Mustapha Abarkan

Analysis and Control of the DC Drift in LiNbO

The drift issue induces slow drifting of the optimum operating point for high efficiency or large nonlinearities in analog optical links, and requires complex control of the offset bias voltage for achieving high extinction ratio in digital optical links. We discuss and analyze the different sources of the drift in commercially LiNbO3 Mach-Zehnder modulators. The different extrinsic and intrinsic origins are compared in terms of phase shift and the different corresponding orders of magnitude are given, pointing out the predominant role of the intrinsic (dc) drift. We show the large role played by the electrical inhomogeneities at the surface of the LiNbO3 substrate by highlighting the link between the time dependence of the dc drift and the electrical conductivity measured at the surface and in the volume of the LiNbO3 substrate. This allows to propose a solution to the drift issue which consists in the engineering of the electrical conductivity of the lithium niobate substrate.

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All coefficients of the unclamped and clamped electro-optic tensor of zirconium-doped congruent LiNbO3 single crystals are determined as function of the dopant concentration at room temperature. With a distribution coefficient of zirconium closer to one in the considered range, the dopant concentration is in the range up to 2.5 mol% of ZrO2. The electro-optic coefficients are measured by direct techniques based on interferometric and Senarmont optical arrangements at the wavelength of 633 nm. It is found that all the unclamped and clamped effective electro-optic coefficients are relatively constant, except for the sample grown with 2 mol% of zirconium. The electro-optic behavior of LN:Zr as function of the dopant concentration was confirmed by dielectric characterizations. The concentration equal 2 mol% of ZrO2 can be considered to a threshold concentration for various physical and optical properties.

-Based Mach–Zehnder Modulators

In this work, a combination of experimental and theoretical study of Polyfuran and its oligomers, in their neutral and doped states, was reported. The effect of chain length on optoelectronic properties was discussed using the Density Functional Theory (DFT). Since the opto-electronic properties of this kind of conducting polymers are governed by their band gap, a comparison among Highest Occupied Molecular Orbital, Last Unoccupied Molecular Orbital and band Gap energies of these compounds shall be presented.

The clamped and unclamped effective electro-optic coefficients of zirconium-doped congruent lithium niobate crystals

Polyfuran constitutes polymer belong the conjugated systems which have been pointed out functionalized properties in the electronic and optic fields. In the present paper, experiment and theoretical analysis on Polyfuran with his oligomers have been reported. The interpretation of the infrared and Raman spectra of Polyfuran is presented. In order to discuss the functional properties of oligofurans, we used Density Functional Theory methods and carried out DFT calculations to determinate their electronic, electrochemical and absorption properties. The efficient low band gap allows furan-based polymers to be promising organic materials in photovoltaic application, also the oxygen-based conjugated materials constitute more biodegradable conducting compounds especially for solar cells compared to Sulfur or Selenium.