Diffusion of Iron in Lithium Niobate for applications in integrated optical devices
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In the field of optical signal processing and all-optical integrated devices, photorefractive crystals can be used because of their capability to keep memory of a spatially varying light pattern. Among them, lithium niobate is particularly interesting because
its photorefractive response can be improved or inhibited by adding selected dopants: this opens the possibility of producing an integrated device in a lithium niobate single crystal, where each stage has different properties and different functions according to the doping. In particular, a photorefractive stage can be created by doping with Fe, which is known to enhance photorefractive effect. In the context of integrated devices,
it is necessary to perform a local doping of lithium niobate with Fe, in order to obtain a suitable substrate for photorefractive recording. This thesis deals with the preparation and characterisation of the locally doped crystal, i.e. with an investigation of the preparation conditions and how they affect the crystal quality. Many characterisation techniques, customary in materials science, such as secondary ion mass spectrometry, spectrophotometry and others, have been used and refined specifically for Fe doped lithium niobate. Besides the practical aim to find the best preparation conditions, many basic properties and features of this material have been investigated, leading to an advance in the knowledge of this material, as well as an advance in the usage of characterisation tools.Keywords:
Crystal (programming language)
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Abstract : The development of organic inorganic second order nonlinear optical materials is discussed in light of the need to obtain practical (high performance, stable operation, processable and low cost) alternatives to inorganic crystals. Sol gel materials have well established optical properties attributed to their superior purity and homogeneity. Processing methods of sol gel materials permit the inclusion of numerous dopants to achieve final materials having variable and desirable properties. These materials have low optical losses and physical properties which are amenable to integrated optical devices. A number of chromophores and ormosil materials have been designed, synthesized, processed, and tested. Several composite materials are described which have high optical nonlinearities and low optical losses when they are prepared as optical waveguides. Many of these films demonstrate stable performance at room temperature and can be considered for selected applications. Specific recommendations for continued work in improving thermal stability are suggested.
Electro-optic modulator
Modulation (music)
Harmonic
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Digital holographic memory using photorefractive material is one of the most promising candidates for the next-generation of data storage, which simultaneously provides high capacity, fast transfer rate and short access time. This comes from a three-dimensional volume holographic multiplexing scheme based on two dimensional page oriented read-write mechanisms. However there are numerous hurdles on the road to success. The development of a really satisfactory recording material for holographic data storage applications remains perhaps most important barrier to practical implementation of the technology. The ideal material must simultaneously possess many properties such as good sensitivity, large dynamic range, long data retention times and excellent optical quality. In addition, it must be able to be mass produced. From the above points of view, lithium niobate (LiNbO/sub 3/; abbreviated as LN) is the most promising candidate among all the inorganic photorefractive materials. High quality crystals of up to 3 inches (recently 4 inches) diameter of LN are commercially produced by the Czochralski method as substrate material of SAW devices. Because the growth method has been established, LiNbO/sub 3/ single crystals doped with hundred wt. ppm of Fe have been investigated as photorefractive data storage material. However, the photorefractive properties are not sufficient for applications and further improvements, especially in writing speed is required as a high priority.
Holographic Data Storage
Diffraction efficiency
Optical storage
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Lithium niobate (LiNbO 3 ) is a frequently used material for nonlinear optics, due to its large nonlinear coefficient and high transparency over a large wavelength range. Domain engineering is needed to achieve quasi-phase matching which is necessary to address a wide wavelength range.
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In this contribution we are reporting all-optical poling, or direct domain inversion induced by light without an applied electric field, in lithium niobate. Potential advantages of such a technique are the reduction of fabrication steps, removing the need for photolithography, and allowing the domain microstructuring to be directly defined by the illumination pattern alone. This may lead to smaller domain sizes as compared with electric field poling which is currently limited to domain sizes of several micrometers.
Poling
Ultraviolet
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An illustrative, device systems level desirability optimization analysis has been performed for a number of important electrooptic materials that are candidate for use in high-speed guided-wave optical devices. Ferroelectric materials with high and low transition temperatures, cubic crystals, organic crystals, and alloy semiconductors have been considered. The bulk guided-wave phase modulator has been taken as the initial screening device. Performance measures such as electrical power supply constraints and the device's maximum operating speed have been analyzed as a function of system variables that include material properties and electrode architectures. Desirability analysis has been presented as a composite mathematical function that describes two or more independent performance measures in terms of all relevant system variables. This function has been displayed graphically to identify those sets of system variables that jointly optimize the performance measures of greatest interest. The initial screening analysis has ignored propagation loss and less-than-ideal overlap between electrical and optical fields. Potassium niobate, barium titanate, and lithium niobate have been found to be among the more desirable electrooptic materials. The use of dielectric buffer layers, several thousand Angstroms in thickness, has been found necessary to isolate the modulator electrodes from high dielectric constant, high electrooptic strength materials such as potassium niobate. Buffer layers, however, have been found to be generally unnecessary when using the lower permitivity and lower electrooptic strength materials such as lithium niobate.
Barium titanate
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Reflection
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Lithium niobate (LN) crystal fibers [1,2] represent promising new substrates for optical applications [3]. Indeed, additionally to the numerous properties of LN, the high length-to-width ratio of LN crystal fibers can be very useful for numerous optical applications. Furthermore, the growing methods used to produce these fibers allow to control their composition and to change the nature and concentration of dopants during the growth, easier than in the usual Kyropoulos or Czochralski techniques. This allows the possible creation of multifunction built-in devices within the same substrate, free of signal losses related to the assembly of various devices and multiple interfaces between different functional parts.
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Periodic poling of lithium niobate crystals (PPLN) by means of electric field has revealed the best technique for finely tailoring PPLN structures and parameters, which play a central role in many current researches in the field of nonlinear integrated optics. Besides the most studied technique of bulk poling, recently a novel technique where domain inversion occurs just in a surface layer using photoresist or silica masks has been devised and studied. This surface periodic poling (SPP) approach is best suited when light is confined in a thin surface guiding layer or stripe, as in the case of optical waveguide devices. Also, we found that SPP respect to bulk poling offers two orders of magnitude reduction on the scale of periodicity, so that even nanostructures can be obtained provided a high resolution holographic mask writing technique is adopted. We were able to demonstrate 200 nm domain size, and also good compatibility with alpha-phase proton exchange channel waveguide fabrication. Our first experiments on lithium tantalate have also shown that the SPP technology appears to be applicable to this crystal (SPPLT), whose properties can allow to overcome limitations such as optical damage or UV absorption still present in PPLN devices. Finally, the issue of SPP compatibility with proton exchange waveguide fabrication will be addressed.
Poling
Lithium tantalate
Waveguide
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Domain engineering
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The optical memory on materials having the properties of electron trapping is a new direction at development of information storage and rewrite. Currently are pursued investigations directed on creation of a new type recording medium with the opportunity of information rewrite by optical methods as well as a medium for heteroassociative memory in optical neural systems. Primarily as such medium are used alkaline-earth metal sulphides activated by two rare-earth elements. When creating the memory on materials with electron trapping on the basis of alkaline-earth sulphides there arises a number of difficulties: (1) these materials are chemically unstable, especially they are subject to the action of water vapors; (2) films prepared by electron-beam evaporation technique have a polycrystalline structure with grain sizes in the order of 20 nm what has an essential influence on the signal-to-noise ratio at information reading. The main objective which is pursued by us consists in investigating the optical properties of new synthesized materials having the electron trapping properties which are characterized by chemical stability and are easy manufacture at preparation of amorphous structures. We have also recommended to use CaO (MgO) doped with Eu, Sm. It has known, that the optical stimulated luminescence (OSL) obtains in CaO. But OSL appears in the special prepared structures with defects. For this aim there are some methods: thermochemical reduction or radiation processing by electron beam. Besides that the OSL obtains only by nitrogen temperature (77 K).
Alkaline earth metal
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