Waveguide with shaped assistant layer

An apparatus includes a waveguide extending along a light-propagation direction between a light source and a media-facing surface. The waveguide comprises an assistant layer configured to receive light from a light source, truncated with an intermediate bottom cladding layer. A core layer comprises a coupling end configured to receive light from the assistant layer. The coupling end comprises a taper that widens toward the media-facing surface. A near field transducer is disposed proximate the media-facing surface and is configured to receive the light from the core layer.

SUMMARY

The present disclosure is related to a waveguide extending along a light-propagation direction between a light source and a media-facing surface. The waveguide comprises an assistant layer configured to receive light from a light source, truncated with an intermediate bottom cladding layer. A core layer comprises a coupling end configured to receive light from the assistant layer. The coupling end comprises a taper that widens toward the media-facing surface. A near field transducer is disposed proximate the media-facing surface and is configured to receive the light from the core layer.

According to various embodiments, a waveguide extends along a light propagation direction between a light source and a media-facing surface. The waveguide comprises an assistant layer configured to receive light from a light source. The assistant layer comprises an out-of-plane step and a terminating end with a first taper that narrows toward the media-facing surface. A core layer comprises a coupling end configured to receive light from the assistant layer. The coupling end comprises a second taper having a first width proximate the light source and a second width away from the light source, the second width being greater than the first width. A near field transducer disposed proximate the media-facing surface and configured to receive the light from the core layer.

DETAILED DESCRIPTION

The present disclosure generally relates to writing data with a heat assisted magnetic recording (HAMR) device. This technology, also referred to as energy-assisted magnetic recording (EAMR), thermally-assisted magnetic recording (TAMR), and thermally-assisted recording (TAR), uses an energy source such as a laser to heat a small spot on a magnetic disk during recording. The heat lowers magnetic coercivity at the spot, allowing a write transducer to change magnetic orientation. Due to the relatively high coercivity of the medium after cooling, the data is less susceptible to paramagnetic effects that can lead to data errors.

In some configurations, a HAMR write head has a waveguide that delivers light from an energy source (e.g., a laser diode) to a near-field transducer (NFT), also referred to as a near-field antenna, plasmonic transducer/antenna, 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 during writing. Optimal coupling is achieved by matching the mode profile between the laser diode and the waveguide on slider.

In reference toFIG. 1, 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, rhodium, platinum, iridium, 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 z-direction in this view).

While the example inFIG. 1shows a laser diode102directly mounted to the slider body101, the waveguide system110discussed herein may be applicable to any type of light delivery configuration. For example, a submount (not shown) may be used between a laser diode and the slider body101. In such a case, the submount orients the laser diode so that an active region of the laser diode is oriented in a vertical direction (z-direction in this view) and is aligned with the waveguide system110.

FIGS. 2A-2Cillustrate cross-sectional portions of the slider body101according to various embodiments. The diagram inFIG. 2Ashows a portion of the slider body proximate a light/energy source208(e.g., an edge-emitting laser diode). In this example, the light/energy source is mounted on a submount215. A core210of waveguide110extends along the light propagation direction (z-direction) where it is directly or indirectly coupled to a light/energy source208at a first end of the waveguide core. The waveguide core210has a tapered input coupler region having a first width W0proximate the light source208. The input coupler region flares to a second width W1as it extends away from the light source208.

As seen inFIG. 2B, an assistant layer250is positioned proximate the waveguide core210to couple light from the light source208into the core210at or near the region where the core210tapers from narrower width (W0) to wider width (W1). According to various implementations W0is between about 50 nm and 280 nm or between about 120 nm to about 240 nm. In some cases, W1is chosen such that the waveguide mode is confined to the core as a single mode waveguide. The length of the taper may be about 50-150 μm. The assistant layer250(thickness along y direction and index of refraction) may be optimized to match the mode size of the light source208along y direction and the core width W0adjacent to the light source208is chosen to match the mode size of the light source208along x direction.

As previously described, the core width (along cross-track direction, i.e., the X direction) increases as the distance away from the light source208increases (W1>W0). Light exiting from the light source208is first coupled into the assistant layer250and is transferred into the waveguide core210slowly. The waveguide system110includes side cladding layers212, bottom cladding layer214, and top cladding layer218that surround the waveguide core210and the assistant layer250.

As shown inFIG. 2C, the assistant layer250may be truncated with intermediate bottom cladding240after the light is coupled into the waveguide core210. This may improve the excitation efficiency of the near-field transducer112if the refractive index of intermediate bottom cladding240is lower than that of side cladding layers212. The intermediate bottom cladding240may have a lower index of refraction than the assistant layer250to push the waveguide mode into the side cladding layer212, where a near-field transducer112resides. This increases the field to excite the near field transducer112. The assistant layer250has an index of refraction greater than cladding layers212,214,218According to various implementations, silica (SiO2) is used for the intermediate bottom cladding layer240. In some cases, the intermediate bottom cladding layer240might also uses the same material as the other cladding layers212,214,218. In some cases, the top cladding layer218is SiO2, and has an index refraction of 1.46. The bottom cladding layer214may use Al2O3having an index of refraction of 1.65. According to various implementations, side cladding layers212use Al2O3. Side cladding layers may use atomic layer deposition, having an index of refraction of 1.63. The assistant layer may250may include SiONx and have an index of refraction of 1.70. Materials with index below SiO2 include magnesium fluoride (MgF2, n=1.38) and porous SiO2.

According to various implementations, the waveguide core210is made of dielectric materials of high index of refraction, for instance, Ta2O5, HfO2, TiO2, Nb2O5, Si3N4, SiC, Y2O3, ZnSe, ZnS, ZnTe, Ba4Ti3O12, GaP, CuO2, and Si. The assistant layer250may be formed of a dielectric material having an index of refraction slightly higher than that of the cladding layers214,212, and218but much lower than that of the core, for instance, SiOxNy, AlN, and alloys SiO2—Ta2O5, SiO2—ZnS, SiO2—TiO2. The cladding layers212,214,218,240are each formed of a dielectric material having a refractive index lower than the waveguide core210and the assistant layer250, be made of a material, for instance, Al2O3, SiO, and SiO2. The cladding layers212,214,218,240may be formed of the same material. In some cases, the cladding layers212,214,218,240are formed of different materials. Generally, the dielectric materials are selected so that the refractive index of the core layer210is higher than refractive indices of the cladding layers212,214,218,240. This arrangement of materials facilitates efficient propagation of light through the waveguide system.

InFIG. 2C, the near-field transducer112is shown proximate to a surface of magnetic recording medium232, e.g., a magnetic disk. The waveguide system110delivers electromagnetic energy234to the near-field transducer112, which directs the energy234to create a small hot spot238on the recording medium232. A magnetic write pole236causes changes in magnetic flux near the media-facing surface108in response to an applied current. Flux from the write pole236changes a magnetic orientation of the hot spot238as it moves past the write pole236in the down track direction (y-direction).

In some embodiments, the energy234propagating in the waveguide core210is at a fundamental transverse electric (TE00) mode or a fundamental transverse magnetic (TM00) mode. In some implementations, there may be a mode mismatch between the light source and the waveguide. Efficient coupling from light source to waveguide may be preferred to reduce energy consumption for recording, and also to mitigate heating that occurs from stray light, for instance, light induced writer protrusion. The coupling efficiency is determined by the mode overlap between the light source and the waveguide. For a typical edge-emitting laser diode, the output beam size in l/e2intensity full width is about 1.2 μm along its fast axis direction and 5.2 μm along its slow axis direction. For a waveguide used in heat-assisted magnetic recording, the fundamental mode size is about 0.25 μm normal to waveguide plane and smaller than 0.50 μm parallel to the waveguide plane.

According to various implementations, the light source is a TE (transverse electric) polarized edge-emitting laser diode, orientated such that its fast-axis normal to (along y direction) and slow-axis is parallel to (along x direction) the waveguide plane. The waveguide system110may include a multiplexer that converts the energy234to a combined polarization mode. The combined mode includes a fundamental transverse TM00mode and a first higher-order transverse electric, TE10. The near-field transducer112is excited by the combined mode, and in response, tunnels direct plasmons to the recording medium232.

As described above, the assistant layer may be truncated with an intermediate bottom cladding layer. In accordance with various implementations, the intermediate bottom cladding layer is a different material than the assistant layer. The different materials at the boundary of the assistant layer and the intermediate bottom cladding layer may cause a mode mismatch at the boundary between the intermediate bottom cladding layer and the assistant layer. The assistant layer material is used to match the mode of the light source and, while the material that is chosen for the intermediate bottom cladding layer is used to increase NFT efficiency. Various techniques can be used to improve the mode mismatch between the different materials.

In accordance with various embodiments described herein, the assistant layer is shaped in an effort to improve the mode mismatch between cladding layers.FIG. 3shows a waveguide system300having a shaped assistant layer350. Since the refractive index of the assistant layer is greater than the refractive index of the intermediate bottom cladding layer340, the mode field may extend into the assistant layer350more than that into the intermediate bottom cladding layer340, resulting in mode mismatch and radiation loss. According to various implementations, the assistant layer includes an out-of-plane step to improve the mode mismatch. InFIG. 3, the assistant layer350is positioned proximate the waveguide core310and includes an out-of-plane step319. The step319may be positioned at the interface between the assistant layer350and the intermediate bottom cladding layer340. In some cases, the waveguide core310and the side cladding layers312also include a step as shown inFIG. 3. By fabricating a step, having a width, Δy, the mode mismatch is improved and light delivery efficiency goes up. Since the mode does not fully match at the interface, even with an optimal step size Δy, there may be radiation loss across the interface.FIG. 4shows the efficiency for an out-of-plane step in response to the width of the step. The out-of-plane step increases the efficiency from 0.72 at Δy=0 to 0.77 at a Δy of about 60 nm. According to various embodiments, Δy is between 10-100 nm or between 40 and 80 nm.

According to various implementations, the assistant layer has a taper that narrows towards the media facing surface as shown inFIGS. 5A-5D.FIG. 5Aillustrates an apparatus according to various embodiments that includes an assistant layer having an in-plane taper in accordance with various embodiments. The tapering in the assistant layer starts from W2and ends at W3over length L1. According to various embodiments, the taper starts after the input coupler or near the end of input coupler. As seen inFIG. 5A, a taper starts after the input coupler region of the waveguide core510or near the end of input coupler region510. The tapering in the assistant layer550starts from a first width (W2) and terminates at a second width (W3) over length L1. According to various embodiments, the taper starts after the input coupler or near the end of input coupler. W2may be chosen to be wider than the mode field along X direction, e.g., 3-5 μm. W3may be chosen to be as small as possible, for example, <200 nm to achieve adiabatic mode transformation from assistant layer550material to the intermediate bottom cladding layer540material. The range of W2is between 5 and 6 μm in some embodiments, and may be reached by current photo-lithography using 193 nm UV light with resolution ˜100 nm, for example. The taper length L1may be chosen to minimize mode transmission loss between the assistant layer and the waveguide core. The length of the taper may be chosen to be as short as possible to minimize waveguide sidewall roughness-induced radiation.FIG. 5Aillustrates a linear taper. In other implementations, taper is not linear as shown inFIGS. 5B, 5C, and 5Dfor assistant layers560,570, and580.

FIGS. 6A-6Billustrate the efficiency when using an in-plane taper.FIG. 6Ashows the efficiency using a linear taper versus the length of the taper. As shown, the efficiency reaches the highest using a linear taper having a length greater than 25 μm. According to various embodiments, when using a short taper length, e.g., L1=10 μm, a nonlinear taper can speed up the transition and reach lossless transition.FIG. 6Bshows the efficiency using various taper shapes. A taper with α=1 is linear and α=2 is parabolic. The nonlinear taper may have the form:

z=L1⁢w2α-wαw2α-w3α,
where, z denotes the distance from the top of the taper, W2is the top width and W3is the bottom width, L1is the taper length, and α is the shape factor. Other taper configurations may be used, for example, a cosine shape taper as shown inFIGS. 5A-5D. The efficiency was highest at a taper shape factor of about 0.5.FIG. 6Cshows the efficiency of a nonlinear taper, with α=0.5, versus the top width, W2. In some cases, the efficiency is highest with a taper having a top width between about 5 and 6 μm, e.g., 5.6 μm.

FIG. 7illustrates a cross-sectional view of a slider body according to various embodiments. As seen inFIG. 7, an assistant layer740couples light from the light source into the waveguide core730. The waveguide core730is surrounded by a side cladding layer720, a top cladding layer710, the assistant layer740, and a bottom cladding layer750. According to various implementations, the waveguide core730comprises TiO2and is about 120 nm thick with an index of refraction of 2.36. In some cases, the waveguide core comprises Ta2O5and has a thickness of 0.14 μm and an index of refraction of 2.065. The waveguide core730and the assistant layer740may be surrounded by other cladding layers710,720,750having a lower index of refraction than the waveguide core730. For either configuration, the top cladding may be formed of SiO2having an index of refraction of 1.46. The side cladding may use Al2O3with a thickness of 240 nm and an index of refraction of 1.63. The bottom cladding for either configuration may also use Al2O3and have an index of refraction of 1.65. In some cases, the bottom cladding layer comprises Al2O5. The side cladding layers720may be 220 nm thick, for example. According to various implementations, the thickness of the assistant layer740(ta) is 0.7 μm. the index of refraction of the assistant layer740may be 1.70. The light source is a TE (transverse electric) polarized edge-emitting laser diode, orientated such that its fast-axis normal to (along y direction) and slow-axis parallel to (along x direction) the waveguide plane. The output beam size in 1/e2intensity full width is about 1.2 μm along its fast axis direction and 5.2 μm along its slow axis direction. Modeling with a beam-propagation-method shows that the optimal assistant layer is about 0.7 μm thick and its index of refraction n=1.70. The Ta2O5core tapes linearly from W0=0.16 μm to W1=0.6 μm over 100 μm long.

According to various implementations, the assistant layer840is channeled and is surrounded by cladding layers. As shown inFIG. 8, the assistant layer840is also surrounded by cladding layers860,870. The cladding layers860and870may comprise the same material as the intermediate bottom cladding layer, for example.

According to various configurations described herein, an apparatus includes both an out-of-plane step and an in-plane taper as shown inFIG. 9A. The waveguide core includes an out-of-plane step940. The assistant layer940is tapered and is truncated by an intermediate bottom cladding layer970. The core950and the assistant layer940are surrounded by other cladding layers960,965.

FIG. 9Billustrates a shallow trench wall slope that can be used to reduce the mode mismatch between the assistant layer945and the intermediate bottom cladding layer975. According to various embodiments, an apparatus includes an out-of-plane slope near the interface of the assistant layer and the intermediate bottom cladding layer as shown inFIG. 9B.

According to various embodiments, a method involves receiving light from a light source by an assistant layer that comprises an out-of-plane step. In some cases, the assistant layer comprises an out-of-plane slope from the assistant layer to the intermediate bottom cladding layer. Light is received from the assistant layer by a core layer, the core layer comprising a taper that widens toward the media-facing surface. Light is received from the core layer by a near field transducer that is disposed proximate a media facing surface.