To study the fiber-sensor film applied in detecting Organophosphorus pesticide, methyltriethoxysilane was used as
precursor, which was doped by FITC- AchE. Consequently, the excellent Acetylcholinesterase biology sensitivity film
was prepared. Physics characteristic of the film and sensitivity of Organophosphorus pesticide were researched. In
organophosphorus pesticide residue testing, the experimental results indicated that the linear measurement range could
reach 10-7~10-6 mol/L, moreover the detection limit is 10-8 mol/L. The sensor could be applied in biological / chemical
research, clinical medicine, environmental protection, food inspection, biochemical preventive war field and so on.
To study the photonic-crystal fiber applied in the chemical sensor, the photonic-crystal fiber was used as transmission
medium. With Sol-Gel method, we selective coated thin film containing fluorescent probe in the photonic-crystal fiber
core, then attained an excellent photonic-crystal fiber acetylcholinesterase sensor. The sensor could be applied in
biological / chemical research, clinical medicine, environmental protection, food inspection, biochemical preventive war
field and so on. In organophosphorus pesticide residue testing, the experimental results indicated that the linear
measurement range could arrive to 1×10-9~ 1×10-3 mol/L, moreover the detection limit is 1×10-10 mol/L.
The spectral characteristics of long period fiber grating (LPFG) coated with sensitive film whose refractive index is
higher than that of cladding is analyzed based on four-layer-step geometrical model both theoretically and experimentally.
It is pointed out that the resonant wavelength of LPFG has a regular variation with the refractive indices of both
ambience and the film besides film thickness. Blue shift appears due to the increase of film thickness. Optimal film
thickness corresponding to the maximum values of both sensitivity and the change rate of resonant wavelength merely
depends on ambient refractive index when the refractive index of the film is a constant. According to above theories, the
new LPFG sensors sensitive to refractive index of chemical medium with higher sensitivities and wider range of
application will be designed. Five LPFG sensors with different film thicknesses have been prepared by coating 2-6 layers
SiO2-WO3 nanoscale multiforamen films on five claddings of LPFG respectively. When we put them in NO with 2%
volume fraction, some changes happened only on the LPFG coated with three layers, whose resonant peak red shift
4.77nm, the loss change from -9.93db to -8.53db, the gas sensitivity, response time and recovery time also reached to 3%,
10s and 20s respectively.
Firstly we studied the sensitivity of long-period fiber gratings (LPFG) to the refractive index of ambient medium using the coupled modes theory. Then we presented numerical calculation based on long period fiber grating to show the relationship between the resonant wavelength of transmission spectrum and the ambient refractive index. Secondly we analyzed the optical mechanics of the semiconductor oxide film with gas-sensitivity and found that when touching the thin film gas can make its extinction coefficient, absorption coefficient and corresponding refractive index change. Thus we can coat the grating surface with gas-sensitive film and make use of the character that the refractive index will change with the component and density of ambient gas. Furthermore the change will influence the resonant wavelength of transmission spectrum of LPFG therefore we can get information about the gas component and density by way of monitoring changes of wavelength. The LPFG is more sensitive to ambient refractive index than fiber and the sensed signal is wavelength-modulated so the signal is not reflected by the fluctuation of light intensity and the fiber loss. Therefore the LPFG is more sensitive than intensity-type fiber gas sensor.
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