Développement de capteurs à fibre optique basés sur la résonance ...

Article 2 Accepted by Sensor & Actuator A ( on 5 Nov., 1999, Reg. No. 99433 )
angles of 5° and 20° where the sensing signals are most notable. Assuming that the sensor is
used to monitor the bulk environments of the refractive indices of 1.34, 1.35, 1.36 and 1.37
respectively and the incident light is set to be p-polarization, a change of the index of 8x104
in each detected bulk medium occurs, the maximal sensing signals as a function of li can be
predicted by means of this model and shown in figure 11. Similarly, ifa mm thick molecular
layer with index of 1 .46 adsorbs on the surface of gold film in the same bulk environments,
the maximal sensing signals as a function of l are plotted in figure 12. The i and 12 are
assumed to remain unchanged in these two examples. It can be seen from Fig.11 and Fig.12
that the maximal sensing signal in this two cases is about 0.02 as l >16mm.
0 03
w
0 02
P - poIrization
(.1)
0.00
e* 134
1.35
1.36
1 37
AdsoVption of thin Ia'er
Thicknss: i nrr / Index:1 .46
1 (mm)
20 25 30
Fig.12 Computed curves of the maximal sensing signals as a function oft1 (l=15mm and
12=8lmm, thickness of gold film=55nm, an adsorbed layer of mm thickness with index of
1.46 on the gold surface in bulk media with indices of 1.34, 1.35, 1.36 and 1.37
respectively)
Comparing with the previous result that the possible error is as great as 0.02 while / >
16mm if the influences of polarization of the incident light are ignored, it can be recognized
that this error is approximately equivalent to a possible uncertainty in refractive index of
8xl04 for the detected bulk media or in the thickness of lnrn ( with index of 1.46 ) for the
adsorbed dielectric layer. Therefore, when a weak sensing signal needs to be quantitatively
interpreted, the influences of the polarization for the incident light should not be neglected
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