Conference/Symposia

Abstract:

ptical beams possessing orbital angular momentum (OAM), also known as twisted light beams or vortex beams have gained much interest in recent years due to the potential use in optical tweezers, high resolution microscopy, material processing, and free-space communications. Specifically, higher order OAM modes are quite attractive for the above applications as they provide multiple orthogonal light paths. Although several promising techniques exist in the literature for exciting such OAM modes, none of them are directly fiber compatible and not all of them can multiplex many OAM modes with low loss.
During the first part of this talk, we will discuss the experimental demonstration of an all-fiber technique for the excitation of an OAM mode using a fused fiber coupler. Our approach is based on mode-selective coupling between different modes in two dissimilar fibers. Specifically, the phase matching between the HE11 mode in the SMF and the desired mode in the ring-core fiber is achieved by pre-tapering the SMF and then fusing both fibers. As such, it provides the promising pathway to directly couple the traditional Gaussian beam to the desired OAM beams with high purity and good stability in an entirely integrated scheme.
Recently, we also experimentally demonstrated the amplification of an OAM beam. Such a task is quite challenging in a conventional rare-earth (RE) doped fiber amplifier due to gain compression as well as the presence of amplified spontaneous emission, which lead to significant crosstalk with other eigenmodes of the fiber. Raman amplification in passive fibers provide an exciting pathway to overcome the above limitations, thereby also relaxing the tight constraints in the doping profile of a conventional RE-doped amplification approach.

Abstract:

According to International Telecommunication Union (ITU), till 2016 almost 7 Billion people around the world are connected by the mobile network facility. These data signifies that irrespective of rural or urban region, a cellular phone is accessible everywhere. Out of these 7 Billion cellphone users approximately 40% of them can be considered as smartphone. A smartphone in general is equipped with different high-end opto-electronic sensors, fast central processing unit, an ever improving RAM-ROM and graphical user interface; which facilitate a user to use it for different applications. Again, for analysis and data processing, a need based mobile application can be developed within the phone itself. Due to vast availability of smartphones and its continuous improvement both in software and hardware part, effort has been made by the researchers around the world to convert it into a useful tool for sensing and imaging of various chemical and biological samples. In this presentation, a brief research activity related to design of smartphone platform sensing system currently undertaken by the speaker at his parent institution -Tezpur University will be discussed.

Abstract:

In a landmark publication in 1956 Pancharatnam showed that if polarized light is brought back to its initial state of polarization through a series of polarization transformations, the polarization phase associated with the light beam is proportional to the solid angle subtended by the area of the Poincare sphere enclosed by the locus of the polarization path traversed by the light beam. What distinguishes polarization phase from propagation phase is the fact that the former is completely independent of the wavelength of light. The talk attempts to explain the origin of Pancharatnam phase, discuss optical configurations to realize dynamical implementation of Pancharatnam phase and explore its areas of application in phase shifting interferometry, digital holography, quantitative phase microscopy and total internal reflection microscopy.