  We provide a solution toward compact and low-loss three dimensional (3D)
photonic circuits by femtosecond laser direct writing of 3D waveguides in fused
silica. We suppress the bend loss by sandwiching the waveguide between a pair
of walls formed by internal modification of glass. Our method allows to reduce
the bend loss of a curved waveguide with a bending radius of 15 mm by more than
one order of magnitude.
