System and method of diffractive focusing of light in a waveguide

Description

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit of U.S. Provisional Application No. 61/953,564 entitled “System and Method of Diffractive Focusing of Light in a Waveguide of a Heat Assisted Magnetic Recording Head,” filed on Mar. 14, 2014, which is expressly incorporated by reference herein in its entirety.

BACKGROUND

Information storage devices are used to retrieve and/or store data in computers and other consumer electronics devices. Energy assisted magnetic recording (EAMR) or heat assisted magnetic recording (HAMR) technology may be used to increase areal density (AD) of hard disks. A laser beam is delivered through an optical target waveguide and excites a near field transducer (NFT) at an air bearing surface (ABS) adjacent the magnetic disk surface. The NFT generates a very strong localized electromagnetic field. When the localized electromagnetic field is close enough to the magnetic recording medium, the recording medium absorbs part of the localized electromagnetic field and heats up in a region limited in part by the small dimension of the NFT. This heating lowers the coercivity of the magnetic medium locally and enables a write pole to magnetize the media with high density, which helps to realize the magnetic recording process with increased AD.

Various methods for focusing the laser to the NFT are known, such as mirror focusing. However, there are deficiencies with the known systems. For example, when using mirror focusing (e.g., parabolic solid immersion mirror), the focus tightness is limited.

There is a need in the art for improved focusing of a laser to an NFT in EAMR/HAMR technology.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of the present invention will now be presented in the detailed description by way of example, and not by way of limitation, with reference to the accompanying drawings, wherein:

FIG. 1 is a conceptual plan view of an example of a HAMR disk drive, for use in accordance with aspects of the present invention;

FIG. 2 is a conceptual elevation view of an embodiment of a slider with a HAMR transducer arranged with a light source.

FIG. 3 is a conceptual perspective view of the example embodiment of the slider with the HAMR transducer arranged with the light source of FIG. 2.

FIGS. 4A and 4B show a front view of an example embodiment of a waveguide alongside a cross section view of the waveguide.

FIGS. 5A, 5B, and 5C show a front view of another example of a waveguide alongside a cross section view of the waveguide.

FIGS. 6A, 6B, 6C, 6D, 6E, and 6F show a front view of further example embodiments of an effect pattern for a waveguide.

FIGS. 7A and 7B show cross sectional views of various example types of alterations in a waveguide.

FIGS. 8A and 8B show cross sectional views of example alterations in a waveguide.

FIG. 9 is a perspective view of another example embodiment of a waveguide.

DETAILED DESCRIPTION

In light of the above described problems and unmet needs, an improved focusing structure is presented herein. The focusing structure may be used in HAMR along with other potential applications, including microwave imaging, infrared and visible optics, far ultraviolet (UV) applications such as UV lithography, and X-ray focusing/imaging. The improved focusing structure ensures tight focusing while being easy to manufacture and maintaining compact dimensions.

Aspects of a focusing structure include a first end, a second end, and an optically altered portion between the first and second ends, wherein the optically alerted portion focuses light into one or more focal points or zones located toward the second end when light is incident from the first end. The altered portion comprises an array of localized optical alterations that alter the propagation of light through the focusing structure to diffractively focus the light as it exits the focusing structure, the array of optical alterations being formed along either a straight or a curved surface within a cross section of the focusing structure.

Aspects presented herein may be applied, e.g., in an HAMR waveguide having an entrance at a first end, a second end opposing the first end, and an optically altered portion located between the first and second ends. The optically altered portion forms a focusing element comprised in the waveguide. The optically altered portion may focus light into one or more focal points or zones located toward the second end, when light is incident from the first end. A near field transducer may be located at the one or more focal points. The focusing element includes an array of localized optical alterations that alter the propagation of the laser beam through the waveguide to diffractively focus the laser beam approximately at the near field transducer. The optical alterations may be formed along either a straight line or a curved line. The HAMR transducer may include a near field transducer located at the one or more focal points. The first surface of the HAMR transducer may be aligned to an air bearing surface (ABS) of the slider and the second surface of the HAMR transducer may be aligned to a surface of the slider opposite the ABS.

Additional advantages and novel features of these aspects will be set forth in part in the description that follows, and in part will become more apparent to those skilled in the art upon examination of the following or upon learning by practice of the invention.

The word “exemplary” is used herein to mean serving as an example, instance, or illustration. Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. Likewise, the term “embodiment” of an apparatus, method or article of manufacture does not require that all embodiments of the invention include the described components, structure, features, functionality, processes, advantages, benefits, or modes of operation.

FIG. 1 is a conceptual plan view of an example embodiment of a HAMR disk drive for use in accordance with aspects of the present invention. The HAMR drive disk 100 is shown with a rotatable magnetic disk 102. The magnetic disk 102 may be rotated on a spindle 104 by a disk drive motor located under the magnetic disk 102. A head may include read and write poles that detect and modify the magnetic polarization of the recording layer on the disk's surface. The head may generally be integrally formed with a slider 106. The function of the slider 106 may be to support the head and any electrical connections between the head and the rest of the HAMR disk drive 100. The slider 106 may be mounted to a positioner arm 110, which may be used to move the head on an arc across the rotating magnetic disk 102, thereby allowing the head to access the entire surface of the magnetic disk 102. The arm 110 may be moved using a voice coil actuator 112 or by some other suitable features and/or methods.

The slider 106 may be aerodynamically designed to fly above the magnetic disk 102 by virtue of an air bearing created between the surface of the slider 106 and the rotating magnetic disk 102. This surface of the slider 108 is also interchangeably referred to herein as an air bearing surface (ABS). The ABS may include the portion of the slider 106 surface that is closest to the rotating magnetic disk 102, which is typically, for example, the head. A HAMR transducer 214, as described in connection with FIGS. 2 and 3, may be coupled to the distal end of the slider 106 to assist writing data to the magnetic disk 102. The HAMR transducer 214 may include an NFT aligned with the ABS of the slider 106. Light from a laser may be coupled to the HAMR transducer 214 and guided by waveguide to the NFT. The NFT may focus (or concentrate) the light to the magnetic disk 102, and heat a small region of the media. The head may magnetically write data to the heated region of the media by energizing the write pole, for example. When the laser, as the heat source, is turned off, the localized magnetic media may cool, and the written bit may become thermally stable at ambient temperature.

FIG. 2 is a conceptual elevation view of an example embodiment of a slider with a HAMR transducer arranged with a light source. FIG. 3 is a perspective view of the example HAMR transducer 214 of FIG. 2, arranged with the light source 204 of FIG. 2. The HAMR disk drive 100 may include the magnetic disk 102, a subassembly 202, and a slider 106. A HAMR transducer 214 may be formed on the distal end of the slider 106. The subassembly 202 may include a light source, such as a laser diode 204 having an emission exit 206, attached to a submount 208. The slider 106 may have a back side 210 to which the submount 208 may be bonded. In the example shown, the back side 210 is opposite to the ABS. However, in other variations, the back side 210 (i.e., the side to which the submount 208 is bonded) may not be opposite to the ABS.

The HAMR transducer 214 may be mounted on a distal end of the slider 106 below the laser diode 204, such that a waveguide fabricated in the HAMR transducer 214 is aligned with the emission exit 206 of the laser diode 204. The HAMR transducer 214 may include a first surface aligned to the ABS of the slider 106 and second surface aligned to a surface of the slider 106 opposite the ABS.

An important aspect of waveguide applications, including HAMR-related waveguide applications is the ability to concentrate or focus light at a desired focal point. In HAMR applications, the desired focal point is the NFT.

Arrays of localized optical alterations in a waveguide may be used to concentrate light on (or redirect towards) a desired focal position. The desired focal position may be, e.g., the NFT for energy assisted magnetic recording applications. The alterations can be placed in the waveguides to block or alter the propagation of certain zones to ensure focusing at the desired position. The optical alterations may be spaced to form optically non-obstructing slits for producing one or more interferometric light energy patterns by phase coincidences. Such slits may be used to focus light into one or more focal points or zones located.

Thus, the waveguide may form alterations in the waveguide that diffractively focus the light similar to a zone plate. This can be beneficial in HAMR, e.g., because the use of coherent light enables the zones of desired phase to be well-defined.

The use of the optical alterations formed in the waveguide, as presented herein, offers a large numerical aperture while maintaining very compact dimensions. For example, in both Fresnel zone plates and Rayleigh-Wood plates, the resolution is comparable to the thickness of the last, e.g., thinnest, zone ring. In order to achieve a tight focus, e.g., a decent numerical aperture, very large plates containing hundreds of zones may be needed. The arrays of optical alterations in a waveguide described herein provide a desirable numerical aperture with compact dimensions.

Phase control and manufacturing are both simplified. For example, during manufacturing, certain portions of the waveguide altered, or spoiled, in order to achieve the focusing. The benefits can be obtained without the need for optical quality boundaries between different parts of the waveguide.

In HAMR, the NFT may be positioned adjacent to a magnetic recording medium, such that electromagnetic radiation emitted at the end of the NFT can be used to heat a portion of the recording medium. If the NFT is chosen with the correct dimensions, particularly the correct length, then it resonates with the incident light and creates extremely large electric fields in a recording medium in the vicinity of the end of the transducer.

Two example waveguides are shown in FIGS. 4A, 4B, 5A, 5B, and 5C, which are discussed below. FIGS. 4A and 4B show a front view (a) of an example waveguide 400 having optical alterations as described herein and a cross section view (b) of the waveguide. As shown in FIG. 4A, the waveguide may be an inverse taper waveguide, e.g., the waveguide at the input port may be smaller than in the case of a forward taper waveguide, and expand away from the input port. The waveguide may include a plurality of spaced alterations 402 in a particular pattern. The array of localized optical alterations 402 may be part of a focusing element to diffractively focus the laser beam emitted, e.g., from laser chip 406, approximately at near field transducer 408.

As shown in FIGS. 4A and 4B, the alterations may be in the form of holes or other openings formed in the waveguide, and may be filled with a different material than the material of the waveguide. However, as discussed in further detail below, the alterations may be in the form of any suitable structure or other feature that creates relatively opaque zones that allow light to diffract around the relatively opaque zones. The waveguide may include a core layer sandwiched between two cladding layers. The laser may be emitted from a laser. The NFT may be positioned at or near the end of the waveguide.

As shown in FIG. 4A, the alterations may be positioned along a curved line. The curved line may be a parabolic fashion. Additionally, the size of the openings/alterations may be similar or may differ, e.g., with the largest alterations being positioned nearer the center of the waveguide. The alterations may decrease in size along the semicircle path toward the end of the waveguide, with the smallest alterations being located adjacent the end of waveguides. Furthermore, the distance between adjacent alterations may decrease along the semicircle path toward the end of the waveguide. For example, the distance between the two alterations closet to the end of the waveguide may be about ⅕^th or greater the distance between the two alterations closest to the center of the waveguide, for the size of the waveguide shown in FIG. 4A. The particular position and location of the alterations may be selected so as to optimize the diffractive focus of the laser and reduce lithography requirements. The localized alterations may block or alter the propagation of certain zones so as to ensure focusing at the desired position. For example, the alterations shown in FIGS. 4A and 4B may lie on a semicircle in a phase-offset curved diffractive array. For example, holes, openings or other alterations may be formed in locations determined or otherwise identified to produce a desired focus or other effect. The openings may be formed using different methods depending on the application. For example, openings forming a focusing element for use in HAMR may be lithographically formed, e.g., etched. A microwave focusing element may be drilled.

The array of optical alterations in the waveguide may be used in combination with other focusing elements. Thus, the waveguide may comprise at least one additional focusing element or aspect. Fiber/waveguide tapering may be used as an additional focusing aspect, as illustrated in FIG. 4A. Focusing lenses and/or focusing mirrors may also be used in combination with the array of optical alterations in order to further assist in focusing the light.

FIGS. 5A, 5B, and 5C show another example of a wave guide 500 with alterations 502 for producing diffractive focus or other similar effect. As shown in FIGS. 5A, 5B, and 5C the alterations lie on a semicircle in the appropriate zones. FIG. 5B illustrates a side view of the waveguide 500, which shows the alterations 502 extending through cladding and core layers of the waveguide. FIG. 5C illustrates a view of the waveguide from the side at which the NFT is located. In the waveguide of FIGS. 5A, 5B, and 5C, the NFT is positioned in front of the waveguide and is coated with a metal deposit and a protective coating.

FIGS. 6A-6F show various examples of the alterations described in connection with FIGS. 4A, 4B, and 5A, 5B, and 5C. The waveguide may comprise, e.g., a first cladding layer 602, a second cladding layer 604, and a core layer 606 provided between the first and second cladding layers. FIG. 6A shows an example where the alteration 608 is a hole or other opening, for example, passing through the one of the cladding layers 602, through the core layer 606, and into another cladding layer 604. The hole or opening 608 may be lithographically formed, e.g., etched, into the waveguide 600. When a hole is used for the alteration 608 (e.g., a hole that is not filled with another material), the alteration may block the wave propagation.

FIG. 6B shows an example where the alteration includes a hole or other opening 608 similar to FIG. 6A, except that the hole or other opening is filled with a material 610. For example the hole, or other opening, may be backfilled with cladding material or another dielectric material having an appropriate refraction index. Alternately, the opening may be backfilled with a reflective material, such as a metal, such that the backfilled material reflects or absorbs light in the undesired zones. When a backfilled hole 610, 612 is used for the alteration (e.g., a hole that is filled with a cladding material), the alteration may change the phase of the wave propagation. In other words, the backfilled hole may change the effective index of refraction.

FIG. 6C shows an example where the alteration includes a hole or other opening 608 similar to FIG. 6B, except that the backfilled hole 612 or other opening only extends through one of the cladding layers 602 and only partly through the core layer 606.

FIG. 6D shows an example an example where the alteration 614 is present in one of the cladding layers and does not contact the core layer. In this case, the change of the zone propagation may be induced by proximity effect, for example. Specifically, the effective index of refraction in the waveguide may depend on cladding properties, as well as on core structure, for example. The index of refraction change caused by the alteration as shown in FIG. 6D may be slight, so the cladding alteration may therefore be extended in the direction of the desired wave propagation to ensure appropriate phase accumulation.

FIG. 6E shows an example similar to the alteration of FIG. 6D, except that the alteration 614, 616 is present in both of the cladding layers sandwiching the core layer, without the alteration contacting the core layer. The alteration of FIG. 6E may increase the proximity effect as compared to the alteration of FIG. 6D, for example. Since the core 606 is unaffected, in the alterations of FIGS. 6D and 6E, low reflection and therefore high efficiency of focusing may be achieved.

FIG. 6F shows an example embodiment where the alteration 618 is formed by ion bombardment/implantation of the waveguide 600. This alteration 618 may decrease or completely eliminate propagation of the zones that do not enhance focus or other similar desired effects. The alteration of FIG. 6F may be formed by directing a high energy ion beam into the area where it is desired to change the properties of the material (e.g., the index of refraction). The ion beam destroys or spoils the lattice of cladding and/or core. And then, ions trapped in the crystalline layers may grow back into tiny crystals. Any method that provides this change in result may be used.

Each of the various types of alterations shown in FIG. 6A-6F may be implemented independently or in combination with one or more of the others. For example, a part-way hole or other opening alteration may be used atop a buried proximity layer alteration. In another example, offset (e.g., top to bottom) may sandwich one or more structures (proximity or part-way protruding features).

FIGS. 7A and 7B show example patterns of alterations 702 for a waveguide. FIG. 7A shows alterations 702 positioned approximately along a straight line within a cross section of the waveguide 700. FIG. 7B shows alterations 702 positioned approximately along a curved surface within a cross section of the waveguide 700. The curved line along which the optical alterations extend may be semi-circular or parabolic. The placement along the curved surface enables the alterations to be spaced further apart while limiting the lateral dimensions of the waveguide and the number of holes. Although the optical alterations 702 are shown having a circular shape, the alterations 702 may also be formed as an elliptical shape.

As illustrated in FIG. 7B, the optical alterations may comprise a rounded shape of approximately the same size. As illustrated in FIG. 7A, the cross sections of the optical alterations may differ in size. For example, cross sections of the optical alterations may comprise rounded shapes of differing sizes that lessen in size, e.g., diameter, as they extend from a center of the array to an outer portion.

FIGS. 8A and 8B illustrate additional aspects of patterns of alterations 802 for a waveguide 800. In FIG. 8A, the optical alterations are disposed on two sides of an optical axis, e.g., shown having “0” at its center. In FIG. 8A, the two sides are disposed approximately evenly on either side of the optical axis. In contrast, in FIG. 8B, the optical alterations on the two sides of the optical axis are shifted relative to each other. Such shifting may be used in order to achieve a desired polarization of the light at the desired focal position. For example, the optical alterations 802 may be located along a curved line in undesired zones. As illustrated, the alterations may be rounded openings placed at the undesired zones between neutral points for producing focus or other similar effects (e.g., p/2 and 3p/2 phase delay).

The focusing element formed using the optical alterations may be used as a single focusing element or in combination with other focusing elements, e.g., in order to form a compound lens. For example, the optical alterations may be configured to include multiple curved lines of alterations extending within a cross section of a waveguide. FIG. 9 is a perspective view of one example waveguide having arrays of optical alterations 902, 904 that formed along multiple curved surfaces extending within a cross section of a waveguide 900, e.g., along first curved line 902 comprising a convex shape and along a second curved line 904 having a concave shape. Although FIG. 9 illustrates an example, having six alterations along the concave line and six alterations along the convex line, the number and size of the alterations may be selected depending on the application. The focusing element may also be used in combination with other focusing means, such as lenses, mirrors, tapering, etc.

FIG. 9 shows focusing properties of a semi-circular alteration arrangement containing six alterations of equal diameter on each side of the optical axis, thus providing twelve alterations. The alterations may be holes backfilled with cladding material. The waveguide may have a core with an index of 2 and a cladding index of 1.4. As shown in FIG. 9, the first six alterations have a convex semi-circle pattern, followed by the second six alterations that have a concave semi-circle pattern. In FIG. 9, light propagates from left to right (i.e., along the x-axis). In this manner, the waveguide of FIG. 9 is analogous to a compound lens.

FIGS. 4-8 illustrate a flat cross section of a waveguide, which shows the optical alterations having a rounded shape. FIG. 9 illustrates a view showing that such optical alterations may comprise a substantially cylindrical shape within the waveguide 900,

Although the aspects presented herein have been described using the example of an HAMR-related waveguide, the aspects presented herein can be used in focusing structures for additional applications. For example, the optical alterations described in connection with FIGS. 4-9 may be used for any focusing structure. Conventional Fresnel-style or Rayleigh-Wood “zone plates” are provided along a straight line/plane. In contrast, by providing the array of optical alterations along a curved surface within a cross section of a focusing structure enables extremely fine focusing substantially without side lobes/maxima. Among others, such potential applications include microwave imaging, infrared and visible optics, far UV applications such as UV lithography, and X-ray focusing/imaging.

The various example embodiments are provided to enable one of ordinary skill in the art to practice various aspects of the present invention. Modifications to example embodiments presented throughout this disclosure will be readily apparent to those skilled in the art, and the concepts disclosed herein may be extended to other devices. All structural and functional equivalents to the various components of the example embodiments described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference.