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

Ultrafast laser inscription is a standard technique to fabricate embedded waveguides in glasses or crystals. Tightly focused femtosecond laser-pulses induce an increase in refractive index inside the material via non-linear absorption. By moving the sample through the focus virtually arbitrary threedimensional paths can be created. The transfer of this technique to polymers has already delivered promising results [1, 2] but is limited so far by the reported high propagation losses between 3– 6 dB/cm [3]. Here we present a new approach to femtosecond laser writing of waveguides in bulk poly (methyl methacrylate) (PMMA) by exploiting a refocusing effect during the writing process.