Data storage device adjusting laser input power to compensate for temperature variations

• US 9,025,421 B1
• Filed: 10/08/2014
• Issued: 05/05/2015
• Est. Priority Date: 10/08/2014
• Status: Active Grant

• Current Assignee: Western Digital Technologies Incorporated (Western Digital Corporation)
• Original Assignee: Western Digital Technologies Incorporated (Western Digital Corporation)
• Inventors: Chia, Galvin T., Prabhu, Navin E., Haralson, Phillip S.
• Primary Examiner(s): Agustin, Peter Vincent
• Application Number:
  US14/509,322
• Time in Patent Office: 209 Days
• Field of Search: None
• US Class Current: 369/13.26
• CPC Class Codes: G11B 20/10027 adjusting the signal strength during recording or reproduction, e.g. variable gain amplifiers optimum power control for optical discs G11B7/125
• CPC Class Codes: G11B 20/105 selecting parameter values from a plurality of predetermined settings
• 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 5/02 Recording, reproducing, or erasing methods; Read, write or erase circuits therefor
• 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 5/5534 Initialisation, calibration, e.g. cylinder "set-up"
• CPC Class Codes: G11B 5/607 using thermal means

Abstract

A data storage device is disclosed comprising a head actuated over a disk, wherein the head comprises a laser configured to heat the disk while writing data to the disk. A temperature is measured, and a first input power is generated based on a first function of the measured temperature, wherein the first function compensates for a temperature dependent output power of the laser. A second input power is generated based on a second function of the measured temperature, wherein the second function compensates for a temperature dependent coercivity of the disk. The first input power is combined with the second input power to generate a write power applied to the laser while writing data to the disk.

Claims

1. A data storage device comprising:

a disk;

a head actuated over the disk, wherein the head comprises a laser configured to heat the disk while writing data to the disk; and

control circuitry configured to;

measure a temperature;

generate a first input power based on a first function of the measured temperature, wherein the first function compensates for a temperature dependent output power of the laser;

generate a second input power based on a second function of the measured temperature, wherein the second function compensates for a temperature dependent coercivity of the disk; and

combine the first input power with the second input power to generate a write power applied to the laser while writing data to the disk.

2. The data storage device as recited in claim 1, wherein the control circuitry is further configured to:

measure the output power of the laser over a plurality of temperatures; and

generate the first function based on the measured output powers.

3. The data storage device as recited in claim 2, wherein the head further comprises a photodiode, and the control circuitry is further configured to measure the output power of the laser over the plurality of temperatures based on the photodiode.

4. The data storage device as recited in claim 1, wherein the control circuitry is further configured to:

use the first function to generate a first calibration power based on a first temperature;

apply the first calibration power to the laser at the first temperature and calibrate a first write power that provides adequate write quality;

use the first function to generate a second calibration power based on a second temperature;

apply the second calibration power to the laser at the second temperature and calibrate a second write power that provides adequate write quality; and

generate the second function based on the first and second temperatures and the first and second calibrated write powers.

5. The data storage device as recited in claim 1, wherein:

the first function comprises a substantially non-linear function; and

the second function comprises a substantially linear function.

6. The data storage device as recited in claim 1, wherein the control circuitry is further configured to:

measure a degradation of the laser over time; and

adjust the first function based on the measured degradation of the laser.

7. The data storage device as recited in claim 1, wherein the control circuitry is further configured to:

measure an operating interval of the laser over a life of the data storage device; and

adjust the first function based on the measured operating interval.

8. The data storage device as recited in claim 7, wherein the control circuitry is further configured to adjust the second function based on at least one of the adjusted first function and the measured operating interval.

9. A method of operating a data storage device, the method comprising:

measuring a temperature;

generating a first input power based on a first function of the measured temperature, wherein the first function compensates for a temperature dependent output power of a laser;

generating a second input power based on a second function of the measured temperature, wherein the second function compensates for a temperature dependent coercivity of a disk; and

combining the first input power with the second input power to generate a write power applied to the laser while writing data to the disk.

10. The method as recited in claim 9, further comprising:

measuring the output power of the laser over a plurality of temperatures; and

generating the first function based on the measured output powers.

11. The method as recited in claim 10, further comprising measuring the output power of the laser over the plurality of temperatures based on a photodiode.

12. The method as recited in claim 9, further comprising:

using the first function to generate a first calibration power based on a first temperature;

applying the first calibration power to the laser at the first temperature and calibrate a first write power that provides adequate write quality;

using the first function to generate a second calibration power based on a second temperature;

applying the second calibration power to the laser at the second temperature and calibrate a second write power that provides adequate write quality; and

generating the second function based on the first and second temperatures and the first and second calibrated write powers.

13. The method as recited in claim 9, wherein:

the first function comprises a substantially non-linear function; and

the second function comprises a substantially linear function.

14. The method as recited in claim 9, further comprising:

measuring a degradation of the laser over time; and

adjusting the first function based on the measured degradation of the laser.

15. The method as recited in claim 9, further comprising:

measuring an operating interval of the laser over a life of the data storage device; and

adjusting the first function based on the measured operating interval.

16. The method as recited in claim 15, further comprising adjusting the second function based on at least one of the adjusted first function and the measured operating interval.