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

Article 2 Accepted by Sensor & Actuator A (on 5 Nov., 1999, Reg. No. 99433
4.2 Effects of polarization of incident light
Attention is next turned to study the conditions at which the influences of electric field
polarization of the incident light can be negligible or reversely need to be taken into account.
Assuming that the SPR sensing part keeps the same distance to the output end of the fiber, i.e.
12=8lmm (cf. fig.1 ), we deal with the differences of normalized light power curves between
p- and s- polarized illuminations and see how they vary with ¡. The maximal difference of
these two curves is evaluated between the incident angles of 5° and 20° where the influences
of p- and s- polarization are most important. Furthermore the maximal difference as a
function of l is calculated and the four curves correspondent to four monitored environments
with the indices of 1.34, 1.35, 1.36 and 1.37 respectively are plotted in figure 10. The
corrugations in the curves come from the spiral way of the light propagation in the multimode
optical fiber described in Section 3.2. It makes clear that while l
is greater than 16mm, the
influences of polarization illuminations are rather small. The maximum of the four curves at '1
>16mm is only about 0.02. If it can be considered negligible, the responses of the sensors will
show identical to whatever polarization of the incident light, The earlier experimental
results[3] can be well explained in this case.
02
018
Q)
0.15
0,14
0.12
o
w 01
'D
(3
0.08
Q)
o 0.05
0.04
Q)
002
10 15 20 25 30
Il mm)
Fig. 10 Computed curves of the maximal differences of normalized light power between
the p- and the s- polarized illuminations as a function o. I (/15mm and /2=8lmm, cf.
fig. 1. thickness of gold film=55nm, indices of monitored bulk media=l .34,1.35,1.36 and
1,37 respectively)
37