Controlling laser output in a HAMR device

• US 9,355,671 B2
• Filed: 05/15/2014
• Issued: 05/31/2016
• 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): PENDLETON, DIONNE
• Application Number:
  US14/278,377
• Publication Number:
  US 20150332725A1
• Time in Patent Office: 747 Days
• US Class Current: 1/1
• 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 5/012 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 7/00736 Auxiliary data, e.g. lead-in, lead-out, Power Calibration Area [PCA], Burst Cutting Area [BCA], control information sector headers or adresses in prepits G11B7/00745; address data in track wobble G11B7/24082
• CPC Class Codes: G11B 7/1263 Power control during transducing, e.g. by monitoring
• CPC Class Codes: G11B 7/1267 Power calibration

Abstract

A method of controlling laser output in a heat assisted magnetic recording device can be performed by control circuitry in a data storage device. The method includes measuring a temperature, measuring laser output power of a laser, determining a power error by subtracting an optimal laser output power from the measured laser output power and comparing the power error to at least one threshold to determine whether an applied current to the laser needs to be adjusted. The at least one threshold is related to how great the power error can be while maintaining the integrity of data on a recording medium.

Claims

1. A method comprising:

measuring a temperature;

measuring laser output power of a laser in a heat assisted magnetic recording device;

determining a power error by subtracting an optimal laser output power from the measured laser output power;

comparing the power error to at least one threshold to determine whether an applied current to the laser needs to be adjusted, wherein the at least one threshold is related to how great the power error can be while maintaining the integrity of data on a recording medium;

adjusting the applied laser input current to the laser as a function of the power error and the measured temperature when the power error is greater than a first threshold, wherein adjusting the applied laser input current to the laser includes accessing a relationship amongst temperature, applied laser input current and laser output current; and

recharacterizing the relationship amongst temperature, applied laser input current and laser output power when the power error is greater than a second threshold that is different from the first threshold.

2. The method of claim 1, wherein the relationship amongst temperature, applied laser input current and laser output power is linear and wherein the value of a slope at the measured temperature is used to adjust the applied laser input current.

3. The method of claim 1, wherein re-characterizing the relationship amongst temperature, applied laser input current and laser output power further comprises determining whether the re-characterization of the relationship amongst temperature, applied laser input current and laser output power provides an acceptable recording performance.

4. The method of claim 1, wherein measuring the laser output power comprises measuring the laser output power when the laser is sufficient to record data to the recording medium.

5. The method of claim 1, wherein measuring the laser output power comprises measuring the laser output power when the laser is insufficient to record data to the recording medium.

6. A data storage device comprising:

a medium;

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

control circuitry configured to;

measure the data storage device temperature;

measure laser output power of the laser;

determine a power error by subtracting a desired laser output power from the measured laser output power;

compare the power error to at least one threshold to determine whether an applied current to the laser needs to be adjusted, wherein the at least one threshold is related to how great the power error can be while maintaining the integrity of data on a recording medium;

adjust the applied laser input current to the laser as a function of the power error and the measured temperature when the power error is greater than a first threshold, wherein adjusting the applied laser input current to the laser includes accessing a table of values that characterize a relationship amongst the temperature, the applied laser input current and the laser output power; and

re-characterize a relationship amongst the temperature, the applied laser input current and the laser output power when the power error is greater than a second threshold that is different from the first threshold.

7. The data storage device of claim 6, wherein adjusting the applied laser input current to the laser further comprises setting the laser input current by writing the laser input current to a register in a preamplifier.

8. The data storage device of claim 6, further comprising a thermistor located in proximity to the heat assisted magnetic recording device for sensing the data storage device temperature.

9. The data storage device of claim 6, further comprising a photodetector located in proximity to the heat assisted magnetic recording device for sensing the laser output power.

10. The data storage device of claim 6, further comprising a bolometer coupled to an optical wave guide in the recording head for sensing laser output power.

11. A method comprising:

measuring a temperature;

measuring laser output power of a laser in a heat assisted magnetic recording device;

supplying the measured laser output power to compensation circuitry in a preamplifier;

supplying an optimal laser output power based at least on the measured temperature to the compensation circuitry in the preamplifier, wherein the optimal laser output power is accessed from a relationship amongst temperature, applied laser input current and laser output power;

receiving a notification from the preamplifier that an adjustment that is needed to the applied laser input current to achieve the optimal laser output power is greater than a threshold; and

re-characterizing a relationship amongst temperature, applied laser input current and laser output power by applying a first laser current to a test track, measuring a first laser power based on the applied first laser current, applying a second laser current to the track, measuring a second laser power based on the applied second laser current.

12. The method of claim 11, wherein re-characterizing the relationship amongst temperature, applied laser input current and laser output power further comprises determining whether the re-characterization of the relationship amongst temperature, applied laser input current and laser output power provides an acceptable recording performance.