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Manipulation of Phase of Light using a Digital Micromirror Device

Manipulation of Phase of Light using a Digital Micromirror Device

Date13th Aug 2020

Time12:00 PM

Venue Google meet

PAST EVENT

Details

Laser beam shaping has been of interest over several years because it is required in a variety of applications in optical physics, like optical communication,microscopy, optical tweezing, etc. Generating structured beams using laser beam shaping is a particularly important aspect when using light in such applications. Structured light beams are beams whose wavefronts are modulated such that they possess certain special properties that ordinary Gaussian beams do not, such as orbital angular momentum, higher resilience to noise, self-healing, higher information carrying capacity using multiplexing, etc. These structured light beams can be generated from a Gaussian beam in many different ways, like using fabricated diffractive optical elements (DOEs), holographic plates, spatial light modulators (SLMs) and digital micromirror devices (DMDs). While fabricated DOEs and holographic plates provide maximum efficiency with respect to optical power, they are not programmable after they are fabricated. Hence, programmable devices like SLMs and DMDs are preferred for certain applications. These devices contain pixels that, when incident with a beam, change certain properties of the beam, thus shaping it. A DMD is a grid of individually addressable micromirrors, where each micromirror is a pixel that can be turned ON or OFF. This provides the user a binary control over the intensity of light. Since phase cannot directly be modulated using a DMD, certain algorithms are used to generate patterns which allow the modulation of phase after going through certain optics. Using simulation and experimental results, this talk presents a detailed comparison of three methods, namely the Lee, the Lohmann and the Goorden techniques. Surprisingly, the Lohmann or the binary Fraunhofer holography method had not been used earlier to generate structured light beams. Our results will be presented. In addition, this technique was used to carry out modal decomposition of multiplexed beams with orbital angular momentum. Simulation results will be discussed in the talk. The Lee method was exploited during a 2 month project visit to the University of Witwatersrand, Johannesburg, South Africa for the evaluation of state of polarization or vectorness of a beam. The experimental results of this study have been published and will be discussed.

Speakers

Amogh Manthalkar (EE17S003)

Department of Electrical Engineering