HIGHLY SENSITIVE DETECTION OF LEAD IONS IN WATER USING ETCHED FBG

- Lead is a soft, ductile, malleable and naturally present in earth’s crust. Lead is highly toxic element affects living organism even at lower concentration. Lead is used in many industries and its disposable is very difficult. Therefore, it may lead to various environmental hazardous problems. World Health Organization (WHO) and other organisation specify the presence of lead in drinking water not greater than 20 ppb. In the present work, a simple, affordable and precise way to detect the concentration of lead in water using Fibre Bragg gratings (FBG) is presented. FBG are formed using Phase mask technique and the cladding part over the grating region is etched with 40% Hydrofluoric acid (HF) solution. The sensor so developed is sensitive enough to find the presence of lead in water in the range 5-25 ppb.

Angle sensitivity testing of equal-period plane diffraction grating fabricated through electron beam lithography line-by-line method

An equal-period plane diffraction grating fabricated through electron beam lithography line-by-line method was designed and applied to the experiment of angle sensitivity testing. The size of the fabricated grating region was [Formula: see text] mm and the period was 1526 nm. The incident light was transmitted via the Y-type fiber to collimator lens fixed on the angle disc, which can be adjusted to change the incident light angle. The diffraction spectra generated by the incident light irradiating the grating surface were collected by the optical spectrum analyzer. In this experiment, the incident light angle was fixed at 25[Formula: see text]. When the spot moved horizontally by 50 mm, the diffraction wavelength was basically unchanged. When the incident light angle was adjusted from 15[Formula: see text] to 31[Formula: see text], the diffraction wavelength was changed from 834.03 nm to 1589.80 nm, the angular sensitivity was 47.508 nm/[Formula: see text], and the linearity was 0.9998.

A femtosecond laser inscribed fiber Bragg grating as a refractive index and temperature sensor based on side-polished method

A fiber Bragg grating (FBG), inscribed directly by a femtosecond laser and based on the side-polished technique, was proposed and experimentally demonstrated for refractive and temperature sensing. The first-order FBG was inscribed by a 800 nm femtosecond pulsed laser, using the point-by-point method, in a fiber core with a length of 3 mm; the grating period was 537 nm. The fiber grating region was subsequently polished for 5 h and a light leak window was polished through the fiber cladding, with a length and depth of 20 mm and 37.5 [Formula: see text]m, respectively. This changed the evanescent field around the grating area to realize refractive index (RI) sensing. In the experiment, the NaCl solution RI sensitivity of the proposed fiber sensor was 854.2 nm/RIU and the linearities were 0.9989. For the temperature measurement, the sensitivity was 11.66 pm/[Formula: see text]C and the linearities were 0.9854, between 50–450[Formula: see text]C.

Generation of three-port splitter by double-layer grating in second-order Littrow configuration

In this paper, a novel double-layer three-port grating is described. The incident grating structure is in the second-order Littrow configuration. The grating region is composed of fused silica and Ta2O5. The designed grating beam splitter has high efficiency under TE polarization and TM polarization, respectively. The efficiency of two polarizations is more than 90%. In addition, compared with a single-layer three-port grating, this new beam splitter has good fabrication tolerance and incident bandwidth. Therefore, the optimized structure has a good application value.

An ultra-narrowband TE-polarization absorber with a dielectric grating and metal substrate

We report an ultra-narrowband absorber with a dielectric grating and metal substrate. The simulation results show that we can achieve ultra-narrowband absorption with the absorption bandwidth less than 0.6 nm and the absorption rate more than 0.99 for TE-polarization (electric field is parallel to grating grooves). The simulation results also show the guide-mode resonance in the grating region and low power loss at the absorption peak. In addition, the ultra-narrowband absorption peak can be tuned by shrinking or enlarging the structure parameters. The figure of merit (FOM) is larger than 760 if this absorber is applied as a refractive index sensor.

Semiconductor Thin Films Combined With Metallic Grating for Selective Improvement of Thermal Radiative Absorption/Emission

We propose in this work a structure of semiconductor thin films combined with a one-dimensional metallic grating which allows for selective improvement of thermal radiative absorptivity (also emissivity) of the structure. We numerically demonstrate with a 2-D rigorous coupled-wave analysis (RCWA) algorithm that the proposed structure exhibits enhanced spectral absorptivity (for p-polarization) for photon energy slightly above the gap energy of the semiconductor (silicon in this work). The enhanced absorptivity is explained as due to excitations of surface polaritons (SPs) in the grating region, along with interactions of multiple-order diffracted waves in the semiconductor layer. Furthermore, the enhanced absorptivity of the structure can be achieved for a wide range of incidence angles so that it may have potential applications in energy conversion purposes.

Liquid Phase Epitaxial Growth and Characterization of GaAs on InP Substrates

ABSTRACTOptimum growth conditions were investigated to obtain high quality heteroepitaxial GaAs layers on InP substrates by liquid phase epitaxy (LPE). Addition of about 0.005wt% of Se to the Ga growth melt effectively suppressed dissolution of the InP substrates into the melt during the initial stage of the growth, resulting in a significantly improved surface morphology. The crystallinity and the surface morphology could be further improved by growing undoped GaAs layers on thin Se-doped buffer GaAs as well as using InP substrates patterned with grating structure. The transmission electron microscopy observation indicated that the misfit dislocations interact with each other at the grating region, resulting in a lower dislocation density in the upper GaAs layer. The (400) double crystal X-ray diffraction peaks of the undoped GaAs showed fullwidth- at-half-maximum of about 380 arcsec, which is comparable with the previously reported values using more sophisticated growth techniques.

Enhanced photoluminescence from AlGaAs/GaAs superlattice gratings fabricated by Si FIB implantation

ABSTRACTResults are presented on the fabrication of optical gratings on an Al0.3Ga0.7As/GaAs superlattice (SL) with equal 3.5 nm barrier and well widths, by using locally FIB-enhanced mixing. As the first step, the mechanism of the mixing was studied. Si++ was accelerated to 50 kV and lOOkV and implanted at doses ranging from 1013 to 1015/cm2. A rapid thermal anneal of 10 s at 950°C was utilized. The average Al inter-diffusion coefficient and length were calculated as a function of FIB dose from SIMS depth profiling. The mixing was significantly enhanced by the FIB implantation. The ion dose as low as l×1014/cm2 followed by RTA yields a mixing parameter of ∼90% and results in a two-order of magnitude increase in the diffusion coefficient, to a value of 4.5×10−14cm2/sec, in contrast to 1.3×10−16cm2/sec from RTA-only. The maximum mixing occurred in the region where neither Si ions nor vacancies have their maximum concentration. Instead, it coincides with the location of the positive maximum of the second derivative of the vacancy concentration profile. This fact suggests that in the time frame of RTA and with low dose, the diffusion of nonequilibrium point defects plays a major role in the process of enhancing Al-Ga interdiffusion. DBR optical gratings, consisting of thousands of spacing lines with 350nm period, were fabricated with a lOOkV FIB dose of 2×1013 andl×1014/cm2. Photoluminescence (PL) spectra were taken from the grating region as well as the unimplanted superlattice region. The PL intensity from cavity region of the DBR was about 16 times higher than that from the original SL. This PL enhancement was verified to occur in the cavity region only by spatially scanning over the entire sample. A possible mechanism for this PL enhancement is optical feedback provided by the gratings.