Abstract

In this paper, we report good quality waveguides (loss<ldb/cm) formed from pure gelatin, i.e., gelatin without ammonium dichromate. Pure gelatin solutions with various water to gelatin ratios were spun on top of soda-lime glass (N=1.512 at 632.8nm). When gelatin first goes into aqueous solution the molecules exist as single chains encircled by water molecules. Upon standing at temperatures below 30 °C, solutions containing more than 1% gelatin become rigid through cross linking and exhibit rubber-like mechanical properties. In this work optical waveguides were thus formed. The waveguiding properties were examined through the prism coupling method. The measured effective indices for TE and TM guided waves were the same for each sample. This implies that no birefringence exists in the gelatin layer. The guiding layer index profiles of multi-mode gelatin waveguides were determined by the inverse WKB method commonly used in integrated optics[l]. Graded index profile of a multi-mode waveguide can be accurately determined by IWKB method. Step indices can also be determined through this method with a small deviation at the turning point [2]. The calculated index profile of sample #D1, composed of 15 grams of gelatin, 100 CC water and spun at 100 rpm, is given in Fig.1, curve A. The measured surface index of various samples with different water-gelatin ratios is shown in Fig.2. Surface index variation from 1.522 to 1.543 was observed. Each data point of Fig.2 was determined by the 0^th order mode of the corresponding multimode waveguide (total number of modes >10). Since the guiding layer has a step index, the 0^th order mode effective index is almost equal to the surface index. The plotted index profiles of the various gelatin waveguides before wet processing demonstrates that the gelatin layer forms a step index layer and the index refraction increases as the gelatin ratio increases.

© 1989 Optical Society of America