Measuring NFT protrusion in a heat assisted magnetic recording drive using burst writing and a constant laser diode temperature
Various illustrative aspects are directed to a data storage device comprising one or more disks; one or more heads, including a first head having a first laser diode and a near field transducer; and one or more processing devices configured to: preheat the first LD to a steady state temperature; write a first and a second series of writings at a plurality of thermal fly-height control powers, wherein the first and the second series of writings are written at the steady state temperature, and the first series of writings are of a shorter duration than the second series of writings; determine, for the first head, an NFT protrusion measurement based at least on a difference in TFC power used between (1) one of the first of writings and (2) one of the second series of writings, at a corresponding written signal amplitude.
1. A data storage device configured for heat assisted magnetic recording (HAMR), the data storage device comprising:
one or more disks;
one or more heads, including at least, a first head having a first laser diode (LD) and a near field transducer (NFT); and
one or more processing devices or components, configured, individually or in combination, to:
preheat the first LD to a steady state temperature;
after the preheating,
write, using the first head, a first series of writings at a plurality of thermal fly-height control (TFC) powers;
write, using the first head, a second series of writings at the plurality of TFC powers, wherein the first series of writings are of a shorter duration than the second series of writings; and
determine, for the first head, an NFT protrusion measurement based at least on a difference in TFC power used between (1) one of the first of writings and (2) one of the second series of writings, at a corresponding written signal amplitude.
2. The data storage device of claim 1 , wherein the first series of writings comprise burst writings, and the second series of writings comprise sector writings.
3. The data storage device of claim 1 , wherein,
the first series of writings are each under 200 nanoseconds (ns) long, and
the second series of writings are each at least 100 microseconds (μs) long.
4. The data storage device of claim 3 , wherein each writing of the first series of writings is performed for a shorter duration than one or more of a protrusion time constant for the NFT of the first head and a gas bearing surface (GBS) response time, wherein the GBS response time corresponds to a time required for the GBS to reach steady-state fly height.
5. The data storage device of claim 1 , wherein preheating the first LD comprises preheating the first LD using dark laser heating (DLH).
6. The data storage device of claim 1 , wherein preheating the first LD comprises applying a reverse bias (RB) to preheat the first LD.
7. The data storage device of claim 1 , wherein preheating the first LD to the steady state temperature reduces or minimizes effects of LD temperature transients on one or more written signal amplitudes corresponding to each of the first and the second series of writings.
8. The data storage device of claim 1 , further comprising one or more additional LDs, including at least a second LD associated with a second head, and wherein the one or more processing devices or components are further configured, individually or in combination, to:
preheat the second LD to the steady state temperature;
write, using the second head, a third series of writings at the plurality of TFC powers, based at least in part on preheating the second LD;
write, using the second head, a fourth series of writings at the plurality of TFC powers, based at least in part on preheating the second LD; and
determine, for the second head, an NFT protrusion measurement based at least in part on a difference in TFC power used between (1) one of the third series of writings, and (2) one of the fourth series of writings, at a corresponding written signal amplitude.
9. The data storage device of claim 8 , wherein:
the first series of writings and the third series of writings comprise burst writings,
the second series of writings and the fourth series of writings comprise sector writings,
the first series of writings have a shorter duration than the second series of writings, and
the third series of writings have a shorter duration than the fourth series of writings.
10. A method of operating a data storage device utilizing heat assisted magnetic recording (HAMR), the method comprising:
preheating a first laser diode (LD) to a steady state temperature, wherein the first LD is associated with a first head of the data storage device, the first head comprises a near field transducer (NFT);
after the preheating,
writing, using the first head, a first series of writings at a plurality of thermal fly-height control (TFC) powers;
writing, using the first head, a second series of writings at the plurality of TFC powers, wherein the first series of writings are of a shorter duration than the second series of writings; and
determining, for the first head, an NFT protrusion measurement based at least on a difference in TFC power used between (1) one of the first of writings and (2) one of the second series of writings, at a corresponding written signal amplitude.
11. The method of claim 10 , wherein the first series of writings comprise burst writings, and where the second series of writings comprise sector writings.
12. The method of claim 10 , wherein,
the first series of writings are each under 200 nanoseconds (ns) long, and
the second series of writings are each at least 100 microseconds (μs) long.
13. The method of claim 12 , wherein each writing of the first series of writings is performed for a shorter duration than one or more of a protrusion time constant for the NFT of the first head and a gas bearing surface (GBS) response time, wherein the GBS response time corresponds to a time required for a GBS to reach steady-state fly height.
14. The method of claim 10 , wherein preheating the first LD comprises preheating the first LD using dark laser heating (DLH).
15. The method of claim 10 , wherein preheating the first LD comprises applying a reverse bias (RB) to preheat the first LD.
16. The method of claim 10 , wherein preheating the LD reduces or minimizes effects of LD temperature transients on one or more written signal amplitudes corresponding to the first series of writings.
17. The method of claim 16 , wherein preheating the LD further reduces or minimizes effects of LD temperature transients on the one or more written signal amplitudes corresponding to the second series of writings.
18. The method of claim 10 , wherein the data storage device further comprises one or more additional LDs, including at least a second LD associated with a second head, the method further comprising:
preheating the second LD to the steady state temperature;
writing, using the second head, a third series of writings at the plurality of TFC powers, based at least in part on preheating the second LD;
writing, using the second head, a fourth series of writings at the plurality of TFC powers, based at least in part on preheating the second LD, and wherein the third series of writings are of a shorter duration than the second series of writings; and
determining, for the second head, an NFT protrusion measurement based at least in part on a difference in TFC power used between (1) one of the third series of writings, and (2) one of the fourth series of writings, at a corresponding written signal amplitude.
19. The method of claim 18 , wherein:
the first series of writings and the third series of writings comprise burst writings, and
the second series of writings and the fourth series of writings comprise sector writings.
20. One or more processing devices or components, comprising:
means for preheating a first laser diode (LD) of a data storage device to a steady state temperature, wherein the first LD is associated with a first head of the data storage device, and wherein the data storage device is configured for heat assisted magnetic recording (HAMR);
after the preheating,
means for writing, using the first head, a first series of writings at a plurality of thermal fly-height control (TFC) powers;
means for writing, using the first head, a second series of writings at the plurality of TFC powers, wherein the first series of writings have a shorter duration than the second series of writings; and
means for determining, for the first head, an NFT protrusion measurement based at least on a difference in TFC power used between (1) one of the first of writings and (2) one of the second series of writings, at a corresponding written signal amplitude.