There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Fiber ring interferometer

Gas sensors fabricated with nanowires as the detecting elements are powerful due to their many improved characteristics such as high surface-to-volume ratios, ultrasensitivity, higher selectivity, low power consumption, and fast response. This paper gives an overview on the recent process of the development of nanotechnology and nanowire-based gas sensors. The two basic approaches, top-down and bottom-up, for synthesizing nanowires are compared. The conduction mechanisms, sensing performances, configurations, and sensing principles of different nanowire gas sensors and arrays are summarized and discussed. Meanwhile, an emerging nanowires fabrication method and a self-powered nanowire pH sensor are highlighted. The scientific and technological challenges in the field are discussed at the end of the review. © 2012 Elsevier B.V. All rights reserved.

Nanowire-based gas sensors

Publisher Summary Polarization mode dispersion (PMD) is a linear effect that can be compensated in principle. In an ideal circularly symmetric fiber, the two orthogonally polarized modes have the same group delay. However, in reality, fibers exhibit a certain amount of birefringence because of imperfections in the manufacturing process or mechanical stress on the fiber after manufacture. It is noted that fluctuations in the polarization mode and fiber birefringence produced by the environment lead to dispersion that varies statistically with time and frequency. PMD causes different delays for different polarizations and when the difference in the delays approaches a significant fraction of the bit period, it leads to pulse distortion and system penalties. Environmental changes— including temperature and stress—cause the fiber PMD to vary stochastically in time. PMD, illustrating the basic concepts, the measurement techniques, the PMD measurement, the PMD statistics for first- and higher orders, the PMD simulation and emulation, the system impairments, and the mitigation methods has been summarized in the chapter. Both the optical and the electrical PMD compensations are considered.

Polarization-Mode Dispersion

The impact-induced deposition of Al13 clusters with icosahedral structure on Ni(0 0 1) surface was studied by molecular dynamics (MD) simulation using Finnis–Sinclair potentials. The incident kinetic energy (Ein) ranged from 0.01 to 30 eV per atom. The structural and dynamical properties of Al clusters on Ni surfaces were found to be strongly dependent on the impact energy. At much lower energy, the Al cluster deposited on the surface as a bulk molecule. However, the original icosahedral structure was transformed to the fcc-like one due to the interaction and the structure mismatch between the Al cluster and Ni surface. With increasing the impinging energy, the cluster was deformed severely when it contacted the substrate, and then broken up due to dense collision cascade. The cluster atoms spread on the surface at last. When the impact energy was higher than 11 eV, the defects, such as Al substitutions and Ni ejections, were observed. The simulation indicated that there exists an optimum energy range, which is suitable for Al epitaxial growth in layer by layer. In addition, at higher impinging energy, the atomic exchange between Al and Ni atoms will be favourable to surface alloying.

Nuclear instruments and methods in physics research section B : beam interactions with materials and atoms

In this paper, we present a new fiber optic Bragg grating sensor for petroleum hydrocarbon leak detection. The developed sensor includes fiber section with imprinted in the fiber core Bragg grating covered by special polymer material. This polymer reversibly swells under hydrocarbon influence and strains the fiber section with the Bragg grating inside. As a result of the fiber elongation, the Bragg wavelength shifts to aside longer wavelength. Experimentally demonstrated shift of the grating resonant wavelength was more than 2 nm for 20-min gasoline influence, which significantly exceeds a shift due to possible environmental temperature variation and the width of the grating reflection spectrum, which was about 0.5 nm. The paper presents also the results of the swelling-behavior test of the loaded and unloaded sensitive polymer material under liquid and vapor gasoline influence and the results of the theoretical and experimental investigation of the hydrocarbon sensor performance.

Fiber optic Bragg-grating-based sensor for liquid hydrocarbon leak detection and localization

Multiplexing of grating-based fiber sensors using broadband spectral coding

Optical fiber Bragg gratings (FBG) have numerous features making them very useful for sensing applications. In this work, we demonstrate a multiplexed sensor based on a serial array of twin-grating interferometers. The sensor employs low reflective Bragg gratings and is easy to manufacture. The combination of wavelength- and frequency-division multiplexing was tested experimentally and using a computer simulation. The approach has a great potential in multiplexing of many Bragg grating-based fiber-optic sensors.

http://ieeexplore.ieee.org/iel5/7850/21612/01000534.pdf

Multiplexed twin Bragg grating interferometric sensor

We propose and demonstrate a simple and robust actively Q-switched erbium-doped fiber ring cavity laser. The Q-switching is based on dynamic spectral overlapping of two filters, namely a fiber Bragg grating-based filter and a fiber Fabry–Perot tunable filter. Using 3.5 m of erbium-doped fiber and a pump power of only 60 mW, Q-switched pulses with a peak power of 9.7 W and a pulse duration of 500 ns were obtained. A pulse repetition rate can be continuously varied from a single shot to a few KHz.

http://iopscience.iop.org/article/10.1088/1054-660X/26/2/025105/pdf

Mikhail G. Shlyagin

Papers

Fiber optic Bragg-grating-based sensor for liquid hydrocarbon leak detection and localization

Multiplexing of grating-based fiber sensors using broadband spectral coding

Multiplexed twin Bragg grating interferometric sensor

Active Q-switching of a fiber laser using a modulated fiber Fabry–Perot filter and a fiber Bragg grating

Alarm-condition detection and localization using Rayleigh scattering for a fiber-optic bending sensor with an unmodulated light source