Lithium niobate ridged waveguides with smooth vertical sidewalls fabricated by an ultra-precision cutting method

This paper demonstrates the application of ultra-precision cutting to the fabrication of ridged LiNbO₃ waveguides for use in low-loss photonic integrated circuits. Ridged waveguides with sidewall verticality of 88° and ultra-smooth sidewalls were obtained in LiNbO₃ crystals using this technique. In addition, the possibility of fabricating bent ridged waveguides via this mechanical micromachining method was examined. The root mean square surface roughness of the machined sidewall was 4.5 nm over an area of 2.5 × 10 μm, which is sufficiently low so as to minimize scattering losses of guided light. The propagation loss of the ridged waveguide produced during this work was well below 1 dB/cm at a wavelength of 1550 nm. The present technique should have significant applicability to the micromachining of ferroelectric materials and the fabrication of highly confined optical waveguides such as ridged waveguides and photonic wires.