Theoretical analysis and preliminary fabrication of Ti-diffused LiNbO3 ridge waveguides

Lithium niobate (LN) ridge waveguides have recently attracted considerable attention, and they are usually fabricated by etching LN channel or slab waveguides prepared by Ti indiffusion or proton exchange. The field profile of the fundamental transverse electric (TE) mode guided in each of the two LN ridge waveguides converted from the Ti-indiffused channel and slab waveguides is simulated at 1550 nm wavelength. The simulation results indicate that the LN slab waveguide can offer the resulting ridge structure a stronger confinement of the TE mode as compared with the channel waveguide made under the same Ti-indiffusing conditions. The strong confinement of the guided mode allows for miniaturizing the LN-based photonic devices and for enhancing the electro-optical overlapping factor. It is also simple to fabricate the ridge structure from LN slab waveguides. On the other hand, Ti-indiffused LN slab waveguides are prepared, on which a chromium layer with a pattern of Mach-Zehnder interferometer (MZI) array is fabricated by the micro electro mechanical systems (MEMS) process. The ridge waveguide MZI array is realized by reactive ion etching of the slab LN waveguide in the SF6 atmosphere. Investigations by scanning electron microscopy reveal that the prepared LN ridge waveguides have a ridge height of 670 nm and an isosceles trapezoid cross section and their sidefaces are rather coarse.