Dharmadas Kumbhakar

Single and Multiple Microparticle Trapping Using Non-Gaussian Beams From Optical Fiber Nanoantennas

Optical trapping of dielectric microparticles is reported using an optical tweezers based on two original chemically etched fiber nanoantenna. The nanoantenna converts Gaussian beam into nondiffracting type quasi-Bessel beam, which is used in trapping microparticles. Stable trapping in three distinct positions is observed for an antenna distance of 32.5 μm and for light powers as low as 1.3 mW. Optical trapping properties are studied by applying Boltzmann statistics to the particle position fluctuations. Harmonic trapping potentials with trap stiffness of 3.5 pN μm-1 are observed. The FDTD simulation results on the antenna optics are also included to understand the trapping mechanism.

Evanescent wave assisted nanomaterial coating.

In this work we present a novel nanomaterial coating technique using evanescent wave (EW). The gradient force in the EW is used as an optical tweezer for tweezing and self-assembling nanoparticles on the source of EW. As a proof of the concept, we have used a laser coupled etched multimode optical fiber, which generates EW for the EW assisted coating. The section-wise etched multimode optical fiber is horizontally and superficially dipped into a silver/gold nanoparticles solution while the laser is switched on. The fiber is left until the solution recedes due to evaporation leaving the fiber in air. The coating time usually takes 40-50 min at room temperature. The scanning electron microscope image shows uniform and thin coating of self-assembled nanoparticles due to EW around the etched section. A coating thickness <200 nm is achieved. The technique could be useful for making surface-plasmon-resonance-based optical fiber probes and other plasmonic circuits.

Optical fiber antenna generating spiral beam shapes

A simple method is proposed here to generate vortex beam and spiral intensity patterns from a Gaussian source. It uses a special type of optical fiber antenna of aperture ∼80 nm having naturally grown surface curvature along its length. The antenna converts linearly polarized Gaussian beam into a beam with spiral intensity patterns. The experimentally obtained spiral patterns with single and double spiral arms manifest the orbital angular momentum, l = ±1, 2, carried by the output beam. Such beam can be very useful for optical tweezer, metal machining, and similar applications.

Modeling of Optical Fiber Based Axicon for Generation of Bessel Beam

We present simulation based modeling on optical-fiber based sub-micron Axicons and Bessel beam. It compares results of positive, negative and double negative Axicon. The study helps selecting ideal Axicon and Bessel beam for specific application

Accurate Estimate of Some Propagation Characteristics for the First Higher Order Mode in Graded Index Fiber with Simple Analytic Chebyshev Method

Abstract Using Chebyshev power series approach, accurate description for the first higher order (LP11) mode of graded index fibers having three different profile shape functions are presented in this paper and applied to predict their propagation characteristics. These characteristics include fractional power guided through the core, excitation efficiency and Petermann I and II spot sizes with their approximate analytic formulations. We have shown that where two and three Chebyshev points in LP11 mode approximation present fairly accurate results, the values based on our calculations involving four Chebyshev points match excellently with available exact numerical results.

Deep Seated Negative Axicon in Selective Optical Fiber Tip and Collimated Bessel Beam

In this letter, we have demonstrated the fabrication of a deep seated negative axicon (DSNA) with micrometer dimensions inside a selective optical fiber tip for the generation of optical Bessel beams (BBs). The DSNA is prepared by simple chemical etching of the fiber tip in hydrofluoric acid under the influence of capillary action. The selective optical fiber has a high numerical aperture of 0.3 and a small core diameter of about

An all optical method of implementing a wavelength encoded simultaneous binary full adder–full subtractor unit exploiting nonlinear polarization rotation in semiconductor optical amplifier

4~\mu \text{m}

Simulation of two photon absorption in silicon wire waveguide for implementation of all optical logic gates

. The higher etching rate of the optical fiber core contributes to fabricate the DSNA, which converts Gaussian-like beam into BB. The central spot of the BB shows quasi-invariant spot-size over the propagation distance of sub-millimeter and centimeter range. The self-protected DSNA can be useful for scanning optical fiber endoscopy applications as well as can be integrated into systems, where non-diffracting BB is preferred.