Investigation of an In-Line Slot Waveguide Sensor Built in a Tapered D-Shaped Silicon-Cored Fiber

An in-line slot waveguide sensor built in a polished flat platform of a D-shaped silicon cored fiber with a taper coupled region is proposed and investigated thoroughly. Simulation results show that the single-mode light field sustained in the silicon cored fiber can be efficiently transferred to the slot waveguides through the tapered region. The geometry parameters of the slot waveguide sensors are optimized to have the corresponding highest power confinement factors and the resultant sensor sensitivities. The three-slot waveguide sensor is found to have the best performance among one-, two- and three-slot waveguides at the mid-IR wavelength.

Effects of Tungsten Disulphide Coating on Tapered Microfiber for Relative Humidity Sensing Applications

Tungsten disulphide (WS2) is a two-dimensional transition-metal dichalcogenide material that can be used to improve the sensitivity of a variety of sensing applications. This study investigated the effect of WS2 coating on tapered region microfiber (MF) for relative humidity (RH) sensing applications. The flame brushing technique was used to taper the standard single-mode fiber (SMF) into three different waist diameter sizes of MF 2, 5, and 10 µm, respectively. The MFs were then coated with WS2 via a facile deposition method called the drop-casting technique. Since the MF had a strong evanescent field that allowed fast near-field interaction between the guided light and the environment, depositing WS2 onto the tapered region produced high humidity sensor sensitivity. The experiments were repeated three times to measure the average transmitted power, presenting repeatability and sensing stability. Each MF sample size was tested with varying humidity levels. Furthermore, the coated and non-coated MF performances were compared in the RH range of 45–90% RH at room temperature. It was found that the WS2 coating on 2 µm MF had a high sensitivity of 0.0861 dB/% RH with linearity over 99%. Thus, MF coated with WS2 encourages enhancement in the evanescent field effect in optical fiber humidity sensor applications.

Detection of dengue using PAMAM dendrimer integrated tapered optical fiber sensor

The exponential escalation of dengue cases has indeed become a global health crisis. This work elaborates on the development of a biofunctionalized tapered optical fiber (TOF) based sensor with the integration of polyamidoamine (PAMAM) dendrimer for the detection of dengue E protein. The dimension of the TOF generated an evanescent field that was sensitive to any changes in the external medium while the integration of PAMAM promoted more adhesion of bio-recognition molecules; anti-DENV II E protein antibodies; that were complementary to the targeted protein. This in return created more active sites for the absorption of DENV II E proteins onto the tapered region. The resolution and detection limit of the sensor are 19.53 nm/nM and 1 pM, respectively with Kd = 1.02 × 10−10 M.

Numerical Analysis of Soliton Propagation in a Tapered Waveguide

In this paper, dispersion decreased profiled tapered fiber is designed whose dispersion characteristics and soliton propagation is investigated numerically using Darboux transformation. The result reveals that solitons pulse gets compression as it propagates along the length of the tapered region.

Layer-by-layer and step-flow growth mechanisms in GaAsP/GaP nanowire heterostructures

GaP–GaAsP segmented nanowires (NWs), with diameters ranging between 20 and 500 nm and lengths between 0.5 and 2 μm, were catalytically grown from Au particles on a GaAs (111)B substrate in a gas source molecular beam epitaxy system. The morphology of the NWs was either pencil-shaped with a tapered tip or rod-shaped with a constant diameter along the entire length. Stacking faults were observed for most NWs with diameters greater than 30 nm, but thinner ones tended to exhibit fewer defects. Moreover, stacking faults were more likely found in GaAsP than in GaP. The composition of the pencil NWs exhibited a core–shell structure at the interface region, and rod-shaped NWs resulted in planar and atomically abrupt heterointerfaces. A detailed growth mechanism is presented based on a layer-by-layer growth mode for the rod-shaped NWs and a step-flow growth mode for the tapered region of the pencil NWs.

Symmetrically Tapered <30-μm-thick Quasi-Planar Germanium Waveguides as Chemical Sensors for Microanalysis

Symmetrically tapered planar IR waveguides have been fabricated by starting with a ZnS coated concave piece of single-crystal Ge, embedding it in an epoxide resin as a supporting substrate, and then grinding and polishing a planar surface until the thickness at the taper minimum is <30 μm. Such tapering is expected to enhance a waveguide's sensitivity as an evanescent wave sensor by maximizing the amount of evanescent wave energy present at the thinnest part of the waveguide. As predicted by theory, the surface sensitivity, i.e., the absorbance signal per molecule in contact with the sensing region, increases with decreasing thickness of the tapered region even while the total energy throughput decreases. The signal-to-noise ratio obtained depends very strongly on the quality of the polished surfaces of the waveguides. The surface sensitivity is superior to that obtained with a commercial Ge attenuated total reflection (ATR) accessory for several types of sample, including thin films (<10 ng) and small volumes (<1 μL) of volatile solvents. By using the waveguides, light-induced structural changes in the protein bacteriorhodopsin were observable using samples as small as ∼50 pmol (∼1 μg). In addition, the waveguide sensors can reveal the surface compositions on a single human hair, pointing to their promise as a tool for forensic fiber analysis.

The Mechanism of Tongue Projection in Chameleons: II. Role of Shape Change in a Muscular Hydrostat

In this paper we investigate the interaction between the accelerator muscle (the muscle that powers tongue projection) and the entoglossal process (the tongue's skeletal support) that occurs during tongue projection in chamaeleonid lizards. Previous work has shown that there is a delay of about 185 ms between the onset of accelerator muscle activity and the onset of tongue projection. In conjunction with anatomical observations, in vitro preparations of the accelerator muscle mounted on isolated entoglossal and surrogate processes were stimulated tetanically, and the resulting movements were recorded on video at 200 fields s−1. Three results indicate that morphological features of the entoglossus and the accelerator muscle delay the onset of tongue projection following the onset of accelerator contraction: (1) the entoglossus is parallel-sided along the posterior 90% of its shaft, only tapering at the very tip, (2) the sphincter-like portion of the accelerator muscle, which effects tongue projection, makes up the posterior 63% of the muscle and does not contact the tapered region of the entoglossus at rest, and (3) accelerator muscles mounted on the entoglossus undergo longitudinal extension and lateral constriction for 83 ms following the onset of electrical stimulation, before projecting off the entoglossus. It is proposed that, during elongation of the accelerator muscle, the sphincter-like region ultimately comes into contact with the tapered region of the entoglossus, causing the onset of projection. This conclusion is supported by the observation that the time between the onset of stimulation and the onset of projection was longer in preparations with surrogate entoglossal processes that had no tapered tip and shorter with surrogate processes that had a tapered tip about four times as long as the natural entoglossus. Tetanically stimulated accelerator muscles reached 90% of peak force 110 ms after the onset of stimulation, indicating that the 185 ms delay between the onset of accelerator activity and the onset of projection seen in vivo allows the accelerator to achieve peak force prior to the onset of projection. Thus, the delay in projection may be crucial in maximizing the acceleration and velocity achieved by the projected chameleon tongue.