Florin Garoi

"We report secure data transmission performed using chaotic lasers with different external cavity geometries and applying the chaotic masking method based on subcarrier and phase modulations of the chaotic optical carrier. Two semiconductor lasers with similar multimode emission spectra and self-optical feedback provided, respectively, by ring and linear external cavities, were optically coupled and chaotically synchronized into a master – slave scheme. The transmitted message frequency modulates the radio frequency signal which modulates in phase the master chaotic carrier. Based on the robustness of the used encryption method and the synchronization characteristics of the two lasers, the decryption is conducted by the simple radio frequency spectrum monitoring of the slave emission."

The paper introduces a method for the measurement of monochromatic light using the geometric phase shift in a polarizing interferometer and applying the Fourier transform spectroscopy method. This is achieved with no mirror displacement or change in the actual optical path difference. Our method uses the rotation of a half-wave plate with increments on the order of degrees of arc, which is easier to control and reliable to reproduce. This approach provides flexibility in choosing the spectral range and a novel way of performing such measurements. It is demonstrated how the achromatic nature of the geometric phase allows only for monochromatic measurements to be acquired. The method is described theoretically and its performance is validated via measurements of several low-coherence light sources. Three possible applications of the method are also described, two of which are advantaged by using a detector array and, surprisingly, the achromaticity of the geometric phase.

Structural and optical characteristics determined by the sputtering deposition conditions of oxide thin films

The influence of film thickness on the structural and optical properties of silicon dioxide (SiO₂) and zinc oxides (ZnO) thin films deposited by radio frequency magnetron sputtering on quartz substrates was investigated. Deposition conditions were optimized to achieve stoichiometric thin films. The orientation of crystallites, structure and composition were investigated by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), while the surface topography of samples was analyzed using scanning electron microscopy (SEM). The optical characteristics were measured for samples with the same composition but obtained with different deposition parameters, such as increasing thickness. Optical constants (i.e. refractive index n, extinction coefficient k, and absorption coefficient α) of the SiO₂ and ZnO oxide films were determined using Swanepoel’s method from the transmission spectra recorded in the range 190 - 2500 nm, while the energy bandgap was calculated from the absorption spectra. The influence of thickness on the structural and optical properties of the oxide films was investigated. A good optical quality and real performance was noticed, which makes these thin films deem worthy of integration into metamaterial structures.

Rapid thermal annealing for high-quality ITO thin films deposited by radio-frequency magnetron sputtering

Single Pixel Camera (SPC) is an alternative architecture for imaging systems that emerged as an application of Compressive Sensing theory. The SPC distinctive feature is the single detector that measures linear combinations of pixels instead of pixels as in imaging array cameras. The measurements are obtained by projecting the scene on a Spatial Light Modulator (SLM), the other distinctive component of the SPC architecture. This paper discusses the problem of resolution in SPC. We show that in terms of Point Spread Function (PSF), the resolution model is similar to that of an imaging array camera except the fact that the role of the imaging array is taken over by the SLM. This reduces the contribution of the optics to the SPC resolution comparing with the CCD cameras. Relying on an existing method, we develop a procedure that uses a circular chart to measure the camera PSF. Our procedure has as additional facilities the correction of chart tilt and the capability to work with non-circular apertures. At low noise, tilts up to 15 degrees are practically removed.