Direct-write e-beam sub-micron domain engineering in lithium niobate thin films grown by liquid phase epitaxy

Wavelength division multiplexing (WDM) is a technique to improve the capacity of optical telecommunication networks by multiplexing wavelengths carrying optical signals. WDM systems require efficient add/drop filters. Currently, most add/drop filters are static, based on fiber Bragg gratings. In this approach, each wavelength channel requires filters and switches, which makes the system costly and inefficient. One promising solution is using dynamically switchable filters that can switch wavelength channels dynamically depending on signal traffic conditions. A potentially useful device is based on switching a grating in a periodically poled lithium niobate (PPLN) waveguide using the electro-optic effect. The biggest challenge to building such a filter is realizing a sub-micron (∼360 nm) periodically poled ferroelectric domain structure in lithium niobate waveguides.; In this study a direct-write electron beam poling technique is employed as a promising method that does not require optical lithography and has very high spatial resolution. Several material LiNbO3 systems are investigated, including stochiometric and congruent bulk LiNbO3 as well as liquid phase epitaxy (LPE) thin film LiNbO3 grown using a LiVO3-LiNbO 3 flux.; By using the direct-write e-beam technique with LPE LiNbO3, sub-micron domain structures with a width of 200∼400 nm, and periods of ∼1.1 mum and ∼790 nm have been successfully produced. In comparison with single crystal congruent LiNbO3 (CLN) and stoichiometric LiNbO3 (SLN), LPE LiNbO3 is shown to be the best material for producing superior domain regularity and finer domain sizes than single crystals. We believe that the vanadium incorporation and distortion due to the lattice mismatch between films and substrates enhance electron localization, domain wall pinning and domain nucleation in LPE materials, giving rise to better structures.; We have studied the effects of varying e-beam parameters on domain structure regularity. We achieved approximately 500 mum-long gratings with a period around 1.1 mum, and with domain sizes around 180 nm. Using an optical simulation of reflectance, we show that stitching effects between sections of the grating do not significantly affect overall reflectance properties. The results indicate that by using direct write e-beam techniques in LPE LiNbO3, switchable Bragg filters for optical communication appear feasible.