Laser mode hopping detection method and apparatus for a heat-assisted magnetic recording device

1. A method, comprising:

performing, using a heat-assisted magnetic recording head, multiple writes to a recording medium;

recording a metric of write performance for each of the writes;

calculating fluctuations in the metric;

detecting whether the head has a laser mode hopping (LMH) problem using the metric fluctuations; and

categorizing a severity of the LMH problem as one of:

an acceptable or nonexistent LMH problem;

a non-severe or nonexistent LMH problem with self-heating of a laser diode of the head; and

a severe LMH problem.

2. The method of claim 1 , wherein detecting whether the head has an LMH problem comprises:

calculating one or more differences in the write performance metrics; and

comparing the one or more metric differences to one or more thresholds.

3. The method of claim 1 , wherein detecting whether the head has an LMH problem comprises:

calculating a first difference in the write performance metrics indicative of a maximum difference in the metrics;

calculating a second difference in the write performance metrics indicative of a difference between a minimum of the metrics and a metric for the last write;

comparing the first difference to a first threshold; and

comparing the second difference to a second threshold.

4. The method of claim 3 , wherein categorizing the severity of the LMH problem comprises:

categorizing the severity of the LMH problem as a non-severe or nonexistent LMH problem with self-heating of a laser diode of the head in response to the first difference exceeding the first threshold and the second difference failing to exceed the second threshold.

5. The method of claim 3 , wherein categorizing the severity of the LMH problem comprises:

categorizing the severity of the LMH problem as a severe LMH problem in response to the first difference exceeding the first threshold and the second difference exceeding the second threshold.

6. The method of claim 3 , wherein categorizing the severity of the LMH problem comprises:

categorizing the severity of the LMH problem as an acceptable LMH problem or an absence of an LMH problem in response to the first difference failing to exceed the first threshold.

7. The method of claim 1 , wherein the method comprises:

performing the method for a plurality of HAMR heads during head manufacture; and

sorting the heads between usable and unusable heads based on the severity categorization.

8. The method of claim 1 , wherein the method comprises:

performing the method during a service life of the head; and

taking corrective action if warranted based on the severity categorization.

9. The method of claim 8 , wherein the corrective action is one or more of tuning a laser bias current, implementing a write protect procedure, instigating short writes rather than long writes, implementing a read-after-write protocol, and notifying a host to refrain from long writes.

10. The method of claim 1 , comprising compensating for the self-heating of the laser diode in response to categorizing the severity of the LHM problem as the non-severe or nonexistent LMH problem with self-heating of the laser diode.

11. The method of claim 10 , wherein compensating for the self-heating of the laser diode comprises implementing a laser bias compensation procedure.

12. An apparatus, comprising:

a heat-assisted magnetic recording head comprising a reader, a writer, and a near-field transducer optically coupled to a laser diode via an optical waveguide; and

a controller of the head configured to:

perform multiple writes to a recording medium;

record a metric of write performance for each of the writes;

calculate fluctuations in the metric;

detect whether the laser diode has a laser mode hopping (LMH) problem using the metric fluctuations; and

categorize a severity of the LMH problem as one of:

an acceptable or nonexistent LMH problem;

a non-severe or nonexistent LMH problem with self-heating of a laser diode of the head; and

a severe LMH problem.

13. The apparatus of claim 12 , wherein the controller is configured to:

calculate one or more differences in the write performance metrics; and

compare the one or more metric differences to one or more thresholds.

14. The apparatus of claim 12 , wherein the controller is configured to:

calculate a first difference in the write performance metrics indicative of a maximum difference in the metrics;

calculate a second difference in the write performance metrics indicative of a difference between a minimum of the metrics and a metric for the last write;

compare the first difference to a first threshold; and

compare the second difference to a second threshold.

15. The apparatus of claim 14 , wherein the controller is configured to:

categorize the severity of the LMH problem as a non-severe or nonexistent LMH problem with self-heating of the laser diode in response to the first difference exceeding the first threshold and the second difference failing to exceed the second threshold.

16. The apparatus of claim 14 , wherein the controller is configured to:

categorize the severity of the LMH problem as a severe LMH problem in response to the first difference exceeding the first threshold and the second difference failing to exceed the second threshold.

17. The apparatus of claim 14 , wherein the controller is configured to:

categorize the severity of the LMH problem as an acceptable LMH problem or an absence of an LMH problem in response to the first difference failing to exceed the first threshold.

18. The apparatus of claim 12 , wherein the controller is configured to take corrective action if warranted based on the severity categorization.

19. The apparatus of claim 18 , wherein the corrective action is one or more of tuning a laser bias current, implementing a write protect procedure, instigating short writes rather than long writes, implementing a read-after-write protocol, and notifying a host to refrain from long writes.

20. The apparatus of claim 12 , wherein the controller is configured to compensate for the self-heating of the laser diode in response to categorizing the severity of the LHM problem as the non-severe or nonexistent LMH problem with self-heating of the laser diode.