This paper reports on the development of thin film lithium niobate (TFLN™) electro-optic devices at SRICO.
TFLN™ is formed on various substrates using a layer transfer process called crystal ion slicing. In the ion slicing
process, light ions such as helium and hydrogen are implanted at a depth in a bulk seed wafer as determined by the
implant energy. After wafer bonding to a suitable handle substrate, the implanted seed wafer is separated (sliced) at the
implant depth using a wet etching or thermal splitting step. After annealing and polishing of the slice surface, the
transferred film is bulk quality, retaining all the favorable properties of the bulk seed crystal. Ion slicing technology
opens up a vast design space to produce lithium niobate electro-optic devices that were not possible using bulk
substrates or physically deposited films. For broadband electro-optic modulation, TFLN™ is formed on RF friendly
substrates to achieve impedance matched operation at up to 100 GHz or more. For narrowband RF filtering functions,
a quasi-phase matched modulator is presented that incorporates domain engineering to implement periodic inversion
of electro-optic phase. The thinness of the ferroelectric films makes it possible to in situ program the domains, and thus
the filter response, using only few tens of applied volts. A planar poled prism optical beam steering device is also
presented that is suitable for optically switched true time delay architectures. Commercial applications of the TFLN™
device technologies include high bandwidth fiber optic links, cellular antenna remoting, photonic microwave signal
processing, optical switching and phased arrayed radar.
We report on photonic crystal electro-optic devices formed in engineered thin film lithium niobate (TFLN™) substrates.
Photonic crystal devices previously formed in bulk diffused lithium niobate waveguides have been limited in performance by the depth and aspect ratio of the photonic crystal features. We have overcome this limitation by implementing enhanced etching processes in combination with bulk thin film layer transfer techniques. Photonic crystal
lattices have been formed that consist of hexagonal or square arrays of holes. Various device configurations have been
explored, including Fabry Perot resonators with integrated photonic crystal mirrors and coupled resonator structures. Both theoretical and experimental efforts have shown that device optical performance hinges on the fidelity and sidewall profiles of the etched photonic crystal lattice features. With this technology, very compact photonic crystal sensors on the order of 10 μm x 10 μm in size have been fabricated that have comparable performance to a conventional 2 cm long bulk substrate device. The photonic crystal device technology will have broad application as a compact and minimally invasive probe for sensing any of a multitude of physical parameters, including electrical, radiation, thermal and chemical.