Papers by Author: V. Agarwal

Abstract: Experimental evidence of photon Bloch Oscillations (PBOs) and Zener tunneling (ZT) in dual-periodical (DP) superlattices made of porous silicon (PSi), is presented. An introduction of linear gradient in physical layer thicknesses in DP structure, composed by stacking two different periodic substructures N times, where (N-1) resonances appear, i.e, WSLs resonances and Zener tunneling of the nearest resonances of two consecutive minibands can be observed depending on the values of applied gradient. Theoretical time-resolved reflection and scattering state maps show photonic Bloch oscillations (BOs) and Zener tunneling for a range of incidence angles. Measured reflection reveals the presence of Wannier-Stark ladders (WSLs) and ZT in the near infrared region.

Abstract: To investigate the optical properties in non-periodic dielectric systems, we study here the reflection of light from nanostructured porous-silicon-based period doubling heterostructures. The multilayered systems are fabricated in such a way that the optical thickness of each layer is one quarter of 650nm. The results for the optical reflectance are presented and compared with that of Fibonacci, Thue-Morse, and random structures fabricated under the same conditions. Numerical simulation for the reflectance along the lines of the transfer matrix approach is performed. In addition, optical reflection from Gaussian porous silicon multilayers is also briefly discussed. We find that porous silicon Period Doubling dielectric multilayers could demonstrate the optical properties similar to the classical periodic Febry-Perot interference filters with one or multiple resonant peaks, but with an advantage of having total optical thickness much lesser than that of the periodic structures.

Abstract: In this work, we report the fabrication of porous silicon multilayers using lightly doped, p-type, silicon wafers (resistivity: 14-22 Ω-cm) by pulsed anodic etching. The optical properties have been found to be strongly dependent on the duty-cycle and frequency of the applied current. Less than 50 % of duty-cycle, at low frequencies, is found to show very rough porous silicon – crystalline silicon (PS-cSi) interface. Use of duty cycle above 50 %, in a certain range of frequencies, is found to make the interface smooth. The optical properties of the photonic devices are investigated for 50 % and 75 % of duty-cycle, for different frequencies in the range of 0-1000 Hz, using the current densities of 10, 90 and 150 mA/cm2. The possibility of fabricating rugate filter with this resistivity is also explored.