Designing metamaterials to possess extreme index values requires near resonant properties which, in turn, leads to these properties over diminishing bandwidths. Recent studies have shown that some bandwidth control might be possible by exploiting metamaterial substrates. We have demonstrated the concept in our design, and investigated the trade-offs between substrate structure, bandwidth extension and increase in losses. Loss management can be controlled by choice of metamaterial elements and replacement of metal by semiconductors. This also has the added advantage of some degree of tunability.
High resolution images have been obtained by “coding” evanescent waves from high spatial frequencies into propagating waves using a random medium. Time reversal of the scattered wave propagated back into the same random medium recovers the image. We investigate the scattering properties of a (remote) reciprocal scattering medium to accomplish the same image recovery but without the need for wave detection and followed by time reversal. We present examples of such (metamaterial) scattering media and their reciprocal structures and suggest how they might best be used for remote high resolution imaging. A metamaterial structure offers the possibility of low reflection losses with an index, |n| ~ 1.
We examine the coupling between resonances of closely spaced meta-atoms and investigate the role of extended effective periodicities of clusters of subwavelength sized elements on the overall bulk properties. The possibilities of negative refraction both with and without negative index, as well as the role of strong coupling near resonance on effective medium models and homogenization close to the photonic crystal limit are presented.
We report fabrication of a high pressure nonadiabatic tapered optical fiber (NATOF) for downhole applications by using a
mechanical transducer. The mechanical transducer has been used for increasing the pressure sensitivity and possibility of
installation the sensor in downhole. The NATOF is fabricated by heat pulling method, utilizing a CO2 laser. The limit of
detection of the NATOF was 15 psi.
A single-mode biconical tapered optical fiber (BTOF) sensor was utilized for sensing the variation of refractive index
(RI) with concentration of D-glucose in double distilled deionized water and measuring of RI of amino acids (AAs) in
carbohydrate solutions. This method showed a rewarding ability in understanding the basis of biomolecular interactions
in biological systems. The BTOF is fabricated by heat pulling method, utilizing a CO2 laser. The detection limit of the
BTOF was 50 ppb for the D-glucose concentration ranging from 0 to 80 ppm, and RI detection limit corresponding to
these concentrations in the range at 1.3333 to 1.3404 was 5.4×10-6 as a refractometer sensor. The response of the BTOF
shows that the different kinds of interactions of various groups of AAs such as L-alanine, L-leucine, and L-cystein with
D-glucose, sucrose and water molecules depend on functional groups in AAs such as OH, SH;CH2;NH3+ ,COO-.
These results can be interpreted in terms of solute-solute and solute-solvent interactions and structure making/breaking
ability of solutes in the given solution.
Distributed optical fiber sensors based on Brillouin scattering by measurement on time domain, due to its
capability for strain and temperature measurement continuously for long range, are currently interesting.
These sensors are based on spectral characteristics change of back scattered light at different places along the
fiber. For this method Spatial resolution is limited by pulse length. We want to improve spatial resolution at
time domain sensors by using of sinusoidal frequency modulation of pulse probe and continuous pump light.
In this article, this method is simulated.
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