Laser mode hopping detection for heat-assisted magnetic recording device

• US 9,984,719 B2
• Filed: 12/02/2015
• Issued: 05/29/2018
• Est. Priority Date: 12/02/2015
• Status: Active Grant

• Current Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Original Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Inventors: Matousek, Robert, Lammers, Todd, Trantham, Jon David
• Primary Examiner(s): Dinh, Tan X
• Application Number:
  US14/957,220
• Publication Number:
  US 20170162222A1
• Time in Patent Office: 909 Days
• Field of Search: None
• CPC Class Codes: G11B 11/10534 for recording by magnetising, demagnetising or transfer of magnetisation, by radiation, e.g. for thermomagnetic recording
• CPC Class Codes: G11B 11/10595 Control of operating function
• CPC Class Codes: G11B 19/046 Detection or prevention or problems due to temperature
• 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 5/314 where the layers are extra layers normally not provided in the transducing structure, e.g. optical layers G11B5/3196 takes precedence
• CPC Class Codes: G11B 5/40 Protective measures on heads, e.g. against excessive temperature G11B5/31 takes precedence; protection against wear G11B5/255 ; protective structure of the head: see under structures, e.g. G11B5/3106
• CPC Class Codes: G11B 5/455 Arrangements for functional testing of heads; Measuring arrangements for heads
• CPC Class Codes: G11B 7/126 Circuits, methods or arrangements for laser control or stabilisation
• CPC Class Codes: G11B 7/1263 Power control during transducing, e.g. by monitoring
• CPC Class Codes: G11B 7/1267 Power calibration
• CPC Class Codes: G11B 7/13 Optical detectors therefor

Abstract

Methods and apparatuses for detecting mode hopping in a laser diode or other optical energy source in heat-assisted magnetic recording. An output power of the laser diode or other optical energy source is measured and the output power is differentiated over time to determine a rate of change. If it is determined that the rate of change exceeds a threshold value, a fault signal is asserted indicating a potential mode hopping event.

Claims

1. A method for detecting mode hopping in a laser diode of a storage device, the method comprising steps of:

receiving a time-variant signal from a photodetector optically connected to the laser diode while the laser diode is engaged for writing data to a recording media of the storage device, the time-variant signal indicating a light energy output of the laser diode;

differentiating the signal over time to produce a differentiated signal representing a rate of change in the light energy output of the laser diode;

determining whether the differentiated signal exceeds a threshold value indicating a rapid change in an oscillation wavelength of the laser diode; and

upon determining that the differentiated signal exceeds the threshold value, asserting a fault signal to a controller of the storage device indicating a potential write-fault due to a mode hopping event in the laser diode.

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

3. The method of claim 1, wherein differentiating the signal over time is performed by a high-pass filter.

4. The method of claim 1, wherein differentiating the signal over time is performed by an AC-coupled differentiator circuit.

5. The method of claim 1, wherein determining whether the amplified differentiated signal exceeds a threshold value is performed by a comparator.

6. The method of claim 1, wherein the steps are performed by a fault logic circuit in a preamplifier of a hard disk drive (“

HDD”

) device implementing heat-assisted magnetic recording (“

HAMR”

) technology.

7. A storage device configured to:

measure a voltage output of a photodetector optically connected to a laser diode in an optical heating element of a read/write head configured for heat-assisted magnetic recording (“

HAMR”

) during a write operation of data to a recording media of the storage device, the voltage output representing a light energy output of the laser diode;

determine a rate of change in the voltage output of the photodetector over time;

determine whether the rate of change in the voltage output of the photodetector exceeds a threshold value indicating a rapid change in an oscillation wavelength of the laser diode; and

if the rate of change of the voltage output of the photodetector exceeds the threshold value, assert a fault signal to a controller of the storage device indicating a potential write fault.

8. The storage device of claim 7, wherein determining the rate of change of the voltage output of the photodetector over time is performed by a differentiation circuit.

9. The storage device of claim 8, wherein the differentiation circuit comprises a high-pass filter.

10. The storage device of claim 8, wherein the photodetector comprises a bolometer.

11. The storage device of claim 8, wherein an output of the differentiation circuit is compared to a threshold voltage level corresponding to the threshold value in a comparator to determine if the rate of change of the voltage output of the photodetector exceeds the threshold value.

12. The storage device of claim 8, wherein the controller is configured to, upon assertion of the fault signal, perform error recovery to avoid loss of the data.

13. The storage device of claim 8, wherein the measuring, determining, and asserting are performed by a preamplifier component of the storage device.

14. A preamplifier for a hard disk drive (“

HDD”

) implementing heat-assisted magnetic recording (“

HAMR”

), the preamplifier comprising;

a differentiator circuit configured to receive a signal from a photodetector and produce a differentiated signal representing a rate of change in light energy output of a laser diode at any given time, the photodetector optically coupled to the laser diode in an optical heating element of a read/write head in the HDD; and

a threshold detector configured to determine if the differentiated signal exceeds a threshold voltage level indicating a rapid change in an oscillation wavelength of the laser diode, and upon determining that the differentiated signal exceeds the threshold voltage level, assert a fault signal to a controller of the HDD.

15. The preamplifier of claim 14, further comprising an amplifier configured to amplify the differentiated signal.

16. The preamplifier of claim 14, further comprising a low pass filter to filter out high-frequency noise in the signal from the photodetector.

17. The preamplifier of claim 14, further comprising a rectifier for rectifying the differentiated signal.

18. The preamplifier of claim 14, wherein differentiator circuit comprises a high-pass filter configured in a programmable band-pass filter.