1. Field of the Invention
This invention relates generally to a heat-assisted magnetic recording (HAMR) type of magnetic recording disk drive, and more particularly to a HAMR disk drive with a sensor for measuring laser power.
2. Description of the Related Art
Heat-assisted magnetic recording (HAMR), sometimes also called thermally-assisted recording (TAR), has been proposed. In HAMR disk drives, an optical waveguide with a near-field transducer (NFT) directs heat from a radiation source, such as a laser, to heat localized regions of the magnetic recording layer on the disk. The radiation heats the magnetic material locally to near or above its Curie temperature to lower the coercivity enough for writing to occur by the write head. HAMR disk drives have been proposed for conventional magnetic recording disks where the magnetic recording layer on the disk is a continuous layer of magnetic recording material. HAMR disk drives have also been proposed for bit-patterned media (BPM) where the magnetic recording layer is patterned into small isolated data islands, each island containing a single magnetic “bit” and separated from neighboring islands by nonmagnetic spaces.
It is important during writing that the output power at the NFT be within a predetermined range. If the laser power setting is too low and thus the NFT output power too low, the desired data bit will not be magnetized. If the laser power setting is too high and thus the NFT output power too high, bits adjacent to the desired data bit will also be magnetized. While a photo-detector can be used to monitor the laser power, the additional cost makes this an unattractive solution. An electrically conductive thermal sensor has been proposed, but the response time is so slow that accurate laser power monitoring at each data sector is not possible.
What is needed is a HAMR disk drive that can use a thermal sensor to accurately measure laser power during writing.