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5.4 Future Applications 197
To achieve a high-speed readout, the gap control between the probe and
the medium sample is realized usingan SNOM slider head, which consists
of a flyingslider and an air-bearingspindle motor. However, readout speed
is basically restricted with the resonant frequency of the gap control system.
A schematic diagram of proto-type SNOM slider head is shown in [5.40].
The experimental results indicate the possibility of achievinga density
−2 −1
over 100 Gb in. and a readout speed over 2 Mb s . However, some technical
problems such as nanometer size aperture probe productivity, precise gap and
trackingcontrol for each track independently remain unsolved.

Optically Switched Laser Head
A lensless flyingoptical head suitable for near-field recordingarrangements
was firstly proposed by Ukita et al. in 1987 [5.33,5.41,5.69]. A tapered laser
diode attached on a slider forms an extremely short-external-cavity (ESEC)
with a phase change optical disk as described in Chap. 2. This is called an
OSL head due to its workingmechanism.
After ten years, Partovi et al. [5.42] fabricated a very small aperture laser
(VSAL) for near-field recordingand Chen et al. [5.43] reported a method for
producing a VSAL from a low-cost, commercial index guided edge diode laser.
Recently, Kataja et al. [5.44] presented a numerical study of near-field writing
on a phase change optical disk.
This direct read/write scheme by a laser diode is thought to be a promising
approach for near-field storage because of its structure simplicity, smallness,
and low cost.

Solid Immersion Lens/Solid Immersion Mirror (SIM)
To overcome the fragility and yield of fiber probes of an SPM storage, the
use of an SIL [5.45] or an SIM [5.46] on a flyinghead has been proposed and
studied. An SIL has a higher numerical aperture (NA) and is easier to fabri-
cate than an SIM, however, its lens center is more difficult to align. The flying
height of this head is 20 nm at present [5.47]. Use of an SIL/SLM is not re-
stricted by readout speed but restricted by area recordingdensity due to NA.
However, these devices are also suitable for heat-assisted magnetic record-
ing(HAMR), avoidingthe superparamagnetic limit of the HDD as shown in
Fig. 5.38.
HAMR schemes combininga bow-tie antenna attached on a flyingslider
are under development to achieve storage densities greater than 1 Tb in. −2
(correspondingto a mark size of 25 nm) in many institutes. Moreover, to
achieve recordingdata rates of 500 MHz, the thermal response time of the
◦
medium must be less than 1 ns and a temperature rise of at least a 200 Cis
required. From thermal modelingcalculation, approximately 1 mW of optical
power will cause 200 C temperature rise in a 25 nm spot of a recordingfilm
◦
stack [5.48]. Techniques based on apertures, antennas, waveguides, SILs and