Procedure for setting laser and heater power in HAMR device
A heater power of a heat-assisted magnetic recording head is set to an initial power to induce an initial head-medium clearance. For a plurality of iterations, a heater power at an optimum laser power is determined that achieve a target clearance. If differences in the heater power and optimum laser power between the two subsequent iterations are below a threshold, the iterations are stopped and the heater power and the optimum laser power for one of the two subsequent iterations is used as an operational heater power and laser power for the heat-assisted magnetic recording head.
1. A method comprising:
setting a heater power of a heat-assisted magnetic recording head to an initial power to induce an initial head-medium clearance;
for a plurality of iterations:
varying a laser power of the recording head while writing data to at least one track of a recording medium at the initial head-medium clearance;
determining an optimum laser power based on reading the data;
applying an additional heater power to approach or cause a head-medium contact at the optimum laser power; and
setting the heater power for a next iteration based on an offset from the additional heater power;
wherein, if a first difference in the heater power between two subsequent iterations is below a first threshold and a second difference in the optimum laser power between the two subsequent iterations is below a second threshold, stopping the iterations and using the heater power and the optimum laser power for one of the two subsequent iterations as an operational heater power and an operational laser power for the heat-assisted magnetic recording head.
2. The method of claim 1 , wherein the optimum laser power is determined based on a signal-to-noise ratio of the at least one track.
3. The method of claim 1 , wherein the optimum laser power is determined based on a bit-error rate of only one track.
4. The method of claim 1 , wherein the optimum laser power is determined based on a bit-error rate of multiple adjacent tracks.
5. The method of claim 1 , wherein the optimum laser power is determined based on a servo error rate of the at least one track.
6. The method of claim 1 , wherein the optimum laser power is determined based on a servo variable gain amplifier gain while reading back the at least one track.
7. The method of claim 1 , wherein the optimum laser power is determined based on a width of the at least one track.
8. The method of claim 1 , wherein the optimum laser power is determined based on an amplitude of the at least one track.
9. The method of claim 1 , wherein the optimum laser power is determined based on an amplitude of an overwrite signal.
10. The method of claim 1 , wherein the additional heater power causes a small clearance being detected without head-medium contact at the optimum laser power, the method further comprising detecting the clearance based on a thermal profile at a media-facing surface of the recording head.
11. A apparatus comprising:
a controller configured to control a heat-assisted magnetic recording head, the controller configured to perform a calibration procedure that involves:
setting a heater power of the recording head to an initial power to induce an initial head-medium clearance;
for a plurality of iterations:
varying a laser power of the recording head while writing data to at least one track of a recording medium at the initial head-medium clearance;
determining an optimum laser power based on reading the data;
applying an additional heater power to approach or cause a head-medium contact at the optimum laser power; and
setting the heater power for a next iteration based on an offset from the additional heater power;
wherein, if a first difference in the heater power between two subsequent iterations is below a first threshold and a second difference between the optimum laser power between the two subsequent iterations is below a second threshold, stopping the iterations and using the heater power and the optimum laser power for one of the two subsequent iterations as an operational heater power and an operational laser power for the heat-assisted magnetic recording head.
12. The apparatus of claim 11 , wherein the optimum laser power is determined based on a signal-to-noise ratio of the at least one track.
13. The apparatus of claim 11 , wherein the optimum laser power is determined based on a bit-error rate of only one track.
14. The apparatus of claim 11 , wherein the optimum laser power is determined based on a bit-error rate of multiple adjacent tracks.
15. The apparatus of claim 11 , wherein the optimum laser power is determined based on a servo error rate of the at least one track.
16. The apparatus of claim 11 , wherein the optimum laser power is determined based on a servo variable gain amplifier gain while reading back the at least one track.
17. The apparatus of claim 11 , wherein the optimum laser power is determined based on a width of the at least one track.
18. The apparatus of claim 11 , wherein the optimum laser power is determined based on an amplitude of the at least one track.
19. The apparatus of claim 11 , wherein the additional heater power causes the head-medium contact at the optimum laser power, the calibration procedure further comprising detecting the head-medium contact based on acoustic emissions resulting from the head-medium contact.
20. The apparatus of claim 11 , wherein the additional heater power approaches the head-medium contact at the optimum laser power without contact occurring, the calibration procedure further comprising detecting a head-to-medium clearance via a thermal sensor before the head-medium contact occurs.