Approach for determining the refractive-index profile of graded-index planar waveguides.

We measured the modal indices of a planar waveguide made from GeSeSb glass sandwiched between SiO(2) and air by using the prism-coupling technique. Based on the measured indices of the TE modes, we determined the position of the turning point corresponding to each mode of the waveguide by using the inverse WKB method. Using the modified fitting criterion introduced previously [Appl. Opt. 33, 3227 (1994)], we accurately determined the spatial profile of the refractive index for such a waveguide. Such a graded-index profile is probably caused by compositional variation of the GeSeSb guiding layer.

A photo-stable chalcogenide glass.

Photo-darkening and photo-bleaching are well known phenomena in As-Se and Ge-Se chalcogenide glasses, respectively. Consequently, a systematic dependence of photo-induced optical changes in Ge(x)As(45-x)Se(55) glass series on x is expected between these two extremes. This prediction of photosensitivity on Ge/As ratio has been exploited to demonstrate the first intrinsically photo-stable chalcogenide glass at x approximately 10, which would be suitable for fabricating photo-insensitive optical components for various applications.

In-situ measurement of reversible photodarkening in ion-conducting chalcohalide glass.

We report the kinetics of below band-gap light induced photodarkening in (80-x)GeS(2)-20Ga(2)S(3)-xAgI (x = 0 and 20 mol %) bulk chalcogenide glasses by measuring the time evolution of transmission spectra at every 10 milliseconds. The results prove clearly the enhancement of photosensivity upon doping of AgI compound in glasses. It is interesting to find that PD observed in AgI-doped glass totally disappears two hours later after the laser exposing even at room temperature. In significant contrast to 80GeS(2)-20Ga(2)S(3) glass that the metastable part of PD remains for a long time. We expect such a fast auto-recovery property in AgI-doped glass can be utilized for optical signal processing.

Mid-IR biosensor: detection and fingerprinting of pathogens on gold island functionalized chalcogenide films.

Antibody (human IgG, anti-E. coli O157:H7, and anti-Salmonella) complexes on the surface of IR-transparent Ge-containing chalcogenide glass films were formed via thiol chemistry on 20-nm-thick gold islands. As a first step, the protocol was validated by monitoring fluorescently tagged targets to validate binding. FT-IR spectroscopy confirmed that the coating of the films with 20-nm gold did not have a significant effect on the propagation and penetration of IR evanescent waves through the film. The films functionalized with anti-E. coli O157:H7 and anti-Salmonella antibodies were used to detect E. coli O157:H7 and S. enteriditis through label-free IR fingerprinting. Highly selective detection of bacterial targets was achieved at both the species (E. coli vs. S. enteriditis) and strain level (E. coli O157:H7 vs E. coli K12). A mid-infrared approach could thus be used as a biosensor as well as a molecular fingerprinting tool.