Dense nanocrystalline copper-doped zirconia (CDZ, Cu:Zr=16:84) thin film was coated on the surface of a 125 μm-diameter
long-period fiber grating (LPFG) by a facile synthesis route involving polymeric precursor coating and
subsequent thermal treatments. The CDZ film had a uniform thickness of ~100 nm and grain size of 20 to 35 nm after a
brief annealing step at 700°C for 1 hour. This CDZ thin film coated LPFG (CDZ-LPFG) was evaluated at a high
temperature of 550°C for its change of resonant wavelength (λR) in response to the variation of carbon monoxide (CO) concentration in nitrogen (N2). The λR was found to shift toward longer wavelength when increasing the CO concentration. The CDZ-LPFG sensor response was found to be reproducible and reversible at low level CO
concentrations (<1,000 ppm) but became irreversible when the CO concentration was high (e.g. at 10,000 ppm). The
high temperature stability of the CDZ material in CO-containing atmospheres was studied to understand the limit of CO
measurement range.
In this study, a new zeolite thin film-coated long-period fiber grating (LPFG) sensor was developed and
evaluated for chemical vapor detection. The sensor was fabricated by growing nanoporous MFI-type zeolite (pore
size ~0.55nm) thin film on fiber grating using in situ hydrothermal crystallization method. The hydrothermal
synthesis process was controlled by continuously monitoring the LPFG transmission spectrum evolution, which
indicated the zeolite film formation and growth process. The zeolite-LPFG sensor was activated by calcination in air
to remove the structural directing agent from the zeolite pores and then demonstrated for sensitive detection of
chemical vapor in gas phases.
We report in this paper the fabrication of high performance thermal LPFGs by point-by-point CO2 laser irradiations.
These thermal LPFGs have shown much better temperature tolerance and promised applications in high temperature
harsh environments. The computer-controlled fabrication system with in situ signal monitoring capability is described.
The fabricated LPFGs survived high temperatures up to 800°C. Long term stability test at 550°C for 200 hours indicated
that thermal shock at a higher temperature could significantly reduce the drift.
Recently, we discovered that the nanoporous zeolite materials possess the unique combination of optical and
chemical properties suitable for developing highly sensitive chemical sensors. This paper summarizes our recent
work in developing such highly sensitive chemical sensors by functionally integrating zeolite thin films with optical
fiber devices. These include the zeolite Fabry-Perot interferometric sensor and the zeolite thin film-coated thermal
long period fiber grating sensor. Both types of sensors operate by monitoring the adsorption-induced optical
refractive index changes in the zeolite thin film. The sensors were tested using various organic chemicals with
different molecular sizes and in both vapor and liquid phases.
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