25,136 research outputs found
Tapering photonic crystal fibers for generating self-similar ultrashort pulses at 1550 nm
K.S.N. wishes to thank the Council of Scientific and Industrial Research [No. 03(1264)/12/EMR-11] Government of India for the financial support.Peer reviewedPublisher PD
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Stabilized large mode area in tapered photonic crystal fiber for stable coupling
A rigorous modal solution approach based on the numerically efficient finite element method (FEM) has been used to design a tapered photonic crystal fiber with a large mode area that could be efficiently coupled to an optical fiber. Here, for the first time, we report that the expanded mode area can be stabilized against possible fabrication tolerances by introducing a secondary surrounding waveguide with larger air holes in the outer ring. A full-vectorial -field approach is employed to obtain mode field areas along the tapered section, and the Least Squares Boundary Residual (LSBR) method is used to obtain the coupling coefficients to a butt-coupled fiber
Distributed opto-mechanical analysis of liquids outside standard fibers coated with polyimide
The analysis of surrounding media has been a long-standing challenge of
optical fiber sensors. Measurements are difficult due to the confinement of
light to the inner core of standard fibers. Over the last two years, new sensor
concepts have enabled the analysis of liquids outside the cladding boundary,
where light does not reach. Sensing is based on opto-mechanical, forward
stimulated Brillouin scattering interactions between guided light and sound
waves. In most previous works, however, the protective polymer coating of the
fiber had to be removed first. In this work, we report the opto-mechanical
analysis of liquids outside commercially available, standard single-mode fibers
with polyimide coating. The polyimide layer provides mechanical protection but
can also transmit acoustic waves from the fiber cladding towards outside media.
Comprehensive analysis of opto-mechanical coupling in coated fibers that are
immersed in liquid is provided. The model shows that forward stimulated
Brillouin scattering spectra in coated fibers are more complex than those of
bare fibers, and strongly depend on the exact coating diameter and the choice
of acoustic mode. Nevertheless, sensing outside coated fibers is demonstrated
experimentally. Integrated measurements over 100 meters of fiber clearly
distinguish between air, ethanol and water outside polyimide coating. Measured
spectra are in close quantitative agreement with the analytic predictions.
Further, distributed opto-mechanical time-domain reflectometry mapping of water
and ethanol outside coated fiber is reported, with a spatial resolution of 100
meters. The results represent a large step towards practical opto-mechanical
fiber sensors
High-Q bismuth silicate nonlinear glass microsphere resonators
The fabrication and characterization of a bismuth-silicate glass microsphere resonator has been demonstrated. At wavelengths near 1550 nm, high-modes can be efficiently excited in a 179 ”m diameter bismuth-silicate glass microsphere via evanescent coupling using a tapered silica fiber with a waist diameter of circa 2 ”m. Resonances with Q-factors as high as were observed. The dependence of the spectral response on variations in the input power level was studied in detail to gain an insight into power-dependent thermal resonance shifts. Because of their high nonlinearity and high- factors, bismuth-silicate glass microspheres offer the potential for robustly assembled fully integrated all-optical switching devices
Optical control of photon tunneling through an array of nanometer scale cylindrical channels
We report first observation of photon tunneling gated by light at a different
wavelength in an artificially created array of nanometer scale cylindrical
channels in a thick gold film. Polarization properties of gated light provide
strong proof of the enhanced nonlinear optical mixing in nanometric channels
involved in the process. This suggests the possibility of building a new class
of "gated" photon tunneling devices for massive parallel all-optical signal and
image processing.Comment: 4 pages, 4 figure
Modulational instability in dispersion-kicked optical fibers
We study, both theoretically and experimentally, modulational instability in
optical fibers that have a longitudinal evolution of their dispersion in the
form of a Dirac delta comb. By means of Floquet theory, we obtain an exact
expression for the position of the gain bands, and we provide simple analytical
estimates of the gain and of the bandwidths of those sidebands. An experimental
validation of those results has been realized in several microstructured fibers
specifically manufactured for that purpose. The dispersion landscape of those
fibers is a comb of Gaussian pulses having widths much shorter than the period,
which therefore approximate the ideal Dirac comb. Experimental spontaneous MI
spectra recorded under quasi continuous wave excitation are in good agreement
with the theory and with numerical simulations based on the generalized
nonlinear Schr\"odinger equation
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