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

An approach for directional bending monitoring based on a multimode fiber and a machine learning algorithm is presented. The sensor if formed by splicing a single mode fiber to a multimode elliptical-core fiber. Using this elliptical-core fiber, multimode interference generates an interferogram with non-uniform amplitude and non-periodic shape. These characteristics are important to process the sensing signal using a machine learning algorithm. The machine learning algorithm implemented is the well-known random forest algorithm. In the reported experiments, the fiber is bended in different directions and different magnitudes of bending, generating a specific interferogram in each position, then each bending position is identified by the random forest algorithm. Once the position is identified, the trajectory of the sensor can be calculated. Experimental demonstration for directional bending monitoring, based on a machine learning algorithm, is presented.

Directional bending monitoring using a multimode elliptical-core fiber and a machine learning algorithm

An optical fiber sensor system for location of a vibrational disturbance along the fiber is presented. The sensor system is
based on a serial array of identical F-P interferometers, formed directly in the single mode SMF-28e fiber by pairs of
fiber Bragg gratings with reflectivity of 0.04 % each. Interferometers were interrogated by a DFB diode laser which was
intensity modulated at 10 kHz. A method for localization of a disturbed interferometer and experimental results for a
serial array of 14 sensors are presented. Simple sensor configuration and the use of low-frequency components make it
potentially inexpensive and suitable for applications where a continuous monitoring of long structures has to be
performed for appearance of vibrations.

Location of vibrational disturbance using a serial array of identical low-finesse fiber Fabry-Perot interferometers

This invention relates to an optical device for measuring the pressure variations of fluid in a conduit. The device includes an optical source for emitting incident light; an optical fibre sensor including an interferometer for modulating the incident light; an output detector for providing an electrical output signal representative of the phase variations in the modulated light detected from the interferometer; and locating means for locating the sensor proximate a wall of a fluid conduit such that deformation in the wall of the conduit can be measured by the sensor. It is envisaged that the device will be particularly useful as a blood pressure manometer.

Mikhail G. Shlyagin

Papers

Directional bending monitoring using a multimode elliptical-core fiber and a machine learning algorithm

Location of vibrational disturbance using a serial array of identical low-finesse fiber Fabry-Perot interferometers

Optical device for measuring fluid pressure