Page 624 - Introduction to Information Optics

608 10. Sensing with Optics

1554
J.552K101

•s

}
J.544<10 454
-looo-1600-1200-800 -400 0 400 800 1200 1600 2000
micro strain

1549.5
J. 54*101

3
• 54»<10 J ,548
0 10 20 30 40 50 60 70 80 90 100
JOQ,
Temperature (Centigrade)
Fig. 10.25. Peak wavelength of fiber Bragg grating, (a) Under applied stress, (b) At different
temperatures with zero applied strain.

temperature change of ~0.1°C, or strain change of 1 /i strain. To detect such
a tiny wavelength shift, the technique of using the unbalanced Maeh-Zehnder
interferometer was proposed and implemented [41]. Figure 10.26 shows the
basic configuration of applying an unbalanced interferometer to detect the
wavelength shift of the Bragg grating induced by external perturbations. Due
to the inherent wavelength dependence of the phase of an unbalanced inter-
ferometer on the input wavelength, shifts in Bragg wavelength are converted