# US 8,787,129 B1 · Polarization rotator for thermally assisted magnetic recording > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,787,129 B1 - Document ID: US8787129B1 - Status: Granted - Kind: B1 - Application number: 13/785,280 - Filed: 2013-03-05 - Granted: 2014-07-22 - Earliest claimed: 2013-03-05 - Assignees: Headway Technologies, Inc. - Applicants: Headway Technologies, Inc. - Inventors: Xuhui Jin; Hiroyuki Ito; Yoshitaka Sasaki; Shigeki Tanemura - Web page: https://patentgrep.com/patent/US8787129B1 ## CPC - G02B 6/105: {having optical polarisation effects} - G11B 5/314: {where the layers are extra layers normally not provided in the transducing structure, e.g. optical layers (G11B5/3196 takes precedence)} - G11B 5/4866: {the arm comprising an optical waveguide, e.g. for thermally-assisted recording} - G11B 5/6088: {Optical waveguide in or on flying head} - G02B 2006/12173: {Masking} - G02B 2006/12176: {Etching} - G11B 2005/0021: {Thermally assisted recording using an auxiliary energy source for heating the recording layer locally to assist the magnetization reversal} - Y10T 29/49032: Fabricating head structure or component thereof - G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS - G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R) - Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION ## Abstract A waveguide structure with a light polarization rotator section for converting transverse electric light from a TE light source to transverse magnetic light which is subsequently coupled to a plasmon generator (PG) is disclosed. Wavelengths above 800 nm are advantageously used to reduce resistive heating in the PG, and in adjacent cladding and write pole layers to improve the thermally assisted magnetic recording head lifetime. The light polarization rotator section has a length determined by TE LD light wavelength, and the effective mode index of the two orthogonal fundamental modes, and preferably has a symmetric structure including a sloped side with a 45 degree angle with respect to a bottom surface. A vertical side of the light polarization rotator section may be coplanar with sides of adjacent waveguide sections. Offsets to the cross-track width are used to improve symmetry for higher TE to TM polarization conversion efficiency. ## Claims ### Claim 1 A waveguide in a thermally assisted magnetic recording (TAMR) head comprising: (a) a first section with a first width and a first end at a back end of a slider, the first end receives transverse electric (TE) light from an adjoining laser diode (LD), and a second end that is connected to the first end by two parallel sides which are aligned in a first axis direction that is perpendicular to an air bearing surface (ABS); (b) a tapered section having a first width in a cross-track direction at a first end that adjoins the second end of the first section, and a second width in a cross-track direction at a second end that faces the ABS wherein the second width is less than the first width, the tapered section narrows a beam of TE light that is propagated toward the ABS; (c) a first sub-section that has the second width in a cross-track direction between two sides that are aligned in the first axis direction, and a first end adjoining the second end of the tapered section; (d) a second sub-section that has the second width between two sides that are aligned perpendicular to the ABS, and a first end adjoining the ABS, light propagated through the second sub-section is coupled to an adjacent plasmon generator (PG); and (e) a light polarization rotator section for converting TE light from the first sub-section into transverse magnetic (TM) light which enters the second sub-section and is then coupled to the PG, comprising; (1) a first end adjoining a second end of the first sub-section; (2) a second end adjoining an end of the second sub-section that faces away from the ABS; (3) a vertical side formed between a top surface and a bottom surface; and (4) a sloped side formed between the top surface and the bottom surface wherein the top and bottom surfaces are coplanar with a top and a bottom surface of each of the first section, tapered section, and first and second sub-sections. ### Claim 2 (depends on 1) The waveguide of claim 1 wherein the light polarization rotator section has a length L that is equal to a half beating length of two orthogonal fundamental modes and is expressed as L=λ/[2(n1−n2)] where λ is the wavelength of the LD light in free space, and n1 and n2 are an effective mode index of a first and a second orthogonal fundamental mode, respectively. ### Claim 3 (depends on 1) The waveguide of claim 1 wherein the sloped side and the bottom surface of the light polarization rotator section form an angle of about 45 degrees. ### Claim 4 (depends on 1) The waveguide of claim 1 wherein the light polarization rotator section has a cross-sectional shape in the form of a trapezoid wherein a width of the top surface is less than a width of the bottom surface in a cross-track direction. ### Claim 5 (depends on 4) The waveguide of claim 4 wherein the light polarization rotator section is formed along a center plane in the first axis direction, the center plane bisects the first section, tapered section, and the first and second sub-sections, and the vertical side is formed coplanar with an adjacent side of the first sub-section and with an adjacent side of the second sub-section. ### Claim 6 (depends on 1) The waveguide of claim 1 wherein a length of the first section along the first axis direction is from 0 to about 50 microns, and a length of the tapered section along the first axis direction is about 30 to 100 microns. ### Claim 7 (depends on 1) The waveguide of claim 1 wherein the light polarization rotator section has a curved shape formed proximate to one side of a center plane aligned in the first axis direction, the center plane bisects the first section and tapered section, comprising: (a) a first linear section aligned in a cross-track direction and with an end adjoining the second end of the first sub-section; (b) a second linear section formed parallel to the first linear section and adjoining the second sub-section at an end opposite the ABS; and (c) a curved section formed between the first linear section and the second linear section. ### Claim 8 (depends on 1) The waveguide of claim 1 wherein the second sub-section with a second width has a lengthwise dimension along the first axis direction of about 2 to 50 microns. ### Claim 9 (depends on 5) The waveguide of claim 5 wherein the sloped side of the light polarization rotator section is offset by a first distance from a first side of the second sub-section, and the vertical side is offset by a second distance from a second side of the second sub-section such that each of the first and second offsets shorten a width of the light polarization rotator bottom surface in the cross-track direction. ### Claim 10 (depends on 1) The waveguide of claim 1 wherein the light polarization rotator section has a symmetrical triangular shape wherein a height of the vertical side in a down-track direction equals the width of the bottom surface to enable essentially 100% conversion of TE light to TM light. ### Claim 11 (depends on 9) The waveguide of claim 9 wherein the light polarization rotator section has a symmetrical five sided shape wherein the first distance offset forms a vertical fifth side between the sloped side and bottom surface such that a width of the top surface in a cross-track direction equals a height of the vertical fifth side in a down-track direction, and a height of the vertical side in a down-track direction equals a width of the bottom surface in a cross-track direction. ### Claim 12 A thermally assisted magnetic recording (TAMR) head comprising: (a) a waveguide formed between an air bearing surface (ABS) and a back end of a slider, comprising: (1) a first section with a first width and a first end at a back end of the slider, the first end receives a beam of TE light from an adjoining laser diode (LD), and a second end that is connected to the first end by two parallel sides which are aligned in a first axis direction that is perpendicular to the ABS; (2) a tapered section having a first width in a cross-track direction at a first end that adjoins the second end of the first section, and a second width in a cross-track direction at a second end that faces the ABS wherein the second width is less than the first width, the tapered section narrows the LD light beam as the light propagates toward the ABS through the waveguide; (3) a first sub-section that has the second width in a cross-track direction between two sides that are aligned perpendicular to the ABS, and a first end adjoining the second end of the tapered section; (4) a second sub-section that has the second width between two sides that are aligned perpendicular to the ABS, and a first end adjoining the ABS, light propagated through the second sub-section is coupled to an adjacent plasmon generator (PG); and (5) a light polarization rotator section for converting TE light entering from the first sub-section into TM light that exits into the second sub-section, the light polarization rotator section has a vertical side that connects a top surface to a bottom surface, and a sloped side which is formed between the top and bottom surfaces; and (b) the PG which couples TM light from the second sub-section to a plasmon mode that is propagated along a PG surface to an end of the PG at the ABS and then onto a magnetic medium to enable a weaker magnetic field from a write pole to switch a bit in the magnetic medium during a write process; and (c) the write pole that adjoins the PG and has a lengthwise dimension along the first axis direction. ### Claim 13 (depends on 12) The TAMR head of claim 12 wherein the light polarization rotator section is further comprised of a first end adjoining a second end of the first sub-section, and a second end adjoining an end of the second sub-section that faces away from the ABS, and wherein the top and bottom surfaces are coplanar with a top and a bottom surface of each of the first section, tapered section, and first and second sub-sections. ### Claim 14 (depends on 12) The TAMR head of claim 12 wherein the waveguide is comprised of Ta2O5, HfO2, or Si, and adjoins a plurality of cladding layers made of one or more of alumina, silicon oxide, and silicon nitride. ### Claim 15 (depends on 12) The TAMR head of claim 12 wherein the PG is separated from the second waveguide sub-section by a gap distance of about 10 to 100 nm. ### Claim 16 (depends on 12) The TAMR head of claim 12 wherein the PG has a lengthwise dimension in the first axis direction that is less than a lengthwise dimension of the second sub-section in the first axis direction. ### Claim 17 (depends on 12) The TAMR head of claim 12 wherein the light polarization rotator section has a length L along the first axis direction that is equal to a half beating length of two orthogonal fundamental modes and is expressed as L=λ/[2(n1−n2)] where λ is a wavelength of the LD light in free space, and n1 and n2 are an effective mode index of a first orthogonal fundamental mode and a second orthogonal fundamental mode, respectively. ### Claim 18 (depends on 12) The TAMR head of claim 12 wherein the sloped side and the bottom surface of the light polarization rotator section form an angle of about 45 degrees. ### Claim 19 (depends on 12) The TAMR head of claim 12 wherein the light polarization rotator section has an irregular trapezoid shape wherein a width of the top surface is less than a width of the bottom surface in a cross-track direction. ### Claim 20 (depends on 12) The TAMR head of claim 12 wherein the light polarization rotator section is formed along a center plane in the first axis direction, the center plane bisects the first section, tapered section, and the first and second sub-sections, and the vertical side is formed coplanar with an adjacent side of the first sub-section and with an adjacent side of the second sub-section. ### Claim 21 (depends on 12) The TAMR head of claim 12 wherein a length of the first section along the first axis direction is from 0 to about 50 microns, and a length of the tapered section along the first axis direction is about 30 to 100 microns. ### Claim 22 (depends on 12) The TAMR head of claim 12 wherein the light polarization rotator section has a curved shape formed proximate to one side of a center plane aligned in the first axis direction, the center plane bisects the first section and tapered section, and the curved shape comprises: (a) a first linear section aligned in a cross-track direction and with an end adjoining a second end of the first sub-section; (b) a second linear section formed parallel to the first linear section and adjoining the second sub-section at an end opposite the ABS; and (c) a curved section formed between the first linear section and the second linear section. ### Claim 23 (depends on 20) The TAMR head of claim 20 wherein the sloped side of the light polarization rotator section is offset by a first distance from a first side of the second sub-section, and the vertical side is offset by a second distance from a second side of the second sub-section such that each of the first and second offsets shorten a width of the light polarization rotator bottom surface in the cross-track direction. ### Claim 24 (depends on 12) The TAMR head of claim 12 wherein the light polarization rotator section has a symmetrical triangular shape wherein a height of the vertical side in a down-track direction equals a width of the bottom surface to enable essentially 100% conversion of TE light to TM light. ### Claim 25 (depends on 23) The TAMR head of claim 23 wherein the light polarization rotator section has a symmetrical five sided shape wherein the first distance offset forms a vertical fifth side between the sloped side and bottom surface such that a width of the top surface in a cross-track direction equals a height of the vertical fifth side in a down-track direction, and a height of the vertical side in a down-track direction equals a width of the bottom surface in a cross-track direction.