Sub-micrometer-thick lithium niobate on an insulator is a promising integrated photonic platform that provides optical field confinement and optical nonlinearity useful for state-of-the-art electro-optic modulators and wavelength converters. The fabrication of lithium niobate on insulator on a silicon substrate through ion slicing is advantageous for electronic-photonic integration but is challenging because of debonding and cracking due to the thermal expansion coefficient mismatch between silicon and lithium niobate. In this work, the fabrication of thin film lithium niobate on insulator on a silicon handle wafer is achieved, informed by structural modeling, and facilitated by accommodating for dissimilar wafer bows using a bonding apparatus. Structural finite element analysis of strain energy and stress, due to thermal expansion coefficient mismatch at elevated temperatures, is conducted. High strain energies and stresses that result in debonding and cracking, respectively, are studied through modeling and reduced by selecting optimized substrate thicknesses followed by an experimental technique to bond substrates with dissimilar bows. A lithium niobate thin film with a thickness of 800 nm is successfully transferred to an oxidized silicon wafer with a root mean square surface roughness of 5.6 nm.
The well aligned multiwalled carbon nanotube arrays were synthesized by injecting the acetonitrile-ferrocene solution at regular intervals of time. The carbon nanotube arrays were deposited on quartz substrate which is placed at the centre of the CVD reactor in quartz tube. The injection method in chemical vapor deposition allows-excellent control of the catalyst to carbon ratio which facilitates the better growth of aligned carbon nanotubes. The effect of various reaction parameters such as growth temperature, catalyst concentration, gas flow rate, growth time and substrate surface on growth of carbon nanotubes have been studied. It was observed that the diameter of carbon nanotubes increases with increase in catalyst concentration and temperature of the synthesis. The SEM analysis reveals that the average growth rate of carbon nanotube film synthesis was about 1.1 microm/min when the synthesis time was one hour.
We present lithography and argon plasma etching of lithium niobate on insulator (LNOI) rib waveguides using reflowed photoresist etch masks and 405 nm photolithography. Melting the photoresist at temperatures greatly exceeding its glass transition temperature while minimizing feature distortion through photoresist adhesion control reduces sidewall surface roughness and allows the photoresist to be used both as the pattern mask and the hard etch mask. Waveguide sidewall surfaces exhibiting sub-nm root mean square roughness are fabricated. Dependence of sidewall roughness and angle on feature width, and propagation loss on thermal annealing of the fabricated devices is characterized. Measured quality factors on fabricated microresonators exceed one million. LNOI rib waveguides and resonators with low propagation loss increase nonlinear optical conversion efficiencies and are useful for efficient electro-optic modulation. Photolithography compatible fabrication of low loss LNOI photonic integrated circuits facilitates scalable commercialization.
We repeatedly pole and unpole a lithium niobate thin film second harmonic generator while monitoring the switching of the optical output. Increasing asymmetry in the poling waveform results in increasing optical extinction ratio.
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