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Microstructuring of lithium niobate
No full textThis thesis presents the results from an investigation into methods for micron-scale relief structuring of lithium niobate. A wet etch consisting of HF and HNO3 was applied, and directed by 1) patterning the ferroelectric domain structure of the samples and 2) illuminating the crystals with patterned 488nm light. Post-etch treatment of the structures resulted in ridge waveguides and alignment grooves, while pre-etch manipulation achieved an etch-stop. Ablation was investigated as a method of directly structuring the crystal and for patterning photoresist. The etch was found to leave the +z face untouched. The -z face was etched at a rate, k, in µm/hour given by k = e 20.37 - 6300/T where T is the absolute temperature. This differential etch rate reveals a pattern induced in the ferroelectric domain structure by the technique of electric field patterning. The structures had walls with roughness < 5nm. Straight walls were easily achieved aligned along the y-direction at 120o to this. Other directions can result in facetted walls. Ridge waveguide losses <1dBcm-1, fibre alignment grooves and an etch stop were demonstrated using appropriate pre- and post-etch treatments. The etch was found to be affected by illumination with 488nm radiation. In Fe:LiNbO3 complete and partial frustration of the etch was induced on the -z face. Characteristic features of the partial frustration were sub-micron ridges and triangular pillars, separated by gaps as small as 500nm. In LiNbO3 the etch rate was found to increase on the -z face. The etch rate on the +z face was unaffected in both. Direct ablation with an excimer laser produced relief structures. Aspect ratios > 1:1 resulted in a dendritic structure in the ablated area. Direct ablation was suitable for patterning the photoresist. Surface damage was intentionally induced when producing large (>100µm) openings, however, the effect of surface damage on electric field poling could not be conclusively tested. Submicron openings were also created and subsequent poling produced sub-micron domains, revealed by etching. <br/
Microstructuring lithium niobate: towards new hybrid devices
No full textLithium niobate is among the most important nonlinear optical materials used today in the photonics industry as it combines a variety of very important properties which, apart from the optical nonlinearity, includes electrooptic, pyroelectric, piezoelectric behaviour and an optical transparency which extends from the UV (350nm) to the infrared (5µm) spectral region. In order to benefit from both the optical and electro-mechanical properties of lithium niobate it is necessary to develop methods for the fabrication of suitable surface and/or bulk structures depending on the application involved. Such methods for surface and bulk microstructuring have been developed and are presented here aiming to show that there is significant scope for the broadening of the utility of this very useful material.
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Fabrication of alignment grooves in LiNbO<sub>3</sub> substrates for simplified optical fibre pigtailing
No full textA technique for lubricating alignment grooves in LiNbO3 substrates. The simplified optical fibre attachment, is reported. The grooves are produced through the etching of material that has been domain inverted via spatially selective electric field poling. The etched grooves are of very high surface quality, and have a profile that is determined by the area of domain inversion produced. The technique lends itself to a method of fibre alignment that is simplified, more reliable, and less labour intensive than existing schemes
Light induced frustration of etching in Fe doped LiNbO<sub>3</sub>
No full textWe report frustration of normal etching in iron doped lithium niobate by incident 488nm light. At intensities > 1 Wcm-2 etching is fully suppressed. We report the techniques' resolution and the effect of applied electric field
Microstructuring lithium niobate: A multi directional approach
No full textLithium niobate is a nonlinear optical ferroelectric crystal which has found extended use in the area of optical and conventional telecommunications systems as it possesses a wide range of desirable optical and electromechanical properties. The importance of this nonlinear crystal to the photonics industry has lead to the reproducible growth of commercially available superior quality material. Microstructuring of this material is expected to allow for fabrication flexibility by benefiting from both optical and electromechanical properties and to increase its functionality and applicability. An outline of the main methods used for the fabrication of surface and bulk microstructures in congruent lithium niobate single crystals will he given here where techniques such as ferroelectric domain micro-engineering and laser-material interactions are used to induce spatially resolved differential etching which is the main tool in micro-fabrication processes
Fabrication of piezoelectric micro-cantilevers in domain-engineered LiNbO<sub>3</sub> single crystals
No full textWe report on a novel route for fabrication of micro-cantilevers in ferroelectric single-crystal lithium niobate (LiNbO3). Using the sequential techniques of photolithographic patterning, electric field poling, direct bonding and domain-oriented differential etching, free-standing cantilevers of dimensions 50µm × 50µm × 5 mm in the x, z and y crystallographic directions, respectively, have been fabricated
Ridge waveguides in lithium niobate fabricated by differential etching following spatially selective domain inversion
No full textRidge structures have been fabricated in z-cut LiNbO3 using the technique of differential etching following spatially selective domain inversion. Waveguides within these ridges have been achieved using the techniques of ion beam implantation, proton exchange, and titanium indiffusion. Using this last method, guides with losses <0.8dB/cm have been realised for light at a wavelength of 1.3µm. We briefly discuss applications for these structures
Microstructuring of lithium niobate using differential etch-rate between inverted and non-inverted ferroelectric domains
No full textSingle crystal samples of lithium niobate have been spatially patterned with photoresist, and subsequently domain inverted using electric field poling, to produce a range of two dimensional spatial domain structures. Differential etching has subsequently been carried out using mixtures of hydrofluoric and nitric acids, at a range of temperatures between room temperature and the boiling point. The structures produced show very smooth, well defined, deep features, which have a range of applications in optical ridge waveguides, alignment structures, V-grooves, and micro-tips. Details are given of the fabrication procedures, and examples of structures are shown
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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