KEYWORDS: Absorption, Modulation, Temperature metrology, Signal to noise ratio, Wavelength tuning, Dielectrics, Absorption filters, Directed energy weapons, Absorption spectroscopy, Data processing
Two measuring methods of wide absorption spectrum by DFB-LDs are presented in detecting water vapor absorption line. One is subsection scanning method, it takes advantage of wide spectrum tuning range by temperature modulation and fast spectrum tuning speed by current modulation, specifically, this method is realized by dividing a target spectral region into several sections which corresponding to specific temperature of DFB-LD, and scanning every section by current modulation for hundreds times and average the data to raise SNR, combining all sections to get the whole spectrum. An accuracy of 10 ppmv had been obtained in the measurement of water vapor with a 10-cm path length by this method. Another is data fitting method, based on absorption line-shape function, the absorption line can be described by fitting with partial measured data. The fitting absorption line is fitted well with the measured data, and the square of correlation coefficient (R-square) is no less than 0.99.
SiO2 films have been widely applied in the production of electronic devices, integrated devices, optical thin film devices,
sensors because of their desirable properties, such as good insulation, high light transmittance, strong corrosion
resistance, good dielectric properties, etc. Amorphous silicon dioxide was fabricated by plasma enhanced chemical
deposition on GaAs substrate. The thickness and refractive index are obtained by optical transmittance of the film,
which are measured by ellipsometer. The deposition rate of the film and the refractive index are studied at different time,
pressure, and the ratio of SiH4/N2O. The SiO2 thin film growth rate remained basically unchanged versus time. The
reaction chamber pressure, which make the SiO2 thin film growth rate getting the peak, should be about 105Pa. But the
SiO2 thin film growth rate and the refractive index are anti-related. The enormous changes of the gas flow rate do not
have huge impact to the response rate. However, the refractive index of SiO2 thin film changed greatly when the SiH4flow increased the refractive index of the thin films is highest when the ratio of SiH4/N2O is 200:20
Using soft lithography technology, the 2D photonic crystal superprism structures
with a triangle array of air holes on the polymer slab were designed, simulated and
fabricated successfully. The profile of the molded structures with 450nm in diameter
and 900nm in lattice constant was obtained and observed by SEM. By means of
optical experiment and measurement, when the input incident angle varied from 15°
to 11°, we observed the beam propagation angle change from positive to negative and
the superprism effect was demonstrated effectively at near-infrared wavelength
1550nm.
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