# US 2017/0256277 A1 · Offset waveguide system with a mode converter and a tapered bend

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- Number: US 2017/0256277 A1
- Document ID: US20170256277A1
- Status: Published application
- Kind: A1
- Application number: 15/061,453
- Filed: 2016-03-04
- Published: 2017-09-07
- Earliest claimed: 2016-03-04
- Assignees: Seagate Technology LLC
- Applicants: Seagate Technology LLC
- Inventors: Chubing Peng
- Web page: https://patentgrep.com/patent/US20170256277A1

## CPC

- G11B 5/4866: {the arm comprising an optical waveguide, e.g. for thermally-assisted recording}
- G11B 5/105: Mounting of head within housing {or assembling of head and housing (G11B5/3103 takes precedence)}
- G11B 5/127: Structure or manufacture of heads, e.g. inductive
- 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 5/6088: {Optical waveguide in or on flying head}
- G11B 5/012: Recording on, or reproducing or erasing from, magnetic disks (G11B17/00, G11B19/00 take precedence)
- G11B 2005/0021: {Thermally assisted recording using an auxiliary energy source for heating the recording layer locally to assist the magnetization reversal}
- 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)

## Abstract

A read/write head has an input coupler that receives light at a fundamental mode from an energy source. A mode converter of the read/write head converts light from the fundamental mode to a higher-order mode. The read/write head has a bent waveguide coupled to the mode converter at an interface. The bent waveguide includes a curve with a taper. The taper nullifies the fundamental mode generated in the curve and recovers the higher-order mode at an output of the bent waveguide. A near-field transducer that receives the output of the bent waveguide is offset from the facet of the input coupler in a cross-track direction.

## Claims

### Claim 1

A read/write head, comprising:
an input coupler comprising a facet that receives light from an energy source at a fundamental mode;
a mode converter that converts light from the fundamental mode to a higher-order mode;
a bent waveguide coupled to the mode converter at an interface, the bent waveguide comprising a curve with a taper, the taper nullifying the fundamental mode generated in the curve and matching phases between the fundamental and the higher-order mode to recover the higher-order mode in an output of the bent waveguide; and
a near-field transducer that receives the output of the bent waveguide, near-field transducer being offset from the facet of the input coupler in a cross-track direction.

### Claim 2 (depends on 1)

The read/write head of claim 1, wherein the mode converter comprises a branch waveguide coupled to the bent waveguide and the input coupler at the interface, the branch waveguide extending from the interface in a direction away from a media-facing surface of the read/write head.

### Claim 3 (depends on 1)

The read/write head of claim 1, wherein the bent waveguide further comprises a first bend coupled between the mode converter and the curve, the first bend comprising a curvature opposite that of the curve.

### Claim 4 (depends on 1)

The read/write head of claim 1, wherein the input coupler comprises:
an assistant layer that matches a mode profile of the energy source and input coupler normal to a plane of the bent waveguide; and
a bottom cladding layer below the assistant layer, the bottom cladding layer formed of a first material.

### Claim 5 (depends on 1)

The read/write head of claim 1, wherein the taper comprises a wider cross-track dimension proximate the interface to a narrower cross-track dimension proximate a termination of the bent waveguide.

### Claim 6 (depends on 1)

The read/write head of claim 1, further comprising an output waveguide extending from a termination of the bent waveguide to a media-facing surface of the read/write head.

### Claim 7 (depends on 6)

The read/write head of claim 6, wherein the output waveguide is at a non-normal angle to the media-facing surface.

### Claim 8

A method comprising:
coupling light from an energy source of a read/write head to a facet of an input coupler at a fundamental mode
converting the light from the fundamental mode to a higher-order mode via a mode converter coupled proximate the input coupler at an interface;
coupling the light at the higher-order mode into a bent waveguide comprising a tapered bend that matches phases between the fundamental mode and the higher-order mode to nullify the fundamental mode generated in the bent waveguide and recover the higher-order mode in an output of the bent waveguide; and
coupling the output of the bent waveguide to a near-field transducer of the read/write head, the termination being offset from the facet of the input coupler in a cross-track direction.

### Claim 9 (depends on 8)

The method of claim 8, wherein the bent waveguide comprises aspiral s-bend waveguide.

### Claim 10 (depends on 8)

The method of claim 8, further comprising pushing a mode field of the light onto the near-field transducer via a cladding layer of lower index refraction than a first cladding layer proximate the input coupler.

### Claim 11 (depends on 8)

The method of claim 8, wherein coupling the light to the near-field transducer comprises coupling the light via a straight output waveguide extending from a termination of the bent waveguide to a media-facing surface of the read/write head, the straight output waveguide having a constant cross-track width equal to the narrow dimension.

### Claim 12 (depends on 8)

The method of claim 8, wherein coupling the light to the near-field transducer comprises coupling the light via a tapered output waveguide extending from a termination of the bent waveguide to a media-facing surface of the read/write head.

### Claim 13

A read/write head, comprising:
an input coupler comprising a facet that receives light at a fundamental mode from an energy source;
an s-bend waveguide comprising a first bend coupled to the input coupler at an interface and a second bend comprising a taper, the second bend extending from the first bend to a termination of the s-bend waveguide proximate a near-field transducer of the read/write head, the second bend, the termination being offset from the facet of the input coupler in a cross-track direction; and
a branch waveguide coupled to the s-bend waveguide and the input coupler proximate the interface, the branch waveguide extending away from a media-facing surface of the read/write head and converting the light from the fundamental mode to a higher-order mode that is coupled through the s-bend waveguide.

### Claim 14 (depends on 13)

The read/write head of claim 13, wherein the s-bend waveguide comprises a polynomial spiral.

### Claim 15 (depends on 13)

The read/write head of claim 13, wherein the taper of the s-bend waveguide nullifies the fundamental mode generated along the s-bend waveguide and recovers the higher-mode mode in an output of the s-bend waveguide by matching phase between the fundamental mode and the higher-order mode.

### Claim 16 (depends on 13)

The read/write head of claim 13, wherein the input coupler comprises:
an assistant layer that matches a mode profile of the energy source and input coupler normal to a plane of the s-bend waveguide; and
a bottom cladding layer below the assistant layer, the bottom cladding layer formed of a first material.

### Claim 17 (depends on 16)

The read/write head of claim 16, wherein the bottom cladding layer transitions to a second material of lower index refraction than the first material proximate the s-bend waveguide.

### Claim 18 (depends on 13)

The read/write head of claim 13, wherein the fundamental mode comprises a TE00 mode and the higher-order mode comprises a TE10 mode.

### Claim 19 (depends on 13)

The read/write head of claim 13, wherein the taper comprises a wider cross-track dimension proximate the first bend to a narrower cross-track dimension proximate the termination.

### Claim 20 (depends on 13)

The read/write head of claim 13, further comprising an output waveguide extending from a termination of the s-bend waveguide to a media-facing surface of the read/write head.