Fabrication of refractive index distributions in polymer using a photochemical reaction

We demonstrate that a photochemical reaction can create various distributio ns of refractive index in polymer. When the polymer containing a photochemi cally active material is irradiated by UV light, the photochemical reaction which breaks the pi-conjugated system in the material and decreases its li near polarizability can reduce refractive index of the polymer. We prepared a PMMA film added DMAPN ((4-N,N-dimethylaminophenyl)-N'-phenylnitrone) wit h a rate of 23 wt % by use of spin coating. Electronic structural change of DMAPN and refractive indices of the film before and after UV irradiation w ere evaluated by UV absorption spectra and m-line method, respectively. The UV irradiation decreased lambda(max) at 380 nm in the absorption spectra, which is attributed to nitrone, and the refractive indices exponentially wi th irradiation time. The change of refractive indices reached 0.028. The re fractive index profile upon depth of the film was investigated by measuring refractive indices of stacked DMAPN/PMMA films. When UV with a power of 10 .7 mW/cm(2) irradiated upon three stacked DMAPN/PMMA films for 35 s, variat ion of the refractive index change showed a quadratic profile. The refracti ve index profile with various irradiation time can be accounted with the co mbination of the chemical kinetics with the steady state approximation and Lambert-Beer's law. Thus, the photochemical reaction can be used to control the refractive index distribution in polymer. (C) 2000 American Institute of Physics. [S0021-8979(00)04902-1].