Characterizing laser output in a HAMR device

• US 9,153,272 B1
• Filed: 05/15/2014
• Issued: 10/06/2015
• Est. Priority Date: 05/15/2014
• Status: Active Grant

• Current Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Original Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Inventors: Rausch, Tim, Trantham, Jon D., Dykes, John W., Yang, Won Choul
• Primary Examiner(s): Neyzari, Ali
• Application Number:
  US14/278,386
• Time in Patent Office: 509 Days
• Field of Search: 369/13.33, 369/13.32, 369/13.24, 369/13.01, 369/112.27, 369/13.13, 369/13.27, 369/13.26
• US Class Current: 1/1
• 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 5/314 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 5/455 Arrangements for functional testing of heads; Measuring arrangements for heads
• CPC Class Codes: G11B 5/6088 Optical waveguide in or on flying head
• CPC Class Codes: G11B 7/1263 Power control during transducing, e.g. by monitoring
• CPC Class Codes: G11B 7/1267 Power calibration

Abstract

At least one laser input current is applied to a laser in a heat assisted magnetic recording device. Laser output power of the laser is measured at the at least one applied laser current. A relationship is characterized amongst temperature, applied laser input current and laser output power. Laser current is set to an optimal laser current as determined at manufacturing. A metric of recording performance is measured to determine if the relationship is acceptable.

Claims

1. A method comprising:

applying at least one laser input current to a laser in a heat assisted magnetic recording device;

measuring laser output power of the laser at the at least one applied laser current;

characterizing a relationship amongst temperature, the applied laser input current and the laser output power;

setting the laser input current to an optimal laser current as determined at manufacturing; and

measuring a metric of recording performance to determine if the relationship is acceptable.

2. The method of claim 1, wherein applying the at least one laser current to the laser and measuring the laser output power of the laser comprises applying the at least one laser current to the laser when the heat assisted magnetic recording device is positioned over a reserved test track.

3. The method of claim 1, wherein applying the at least one laser current to the laser and measuring the laser output power of the laser comprises:

applying a first laser input current to the laser;

measuring a first laser output power of the laser at the first laser input current;

applying a second laser input current that is different from the first laser input current to the laser; and

measuring a second laser output power of the laser at the second laser input current.

4. The method of claim 1, wherein characterizing the relationship amongst temperature, the applied laser input current and the laser output power comprises characterizing a linear relationship amongst the temperature, the applied laser input current and the laser output power by computing a slope and a y-intercept based on the at least one laser current applied to the laser and the measured laser output power.

5. The method of claim 1, further comprising adjusting a fly height of a slider of the heat assisted magnetic recording device after setting the laser current to the optimal laser current as determined at manufacturing.

6. The method of claim 1, wherein measuring the metric of recording performance to determine if the relationship is acceptable comprises measuring one of track average amplitude, track width, an ability to erase known information and bit-error rate.

7. The method of claim 1, wherein measuring the metric of recording performance to determine if the relationship is acceptable comprises:

measuring bit-error rate with squeeze; and

determining if the bit-error rate with squeeze is acceptable.

8. The method of claim 7, further comprising:

measuring bit-error rate on an isolated data track if the measured bit-error rate with squeeze is unacceptable; and

determining if the bit-error rate on the isolated data track is acceptable.

9. The method of claim 8, further comprising:

reducing the laser output power of the laser if the measured bit-error rate on the isolated data track is acceptable; and

repeating the step of measuring bit-error rate with squeeze if the number of times the bit-error rate has been measured has not exceeded a threshold value and until the bit-error with squeeze is acceptable.

10. The method of claim 9, further comprising adjusting fly height of a slider of the heat assisted magnetic recording device after reducing the laser output power of the laser.

11. The method of claim 8, further comprising:

increasing the laser output power of the laser if the measured bit-error rate on the isolated data track is unacceptable; and

repeating the step of measuring bit-error rate with squeeze if the number of times the bit-error rate has been measured has not exceeded a threshold value and until the bit-error rate with squeeze is acceptable.

12. The method of claim 11, further comprising adjusting fly height of a slider of the heat assisted magnetic recording device after increasing the laser output power of the laser.

13. A data storage device comprising:

a medium;

a heat assisted magnetic recording device including a laser for heating the medium while writing data; and

control circuitry configured to;

apply at least one laser current to a laser in the heat assisted magnetic recording device;

measure laser output power of the laser at the at least one applied laser current;

characterize a relationship amongst temperature, the applied laser input current and the laser output power; and

measure a metric of recording performance to determine if the relationship is acceptable.

14. The data storage device of claim 13, wherein when the control circuitry applies the at least one laser current to the laser and measures the laser output power of the laser, the control circuitry is configured to:

apply a first laser input current to the laser;

measure a first laser output power of the laser at the first laser input current;

apply a second laser input current that is different from the first laser input current to the laser; and

measure a second laser output power of the laser at the second laser input current.

15. The data storage device of claim 13, wherein when the control circuitry characterizes the relationship amongst the temperature, the applied laser input current and the laser output power, the control circuitry is configured to characterize a linear relationship amongst the temperature, the applied laser input current and the laser output power by computing a slope and a y-intercept based on the at least one laser current applied to the laser and the measured laser output power.

16. The data storage device of claim 13, wherein the control circuitry is further configured to adjust a fly height of a slider of the heat assisted magnetic recording device after setting the laser current to an optimal laser current as determined at manufacturing.

17. A method comprising:

measuring a first laser output power of a laser used to record data on a head assisted magnetic recording medium, the first laser output power is measured at a first laser input current;

measuring a second laser output power of the laser, the second laser output power is measured at a second laser input that is greater than or less than the first laser input current;

characterizing a relationship amongst temperature, the laser input current and the laser output power; and

verifying the relationship by measuring a metric of recording performance.

18. The method of claim 17, wherein the first laser input current and the second laser input current comprise currents that are insufficient to record or erase data on the recording medium.

19. The method of claim 17, wherein the first laser input current and the second laser input current comprise currents that are sufficient to record or erase data on the recording medium.

20. The method of claim 19, wherein characterizing the relationship amongst the temperature, the applied laser input current and the laser output power comprises characterizing a linear relationship amongst the temperature, the applied laser input current and the laser output power by computing a slope and a y-intercept based on the first laser current applied to the laser, the first measured laser output power, the second laser current applied to the laser and the second measured laser output power.