Now, we investigate how the coupling rate c1 relates to the
device parameters. Based on simulations, it is found that the substrate
thickness h is a crucial parameter to influence c1. To illustrate
this, the absorption spectrums are calculated numerically
by increasing h from 0.25 lm to 3.5 lm while keeping other
parameters unchanged. As shown in Fig. 2(c), when h rises from
0.25 lm to 1.5 lm, the resonant absorption rate increases from
10% to 100% with the broaden of the bandwidth. This result suggests
that c1 increases at this region, and equals to c0 at
h = 1.5 lm. Then as exhibited in Fig. 2(d), when h further increases
the absorption peak drops and becomes nearly zero at h = 3.5 lm,
and in this process the bandwidth gets narrower. These results
signify c1 now decreases and becomes zero at h = 3.5 lm. We also
simulated the case when h > 3.5 lm, and find that c1 first increases
from zero at h = 3.5 lm till reaches the maximum value at about
4.3 lm, and then drops to zero again at h = 7 lm