Polymer films coating optical waveguide

This study represents the first systemmatic application of the optical waveguide technique to the study of the response of polymer film coatings to condensed vapor molecules. These results indicate that the technique is useful for surveying rapidly potential polymeric films as possible vapor sensor coatings. Moreover, this work has further substantiated that the vapor pressure is an important physical property to be taken into account when employing polymeric films as surface coatings. 

Figure 2 shows a d.c. recorder retracing of a typical set of dry air/saturated vapor cycling responses of the optical waveguide coated with the polymer, poly-epichlorohydrin (PEH) and exposed cyclically to benzene vapors. Aside from the clearly detected electrical signals above the dry air baseline reference, their amplitudes appear to show apparent reversibility over the four exposure cycles indicated in the figure. Also, the rise time and decay of these signals are rather symmetric and indicate a film response time of less than one minute. 

Figure 4. Plot of the optical waveguide response for each polymer coating as a function of the vapor pressure of the vapors to which these caotings are exposed. The scale of the ordinate is taken from the absolute heights shown in the bar chart data shown in Figure 3. It is clearly seen that for all these polymeric films their response increases inversely as the vapor pressure for the particular volatile material tested.

Figure 6. Optical transmittance change at 660 nm as a function of various DMMP concentrations for the optical waveguide surface coated with the PEM polymer film.

Fig. 5.11. (a) Spin-coated polymer 1 films (40-80 nm thick, with refractive index (n 1.70) are coated on a transparent 200-nm-thick film of chemical vapor deposited parylene (n 1-67), forming a two-layer index-matched waveguide on glass (n 1.45). (b) Spin-coated polymer 1 films (40nm) coated on DFB gratings fabricated from PDMS. (c) Ring-mode laser structure produced by dip-coating polymer 1 on a 25 mm diameter silica optical fiber... 

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