  We present a novel method to fabricate low bend loss femtosecond-laser
written waveguides that exploits the differential thermal stabilities of laser
induced refractive index modifications. The technique consists of a two-step
process; the first involves fabricating large multimode waveguides, while the
second step consists of a thermal post-annealing process, which erases the
outer ring of the refractive index profile, enabling single mode operation in
the C-band. By using this procedure we report waveguides with sharp bends (down
to 16.6 mm radius) and high (80%) normalized throughputs. This procedure was
used to fabricate an efficient 3D, photonic device known as a pupil-remapper
with negligible bend losses for the first time. The process will also allow for
complex chips, based on 10's - 100's of waveguides to be realized in a compact
foot print with short fabrication times.
