Fabrication of strong long-period gratings in hydrogen-free fibers with 157-nm F2-laser radiation

Ultrahigh sensitive long-period fiber grating-based sensor for detection of adulterators in biofuel

An ultra-sensitive sensor based on dual resonance long-period fiber gratings has been fabricated for the detection of methanol and water content in ethanol. The developed sensor is compact in size and light weight and employs a highly accurate spectral interrogation technique for adulterant detection, increasing its applicability compared to conventional surface plasmon resonance based sensors, which are generally expensive, as they require metal film deposition. We demonstrate that the sensor is capable of achieving sensitivity of 802.66 pm/V% methanol and 749.06 pm/V% water in the ethanol solution. The estimated detection limit using the experimental data and spectral resolution of the interrogator is found to be ∼1.3×10^-3V% in the 1300-1700 nm wavelength range. We also present the sensor's theoretical study, and good agreement is found between theoretical and experimental results.

Arc-Induced Long-Period Fiber Gratings at INESC TEC. Part I: Fabrication, Characterization and Mechanisms of Formation

In this work, we reviewed the most important achievements of INESC TEC related to the fabrication of long-period fiber gratings using the electric arc technique. We focused on the fabrication setup, the type of fiber used, and the effect of the fabrication parameters on the gratings' transmission spectra. The theory was presented, as well as a discussion on the mechanisms responsible for the formation of the gratings, supported by the measurement of the temperature reached by the fiber during an electric arc discharge.

Nanoporous TiO2/polyion thin-film-coated long-period grating sensors for the direct measurement of low-molecular-weight analytes

We present novel nanoporous TiO(2)/polyion thin-film-coated long-period fiber grating (LPFG) sensors for the direct measurement of low-molecular-weight chemicals by monitoring the resonance wavelength shift. The hybrid overlay films are prepared by a simple layer-by-layer deposition approach, which is mainly based on the electrostatic interaction of TiO(2) nanoparticles and polyions. By the alternate immersion of LPFG into dispersions of TiO(2) nanoparticles and polyions, respectively, the so-formed TiO(2)/polyion thin film exhibits a unique nanoporous internal structure and has a relative higher refractive index than LPFG cladding. In particular, the porosity of the thin film reduces the diffusion coefficient and enhances the permeability retention of low-molecular-weight analytes within the porous film. The increases in the refractive index of the LPFG overlay results in a distinguished modulation of the resonance wavelength. Therefore, the detection sensitivity of LPFG sensors has been greatly improved, according to theoretical simulation. After the structure of the TiO(2)/polyion thin film was optimized, glucose solutions as an example with a low concentration of 10(-7) M was easily detected and monitored at room temperature.

Scalable multichannel micromachining with pseudo-nondiffracting vacuum ultraviolet beam arrays generated by thin-film axicons

Scalable multichannel microstructuring was demonstrated by multiplexing a focused molecular fluorine laser beam with cylindrical nanolayer microaxicons into an array of converging pseudo-nondiffracting subbeams. The axicons were fabricated by shadow-mask vapor deposition of magnesium fluoride onto substrates of identical material. Long-period surface gratings of variable pitch were generated on poly(methyl methacrylate) by varying the target position within the converging periodic focal lines.

Inscription of fiber Bragg gratings by ultraviolet femtosecond radiation

We report on what is to our knowledge the first fabrication of fiber Bragg gratings by UV femtosecond radiation. The Bragg gratings, with photoinduced refractive-index modulation up to 1.92 x 10(-3) in H2-loaded SMF-28 and up to 1.05 x 10(-3) in Nufern GF1 fibers, were written by high-intensity (31-77-GW/cm2) femtosecond pulses at 264 nm. The dependence of the refractive-index modulation on intensity at equal fluences points to a two-photon absorption mechanism for grating inscription.