Randhir Bhatnagar

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.

Magnetron Sputtering Coated Optical Fiber Probe Designs for Surface Plasmon Resonance Sensor

In this paper, we have reported the design of the surface plasmon resonance probes prepared from partially etched polymer optical probe and specially tapered single-mode fiber tip probe which are gold coated in magnetron-sputtering unit. The coating parameters and conditions are discussed in details to achieve sensitive surface plasmon resonance probes. The sensor probes work in transmission modes. The gold-coated etched in-line polymer fiber probe demonstrates high sensitivity, ~2459 nm/RIU and working range includes visible to infrared wavelength. The fiber tip probe with very small interaction area demonstrates sensitivity, ~166 nm/RIU. The in-line fiber probe could be used for large volume sample and the pointed fiber tip could be used for small volume samples.

Sensitive detection of E. Coli cells by long period gratings based optical sensor

We present a novel bacterial sensing platform based on long period gratings written in photosensitive single mode optical fiber by UV eximer laser (248 nm). Shift in wavelength with varied concentrations were observed in transmission spectrum. Significant wavelength shifts were noted for all dilutions with Outer Membrane Protein Complex (OMPC) antibody immobilized LPG sensing probe. A considerable shift of 0.55938 nm in wavelength is observed when 10−5 dilution (180 CFU/ ml) of E.Coli is passed over OMPC immobilized sensing probe.

Hollow Core PHOTONIC CRYSTAL FIBER based methane gas sensor

Hollow core photonic crystal fiber (HC-PCF) based methane gas sensor has been experimentally demonstrated and results obtained are reported. The influence of laser modulation frequency at fixed modulating current is investigated over gas sensitivity.

Strain Monitoring of Concrete Bridge using Fiber Bragg Grating Sensors

The distributed strain monitoring of a concrete bridge using packaged FBG sensors is presented. The responses of FBG sensors and conventional sensors were recorded under bridge loading conditions and shown to be in good agreements.

Study of FBG sensors for cryo temperature monitoring

Experimental characterization of a fiber Bragg grating sensor probe has been carried out for cryo-temperature monitoring. The temperature sensitivity was found to be 16.7 pm/°C at room temperature and 90 pm/°C pm/°C near liquid nitrogen temperature.