Method and apparatus for detecting and remediating in response to insufficient or excessive HAMR optical power

• US 9,916,849 B1
• Filed: 11/09/2016
• Issued: 03/13/2018
• Est. Priority Date: 11/09/2016
• Status: Active Grant

• Current Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Original Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Inventors: Mader, Drew Michael, Rausch, Tim, Angelo, James E.
• Primary Examiner(s): Dinh, Tan X
• Application Number:
  US15/347,129
• Time in Patent Office: 489 Days
• Field of Search: None
• CPC Class Codes: G11B 11/10506 by modulating only the light beam of the transducer
• CPC Class Codes: G11B 11/1051 by modulating both the magnetic field and the light beam at the transducers
• CPC Class Codes: G11B 2005/0021 Thermally assisted recording using an auxiliary energy source for heating the recording layer locally to assist the magnetization reversal
• CPC Class Codes: G11B 5/012 Recording on, or reproducing or erasing from, magnetic disks G11B17/00, G11B19/00 take precedence
• CPC Class Codes: G11B 5/6088 Optical waveguide in or on flying head
• CPC Class Codes: G11B 7/126 Circuits, methods or arrangements for laser control or stabilisation
• CPC Class Codes: G11B 7/1267 Power calibration

Abstract

An optical power level applied via a laser when recording data to a track of a heat-assisted recording medium is determined. In response to the optical power level being too low or too high, remedial action is taken to prevent loss of data on one or more of the track and an adjacent track.

Claims

1. A method comprising:

determining high and low power levels applied via a laser used to record data to a heat-assisted recording medium using the laser, the high power level resulting in interference with an adjacent track and the low power level resulting in reduced reliability of the data recorded to the track;

determining, via a power sensor, an optical power level applied via the laser when recording a track to the heat-assisted recording medium; and

in response to the optical power level being at or below the low power level or at or above the high power level, taking remedial action to prevent loss of data on one or more of the track and the adjacent track, wherein the remedial action comprises one of;

adjusting a first counter of adjacent track writes associated with the adjacent track, the adjacent track being rewritten when the first counter exceeds a first threshold; and

adjusting a second counter of adjacent track writes associated with the track, the track being rewritten when the second counter exceeds a second threshold.

2. The method of claim 1, wherein the power sensor comprises a photodetector.

3. The method of claim 1, wherein the power sensor comprises a bolometer.

4. The method of claim 1, wherein the remedial action includes adjusting the first counter of adjacent track writes the adjusting of the first counter causing the adjacent track to be rewritten sooner than would occur if the optical power was between the low power level and the high power level when recording the track.

5. The method of claim 4, wherein the remedial action includes adjusting the second counter of adjacent track writes, the adjusting of the second counter causing the track to be rewritten sooner than would occur if the optical power was between the low power level and the high power level when recording the track.

6. The method of claim 1, wherein the remedial action includes adjusting the second counter of adjacent track writes, the adjusting of the counter causing the track to be rewritten sooner than would occur if the optical power was between the low power level and the high power level when recording the track.

7. The method of claim 1, wherein the optical power level is at or above the high power level or at or below the low power level due to mode-hopping of the laser.

8. The method of claim 1, further comprising determining that side peaks of a dibit response of the track have exceeded a threshold, indicating the track is written off-center and a direction thereof, and wherein the remedial action is taken further in response to the side peaks of the dibit response exceeding the threshold.

9. An apparatus comprising:

circuitry configured to read a signal from a power sensor that detects an optical power level applied via a laser when recording data to a track of a heat-assisted recording medium;

and a controller coupled to the circuitry and configured to;

determine a high power level that when applied to the laser during recording, results in interference with an adjacent track;

determine a low power level that, when applied to the laser during recording, results in reduced reliability of the data;

determine, via the power sensor, that the optical power when recording data to the track is at or below the low power level or at or above the high power level; and

in response to the optical power level being at or below the low power level or at or above the high power level, take remedial action to prevent loss of data on one of the track or an adjacent track, wherein the remedial action comprises one of;

adjusting a first counter of adjacent track writes associated with the adjacent track, the adjacent track being rewritten when the first counter exceeds a first threshold; and

adjusting a second counter of adjacent track writes associated with the track, the track being rewritten when the second counter exceeds a second threshold.

10. The apparatus of claim 9, wherein the power sensor comprises one of a photodetector or a bolometer.

11. The apparatus of claim 9, wherein the remedial action includes adjusting the first counter of adjacent track writes, the adjusting of the first counter causing the adjacent track to be rewritten sooner than would occur if the optical power was between the low power level and the high power level when recording the track.

12. The apparatus of claim 11, wherein the remedial action further includes adjusting the second counter of track writes, the adjusting of the second counter causing the track to be rewritten sooner than would occur if the optical power was between the low power level and the high power level when recording the track.

13. The apparatus of claim 9, wherein the remedial action further includes adjusting the second counter of track writes, the adjusting of the first counter causing the track to be rewritten sooner than would occur if the optical power was between the low power level and the high power level when recording the track.

14. The apparatus of claim 9, wherein the optical power level is at or above the high power level or at or below the low power level due to mode-hopping of the laser.

15. The apparatus of claim 9, wherein the controller is further configured to determine that side peaks of a dibit response of the track have exceeded a threshold, indicating the track is written off-center and a direction thereof, and wherein the remedial action is taken further in response to the side peaks of the dibit response exceeding the threshold.

16. A method comprising:

determine, via a power sensor optically coupled to a laser of a read/write head, that an optical power level has exceeded a first threshold by a power level delta when recording a target track to a heat-assisted recording medium;

determining that side peaks of a dibit response of the target track have exceeded a second threshold, indicating the target track is written off-center and a direction thereof;

determining a combined metric comprising the power level delta and the side peaks of the dibit response; and

in response to the combined metric exceeding a remedial response threshold, rewrite one or more adjacent tracks adjacent to the target track to prevent loss of data on the one or more adjacent tracks due to adjacent track interference.

17. The method of claim 16, wherein rewriting the one or more adjacent track includes adjusting respective counters of adjacent track writes associated with the one or more adjacent tracks, the one or more adjacent tracks being rewritten when the counters exceed a threshold, the adjusting of the counters causing the one or more adjacent tracks to be rewritten sooner than would occur than if the combined metric was below the remedial response threshold when recording the target track.

18. The method of claim 17, further comprising adjusting a second counter of adjacent track writes associated with the target track, the target track being rewritten when the second counter exceeds a threshold, the adjusting of the second counter causing the target track to be rewritten sooner than would than if the combined metric was below the remedial response threshold when recording the target track.

19. The method of claim 17, wherein the one or more adjacent tracks comprise two or more adjacent tracks on either side of the target track, the counters being adjusted by different amounts to account for the direction that the target track is off-center.