As optical components continue to replace electronics in ultrafast signal processing applications, a growing interest in
further miniaturization and integration of photonic devices on a single chip is observed. Therefore, optical waveguides of
high refractive index contrast of core and cladding materials are developed since a couple of years. They can have a very
small cross section and also bending radius, enabling the development of ultra-compact photonic integrated devices and
circuits. Silicon-On-Insulator (SOI) waveguides ("photonic wires") and devices are the most prominent examples.
A corresponding technology for Lithium Niobate-On-Insulator (LNOI) waveguides is still in its infancy, though LN
offers - in contrast to SOI - excellent electro-optic, acousto-optic, and nonlinear optical properties. Moreover, it can be
easily doped with rare-earth ions to get a laser active material. Therefore, LNOI photonic wires will enable the
development of a wide range of extremely compact, active integrated devices, including electro-optical modulators,
tunable filters, nonlinear (periodically poled) wavelength converters, and amplifiers and lasers of different types.
The state-of-the-art of LNOI films as platform for high-density integrated optics is reviewed. Using a full-wafer
technology (3" diameter), sub-micrometer thin LN films are obtained by high-dose He+ ion implantations,
crystal-bonding to a low-index substrate (preferably SiO2) and cleaving by a special annealing step ("ion-beam-slicing").
Various LNOI structures, also combined with metallic layers, are presented. Based on such platforms, photonic wires
and micro-photonic devices are developed using different micro- and nano-structuring techniques. To be specific, the
fabrication and characterization of LNOI photonic wires with cross-section < 1 μm2, and periodically poled LNOI
photonic wires for second harmonic generation are reported in detail.
The development of wafer-scale (3'' diameter) smart-cut lithium niobate (LN) single-crystal films of sub-micrometer
thickness is reported. Z-cut LN wafers, implanted by high energy He-ions, are crystal-bonded to a SiO2 layer on another
Z-cut LN handle sample. The bonded pair of samples splits along the He-implanted layer by appropriate annealing. As
this fabrication method is similar to the process widely used for silicon-on-insulator (SOI) fabrication, the resulting
material is called LNOI.
Two different routes to develop periodically poled LNOI photonic wires are discussed. The first one starts with poling of
planar LNOI samples; the photonic wires are fabricated afterwards by ICP-etching. The second one starts with the
fabrication of LNOI photonic wires; they are "locally" poled afterwards. As both approaches were not yet successful, a
PPLN-substrate was ion beam sliced to generate a planar periodically poled LNOI sample directly.
Using planar LNOI samples as starting material, high-quality photonic wires have been developed. The smallest
structure has a cross-section of ~ 1 x 0.7 μm2 only. Its optical properties with mode distributions, waveguide propagation
losses, and group index were investigated. Moreover, the first periodically poled LNOI photonic wires were successfully
fabricated, but not yet investigated optically. They are of great potential for second order nonlinear integrated optics.
Lithium Niobate is an important material in optical communication due to its special characteristics (high electrooptic coefficients and high optical transparency in the near infrared wavelengths). In this paper, we investigated the effects of 775-nm, femtosecond laser radiation on the Lithium Niobate crystal. By focusing the laser beam through a microscope objective, a certain refractive index change may be induced in Lithium Niobate substrate. Based on this effect, channel waveguides and other waveguide structures were fabricated. The output optical fields through them were measured, and the refractive index change of ~6×10-4 was calculated with the Near-field Method. The properties of these waveguide structures were discussed. We also investigated the waveguides effect induced with different fabrication conditions. The experimental results revealed that different fabrication conditions affect the waveguide effect greatly.