44 research outputs found
Brillouin spectral deconvolution method for centimeter spatial resolution and high-accuracy strain measurement in Brillouin sensors
This paper was published in Optics Letters and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://www.opticsinfobase.org/abstract.cfm?URI=ol-30-7-705. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.Shahraam Afshar V., Xiaoyi Bao, Lufan Zou, and Liang Che
Nonlinear self-flipping of polarization states in asymmetric waveguides
Waveguides of subwavelength dimensions with asymmetric geometries, such as
rib waveguides, can display nonlinear polarization effects in which the
nonlinear phase difference dominates the linear contribution, provided the
birefringence is sufficiently small. We demonstrate that self-flipping
polarization states can appear in such rib waveguides at low (mW) power levels.
We describe an optical power limiting device with optimized rib waveguide
parameters that can operate at low powers with switching properties
Enhancement of stimulated Brillouin scattering of higher-order acoustic modes in single-mode optical fiber
This paper was published in Optics Letters and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://www.opticsinfobase.org/abstract.cfm?URI=ol-30-20-2685. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.Solving the elastic wave equation exactly for a GeO2-doped silica fiber with a steplike distribution of the longitudinal and shear velocities and density, we have obtained the dispersion, attenuation, and fields of the leaky acoustic modes supported by the fiber. We have developed a model for stimulated Brillouin scattering of these modes in a pump-probe configuration and provided their Brillouin gains and frequencies for an extended range of core sizes and GeO2 doping. Parameter ranges close to cutoff of the acoustic modes and pump depletion enhance the ratio of higher-order peaks to the main peak in the Brillouin spectrum and are suitable for simultaneous strain-temperature sensing.Shahraam Afshar V., V. P. Kalosha, Xiaoyi Bao, Liang Che
Unseeded One-Third Harmonic Generation in Optical Fibers
We propose a new concept to generate efficient one-third harmonic light from
an unseeded third harmonic process in optical fibers. Our concept is based on
the dynamic constant (Hamiltonian) of the nonlinear third harmonic generation
in optical fibers and includes a periodic array of nonlinear fibers and phase
compensation elements. We test our concept with a simulation of the nonlinear
interaction between the fundamental and third harmonic modes of a realistic
optical fiber, demonstrating high-efficiency one-third harmonic generation. Our
work opens a new approach to achieving the so far elusive one-third harmonic
generation in optical fibers
Method for predicting whispering gallery mode spectra of spherical microresonators
A full three-dimensional Finite-Difference Time-Domain (FDTD)-based toolkit
is developed to simulate the whispering gallery modes of a microsphere in the
vicinity of a dipole source. This provides a guide for experiments that rely on
efficient coupling to the modes of microspheres. The resultant spectra are
compared to those of analytic models used in the field. In contrast to the
analytic models, the FDTD method is able to collect flux from a variety of
possible collection regions, such as a disk-shaped region. The customizability
of the technique allows one to consider a variety of mode excitation scenarios,
which are particularly useful for investigating novel properties of optical
resonators, and are valuable in assessing the viability of a resonator for
biosensing.Comment: Published 10 Apr 2015 in Opt. Express Vol. 23, Issue 8, pp.
9924-9937; The FDTD toolkit supercomputer scripts are hosted at:
http://sourceforge.net/projects/npps/files/FDTD_WGM_Simulator
Predicting the whispering gallery mode spectra of microresonators
The whispering gallery modes (WGMs) of optical resonators have prompted
intensive research efforts due to their usefulness in the field of biological
sensing, and their employment in nonlinear optics. While much information is
available in the literature on numerical modeling of WGMs in microspheres, it
remains a challenging task to be able to predict the emitted spectra of
spherical microresonators. Here, we establish a customizable Finite- Difference
Time-Domain (FDTD)-based approach to investigate the WGM spectrum of
microspheres. The simulations are carried out in the vicinity of a dipole
source rather than a typical plane-wave beam excitation, thus providing an
effective analogue of the fluorescent dye or nanoparticle coatings used in
experiment. The analysis of a single dipole source at different positions on
the surface or inside a microsphere, serves to assess the relative efficiency
of nearby radiating TE and TM modes, characterizing the profile of the
spectrum. By varying the number, positions and alignments of the dipole
sources, different excitation scenarios can be compared to analytic models, and
to experimental results. The energy flux is collected via a nearby disk-shaped
region. The resultant spectral profile shows a dependence on the configuration
of the dipole sources. The power outcoupling can then be optimized for specific
modes and wavelength regions. The development of such a computational tool can
aid the preparation of optical sensors prior to fabrication, by preselecting
desired the optical properties of the resonator.Comment: Approved version for SPIE Photonics West, LASE, Laser Resonators,
Microresonators and Beam Control XV
Subpeaks in the Brillouin loss spectra of distributed fiber-optic sensors
This paper was published in Optics Letters and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://www.opticsinfobase.org/abstract.cfm?URI=ol-30-10-1099. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under lawYidun Wan, Shahraam Afshar V., Lufan Zou, Liang Chen and Xiaoyi Ba