Time resolved confocal luminescence investigations on Reverse Proton Exchange Nd:LiNbO3 channel waveguides

This paper was published in Optics Express and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://dx.doi.org/10.1364/OE.15.008805. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under la

Surface domain inversion in ferroelectric lithium niobate

Periodic inversion is reported for ferroelectric domains near the surface of z-cut lithium niobate crystals by a modified electric field poling technique. The depth of the inverted domain region extends to values of order a few µm (5-10 µm) below the surface of the crystal, thereby removing the high aspect ratio instability problems associated with bulk poling, and therefore allowing the fabrication of fine period ferroelectric domain structures. Using this method periods as short as 1µm have been achieved. Such periodic domain distributions have been fabricated in Ti-indiffused and proton exchanged lithium niobate waveguides and our first quasi-phase-matching results are shown

First-order quasi-phase-matched blue light generation in surface-poled Ti-indiffused lithium niobate waveguides

We demonstrate efficient first-order quasi-phase-matched second-harmonic generation in a surface periodically poled Ti:indiffused lithium niobate waveguide; 6 mW of continuous-wave blue radiation (=412.6 nm) was produced showing the potential of surface domain inversion for efficient nonlinear waveguide interactions

Efficient blue light generation from surface periodically poled Ti-indiffused channel waveguides

We report first-order quasi-phase matched blue light generation at 413.17 nm, in a surface-poled Ti-indiffused channel waveguide in lithium niobate. For 70mW of incident c.w. pump, 3.46 mW (uncorrected for reflection losses) was generated at the second harmonic

Surface engineered ferroelectric domains in congruent lithium niobate crystals

We report on the fabrication of high quality, fine period (~1µm) surface ferroelectric domains in congruent lithium niobate single crystals suitable for first order quasi-phase-matched nonlinear interactions in lithium niobate channel waveguides

Surface domain inversion in ferroelectric lithium niobate

Periodic inversion is reported for ferroelectric domains near the surface of z-cut lithium niobate crystals by a modified electric field poling technique. The depth of the inverted domain region extends to values of order a few µm (5-10 µm) below the surface of the crystal, thereby removing the high aspect ratio instability problems associated with bulk poling, and therefore allowing the fabrication of fine period ferroelectric domain structures. Using this method periods as short as 1 µm have been achieved. Such periodic domain distributions have been fabricated in Ti-indiffused and proton exchanged lithium niobate waveguides and our first quasi-phase-matching results are shown

Surface domain engineering in congruent lithium niobate single crystals: a route to sub-micron periodic poling

We describe a technique for surface domain engineering in congruent lithium niobate single crystals. The method is based on conventional electric-field poling, but involves an intentional overpoling step that inverts all the material apart from a thin surface region directly below the patterned photoresist. The surface poled structures show good domain uniformity, and the technique has so far been applied to produce domain periods as small as ~1 µm. The technique is fully compatible with nonlinear optical integrated devices based on waveguide structures

Surface periodic poling of lithium niobate for efficient non-linear optical waveguide applications

Domain engineering of LiNbO3 has been researched for a range of applications in areas as diverse as second harmonic generation and parametric oscillation, electro-optic Bragg gratings and piezoelectric micro-actuated devices. Non-linear frequency conversion achieved by quasi-phase-matched interaction remains an attractive route for realising efficient coherent blue-green light sources. Such quasi-phase-matching requires precise control of periodic domain inversion, with periods that can be as small as ~2µm for first order conversion via second harmonic generation (SHG) from the near I.R. into the blue spectral region Application of an electric field greater than the crystal's coercive field is the most widely employed route for fabrication of periodically inverted domain structures for non-linear quasi-phase matched interactions. It is experimentally very difficult to achieve such high aspect ratios in bulk poled material of typical thickness ~500µm. The high coercive fields required for domain inversion, together with the inherent non-uniformities and defects present in commercially available materials, restrict the routine applicability of electric field poling to periods of the order of >4-5 µm in samples of this thickness. To circumvent this problem wafers can be thinned to ~100-150 µm to achieve such small domain periods, but this pre-treatment is both undesirable, expensive and for waveguide applications, unnecessary. Several other techniques such as controlled spontaneous backswitching , and the use of multiple short current pulses, have also been successfully used to generate periods of the order of 2.2-3.0 µm in bulk and waveguide geometries respectively. However fabrication of such poled crystals with very small periods particularly of sub-micron scales remains an elusive goal. Achieving large uniform periodically poled areas is difficult: we however have achieved periods of 1µm by our technique which relies on over-poling the sample, thereby achieving the apparently undesirable effect of domain spreading and merging beneath the lithographically patterned photoresist layer. This technique results in superficial or surface domain inversion, which can be used in conjunction with a waveguide geometry for higher conversion efficiencies in non-linear interactions. Second harmonic generation experiments yielding blue light have been performed with surface poled annealed proton exchanged and Ti-indiffused waveguides confirming the utility of our technique

SiPM as miniaturised optical biosensor for DNA-microarray applications

A miniaturized optical biosensor for low-level fluorescence emitted by DNA strands labelled with CY5 is showed. Aim of this work is to demonstrate that a Si-based photodetector, having a low noise and a high sensitivity, can replace traditional detection systems in DNA-microarray applications. The photodetector used is a photomultiplier (SiPM), with 25. pixels. It exhibits a higher sensitivity than commercial optical readers and we experimentally found a detection limit for spotted dried samples of ~1 nM. We measured the fluorescence signal in different operating conditions (angle of analysis, fluorophores concentrations, solution volumes and support). Once fixed the angle of analysis, for samples spotted on Al-TEOS slide dried, the system is proportional to the concentration of the analyte in the sample and is linear in the range 1. nM-1. \u3bcM. For solutions, the range of linearity ranges from 100. fM to 10. nM. The system potentialities and the device low costs suggest it as basic component for the design and fabrication of a cheap, easy and portable optical system

Surface hexagonally poled lithium niobate waveguides

We report on surface hexagonally poled lithium niobate for two-dimensional non-linear interactions in optical waveguide structures. A method for surface inversion of ferroelectric domains has been applied for the fabrication of a hexagonal two-dimensional periodic domain structure with a period of 7.6 µm on an annealed proton exchanged lithium niobate waveguide. This periodic pattern is suitable for quasi-phase-matched second harmonic generation at the fundamental wavelength of 1.06 µm by means of the first order (G10) reciprocal lattice vector