In this study, we report for the first time the epitaxial growth of CBN thin films on Magnesium Oxide (MgO) substrates for optical device applications. A high deposition temperature (greater than or equal to to 800 oC) is required to obtain the epitaxial growth of CBN films. A parametric study is proposed in order to elaborate CBN thin films with a crystal structure as close as possible to that of a CBN bulk single crystal and with good optical characteristics. In particular, a low oxygen pressure (1 mTorr) allows synthesizing high-quality CBN thin films with an out-off plane lattice parameter comparable to the one of CBN bulk material at low surface roughness. The optical characterization of the high-quality CBN thin films reveals a high optical transmission (greater than or equal to 85 %) and a refractive index equal to 2.22 at 1.55 μm for certain deposition conditions. These optical properties clearly indicate the potential of CBN thin films for waveguide applications. This work presents a significant first step toward the integration and the potential use of CBN films for optical device applications.
Temporal Talbot effect is the time domain counterpart of spatial self imaging phenomenon. When a periodic time signal is propagated through a first order dispersive medium, exact replicas of the signal are reproduced at specific distance along the direction of propagation. At other distances, the signal is self imaged with a higher repetition-rate than the original periodic sequence (Fractional Talbot effect).
In this paper, the problem of propagation of an ideal periodic optical pulse sequence through a linear dispersive fiber is investigated in the joint time-frequency domain using an optimized representation [i.e. Wigner Ville-Multiresolution spectrograms providing an optimal resolution in both time and frequency domains with reduced cross-term interferences]. Based on these optimized representations, complete numerical simulations were carried out to analyze the evolution of the time-frequency distribution of a periodic signal propagating through a linear dispersive medium, thus providing a deeper insight into the physics of the temporal Talbot problem.
Moreover, we have used an elegant ray-matrix approach to describe the signal propagation in phase space and we have showed that for the fractional temporal Talbot effect (repetition rate factor M), each newly generated individual temporal pulse has contributions only from every Mth spectral component of the train's discrete spectrum. This interpretation is in fact in very good agreement with the notion that the fractional temporal Talbot effect can be explained as a result of interference between consecutive, chirped TF patterns. Our numerical simulations have confirmed our heuristic descriptions of the Talbot phenomena.