Fabrication of ultra-low bend loss optical waveguides

A novel way to fabricate low bend loss femtosecond-laser written optical waveguides is presented. First, large-diameter waveguides which are multimode at 1550 nm and exhibit a relatively complex refractive index distribution is fabricated. In a second step, thermal post-processing results in the selective removal of part of the previously induced refractive index change, leaving behind a very high index contrast waveguide that enables single mode operation in the C-band. This procedure enables the fabrication of waveguides with unprecedented small bends (down to 16.6 mm radius) with high (80%) normalized throughputs.