Effect of curing beam intensity and photoinitiator concentration on the geometrical features and optical transmission of light induced polymer waveguides

Self-written polymer wave guide was constructed between two single mode fibers by photopolymerization using monochromatic laser beam and incoherent light source. Geometrical and optical properties of polymer waveguides have been investigated by changing curing beam power and photoinitiator concentration. For longer bridges beyond 500 µm some surface degradation appeared which caused extra optical loss. We also compared characteristics of two bridges when curing beam power for the second one was reduced from 12.8 µW to 6.4 µW, maintaining all the other fabrication parameters similar. Illumination with high power and longer exposure time leads to a thick waveguide which is wider than the core of the fibers, whereas illumination with reduced beam power and shorter exposure time results in thin bridge with considerable mode mismatching with fibers. Thicker bridge has insertion loss of about 0.4 dB but it is about 2.7 dB for the thinner one. Regarding the effect of photoinitiator density, three different monomer systems were studied. Polymer bridges associated with Eosin concentration 0.5 wt% present optimum surface morphology and optical transmission.