Novel phase-tunable three-dimensional hollow waveguides with variable air core

We propose novel micromachined tunable waveguide devices based on hollow optical waveguides. The combination of hollow waveguides and mechanical movable elements gives us a large change in a propagation constant of guided waves in a hollow waveguides. We fabricated a three-dimensional (3-D) hollow waveguide and experimentally demonstrated the change of the propagation constant in the 3-D hollow waveguide with a variable air core. We observed the wavelength shift of 1.8 nm in a hollow waveguide resonator with a displacement of 6 μm in an air core.