Holographic Gratings in Photopolymers as Optical Gas Monitors
Gratings form efficient integrated optical devices for coupling into and out of a waveguide. Grating couplers have been proposed as chemical sensors1. The adsorption and desorption of chemical vapors on lightguide surfaces alters the evanescent field of the guide and changes ist coupling efficiencies2. Using low refractive index material like Si O2 on MgF2 the adsorption or desorption of chemical vapors alters the effective index of planar waveguides significantly and the coupling angle of a grating coupler is shifted. This shift can be detected and used for measuring chemical vapor concentrations3. Changing the effective refractive index of gratings in Si O2 on Ti O2 the angle of the out coupled light could be changed significantly. Output gratings of this type were succesfully used as chemical and biological sensors4, 5.
KeywordsDiffraction Efficiency Planar Waveguide Polyimide Film Holographic Grating Refractive Index Modulation
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