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2.4 Applications 65
10
N = 3(h = 1.2mm)
T
B
T
T
F = (P N -P N )/(P N -P N+1 )
T
P N
T
Variation ratio 5
P N+1
P N B

1
0
10 -5 10 -4 10 -3 10 -2 10 -1 1
Reflectivity

Fig. 2.41. Variation ratio versus facet reflectivity at the optimum bias current for
OSL readout operation

2.4 mm
MHz
1.0
0.5
0.2
0.1

Fig. 2.42. Written bit patterns by 16 mW laser pulses at various frequencies

have developed a high-precision bonding machine to satisfy this requirement.
Length measurement accuracy is 0.1 µm with an autofocus mechanism, and
movingresolution accuracy is 0.1 µm with electrically controlled motion as
described in Sect. 2.3.1.

Write Performance

Figure 2.42 shows the dependence of write frequency on written bit patterns
for 16 mW light pulses with a duty cycle of 50%. These bits were written as
spots crystallized from the as-deposited state in this experiment. The phase
change was caused by the thermal energy of the light output with a fixed
write current. This figure suggests that both the bit shapes and the levels of
crystalization are uniform. Bit pitch was 2.4 µm at a write frequency of 1 MHz.
These bits are readout with a high SNR as the medium reflectivity changed
between the two states (shown in the lower traces). The medium velocity here