Compact mode converter having first and second straight portions for a heat-assisted magnetic recording device

A write head includes an input coupler configured to receive light excited by a light source. A waveguide core is configured to receive light from the input coupler at a fundamental transverse electric (TE00) mode. The waveguide core has a first straight portion. The waveguide core has a mode converter portion comprising a branched portion extending from the first straight portion. The mode converter portion is configured to convert the light to a higher-order (TE10) mode, the mode converter portion spaced apart from the input coupler. The waveguide core has a second straight portion between the mode converter portion and a media-facing surface. The write head has a near-field transducer at the media-facing surface, the near-field transducer receiving the light at the TE10 mode from the waveguide and directing surface plasmons to a recording medium in response thereto.

SUMMARY

Embodiments described herein are directed to a write head comprising an input coupler configured to receive light excited by a light source. A waveguide core is configured to receive light from the input coupler at a fundamental transverse electric (TE00) mode. The waveguide core comprises a first straight portion. The waveguide core comprises a mode converter portion comprising a branched portion extending from the first straight portion. The mode converter portion is configured to convert the light to a higher-order (TE10) mode, the mode converter portion spaced apart from the input coupler. The waveguide core comprises a second straight portion between the mode converter portion and a media-facing surface. The write head comprises a near-field transducer at the media-facing surface, the near-field transducer receiving the light at the TE10mode from the waveguide and directing surface plasmons to a recording medium in response thereto.

Embodiments are directed to an apparatus comprising an input coupler configured to receive light excited by a light source. A waveguide core is configured to receive light from the input coupler at a fundamental transverse electric (TE00) mode. The waveguide core comprises an input portion configured to receive light from the input coupler. The waveguide core comprises a mode converter portion comprising a branched portion extending from the input portion. The mode converter portion is configured to convert the light to a higher-order (TE10) mode. The mode converter portion is spaced apart from the input coupler. The waveguide core comprises an output portion between the mode converter portion and a media-facing surface. The write head comprises a near-field transducer at the media-facing surface, the near-field transducer receiving the light at the TE10mode from the waveguide and directing surface plasmons to a recording medium in response thereto.

DETAILED DESCRIPTION

The present disclosure is generally related to an apparatus (e.g., a HAMR write head) having a waveguide that delivers light from an energy source (e.g., laser diode) to a near-field transducer (NFT). The NFT may also be referred to as a plasmonic transducer, plasmonic antenna, near-field antenna, nano-disk, nan-patch, nano-rod, etc. The light generates a surface plasmon field on the NFT, and the surface plasmons are directed out of a surface of the write head onto a magnetic recording medium. This creates a hotspot on the recording medium, lowering its magnetic coercivity and enabling a local magnetic field generated by a write pole to write data to the hotspot.

In reference toFIG. 1A, a perspective view shows a HAMR write head100according to an example embodiment. The write head100includes a laser diode102located on input surface103of a slider body101. In this example, the input surface103is a top surface, which is located opposite to a media-facing surface108that is positioned over a surface of a recording media (not shown) during device operation. The media-facing surface108faces and is held proximate to the moving media surface while reading and writing to the media. The media-facing surface108may be configured as an air-bearing surface (ABS) that maintains separation from the media surface via a thin layer of air.

The laser diode102delivers light to a region proximate a HAMR read/write transducer106, which is located near the media-facing surface108. The energy is used to heat the recording media as it passes by the read/write transducer106. Optical coupling components, such as a waveguide system110, are formed integrally within the slider body101(near a trailing edge surface104in this example) and function as an optical path that delivers energy from the laser diode102to the recording media via a near-field transducer112. The near-field transducer112is located near the read/write transducer106and causes heating of the media during recording operations. The near-field transducer112may be made from plasmonic materials such as gold, silver, copper, etc.

The laser diode102in this example may be configured as either an edge-emitting laser or surface-emitting laser. Generally, the edge-emitting laser, also called in-plane laser, emits light along the wafer surface of a semiconductor chip and a surface emitting laser emits light in a direction perpendicular to a semiconductor wafer surface. An edge-emitting laser may be mounted on the top surface103of the slider body101(e.g., in a pocket or cavity) such that the light is emitted in a direction perpendicular to the media-facing surface (along the negative y-direction in this view).

In some cases, the laser may be configured to have an offset light path. The offset light path may be used when a laser is not centered on the submount, for example. The light path may be offset in a range of about 3 μm to about 55 μm or in a range of about 4 μm to about 49.5 μm. To accommodate the offset laser, the light path may include an S-curve as shown in the read/write head120ofFIG. 1B. In some cases, the light path may be tilted as shown in the read/write head130shown inFIG. 1C. The different shaped light paths may be accomplished by having a tilted waveguide and/or a waveguide having an s-curve.

In the present disclosure, hard drive recording heads may use a different type of laser than what is shown inFIGS. 1A-1C. A read/write head140using this alternate approach is shown inFIG. 1D, wherein components are given the same reference numbers as analogous components inFIGS. 1A-1C. At least part of a semiconductor laser122or material to form a laser (e.g., epitaxial layer) is not self-supporting (e.g., not a separately packaged device) but is physically transferred to a target read/write head substrate that does contain already or will contain, after further processing, the other components of the read/write head (e.g., write coil and poles, reader stack) without the use of a separate or intermediate support during attachment. Carrying the semiconductor laser122with the read/write head substrate, without a separate or intermediate support substrate, can help to reduce the size and simplify the shape and connection methods, and it can also allow for the use of laser geometries and designs that are very different from simple edge-emitting cleaved facet lasers that have been proposed in the past.

In at least some cases, parts of the laser122(e.g., GaAs active region) are incompatible with epitaxial growth on the target substrate of a slider, which may be formed of a dielectric such as alumina. As such, the laser122cannot be formed using the same layer deposition processes used to form the magnetic and optical components that are integrated into the head. In embodiments described below, the laser may instead be formed on the substrate by transfer printing a thin, non-self-supporting crystalline layer (epitaxial layer), or a stack of such layers, from a growth substrate on which they were formed to a target substrate. Thereafter, the epitaxial layer and substrate are further processed (e.g., masked etched, further layers added) to form the integrated laser diode unit122. This process of transferring non-self-supporting layers of epitaxial-growth-incompatible layers is referred to herein as On-Wafer Laser (OWL) process integration. This process may also be referred to as transfer printing, dry transfer printing, nanoprinting, etc. Embodiments described herein may be implemented in an OWL system.

The waveguide system110discussed herein and shown inFIGS. 1A-1Dmay be applicable to any type of light delivery configuration. For example, a laser may be mounted on the trailing edge surface104instead of the top surface103. In another configuration known as free-space light delivery, a laser may be mounted external to the write head100, and coupled to the slider by way of optic fiber and/or waveguide. An input surface of the slider body101may include a grating or other coupling feature to receive light from the laser via the optic fiber and/or waveguide.

InFIG. 2, a cross-sectional view illustrates portions of the slider body101near the near-field transducer112according to an example embodiment. In this view, the near-field transducer112is shown proximate to a surface of magnetic recording medium202, e.g., a magnetic disk. The waveguide system110delivers electromagnetic energy204to the near-field transducer112, which directs the energy204to create a small hot spot208on the recording medium202. A magnetic write pole206causes changes in magnetic flux near the media-facing surface108in response to an applied current. Flux from the write pole206changes a magnetic orientation of the hot spot208as it moves past the write pole206in the downtrack direction (z-direction).

The waveguide system110includes a core layer210surrounded by cladding layers212,214. The core layer210and cladding layers212,214may be made from dielectric materials such as Al2O3, SiOxNy, SiO2, Ta2O, TiO2, ZnS, Si3N4, Nb2O, AlN, Hf2O3, Y2O3, GaP, SiC, Si, AlOx, etc. Generally, the dielectric materials are selected so that the refractive index of the core layer210is higher than refractive indices of the cladding layers212,214. This arrangement of materials facilitates efficient propagation of light through the waveguide system110.

A first end of the core210(not shown) extends along the crosstrack direction (negative x-direction) where it is directly or indirectly coupled to a light/energy source. For example, a laser diode (e.g., OWL laser diode) may have an output facet that is coupled face-to-face with an end of the waveguide core210. In other configurations, optical components such as lenses, mirrors, collimators, mode converters, etc., may be coupled between the waveguide core210and the light/energy source. In either case, the energy204coupled into the first end of the waveguide core210propagates to a second end210athat is proximate the near-field transducer.

The waveguide system may include a mode converter220. The mode converter may be configured to convert an input mode of light into a different mode or modes of light. In some cases, the mode converter220may be configured to receive a substantially transverse electric (TE) mode from the laser diode and be configured to convert the light into a higher order TM mode and/or a substantially transverse magnetic (TM). According to various embodiments, the mode converter220may be configured to receive fundamental TE mode (TE00) light from the laser mode from the laser and be configured to convert the light into a higher order TE mode, e.g., TE10, mode.

According to various embodiments described herein, the waveguide system includes a compact mode converter that is about 85% shorter than conventional mode converters. Using a compact mode converter allows the mode converter to be placed after the input coupler creating a more modular design. Moving the mode converter out of the input coupler frees up space that can be used to improve the input coupler performance. The compact mode converter may allow for additional optical elements in the light path such as an isolator and/or a mode filter, for example.

FIG. 3illustrates a waveguide system having a mode converter in accordance with embodiments described herein. According to various implementations, the waveguide system shown inFIG. 3may be used in conjunction with a laser on slider configuration such as those shown inFIGS. 1A-1C. Light enters the waveguide310at input location305in a TE00mode and exits the waveguide core in a TE10mode at the ABS315. The waveguide includes a main branch322configured to receive light. A secondary branch324of the waveguide310combines with the main branch322in a mode converter portion320of the waveguide320. After the mode converter portion320, the mode converted light, e.g., substantially TE10, light exits the waveguide and is coupled to an NFT at the ABS315.

FIG. 4illustrates a waveguide system having a mode converter in accordance with embodiments described herein. The waveguide system shown inFIG. 4may be used in conjunction with an on-wafer laser system as shown inFIG. 1D, for example. Light is input into the waveguide system in a TE00mode from a laser. A lens450and optical coupler460couple the TE00mode light from the laser into the waveguide core410. Light from a laser is emitted in a crosstrack direction (x-direction) and has a 180 degree turn435that redirects the light in the opposite crosstrack direction. A second turn445directs the light normal to the media-facing surface of the read/write head where it is directed to a mode converter portion420of the waveguide410. According to various implementations, the second turn445is about a 90 degree turn. Light enters the mode converter portion420in a main branch422. A secondary branch424of the waveguide410combines with the main branch422. After the mode converter portion420, the mode converted light, e.g., substantially TE10, light exits the waveguide and is coupled to an NFT at the ABS415. While the waveguide systems described inFIGS. 3 and 4are used in conjunction with specific laser configurations, it is to be understood that any of the mode converter waveguide systems described herein may be used in conjunction with any laser configuration.

FIG. 5Aillustrates a more detailed view of the mode converter portion of the waveguide in accordance with embodiments described herein. The main branch522has a width (w1) at the point before combining with the secondary branch524. In some cases, w1may be in a range of about 350 nm to about 600 nm or in a range of about 400 nm to about 550 nm. According to some implementations, w1is about 440 nm. In some cases, w1remains constant until the main branch522combines with a secondary branch524. According to various embodiments, w1varies along the length of the main branch522. The secondary branch524has a starting width (wbr1) and a width (wbr2) at a point that the secondary branch524combines with the main branch522. In some cases, wbr1is in a range of about 600 nm to about 800 nm or in a range of about 630 nm to about 750 nm. According to various implementations, wbr1is about 650 nm. The value of wbr1may be the same as wbr2or may be a different value than wbr2in some cases. According to various embodiments, wbr2is substantially the same as w1. In some cases, wbr2may be in a range of about 350 nm to about 600 nm or in a range of about 400 nm to about 550 nm. According to some implementations, wbr2is about 440 nm. wbr2may have substantially the same value as w1in some configurations. The secondary branch524may have a taper angle, θ in a range of 0.6 degrees to about 1.2 degrees.

A gap526may be disposed between the main branch522and the secondary branch524as illustrated inFIG. 5A. The various dimensions of the gap526may be tuned to achieve a desired and/or a maximum amount of mode conversion from TE00to TE10. In some cases, the width of the gap526is constant for the entire length of the gap526. The gap526may not have a constant width portion according to various configurations. For example, the width of the gap526may taper linearly or nonlinearly. According to various configurations, the width of the gap526is in a range of about 100 nm to about 200 nm or in a range of about 135 nm to about 170 nm. In some cases the width of the gap526is about 150 nm. The length of the gap is represented by Lbr. Lbrmay be in a range of about 9 μm to about 15 μm. In some cases, Lbris about 12 μm.

The final width (w2) of the combined main branch522and the secondary branch524may be equal, greater than, or less than the sum of the widths of the main branch522, the secondary branch524, and the gap width. One or both of the main branch522and the secondary branch524may have a taper to accommodate the change in width of the combined waveguide. In the example shown inFIG. 5A, the waveguide includes a tapered portion527that starts at the point where the waveguide branches are combined and continues to taper substantially linearly for a length (Ltap). Ltapmay be in a range of about 2 μm to about 8 μm. In some cases, Ltapis about 5 μm. One or both of the main branch522and the secondary branch524may include the taper. WhileFIG. 5Ashows a linear decreasing taper, it is to be understood that the taper may be non-linear and/or may increase along the light propagation direction.FIG. 5Bis a field plot showing the electric field along the waveguide ofFIG. 5A.

FIG. 5Cillustrates a cross sectional view of the waveguide system ofFIG. 5Afrom the cut-line580. The waveguide core510is surrounded by cladding layers560,562,564,566,568. A first top cladding layer560has a thickness in the range of 0.3 μm to about 2 μm. A second top cladding layer562may have a thickness in a range of 0.1 μm to about 0.5 μm. In some cases the second top cladding layer562has a thickness of about 0.3 μm. A third top cladding layer may be in direct contact with the waveguide core510and may surround three sides of the waveguide core510as shown inFIG. 5C. In some cases, the third top cladding layer564has a thickness in the range of 70 nm to about 200 nm.FIG. 5Calso shows a first bottom cladding layer566that is in contact with the waveguide core510. The first bottom cladding layer566may have a thickness in a range of about 0.6 μm to about 1.0 μm. In some cases, the first bottom cladding layer566has a thickness of about 0.8 μm. A second bottom cladding layer568may have a thickness in a range of 0.4 μm to about 1 μm.

FIG. 5Dillustrates a cross sectional view of the waveguide system shown inFIG. 5Afrom the cut-line585. The view shown inFIG. 5Dshows the main branch522, the secondary branch524, and the gap526disposed between the main branch522and the secondary branch524. The third top cladding layer564has a thickness, tclt, between the waveguide core and the second top cladding layer562. According to various embodiments, tcltmay be in a range of about 0.10 μm to about 0.16 μm. According to various embodiments, tcltis about 0.13 μm, for example.FIG. 5Eis a field plot illustrating the electric field in the cross section of the waveguide system.

FIGS. 6A-6Cillustrate various configurations for the mode converter portion of the waveguide in accordance with various embodiments described herein. Lengths L1, L2, L3of the mode conversion regions of the waveguide may be in a range of about 12 μm to about 30 μm, for example.FIG. 6Ashows an embodiment having a mode conversion region length, L1of about 24 μm. In this example, w1substantially equals wbr2and has a value in a range of about 538 nm to about 562 nm. In some cases, w1and wbr2have a value of about 550 nm. The value of wbr1has a range of about 725 nm to about 775 nm. In some cases, wbr1is about 750 nm. The gap width may have a value of about 135 nm to about 165 nm. In some cases, the gap width is about 150 nm. According to various implementations, the TE10purity after the mode converter portion in this example is about 99.6% and the combined TE00and TE10mode after the mode converter portion is about 0.09%.

FIG. 6Bshows an embodiment having a mode conversion region length, L2of about 17 μm. In this example, w1substantially equals wbr2and have a value in a range of about 422 nm to about 458 nm. In some cases, w1and wbr2has a value of about 440 nm. The value of wbr1has a range of about 620 nm to about 680 nm. In some cases, wbr1is about 650 nm. The gap width may have a value of about 130 nm to about 170 nm. In some cases, the gap width is about 150 nm. According to various implementations, the TE10purity after the mode converter portion in this example is about 99.84% and the combined TE00and TE10mode after the mode converter portion is about 0.003%.

FIG. 6Cshows an embodiment having a mode conversion region length, L3of about 15 μm. In this example, w1substantially equals wbr2and has a value in a range of about 386 nm to about 414 nm. In some cases, w1and wbr2have a value of about 400 nm. The value of wbr1has a range of about 605 nm to about 655 nm. In some cases, wbr1is about 630 nm. The gap width may have a value of about 132 nm to about 168 nm. In some cases, the gap width is about 150 nm. According to various implementations, the TE10purity after the mode converter portion in this example is about 99.61% and the combined TE00and TE10mode after the mode converter portion is about 0.05%.