Systems and methods for increasing media absorption efficiency using interferometric waveguides

[0001] The present invention relates to information storage devices, and more specifically to systems and methods for increasing media absorption efficiency using interferometric waveguides in information storage devices.

[0002] Energy assisted magnetic recording (EAMR) or heat assisted magnetic recording (HAMR) technology is often used to increase areal density of information storage devices such as magnetic disks. In these assisted recording systems, a laser beam is delivered through an optical waveguide and interacts with a near field transducer (NFT) that absorbs part of the optical energy and forms a very strong localized electromagnetic field in the near field region. When the localized electromagnetic field is close enough to the recording medium, the recording medium absorbs part of the localized electromagnetic field energy and heats up thermally, which helps to realize the whole magnetic recording process.

[0003] A primary design goal of EAMR involves getting high media absorption efficiency. Media absorption efficiency is defined as energy being absorbed by media layers divided by incident light energy in the optical waveguide. A key challenge to improving media absorption efficiency is to find a waveguide structure that provides strong interactions between the waveguide mode and the near field transducer (NFT). The stronger the interactions between these components, the stronger the electrical field produced by NFT will be. Therefore, given the strong interactions between the waveguide mode and the NFT, the media absorption efficiency will be larger.

[0004] A number of different light delivery designs have been proposed in an attempt to maximize NFT efficiency. One such design uses a planar waveguide with a parabolic solid immersion mirror to focus laser light on a disk-shaped NFT. The key to realizing this structure is to properly introduce a pi phase shift between the light waves coming to the NFT from the opposite sides of the parabolic mirror.

[0005] Another design uses a channel waveguide to deliver light to an aperture based NFT. The light is coupled into the optical channel waveguide via a mode converter and is guided to the vicinity of the NFT. At the air bearing surface (ABS) side, the light interacts with an NFT and forms a very strong localized electrical field.

[0006] However, the above described designs provide weak interaction between incident light and the NFT resulting in low media absorption efficiency. In addition, these designs impose some challenges to the EAMR manufacturing processes due to tight process tolerances. As such, an improved waveguide structure for increasing media absorption efficiency without negatively impacting current optical waveguide manufacturing processes is needed.

[0007] Aspects of the invention relate to systems and methods for increasing media absorption efficiency using interferometric waveguides in information storage devices. In one embodiment, the invention relates to an interferometric waveguide assembly including a light source, a first waveguide arm and a second waveguide arm, a splitter configured to receive light from the light source and to split the light into the first waveguide arm and the second waveguide arm, and a near field transducer (NFT) configured to receive the light from the first waveguide arm and the second waveguide arm, where the first waveguide arm and the second waveguide arm converge to form a preselected angle at a junction about opposite the splitter, and where the first waveguide arm and the second waveguide arm are configured to induce a preselected phase difference in the light arriving at the NFT.

[0008] In another embodiment, the invention relates to a method for forming an interferometric waveguide assembly, the method including forming a reader, forming a return pole on the reader, forming a cladding layer on the return pole, forming a core layer on the cladding layer, forming the interferometric waveguide assembly within the core layer, where the interferometric waveguide assembly includes a first waveguide arm and a second waveguide arm, and a splitter configured to receive light from a light source and to split the light into the first waveguide arm and the second waveguide arm, where the first waveguide arm and the second waveguide arm converge to form a preselected angle at a junction about opposite the splitter, and where the first waveguide arm and the second waveguide arm are configured to induce a preselected phase difference in the light arriving at a near field transducer (NFT), and forming a write pole on the waveguide assembly.

[0021] Referring now to the drawings, embodiments of systems and methods for increasing media absorption efficiency in an energy assisted magnetic recording (EAMR) head assembly using interferometric waveguides are illustrated. In many embodiments, the EAMR head assemblies with the interferometric waveguides are configured for use within an information storage device. The interferometric waveguides include two waveguide arms configured to induce a preselected phase difference (phase delay or phase advance) in the light passing through the one of the two waveguide arms to efficiently maximize the light energy absorption of a magnetic recording media of the storage device.

[0022] The preselected phase delay or phase advance can be accomplished using a number of different configurations. These configurations can include embodiments where one waveguide arm has an unequal length, an unequal width, an unequal thickness, different materials, and/or different side wall angles than the other waveguide arm. In other embodiments, one waveguide arm may be acted on by a phase retarder, a heater, and/or an electric field. In each case, the interferometric waveguide configuration can induce the preselected phase difference in the light arriving at a near field transducer positioned near a junction where the waveguide arms converge. In such case, the light travelling through the waveguide can be effectively converted into thermal energy delivered to one or more media disks of a storage device. In several embodiments, the preselected phase difference is an odd multiple of 180 degrees (or pi radians).

[0023] FIG. 1a is a front view of an energy assisted magnetic recording (EAMR) head assembly 100 including an interferometric waveguide 102 configured to receive light from a laser 103 and to direct the received light to a near field transducer (NFT) 104 that directs light energy on to a magnetic media 106, where the waveguide 102 is configured to efficiently maximize the media light energy absorption by inducing a preselected phase difference in the light travelling along two waveguide arms (102a, 102b) in accordance with one embodiment of the invention. The waveguide 102 is mounted to a slider 108 (e.g., magnetic transducer for a magnetic storage device). The laser 103 is mounted to a submount 110 that is mounted to the slider 108.

[0024] The light from the laser 103 is received at an upper waveguide inlet 102c and then split into the first waveguide arm 102a and second waveguide arm 102b at an optical splitter 102d. Light travelling along the first waveguide arm 102a is delayed or advanced by the preselected phase difference using one or more of a number of techniques for controlling the phase difference, described in detail below, and efficiently and constructively combines with the light from the second waveguide arm 102b at the NFT 104. The NFT 104 then converts the light energy into near-field electromagnetic energy and directs it into the media 106. In several embodiments, the preselected phase difference is an odd multiple of 180 degrees, or (2n+1) multiplied by 180 degrees where n is an integer.

[0025] Along the waveguide 102 and at a point between the waveguide inlet 102c and the splitter 102d extending to the first waveguide arm 102a and second waveguide arm 102b, the waveguide 102 forms two S-shaped bends (102a-s, 102b-s). Each of the waveguide arms (102a, 102b) extends downward from the S-shaped bends (102a-s, 102b-s) and then changes direction inward at a joining arm (102a-j, 102b-j). The joining arms (102a-j, 102b-j) converge at a junction occupied by the NFT 104. The joining arms (102a-j, 102b-j) form a preselected angle selected from the range of about 80 degrees to about 140 degrees. In another embodiment, the preselected angle is selected from a smaller range of about 100 degrees to about 120 degrees.

[0026] In several embodiments, the preselected phase difference is induced when one of the waveguide arms has an unequal length, an unequal width, different materials, and/or different side wall angles as compared to the other waveguide arm. In other embodiments, the preselected phase difference is induced when one of the waveguide arms is acted on by a phase retarder, a heater, and/or an electric field. In yet other embodiments, the preselected phase difference is induced when one of the waveguide arms has unequal side wall angle, thickness, or another suitable waveguide arm characteristic. In one embodiment, the laser can be replaced with another suitable light source. In several embodiments, the splitter can be a Y-splitter, a multi-mode interference (MMI) splitter, a directional coupler splitter, another suitable splitter known in the art, or some combination of these splitters.

[0027] In the embodiment illustrated in FIG. 1a, the preselected phase difference is accomplished, at least in part, by making a characteristic of one of the two waveguide arms different from the other arm. In other embodiments, the preselected phase difference can be accomplished using other suitable implementations. For example, co-pending U.S. patent application Ser. No., entitled, “SYSTEMS AND METHODS FOR CONTROLLING LIGHT PHASE AT NEAR FIELD TRANSDUCERS OF INTERFEROMETRIC WAVEGUIDES”, having Ser. No. 13/399,325, the entire content of which is expressly incorporated herein by reference, describes a number of suitable techniques for accomplishing the preselected phase difference for an interferometric waveguide that involve controllably heating the light source.

[0028] FIG. 1b is a side view of the EAMR head assembly 100 of FIG. 1a including the interferometric waveguide 102 positioned within the slider 108 and the laser 103 mounted to the submount 110 attached to the slider 108 in accordance with one embodiment of the invention.

[0029] FIG. 2 is a top view of an interferometric waveguide 202 configured to induce a preselected phase difference in the light travelling along two waveguide arms (202a, 202b) using different side wall angles, thicknesses, or materials for the waveguide arms in accordance with one embodiment of the invention. Similar to the interferometric waveguide of FIGS. 1a and 1b, light is received by the waveguide 202 at the upper waveguide inlet 202c and then split into the first waveguide arm 202a and second waveguide arm 202b at an optical splitter 202d. Light travelling along the first waveguide arm 202a is delayed or advanced by the preselected phase difference and efficiently and constructively combines with the light from the second waveguide arm 202b at the NFT 204. In several embodiments, the splitter 204d splits the light between the first waveguide arm 202a and second waveguide arm 202b equally. In another embodiment, the light is delayed or advanced along the second waveguide arm 202b rather than the first waveguide arm 202a.

[0030] In one embodiment for varying the side wall angles, for example, the side wall angle of the second waveguide arm is set to about 90 degrees, while the side wall angle of the first waveguide arm is varied from about 78 degrees to about 102 degrees to achieve the desired preselected phase difference (e.g., about 180 degrees). In one embodiment for varying the waveguide arm materials, for example, the material of the second waveguide arm 202b includes Ta₂O₅ and/or AN, while the material of the first waveguide 202a arm includes SiNxOy, where x and y have suitable values as known in the art. In other embodiments, other suitable side wall angles and materials can be used.

[0031] In several embodiments, the first and second waveguide arms (202a, 202b) have a rectangular cross section (e.g., of a core area of the waveguide). In such case, a thickness (e.g., height of the rectangular cross section) of the second waveguide arm, which is also the core thickness, can be set to a preselected thickness, and the thickness of the first waveguide arm can be set to a preselected thickness, where the thicknesses are different to achieve the desired preselected phase difference. In one such embodiment, the thickness of the second waveguide is about 120 nm, while the thickness of the first waveguide arm is about 160 nm when the core width is about 550 nm and configured with a Ta₂O₅ core and SiO2 cladding. In other embodiments, other suitable thicknesses can be used. In other embodiments, the waveguide arms can have other suitable cross section shapes.

[0032] FIG. 3 is a top view of an interferometric waveguide 302 configured to induce a preselected phase difference in the light travelling along two waveguide arms (302a, 302b) using unequal waveguide arm lengths in accordance with one embodiment of the invention. Similar to several of the interferometric waveguides described above, light is received by the waveguide 302 at the upper waveguide inlet 302c and then split into the first waveguide arm 302a and second waveguide arm 302b at an optical splitter 302d. Light travelling along the first waveguide arm 302a is delayed or advanced by the preselected phase difference and efficiently and constructively combines with the light from the second waveguide arm 302b at the NFT 304.

[0033] As can be seen in FIG. 3, the first waveguide arm 302a is substantially longer than the second waveguide arm 302b. For example, the length difference between the waveguide arms can be about 200 nm to about 300 nm, or an odd integer multiple of such values. In one embodiment, the first waveguide arm 302a has a length of about 100 microns, and the second waveguide arm 302b has a length of about 100.25 microns. In other embodiments, other suitable lengths can be used to provide the desired preselected phase difference. In several embodiments, the desired preselected phase difference is an odd integer multiple of about 180 degrees or pi radians.

[0034] FIG. 4 is a top view of an interferometric waveguide 402 configured to induce a preselected phase difference in the light travelling along two waveguide arms (402a, 402b) using unequal waveguide arm widths in accordance with one embodiment of the invention. Similar to several of the interferometric waveguides described above, light is received by the waveguide 402 at the upper waveguide inlet 402c and then split into the first waveguide arm 402a and second waveguide arm 402b at an optical splitter 402d. Light travelling along the first waveguide arm 402a is delayed or advanced by the preselected phase difference and efficiently and constructively combines with the light from the second waveguide arm 402b at the NFT 404.

[0035] As can be seen in FIG. 4, the first waveguide arm 402a is wider than the second waveguide arm 402b. For example, the first waveguide arm 402a has a width of about 500 to 600 nm, and the second waveguide arm 402b has a width of about 500 nm. In other embodiments, other suitable widths can be used to provide the desired preselected phase difference. In several embodiments, the desired preselected phase difference is an odd integer multiple of about 180 degrees or pi radians. In one embodiment, a waveguide width difference of about 5 nm can cause about 30 degrees phase variation across the waveguide structure 402.

[0036] FIG. 5 is a top view of an interferometric waveguide 502 configured to induce a preselected phase difference in the light travelling along two waveguide arms (502a, 502b) using a phase retarder 505 on one 502a of the waveguide arms in accordance with one embodiment of the invention. Similar to several of the interferometric waveguides described above, light is received by the waveguide 502 at the upper waveguide inlet 502c and then split into the first waveguide arm 502a and second waveguide arm 502b at an optical splitter 502d. Light travelling along the first waveguide arm 502a is delayed or advanced by the preselected phase difference and efficiently and constructively combines with the light from the second waveguide arm 502b at the NFT 504.

[0037] Light is delayed by the phase retarder 505 which is implemented as a thin or plane like sheet of metallic material positioned above the first waveguide arm 502a. The phase retarder 505 is configured to induce the preselected phase delay/difference. In other embodiments, the phase retarder 505 can be positioned in another suitable configuration (e.g., below or along a side of the first waveguide arm 502a) such that the phase retarder 505 is sufficiently near the first waveguide arm 502a to have the intended effect on the phase delay. In one embodiment, the phase retarder 505 is about 9 micrometers in length. In other embodiments, the length can be adjusted to achieve a preselected phase delay. In one embodiment, the phase retarder 505 is made of gold or a gold alloy. In other embodiments, the phase retarder 505 can be made of other suitable materials.

[0038] FIG. 6 is a top view of an interferometric waveguide 602 configured to induce a preselected phase difference in the light travelling along two waveguide arms (602a, 602b) using a heater 605 on one of the waveguide arms 602a in accordance with one embodiment of the invention. Similar to several of the interferometric waveguides described above, light is received by the waveguide 602 at the upper waveguide inlet 602c and then split into the first waveguide arm 602a and second waveguide arm 602b at an optical splitter 602d. Light travelling along the first waveguide arm 602a is delayed or advanced by the preselected phase difference and efficiently and constructively combines with the light from the second waveguide arm 602b at the NFT 604.

[0039] Light is delayed or advanced due to the heat applied by the heater 605 positioned proximate the first waveguide arm 502a. The heater 605 is configured to provide a preselected amount of heat to induce the preselected phase difference. In one embodiment, the heater 605 is implemented as a controllable heat source such as a spiral trace or another suitable trace configuration as known in the art. In other embodiments, the heater 605 can be implemented in other suitable configurations known in the art.

[0040] FIG. 7 is a top view of an interferometric waveguide 702 configured to induce a preselected phase difference in the light travelling along two waveguide arms (702a, 702b) using an electric field applied between two electrodes (705a, 705b) on one 702a of the waveguide arms in accordance with one embodiment of the invention. Similar to several of the interferometric waveguides described above, light is received by the waveguide 702 at the upper waveguide inlet 702c and then split into the first waveguide arm 702a and second waveguide arm 702b at an optical splitter 702d. Light travelling along the first waveguide arm 702a is delayed or advanced by the preselected phase delay and efficiently and constructively combines with the light from the second waveguide arm 702b at the NFT 704.

[0041] Light is delayed or advanced by the electric field 707 extending between electrodes 705a and 705b and across the first waveguide arm 702a. The electric field 707 is configured to induce the preselected phase difference. In one embodiment, a voltage of about 30 to 50 volts applied between the two electrodes 705a and 705b to achieve a sufficient electric field and the preselected phase difference. In other embodiments, the electric field 707 can be implemented using other suitable configurations known in the art. In other embodiments, the electrodes can be positioned in different configurations. In one such embodiment, for example, one electrode is positioned above the waveguide arm and the other below the waveguide arm.

[0042] FIG. 8a is a top schematic view of a Y-splitter 802d-1 that can be used in an interferometric waveguide to split received light into two separate waveguide arms in accordance with one embodiment of the invention. In several embodiments, the Y-splitter 802d-1 can be used in any of the interferometric waveguides described above. In one embodiment, Y-splitter 802d-1 can be used to split received light equally between two waveguide arms. In another embodiment, Y-splitter 802d-1 can be used to split received light unequally between two waveguide arms.

[0043] FIG. 8b is a top schematic view of a multi-mode interference (MMI) splitter 802d-2 that can be used in an interferometric waveguide to split received light into two separate waveguide arms in accordance with one embodiment of the invention. In several embodiments, the MMI splitter 802d-2 can be used in any of the interferometric waveguides described above. In one embodiment, MMI splitter 802d-2 can be used to split received light equally between two waveguide arms. In another embodiment, MMI splitter 802d-2 can be used to split received light unequally between two waveguide arms.

[0044] FIG. 8c is a top schematic view of a directional coupler splitter 802d-3 that can be used in an interferometric waveguide to split received light into two separate waveguide arms in accordance with one embodiment of the invention. In several embodiments, the directional coupler splitter 802d-3 can be used in any of the interferometric waveguides described above. In one embodiment, directional coupler splitter 802d-3 can be used to split received light equally between two waveguide arms. In another embodiment, directional coupler splitter 802d-3 can be used to split received light unequally between two waveguide arms.

[0045] FIG. 9 is a flow chart of a process 900 for manufacturing an interferometric waveguide configured to receive light from a light source and to direct the received light to a near field transducer (NFT) that directs light energy on to a magnetic media, where the waveguide is configured to efficiently maximize the media light energy absorption by inducing a preselected phase difference in the light travelling along one of the two waveguide arms in accordance with one embodiment of the invention. In particular embodiments, the manufacturing process can be used to form one of the interferometric waveguides described above. The process first forms (902) a reader. The process then forms (904) a return pole on the reader. The process forms (906) a cladding layer on the return pole. The process then forms (908) a core layer on the cladding layer.

[0046] The process then forms (910) the interferometric waveguide assembly within the core layer. The interferometric waveguide assembly can include a first waveguide arm and a second waveguide arm, and a splitter configured to receive light from a light source and to split the light into the first waveguide arm and the second waveguide arm, where the first waveguide arm and the second waveguide arm converge to form a preselected angle at a junction about opposite the splitter, and where the first waveguide arm and the second waveguide arm are configured to induce a preselected phase difference in the light arriving at a near field transducer (NFT). The process then forms (912) a write pole on the waveguide assembly.

[0047] In one embodiment, the process can perform the sequence of actions in a different order. In another embodiment, the process can skip one or more of the actions. In other embodiments, one or more of the actions are performed simultaneously. In some embodiments, additional actions can be performed.

[0048] While the above description contains many specific embodiments of the invention, these should not be construed as limitations on the scope of the invention, but rather as examples of specific embodiments thereof. Accordingly, the scope of the invention should be determined not by the embodiments illustrated, but by the appended claims and their equivalents.

[0049] In a number of embodiments described above, the preselected phase difference is effected on a particular waveguide arm of an interferometric waveguide having two waveguide arms. However, in many embodiments, the preselected phase difference can be effected on either one of the two waveguide arms of the interferometric waveguide.