Femtosecond laser written low-loss single-mode waveguides in PMMA

Refraction index modification in transparent materials via non-linear absorption of femtosecond laser radiation has proven a powerful tool in three-dimensional waveguide writing. We present results on femtosecond laser written waveguides in bulk poly(methyl methacrylate) (PMMA). A refocusing effect which occurs at adequate writing parameters – especially the repetition rate plays a crucial role - can be exploited to achieve an increase in refractive index directly below the material modification of the second focus. This zone supports guiding of an almost symmetric fundamental mode at test wavelengths of 520 nm, 660 nm and 850 nm. The process proves to be highly reliable and reproducible. The propagation losses of the waveguides are determined to be in the order of 0.5 dB/cm – the lowest attenuation reported so far for femtosecond laser written waveguides in bulk PMMA. These low losses make them a good candidate for applications on a larger scale like polymer foils with integrated sensor devices.