The mid-IR spectroscopy provides a universal tool for the real-time remote monitoring of various molecular species. In this study, we apply the wave optics based approach to analyze the functionality of spectroscopic sensors with sensing elements based on tapered multimode chalcogenide fibers. By using the method of local modes, the sensing elements transmittance, sensitivity and detection limit have been calculated. These characteristics are shown to depend on the longitudinal profile of the taper diameter, linear or exponential in our case. The ratio of the taper length to the power attenuation length of a local mode is a key parameter for sensitivity optimization. The detection limit of the spectroscopic measurements can be significantly reduced by delivering radiation in the higher-order local modes of the taper.
Chalcogenide glass of the system Ge-Sb-Ga-Se doped with Tb3+ and Dy3+ has been characterized near the fundamental absorption band edge by using the results of transmittance and reflectance measurements in the near-IR spectral range.
Two realizations of the time-resolved pump-probe method have been applied to study comparatively the nonlinear optical response of chalcogenide glasses of the system As-S-Se illuminated by femtosecond laser pulses near their fundamental absorption band edge and near the two-photon absorption band edge. In such conditions, charge carrier’s photo-excitation is going on with participation of gap states. By comparison of the results of measurements and numerical modeling, we have demonstrated that character of the nonlinear optical response depends on how a glass samples was illuminated. If the pump pulse frequency corresponded to the Urbach tail of a glass sample, the carriers trapping and excitons formation was followed by the excitons absorption and excitation of conduction electrons. If a sample was illuminated at the red-edge of its Urbach tail, the photo-excitation was going through the gap states, but excitation of conduction electrons was followed by excitons formation. Due to these peculiarities, calculated spacial distribution of the photo-induced refractive index variation in the sample was different depending on the illumination conditions.
Microresonators are very suitable for sensing application and investigation of nonlinear effects, due to their enormous quality factor and small mode volume. These properties can be extended to the mid-infrared spectral range by creating microresonators from chalcogenide glasses, which are transparent in the mid-infrared and have large third-order optical nonlinearity. We present the analysis of the nonlinear effects observation in chalcogenide microspheres created by inert gas heating.
Fiber-based evanescent wave spectroscopy in the mid-IR is a powerful tool for the remote chemical analysis of liquids and gases in real time. Design of a sensing element of the fiber sensor is important for optimization of its output characteristics. In addition to unclad chalcogenide fibers that were previously used as the sensing elements, we consider core-clad fibers consisting of a multimode core and a ring cladding with the refractive index greater than that one of the core. For numerical analysis, a theoretical approach based on electromagnetic theory of optical fibers has been used. Calculated transmittance of the sensing elements is compared with the measured output characteristics of a sensing element made of an unclad chalcogenide fiber, which was immersed into aqueous acetone solutions.
Chalcogenide fibers are considered as a base for creation of a fiber-optical platform for the mid-IR evanescent wave spectroscopy. In this work, transmittance of a multimode fiber made of Ge26As17Se25Te32 glass, immersed into an aqueous acetone solution was measured in the range of wavelengths 5 - 9 microns at various concentrations of the solution. A theoretical approach based on electromagnetic theory of optical fibers has been applied for analysis of evanescent modes propagation in the fiber. Attenuation coefficients calculated for each HE1m evanescent mode increase with the mode radial order m. This effect can be used for optimisation of the fiber-optic sensing elements for the mid-IR spectroscopy.
This paper reports recent achievements in the field of infrared optical fibers based on vitreous arsenic chalcogenides (As2S3, As2Se3, As2Se1.5Te1.5). The minimum optical losses of the fibers from arsenic sulfide, arsenic selenide and arsenic telluride are equal to 20 - 30 dB/km at 2.2 and 3.3 micrometers , 80 - 100 dB/km at 4.3 micrometers , and 100 - 300 dB/km and 6.7 micrometers , respectively. Among them the double polymer coated two-layer arsenic-sulfide optical fibers have the lowest optical losses (20 - 25 dB/km) and the highest mechanical bending strength (1 - 1.5 GPa).
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.