimal-structure which the following optimizing conditional expression, concerning a light-source-optical path length L3of an internal waveguide of the laser diode and a waveguide-optical path length L4of all interval along length direction of the waveguide, is satisfied.
m3×L4=L3 (m3isanatural number)

Then, the present invention provides a hard disk drive including a head gimbal assembly having a thermally assisted magnetic head, and a magnetic recording medium opposing the thermally assisted magnetic head, the thermally assisted magnetic head including: a slider; and a light source-unit joined to the slider, the slider includes a slider substrate and a magnetic head part formed on the slider substrate, the light source-unit includes a laser diode and a sub-mount which the laser diode is joined; the magnetic head part includes a medium-opposing surface opposing a magnetic recording medium, a light source-opposing surface arranged rear side of the medium-opposing surface and a waveguide which guides laser light, output from the laser diode, from the light source-opposing surface to the medium-opposing surface, the thermally assisted magnetic head includes an optimal-structure which the following optimizing conditional expression, concerning an inlet-optical path length L1of an inlet-interval of the waveguide from the light source-opposing surface to a reflecting-position of the laser light, and an outlet-optical path length L2of an outlet-interval from the reflecting-position to the medium-opposing surface, is satisfied.
m1×L1=L2 (m1isanatural number)

Then, the present invention provides a hard disk drive including a head gimbal assembly having a thermally assisted magnetic head, and a magnetic recording medium opposing the thermally assisted magnetic head, the thermally assisted magnetic head including: a slider; and a light source-unit joined to the slider, the slider includes a slider substrate and a magnetic head part formed on the slider substrate, the light source-unit includes a laser diode and a sub-mount which the laser diode is joined; the magnetic head part includes a medium-opposing surface opposing a magnetic recording medium, a light source-opposing surface arranged rear side of the medium-opposing surface and a waveguide which guides laser light, output from the laser diode, from the light source-opposing surface to the medium-opposing surface, the thermally assisted magnetic head includes an optimal-structure which the following optimizing conditional expression, concerning an inlet-optical path length L1of an inlet-interval of the waveguide from the light source-opposing surface to a reflecting-position of the laser light, and a light-source optical path length L3of an internal waveguide of the laser diode, is satisfied.
m2×L1=L3 (m2isanatural number)

Then, the present invention provides a hard disk drive including a head gimbal assembly having a thermally assisted magnetic head, and a magnetic recording medium opposing the thermally assisted magnetic head, the thermally assisted magnetic head including: a slider; and a light source-unit joined to the slider, the slider includes a slider substrate and a magnetic head part formed on the slider substrate, the light source-unit includes a laser diode and a sub-mount which the laser diode is joined; the magnetic head part includes a medium-opposing surface opposing a magnetic recording medium, a light source-opposing surface arranged rear side of the medium-opposing surface and a waveguide which guides laser light, output from the laser diode, from the light source-opposing surface to the medium-opposing surface, the thermally assisted magnetic head includes an optimal-structure which the following optimizing conditional expression, concerning a light-source optical path length L3of an internal waveguide of the laser diode and a waveguide-optical path length L4of all interval along length direction of the waveguide, is satisfied.
m3×L4=L3 (m3isanatural number)

The present invention will be more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following, embodiments of the present invention will be described with reference to the drawings. Note that the same components will be referred to with the same numerals or letters, while omitting their overlapping descriptions.

(Structure of the Thermally Assisted Magnetic Head)

To begin with, structure of the thermally assisted magnetic head according to the embodiment of the present invention will be explained with reference toFIG. 1toFIG. 5. Here,FIG. 1is a perspective view of the thermally assisted magnetic head180according to the embodiment of the present invention,FIG. 2is a side view of the thermally assisted magnetic head180according to the embodiment of the present invention,FIG. 3is a perspective view, with enlargement, of the principal part of the thermally assisted magnetic head180.FIG. 4is a sectional view of principal part taken along the line4-4inFIG. 1,FIG. 5is a front view, partially omitted, illustrating a medium-opposing surface (Air Bearing Surface, which will hereinafter be referred also to as “ABS”)101of the magnetic head part100.

The thermally assisted magnetic head180has a slider120and a light source-unit160joined to the slider120. The thermally assisted magnetic head180has a complex-slider-structure which the light source-unit160is joined to the slider120.

The slider120has a slider-substrate110and the magnetic head part100formed on the slider-substrate110.

The slider-substrate110is made of ceramic material such as aluminum oxide-titanium carbide (Al2O3.TiC) or the like, and it is formed in a rectangular parallelepiped shape. The slider-substrate110has the ABS101as the medium-opposing surface, opposing to the magnetic recording medium, a light source placing surface111, arranged in the rear side of the ABS101. A part, of the light source placing surface111, of the magnetic head part100side is a light source-opposing surface102. The light source-opposing surface102opposes to the later-described laser diode130of the light source-unit160.

In the thermally assisted magnetic head180, the reflecting-position of laser inside of the core layer25is set up to a later-described optimal reflecting-position25p. Therefore, the unstableness of optical power caused by the mode-hopping is lowered.

Subsequently, the magnetic head part100will be explained with mainly reference toFIG. 4toFIG. 5. The magnetic head part100has a reproducing head90and a recording head91. The magnetic head part100has a structure which the reproducing head90and the recording head91are stacked.

The reproducing head90has an MR device5, arranged near the ABS101, for detecting a magnetic signal. The reproducing head90comprises a lower shield layer3, a lower shield gap film4, an upper shield gap film6and an upper shield layer7.

Then, an insulating layer2is further formed on a thin-film laminated surface111aof the slider-substrate110, and the lower shield layer3made of a magnetic material is formed on the insulating layer2. Further, the lower shield gap film4, as an insulating film, is formed on the lower shield layer3, and the upper shield gap film6shielding the MR device5is formed on the lower shield gap film4. The upper shield layer7made of a magnetic material is formed on the upper shield gap film6, and an insulating layer8is formed on the upper shield layer7.

The MR device5is constituted by a magnetosensitive film exhibiting a magnetoresistive effect, such as AMR (anisotropic magnetoresistive), GMR (giant magnetoresistive), and TMR (tunneling magnetoresistive) devices.

The recording head91has a thin-film coil12, a return magnetic layer20, a core layer25, a lower dielectric-layer24, an upper dielectric-layer26, a near-field light generating layer28, an overcoat layer34, a main magnetic pole layer40, and a linking magnetic pole layer45, and has a structure in which they are stacked on the thin-film laminated surface111a.

The thin-film coil12has four turn parts. The thin-film coil12is wound like a flat spiral about a later-described yoke magnetic pole layer42of the main magnetic pole layer40.

The four turn parts are arranged at respective positions having different distances from the ABS101. Among them, the turn part12D is a part arranged at a position most distant from the ABS101among the four turn parts of the thin-film coil12. The four turn parts are insulated from each other by a photoresist13.

When a current modulated according to data to be recorded on the magnetic recording medium flows through the thin-film coil12, the current causes the thin-film coil12to generate a recording magnetic field.

The return magnetic pole layer20has a connecting magnetic pole layer21, and a rear magnetic pole layer22. The connecting magnetic pole layer21has a magnetic pole end face21aarranged within the ABS101and has a portion that is more distant from the ABS101than is the magnetic pole end face21abeing embedded in the insulating layer8. The connecting magnetic pole layer21has a size reaching a position more distant from the ABS101than is the turn part12D. To the connecting magnetic pole layer21, the rear magnetic pole layer22is joined at a position more distant from the ABS101than is the turn part12D.

The rear magnetic pole layer22is arranged at a position more distant from the ABS101than is the turn part12D, and it is joined to the connecting magnetic pole layer21and the later-described linking magnetic pole layer45.

The return magnetic pole layer20is provided to return a magnetic flux to the main magnetic pole layer40. When a magnetic flux generated by the recording magnetic field is emitted from a later-described magnetic pole end face41gof the main magnetic pole layer40to the magnetic recording medium, the magnetic flux flows back to the return magnetic pole layer20via the magnetic recording medium (a not-depicted soft magnetic layer in detail). This magnetic flux passes through the linking magnetic pole layer45and reaches the main magnetic pole layer40.

The core layer25is a waveguide which guides laser light, generated by the later-described laser diode130of the light source-unit160, from the light source-opposing surface102to the ABS101. The core layer25, as illustrated inFIG. 4, is formed along with a depth direction, passing through between the linking magnetic pole layer45, from the ABS101to the light source-opposing surface102.

The core layer25is formed with dielectric such as tantalum oxide (TaOx) or the like. For example, the core layer25is able to be formed with Ta2O5(for example, the refractive index is about 2.16).

The core layer25is formed so as to be accommodated in a later-described concave part26cof the upper dielectric-layer26, on an upper surface24dof the lower dielectric-layer24. Further, an upper surface25dand both side surfaces, of the core layer25, are in contact with the upper dielectric-layer26, and a lower surface25e, of the core layer25, is in contact with the lower dielectric-layer24.

Then, the upper dielectric-layer26and the lower dielectric-layer24are arranged in the surrounding of the core layer25, the cladding layer is constituted by the upper dielectric-layer26and the lower dielectric-layer24.

The upper dielectric-layer26is formed in a substantially flat plate shape having a width larger than the width of the magnetic pole end part layer41. The upper dielectric-layer26is formed with dielectric, having the lower refractive index than the core layer25, for example, such as aluminum oxide (AlOx) or the like. For example, the upper dielectric-layer26is able to be formed with alumina (Al2O3, for example, the refractive index is about 1.63). Then, the concave part26cis formed on the lower surface26eof the upper dielectric-layer26, the core layer25is accommodated in the concave part26c.

The lower dielectric-layer24is formed so as to be in contact with the lower surface25eof the core layer25and the lower surface26eof the upper dielectric-layer26. The lower dielectric-layer24is able to be formed with dielectric such as aluminum oxide (AlOx) or the like, similar with the upper dielectric-layer26.

For example, the lower dielectric-layer24is able to be formed with alumina (Al2O3).

The near-field light generating layer28has a structure formed in a rectangular shape as a whole, seen from the ABS101.

The near-field light generating layer28is made of metal and formed of, for example, one of Au, Ag, Al, Cu, Pd, Pt, Rh, Ir or an alloy made of a plurality of those elements.

The near-field light generating layer28has a bottom part28c. The bottom part28cis arranged at the deepest positions of the near-field light generating layer28. The bottom part28cextends from the ABS101in the depth direction. The end surface of the bottom part28con the ABS101side is arranged within the ABS101. This end surface is a generating end part28e. The generating end part28egenerates near-field light for heating the magnetic recording medium.

The main magnetic pole layer40has the magnetic pole end part layer41and the yoke magnetic pole layer42. The magnetic pole end part layer41and the yoke magnetic pole layer42have a symmetrical structure formed to be bilaterally symmetrical about a front end part41c.

The front surface including the front end part41cconstitutes the magnetic pole end surface41g. The magnetic pole end surface41gis arranged within the ABS101. The yoke magnetic pole layer42is joined to an upper surface41eof the magnetic pole end part layer41.

The yoke magnetic pole layer42has a rear magnetic pole layer42a, a middle magnetic pole layer42b, and a front magnetic pole layer42c. The yoke magnetic pole layer42has a curved structure extending from the ABS101in the depth direction and leading to the linking magnetic pole layer45straddling the thin-film coil12.

The rear magnetic pole layer42ais arranged at a position more distant from the ABS101than are the four turn parts of the thin-film coil12. The rear magnetic pole layer42ahas a lateral width larger than that of the middle magnetic pole layer42b(the largest lateral width in the yoke magnetic pole layer42) and is joined to the linking magnetic pole layer45. The middle magnetic pole layer42bis arranged above the thin-film coil12. The middle magnetic pole layer42bis connected to the rear magnetic pole layer42aand the front magnetic pole layer42c. The middle magnetic pole layer42bhas a lateral width gradually getting smaller as it approaches to the ABS101. The front magnetic pole layer42cis formed in a downward curved structure getting closer to the magnetic pole end part layer41as it approaches to the ABS101. The front magnetic pole layer42cis joined to the surface41eof the magnetic pole end part layer41.

The linking magnetic pole layer45is arranged in a manner to hold the core layer25from both right and left sides at a position more distant from the ABS101than is the thin-film coil12. Further, the linking magnetic pole layer45is joined to the rear magnetic pole layer22. The linking magnetic pole layer45magnetically links the return magnetic pole layer20to the main magnetic pole layer40, and has a role of returning, to the main magnetic pole layer40, the magnetic flux flown back to the return magnetic pole layer20.

Subsequently, the light source-unit160will be explained. The light source-unit160has the laser diode130and the sub-mount150. The laser diode130is joined to the sub-mount150to constitute the light source-unit160.

As illustrated inFIG. 4, the laser diode130has an n-substrate140, a stripe n-electrode141having band like shape, a light emitting layer145, and a stripe p-electrode142having band like shape, and it has a rectangle parallelepiped shape. In addition, the stripe n-electrode141is joined to a surface on the outside of the n-substrate140. Further, the light emitting layer145is formed on a side of the n-substrate140opposite to the stripe n-electrode141, and the stripe p-electrode142is joined on the light emitting layer145, via a ground layer143.

The light emitting layer145has an active layer146, an n-cladding layer147, and a p-cladding layer148, and has a structure in which the active layer146is sandwiched between the n-cladding layer147and the p-cladding layer148.

Then, the laser diode130is joined to the sub-mount150so that the active layer146opposes to the core layer25, and an emitting part149is arranged in a part, of the light emitting layer145, opposing to the core layer25. The emitting part149is a part, of the laser diode130, which emits the laser light. The laser diode130has an opposing-surface131. The opposing-surface131is a part, of the surface of the laser diode130, which opposes to the sub-mount150. The opposing-surface131opposes to a later-described joint-surface151of the sub-mount150.

The sub-mount150is made of a silicon (Si), and it is formed in a rectangular parallelepiped shape. The sub-mount150has a size larger than the laser diode130. Further, the sub-mount150is able to be formed with semiconductor material such as GaAs, SiC or the like, or a ceramic material such as aluminum oxide-titanium carbide (Al2O3.TiC) or the like.

The sub-mount150of the light source-unit160, having the above-described constitution, is joined to the slider120to constitute the thermally assisted magnetic head180.

In the thermally assisted magnetic head180, the reflecting-position of laser light in inside of the core layer25(referred to also as an “internal reflecting-position”) is optimized. Thereby, as illustrated inFIG. 6, in the thermally assisted magnetic head180, the internal reflecting-position is set up to an optimal reflecting-position25p.

It is necessary that the interference pattern of laser light becomes a pattern which wavelength dependence of the reflected light becomes periodic, so that the internal reflecting-position is set up to the optimal reflecting-position25p. The interference pattern, of laser light concerning the laser diode130and the core layer25, changes according to the following five parameters p1) to p5) (also referred to as “interference parameter”).

p1) the length of the core layer25

p2) the effective refractive index of the core layer25

p3) intervals of the core layer25from the ABS101or the light source-opposing surface102to the reflecting-position

p4) the length of the internal waveguide of the laser diode130

p5) the effective refractive index of the internal waveguide

Therefore, it is necessary that the interference parameters p1) to p5) are set up in a certain range so that the internal reflecting-position is set up to the optimal reflecting-position25p. In the thermally assisted magnetic head180, the conditions, concerning the interference parameters p1) to p5), which the internal reflecting-position is set up to the optimal reflecting-position25p, are defined as the following optimizing conditional expression. In the thermally assisted magnetic head180, the optimizing conditional expression is satisfied, thereby the internal reflecting-position is set up to the optimal reflecting-position25p.

As described later in detail, L1is the optical path length concerning laser light passing through a later-described inlet-interval Lin, L2is the optical path length concerning laser light passing through an outlet-interval Lout. L3is the optical path length concerning laser light passing through the internal waveguide of the laser diode130, L4is the optical path length concerning laser light of the entire core layer25. When the distance, which light travels actually, is dx, the refractive index of the medium is n, the optical path length is ndx.

Then, as illustrated inFIG. 6, when the laser light Q is emitted from the laser diode130, part of the laser light Q is reflected on the light source-opposing surface102, the core layer25, the near-field light generating layer28, the hard disk202. As the result, optical feedback r1, r2, r3, r4 return back to the laser diode130.

In the thermally assisted magnetic head180, because the internal reflecting-position is set up to the optimal reflecting-position25p, the unstableness of optical power, caused by the mode-hopping, is lowered.

Here,FIG. 7is a graph showing a simulation result to investigate the relationship between the interval, of inside the core layer25, from the light source-opposing surface102to the reflecting-position and size of the optical power change. The horizontal axis inFIG. 7shows the inlet-interval Lin(will be described later in detail) illustrated inFIG. 8, the vertical axis shows the size of the optical power change. When numeric value of the vertical axis is large, the optical power becomes unstable, when numeric value of the vertical axis is small, the optical power becomes stable.

As illustrated inFIG. 7, when the inlet-interval Linis shows numeric value within a certain range tx, the optical power becomes stable. Namely, minimal value exists in the optical power change. The optimal reflecting-position25pis able to be set up by the inlet-interval Lin, when the optical power change is limited in the certain range tx including such as the minimal value. The above-described optimizing conditional expression is satisfied on this case. The thermally assisted magnetic head180has an optimal-structure, which the optimizing conditional expression is satisfied. Namely, the internal reflecting-position is set up to the optimal reflecting-position25p, in the thermally assisted magnetic head180.

Then the magnetic head part100, which the internal reflecting-position is set up to the optimal reflecting-position25p, is shown inFIG. 8. In this case, inside of the core layer25, the interval, from the light source-opposing surface102to the optimal reflecting-position25p, is the inlet-interval Lin, the interval, from the optimal reflecting-position25pto the ABS101, is the outlet-interval Lout. Further, the total length of the core layer25(thickness of the slider-substrate110) is a core layer length LSD. The total length of the internal waveguide of the laser diode130is internal waveguide length LLD.

Then, total length of the internal waveguide of the laser diode130is the internal waveguide length LLDthough, it means that parallel mirrors Rr, Rfare arranged at positions away from each other with size of the internal waveguide length LLD. Then, in the laser diode130, the laser light Q oscillates at a frequency defined by the parallel mirrors Rr, Rf.

Here, as illustrated inFIG. 9, for example, the case, which the optical feedback Qa is added to the laser light Q, is supposed. As the optical feedback Qa, the light reflected in inside the core layer25(corresponding to the light reflected by the reflection mirrors Rex1, inFIG. 9) and the light reflected near the ABS101are supposed. In this case, the reflection mirror Rex1corresponds to the optimal reflecting-position25p, the reflection mirror Rex2corresponds to the near-field light generating layer28.

As described above, the interval of the core layer25, from the light source-opposing surface102to the optimal reflecting-position25p, is the inlet-interval Lin, the interval, from the optimal reflecting-position25pto the ABS101, is the outlet-interval Lout.

Therefore, if effective refractive index (refractive index found by considering the spatial distribution inside of the dielectric) of the inlet-interval Linis n1, effective refractive index of the outlet-interval Loutis n2, optical path length of the inlet-interval Lin(corresponding to an inlet-optical path length of the present invention) L1is n1×Lin(the product of the effective refractive index n1and the inlet-interval Lin). Further, optical path length of the outlet-interval Lout(corresponding to an outlet-optical path length of the present invention) L2is n2×Lout.

When the size of the natural number times the inlet-optical path length L1is equal to the outlet-optical path length L2, namely, the following EX1 is satisfied, the internal reflecting-position is set up to the optimal reflecting-position25p, the unstableness of optical power caused by the mode-hopping is lowered. The following EX1 is one of the optimizing conditional expression (first optimizing conditional expression).
m1×L1=L2 (m1isanatural number)  EX1

Here,FIG. 10is the graph showing a relationship between wavelength and mirror loss when the reflecting-position is optimized,FIG. 11is the graph showing a relationship between wavelength and mirror loss when the reflecting-position is not optimized. Both horizontal axes show the wavelength, vertical axes show the mirror loss. As illustrated inFIGS. 10, 11, when the reflecting-position is optimized, the waveform, illustrated in the graph, is periodic. This is useful for the unstableness of optical power.

When the size of the natural numbers times the inlet-optical path length L1is equal to the optical path length of the internal waveguide of the laser diode130(corresponding to a light-source optical path length of the present invention) L3, namely, the following EX2 is satisfied, the internal reflecting-position is set up to the optimal reflecting-position25p, the unstableness of optical power, caused by the mode-hopping, is lowered.

The following EX2 is also one of the optimizing conditional expression (second optimizing conditional expression). If the effective refractive index of the internal waveguide of the laser diode130is nL, the light-source optical path length L3is nL×LLD.
m2×L1=L3 (m2isanatural number)  EX2

When the size of the natural numbers times the optical path length about all interval along length direction of the core layer25(corresponding to a waveguide-optical path length of the present invention) L4is equal to the light-source path length L3, namely, the following EX3 is satisfied, the internal reflecting-position is set up to the optimal reflecting-position25p, the unstableness of optical power, caused by the mode-hopping, is lowered. The following EX3 is also one of the optimizing conditional expression (third optimizing conditional expression). Because the waveguide-optical path length L4is the sum of the optical path length of the inlet-interval Linand the optical path length of the outlet-interval Lin, the waveguide-optical path length L4is n1×Lin+n2×Lout(=L1+L2).
m3×L4=L3 (m3isanatural number)  EX3

The reflecting-position of the core layer25becomes the optimal reflecting-position25pon all the cases of the above-described EX1 is satisfied, the EX2 is satisfied, and the EX3 is satisfied. Therefore, the thermally assisted magnetic head, which the optimizing conditional expression is satisfied, brings the effect that the unstableness of optical power caused by the mode-hopping is lowered.

Further, the case which each one of the optimizing conditional expression of EX1, EX2, EX3 is respectively satisfied, and also the case which at least two of the optimizing conditional expression are satisfied (for example, EX1 and EX3 are satisfied), the unstableness of optical power caused by the mode-hopping is lowered.

(Definition of Internal Reflecting-Position)

As describe-above, the internal reflecting-position of the case, which the optimizing conditional expression of EX1, EX2, EX3 is respectively satisfied (or at least two of the optimizing conditional expression are satisfied), is the optimal reflecting-position25p. In the magnetic head part100, it is necessary that the reflecting-position is defined in the core layer25so that the internal reflecting-position is set up to the optimal reflecting-position25p. When at least any one of the optimizing conditional expressions of EX1, EX2, EX3 is satisfied, concerning the definite reflecting-position, the reflecting-position is the optimal reflecting-position25p.

Here, the core layer125, having a reflector126in the middle position, is shown inFIG. 12. In the case which the core layer125is formed in the magnetic head part100, the inlet-interval Linis decided by the interval from the light source-opposing surface102to the reflector126. Therefore, the reflecting-position is defined easily.

Further, the core layer135, having a first core part135A (first dielectric member) made of first dielectric and a second core part135B (second dielectric member) made of second dielectric, is shown inFIG. 13. In the case which the core layer135is formed in the magnetic head part100, the inlet-interval Linis defined by the interval from the light source-opposing surface102to the boundary part135D between the first core part135A and the second core part135B. Namely, because the boundary part135D is defined as the reflecting-position, the reflecting-position is defined easily.

However, as illustrated inFIG. 14, when the core layer25has a narrow structure including a wide-width part25A, a width-changing part25B and a narrow-width part25C, it is difficult that the reflecting-position is defined. In this case, the reflecting-position is defined according to the following reflecting-position defining method.

The reflecting-position defining method includes a reflectance measuring step, a corresponding diagram forming step, a period decision step and a reflecting-position calculating step.

In the reflectance measuring step, as illustrated inFIG. 15, a plurality of light F1, having different wavelength (also referred to as “test-input light”) are input from the light source-opposing surface102, reflectance (reflection rate) of the reflected light F2, F3is measured. In this case, for example, wavelength tunable light source is used, light having a variety of wavelength is input into the inlet25E of the core layer25. The obtained reflectance is also referred to measured reflectance.

Next, in the corresponding diagram forming step, the corresponding diagram, showing the relationship between the input wavelength and the measured reflectance, is formed. The input wavelength is wavelength of the test-input light F1.

In the subsequent period decision step, a wavelength period is decided using the corresponding diagram formed in the corresponding diagram forming step. When the wavelength of the test-input light F1change, the interference pattern of the light also changes. Then, for example, as illustrated inFIG. 16, peaks of the measured reflectance, such as peaks P1, P2, emerge periodically. Interval of adjacent to peaks such as peaks P1, P2is set up to a peak period T.

Then, in the reflecting-position calculating step, the reflecting-position is calculated according to the following reflecting-position calculating expression. In the reflecting-position calculating expression, the inlet-optical path length L1is calculated using the peak period T, decided by the period decision step and an average wavelength A, between the adjacent peaks. Then, because the L1is n1×Lin, when the effective refractive index n1is calculated, the inlet-interval Linis decided. Because the inlet-interval Linis interval of the core layer25from the light source-opposing surface102to the optimal reflecting-position25p, when the inlet-interval Linis decided, the reflecting-position is calculated.
L1=λ2/2TReflecting-position calculating expression

When the reflecting-position is defined by the reflecting-position defining method, as illustrated inFIG. 15, it is preferable that an AR coat layer109is formed on the core layer25of the ABS101side. When the AR coat layer109is formed, measuring accuracy of the reflectance is improved.

(Embodiments of Head Gimbal Assembly and Hard Disk Drive)

Next, embodiments of the head gimbal assembly and hard disk drive will now be explained with reference toFIG. 17toFIG. 18.

FIG. 17is a perspective view showing a hard disk drive201equipped with the above-mentioned thermally assisted magnetic head180. The hard disk drive201includes a hard disk (magnetic recording medium)202rotating at a high speed and a head gimbal assembly (HGA)210. The hard disk drive201is an apparatus which actuates the HGA210, so as to record/reproduce data onto/from recording surfaces of the hard disk202. The hard disk202has a plurality of (4in the drawing) platters. Each platter has a recording surface opposing its corresponding the thermally assisted magnetic head180.

The hard disk drive201positions the slider120on a track by an assembly carriage device203. Further, the hard disk drive201has a plurality of drive arms209. The drive arms pivot about a pivot bearing shaft206by means of a voice coil motor (VCM)205, and are stacked in a direction along the pivot bearing shaft206. Further, the HGA210is attached to the tip of each drive arm.

Further, the hard disk drive201has a control circuit204controlling recording/reproducing and the generation of light by the laser diode130.

FIG. 18is a perspective view illustrating a rear surface side of the HGA210. In the HGA210, the thermally assisted magnetic head180is fixed to a tip portion of a suspension220. Further, in the HGA210, one end portion of a wiring member224is electrically connected to a terminal electrode of the slider120.

The suspension220has a load beam222, a base plate221provided at a base portion of the load beam222, a flexure223fixed to and supported on the load beam222from the tip end side to the front side of the base plate221and having elasticity, and the wiring member224. The wiring member224has a lead conductor and connection pads electrically connected to both ends of the lead conductor.

In the hard disk drive201, when the HGA210is rotated, the slider120moves in a radial direction of the hard disk202, i.e., a direction traversing track lines.

The aforementioned HGA210and hard disk drive201have the thermally assisted magnetic head180, thereby the unstableness of optical power caused by the mode-hopping is lowered.

Though the above-mentioned embodiments explain a type in which a thin-film coil is wound like a flat spiral about the main magnetic pole layer by way of example, the present invention is also applicable to a type in which the thin-film coil is wound helically about the main magnetic pole layer.

This invention is not limited to the foregoing embodiments but various changes and modifications of its components may be made without departing from the scope of the present invention. Besides, it is clear that various embodiments and modified examples of the present invention can be carried out on the basis of the foregoing explanation. Therefore, the present invention can be carried out in modes other than the above-mentioned best modes within the scope equivalent to the following claims.