Mario Nicola Armenise

TiO2, LiNb3O8, and (TixNb1−x)O2 compound kinetics during Ti:LiNbO3 waveguide fabrication in the presence of water vapors

The presence of water vapor in the annealing atmosphere during Ti:LiNbO3 optical waveguide fabrication prevents Li out‐diffusion, inhibits LiNb3O8 growth, and furthermore decomposes this phase if already formed. As a consequence, the TiO2 and the mixed oxide (TixNb1−x)O2 growth kinetics change. A proton in‐diffusion in LiNbO3 with OH− defects and (Li1−yHy)NbO3 molecule formation is suggested to explain these effects and to account for the detected increase of absorbance at 3480 cm−1.

Fabrication and characteristics of optical waveguides on LiNbO3

Abstract Among the tremendous problems involving integrated optics and/or integrated optoelectronics, in this paper we give mainly a short review and a brief description of fabrication and characterisation techniques of planar optical waveguides made on lithium niobate single crystals. We note that research on waveguide integrated optic devices and systems are nowadays in a rather advanced stage. In fact, several components have been realized and tested, promoting the evolution of coherent optical fibre communications and high-speed signal processing. However integrated optics is still in its youth because, although it is clear what functions it can succesfully perform, much investigation remains to be done especially about a thorough understanding of waveguide technology in order to optimize device and system performances.

Characterization of TiO2, LiNb3O8, and (Ti0.65Nb0.35)O2 compound growth observed during Ti:LiNbO3 optical waveguide fabrication

TiO2, LiNb3O8, and (Ti0.65Nb0.35)O2 compounds have been observed and characterized during the fabrication of optical waveguides by Ti indiffusion in LiNbO3, performed in a flowing dry O2 atmosphere. Ti oxidizes by reacting with both O atoms of the surrounding atmosphere and of the LiNbO3 substrate. TiO2 formation is followed by LiNb3O8 and (Ti0.65Nb0.35)O2 phase growth. With further increasing in the annealing temperature the TiO2 and LiNb3O8 compounds are consumed and vanish. After 30 min at 950 °C both Y‐ and Z‐cut substrates appear covered only by a uniform and epitaxial (Ti0.65Nb0.35)O2 layer which behaves as the real source for Ti diffusion. The LiNb3O8 formation and dissolution were also observed in samples uncoated with Ti. Similar results were observed in LiNbO3 samples annealed in dry N, Ar, and static air.

Characterization of (Ti0.65Nb0.35)O2 compound as a source for Ti diffusion during Ti:LiNbO3 optical waveguides fabrication

During Ti:LiNbO3 integrated optical waveguide fabrication the (Ti0.65Nb0.35)O2 forms at temperatures ranging from 700 to 950 °C, after the Ti oxidation which occurs owing to Ti reaction with oxygen atoms of the surrounding atmosphere and/or of LiNbO3 substrates. The (Ti0.65Nb0.35)O2 compound has been characterized using scanning electron microscopy, secondary ion mass spectrometry, Auger electron spectroscopy, Rutherford backscattering in channeling conditions, and x‐ray diffraction. Results show that the (Ti0.65Nb0.35)O2 phase grows epitaxially on both Z‐ and Y‐cut substrates, the quality depending on both annealing atmosphere and film thickness. The film behaves as a real source for Ti diffusion and consequently is consumed at increasing annealing temperatures and/or times. We did not observe Li‐Ti‐O compounds, although a small amount of Li was detected in the surface layer.

Optical rectangular waveguide in titanium-diffused lithium niobate having its optical axis in the transverse plane

The complex equivalent propagation constants and the field distributions of the hybrid Epqx and Epqy modes of a lossy rectangular waveguide, including a metal film and a dielectric overlay, are derived using the effective-refractive-index method. The effects of the lossy metal cladding and of the direction of the birefringent medium c axis on the electromagnetic waves are examined. In particular, a two-dimensional analysis, required by the method employed, is carried out for any angle θ defining the c orientation with respect to the x direction in the plane transverse to the waveguide axis. We find at θ = 39° a turning point between the TE-like and TM-like polarizations for the well-guided ordinary wave. Investigation of a three-dimensional guide is accomplished for horizontal and vertical c-axis orientation. The modal characteristics of the lossy structure differ little from those obtained from the lossless and first-order perturbation approximate solutions. The results are given in numerical and graphical forms.

Evaluation of the Ti diffusion process during fabrication of Ti:LiNbO3 optical waveguides

Abstract The Ti oxidation and the formation of a surface Ti-Nb-O compound occurring during Ti diffusion process in LiNbO 3 for fabricating optical waveguides have been analysed using backscattering spectrometry and glancing-angle X-ray diffraction. Results show that Ti oxidation partially occurs owing to Ti reaction with oxygen atoms of the substrate and that the Ti-Nb-O compound grows epitaxially and behaves as a real source for Ti diffusion.

Investigation of the guided modes in anisotropic diffused slab waveguide with embedded metal layer

Abstract The optical characteristics of the TE and TM guided modes of a multilayer anisotropic two-dimensional waveguide are investigated by using the field component transformation matrix, and also taking into account the substrate intrinsic dispersion. The embedded thin metal layer effects on the propagation constant for both lossless approximated and exact solutions are presented. The lossless approach is accurate enough for the TE waves, but it is not for the TM ones, which exhibit changes of about 10−6 for the equivalent index. The TM modes also present attenuation constant changes between the lossy and weakly-lossy solutions of the order of 9 dB/cm. Several complex field component mappings are drawn, and the surface plasma waves are also examined.

In‐plane scattering in titanium‐diffused LiNbO3 optical waveguides

In‐plane scattering in Ti‐indiffused LiNbO3 optical waveguides arises from several possible sources. The importance of the different sources changes as a function of the total diffusion time used in waveguide fabrication. This letter describes detailed observations of different sources and shows that at long diffusion times the in‐plane scattering is dominated by an increasing density of misfit dislocations growing in the waveguiding layer.

A Multi-objective Genetic Algorithm Based Approach to the Optimization of Oligonucleotide Microarray Production Process

Microarrays are becoming more and more utilized in the experimental platform in molecular biology. Although rapidly becoming affordable, these micro devices still have quite high production cost which limits their commercial appeal. Here we present a novel multiobjective evolutionary approach to the optimization of the production process of microarray devices mainly aimed at lowering the number of fabrication steps. In order to allow the reader to better understand what we describe we report herein a detailed description of a real-world study case carried out on the most recent microarray platforms of the market leader in this field. A comparative analysis of the most widely used approaches, main potentialities and drawbacks of the proposed approach are presented.

A Novel Guided-Wave Correlator For Real-Time Synthetic Aperture Radar Data Processing

In this paper the design of a novel guided-wave correlator for air-bone synthetic aperture radar (SAR) data processing is illustrated. Correlation in azimuth direction is carried out through an optical transmission mask which includes the azimuth reference signal, and a two-dimensional CCD array working in time delay integration mode. The guided-wave correlator proposed in this paper performs the correlation in ground range direction operating in time integration mode. The device utilizes an optical waveguide formed in z-cut LiNb03 by proton exchange in dilute benzoic acid. The waveguide supports a collimation lens, a surface acoustic wave Bragg deflector and a grating filter which allows to remove the undiffracted beam. This new filtering technique does not require fabrication of lenses performing spatial Fourier transform. Moreover, usual procedures of planar technology can be followed to fabricate the correlator. When a laser beam at X = 0.84 pm is intensity modulated by the reference chirp signal having a bandwidth of 50 MHz, a correlation signal referred to the reference signal carrier is obtained. In this way the separation of the real and imaginary parts of the output signal can be carried out leading to an easy digital post-processing. Small size, light weight and low power consumption are further advatanges of the new correlator. Finally, a range swath of 1 Km with a resolution cell of 3m x 3m is easily achieved for an air-bone SAR data processor.