Mario Bertolotti

Transmission properties of integrated resonator realized with cantor-like code

The spectral transmission properties of a self-similar optical Fabry-Perot resonator are theoretically studied. The considered structure can be realized by alternating two dielectric layers of different refractive index such that the highest refractive layers belong to a triadic Cantor set. The transmission spectrum exhibits localized peaks inside forbidden frequency band gaps. This feature could be very useful in the design of novel filters. Moreover the self- similarity of the structure reflects itself in a weak self-similarity in the transmission spectrum. A comparison with a regular periodic structure is also presented.

Nonlinear optical properties of chalcogenide As-S, As-Se glasses

Optical nonlinear properties of As-S and As-Se chalcogenide thin films are reported for different time scales of the irradiation source.

Low-intensity optical bistability in an active Fabry-Perot mirror induced by input-phase-insensitive parametric downconversion

A Fabry-Perot resonator filled with second-order nonlinear optical material is investigated. Attention is devoted to making the resonator act as a nonlinear mirror for ultralow-intensity light signals that can be switched by a control beam at the second-harmonic frequency. The interaction process is an input-phase-independent parametric downconversion. The theoretical problem is solved through implementation of a dummy variable method optimized for a parametric process. Efficient amplification and bistability of low-intensity signals have been found.

Nonlinear Fabry-Perot cavity with amorphous As2S3 and As2Se3 thin films

An investigation of a chalcogenide glass thin-film Fabry-Perot cavity has been performed in picosecond time regime. Nonlinear behavior of the structure derives from both nonlinear absorption of the material and changes in the resonance of the cavity. The conditions to have bistable behavior have been established.

Photothermal optical losses characterization of channel waveguides

The photodeflection method applied to the propagation losses characterization in channel waveguides is discussed using two different set-up configurations. 3D and 1D models are presented in order to calculate the photodeflection angle. The effects on the measurement of set-up misalignments are studied. Different ways for determining the propagation losses are shown. Comparison between theoretical and experimental results for Ti:LiNbO3 and a glass channel waveguide is also reported. The method has proven suitable to measure losses as low as 0.2 dB/cm.

Comparison between MOL and FDBPM simulations in nonlinear planar waveguide

In this paper the Method of Lines is applied to simulate the electromagnetic field propagation in optical dielectric nonlinear planar waveguides, with saturation of the refractive index. A comparison between the solutions obtained with the Method of Lines and the Beam Propagation Method (which uses paraxial approximation) is performed.

Crystallization and optothermal characteristics of germanate glasses

Glasses with composition corresponding to bismuth germanate crystals have been prepared. All these samples, by means of an appropriate heat treatment, crystallize. Where possible, the kinetics was studied by DSC isothermal runs. The photothermal deflection technique was applied to glasses and polycrystalline materials in order to elucidate the influence of the structure on their thermal properties and to consider them as possible candidates for application in non linear devices.