No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Analysis of phase sensitivity to longitudinal strain in microstructured optical fibers
Abstract
We investigate the influence of air holes on phase sensitivity in microstructured optical fibers to longitudinal strain. According to the numerical simulations performed, large air holes in close proximity to a fiber core introduce significant compression stress to the core, which results in an increase in the effective refractive index sensitivity to longitudinal strain. The theoretical investigation is verified by an experiment performed on four fibers drawn from the same preform and differentiated by air hole diameter. We show that introducing properly designed air holes can lead to a considerable increase in normalized effective refractive index sensitivity to axial strain from -0.21 e-1 (for traditional single mode fiber) to -0.14 e-1.
... Airy guiding modes of HAF show ultralow overlap with thermal sensitive silica cladding 5,20 , thus being insensitive to temperature variation 13 , and negligible overlap between airy guiding modes and silica walls offers low birefringence 21,22 . On the other hand, a large air-filling fraction renders HAF extremely sensitive to mechanical force such as compression, bend, and strain 6,23,24 . Therefore, combination of HAF and modal interferometer represents a promising perspective in sensing application. ...
Hollow-core anti-resonant fiber technology has made a rapid progress in low loss broadband transmission, enabled by its much reduced light-material overlap. This unique characteristic has driven emerging of new applications spanning from extreme wavelength generation to beam delivery. The successful demonstrations appear to suggest progression of the technology toward device level development and all-fiberized systems. We investigate this opportunity and report an in-fiber interferometer built in a dual hollow-core anti-resonant fiber. By placing multiple air cores in a single fiber, coherently interacting transverse modes are excited, which becomes a basis of an interferometer. We use this hollow core based inherent supermodal interaction to demonstrate highly sensitive in-fiber interferometer. Unique combination of the air guidance and the supermodal interaction offers robust, simple yet highly sensitive interferometer with suppressed temperature cross-talk that has been an enduring problem in fiber strain sensing applications. The in-fiber interferometer is further investigated as a sensing element for pressure measurement based on an interferometric phase change upon external strain. The interferometer features 39.3 nm/MPa of ultrahigh sensitivity with 0.14 KPa/°C of negligible gas pressure temperature crosstalk. The performance, which is much improved from prior fiber sensors, testifies advances of hollow core fiber technology toward a device level.
Standard multimode optical fibers normally support transmission over some 100 modes. Large differences in the propagation constant and the spatial distribution of distinct modes degrade the performance of phase-sensitive optical time-domain reflectometry measurements. In this work, we present a new realization of a coherent time-domain interrogation technique using single-mode operation in multimode fibers. We demonstrate effectively distributed strain sensing on three different multimode optical fibers. Up to 4 km of multimode fiber has been correctly interrogated, featuring a spatial resolution of 20 cm.
A particular photonic crystal fiber (PCF) designed with all circle air holes is proposed. Its characteristics are studied by full-vector finite element method (FEM) with anisotropic perfectly matched layer (PML). The simulation results indicated that the proposed PCF can realize high birefringence (up to 10(-2)), high nonlinearity (50W(-1).km(-1) and 68W(-1) .km(-1) in X and Y polarizations respectively) and low confinement loss ( less than 10(-3)dB/km at 1.55um wavelength).(C) 2015 Optical Society of America
We present a multicore fiber dedicated for next generation transmission systems. To overcome the issue of multicore fibers' integration with existing transmission systems, the fiber is designed in such a way that the transmission parameters for each core (i.e., chromatic dispersion, attenuation, bending loss, etc.) are in total accordance with the obligatory standards for telecommunication single core fibers (i.e., ITU-T G.652 and G.657). We show the results of numerical investigations and measurements carried out for the fabricated fiber, which confirm low core-to-core crosstalk and compatibility with standard single-core single-mode transmission links making the fiber ready for implementation in the near future.
We compare, thanks to a Sagnac interferometer, the phase sensitivity to strain of different microstructured optical silica fibers (MSF) that we design and fabricate. Our results show that when a same elongation is applied to different MSF, the induced phase change is equal or lower than the one obtained for a standard fiber, showing no advantage on this parameter for sensing applications.
A topical review of numerical and experimental studies of supercontinuum generation in photonic crystal fiber is presented over the full range of experimentally reported parameters, from the femtosecond to the continuous-wave regime. Results from numerical simulations are used to discuss the temporal and spectral characteristics of the supercontinuum, and to interpret the physics of the underlying spectral broadening processes. Particular attention is given to the case of supercontinuum generation seeded by femtosecond pulses in the anomalous group velocity dispersion regime of photonic crystal fiber, where the processes of soliton fission, stimulated Raman scattering, and dispersive wave generation are reviewed in detail. The corresponding intensity and phase stability properties of the supercontinuum spectra generated under different conditions are also discussed.
Stresses can cause anisotropic and inhomogeneous distribution of the refractive index. Their effects on the performance of optical waveguides have been observed in photoelectric devices. In this paper, the photo-elastic relation and wave equations for inhomogeneous and anisotropic waveguides are reviewed. The effective refractive indexes and mode shapes of planar waveguides under different stress states are obtained analytically. It is found that stress can affect the optical performance; different stress states play different roles: high stress value can change the cutoff thickness, which may induce multimode; in-plane stress causes birefringence, which may induce polarization shift and polarization dependent loss; stress concentration can change the mode shape, which may induced large transition loss; and pure shear stress has little effects on the effective refractive index.
We designed, manufactured and characterized two birefringent microstructured fibers that feature a 5-fold increase in polarimetric sensitivity to hydrostatic pressure compared to the earlier reported values for microstructured fibers. We demonstrate a good agreement between the finite element simulations and the experimental values for the polarimetric sensitivity to pressure and to temperature. The sensitivity to hydrostatic pressure has a negative sign and exceeds -43 rad/MPa x m at 1.55 microm for both fibers. In combination with the very low sensitivity to temperature, this makes our fibers the candidates of choice for the development of microstructured fiber based hydrostatic pressure measurement systems.
We experimentally investigate a supercontinuum generation in a series of photonic crystal fibers pumped with sub-ns pulses. The fibers are designed to have zero dispersion wavelengths close to 1064 nm, but they differ with respect to the lattice constant and air hole size. We focus on the supercontinuum generation mechanism and on the shape of spectra generated with the use of these photonic crystal fibers. A comprehensive study on the influence of the fiber structural parameters on the supercontinuum outcome indicates how to tailor these parameters for specific application where particular spectral characteristics are desired.
We present a PMMA birefringent fiber with enhanced polarimetric sensitivity to hydrostatic pressure, obtained by enlarging selected holes in the microstructured cladding. The fiber shows a linear response to pressure with small hysteresis in the pressure range up to 8.5 MPa and the sensitivity of 48 ${rm rad}/{rm MPa}cdot{rm m}$ at 600 nm. The average temperature sensitivity measured in the range 22–40$^{circ}{rm C}$ is 1 ${rm rad}/{rm K}cdot{rm m}$ at 600 nm. The fiber, however, shows significant hysteresis increasing with the temperature range. We also present the results of numerical simulations of the birefringence and the sensitivity to pressure. The contribution of stress and deformation effects to the overall pressure sensitivity in the investigated PMMA fiber and the silica fiber of the same geometry is compared. This allows us to explain different signs of pressure sensitivity observed in silica and the PMMA fibers.
We present fiber Bragg grating (FBG)-based hydrostatic pressure sensing with highly birefringent microstructured optical fibers. Since small deformations of the microstructure can have a large influence on the material birefringence and pressure sensitivity of the fiber, we have evaluated two microstructured fibers that were made from comparable fiber preforms, but fabricated using different temperature and pressure conditions. The magnitude and sign of the pressure sensitivity are found to be different for both fibers. We have simulated the corresponding change of the Bragg peak separation with finite-element models and experimentally verified our results. We achieve very high experimental sensitivities of -15 and 33 pm/MPa for both sensors. To our knowledge, these are the highest sensitivities ever reported for birefringent FBG-based hydrostatic pressure sensing.
We report on a photonic crystal fiber with a large mode area designed for compact high power fiber lasers and amplifiers. The fiber suppresses higher order modes when bent around a 10-cm radius and enables single mode operation in small footprint laser and amplifier architectures. We experimentally confirm the peculiar bending properties of this fiber in its passive version, by reporting on the measurement results of fundamental mode loss in bent and straight fibers, and of the influence of the bending plane orientation on this fiber loss.
We measured spectral dependence of the polarimetric sensitivity to temperature in three birefringent holey fibres with different geometries. Our results show that thermal properties of the birefringent photonic crystal fibres depend very much on the air hole arrangement. Using the procedure which allows us to determine the sign of temperature sensitivity, we demonstrated that one of the investigated fibres is insensitive to temperature at a certain wavelength. We also measured the temperature sensitivities for the fibres with and without polymer coating and showed that the coating changes significantly the fibre response to temperature. Furthermore, we demonstrated experimentally that the spectral dependence of the polarimetric sensitivity to temperature in birefringent holey fibres obeys a scaling law.
A review of optical fiber sensing demonstrations based on photonic crystal fibers is presented. The text is organized in five main sections: the first three deal with sensing approaches relying on fiber Bragg gratings, long-period gratings and interferometric structures; the fourth one reports applications of these fibers for gas and liquid sensing; finally, the last section focuses on the exploitation of nonlinear effects in photonic crystal fibers for sensing. A brief review about splicing with photonic crystal fibers is also included.
We investigate the phase sensitivity of the fundamental mode of hollow-core photonic bandgap fibers to strain and acoustic pressure. A theoretical model is constructed to analyze the effect of axial strain and acoustic pressure on the effective refractive index of the fundamental mode. Simulation shows that, for the commercial HC-1550-02 fiber, the contribution of mode-index variation to the overall phase sensitivities to axial strain and acoustic pressure are respectively approximately -2% and approximately -17%. The calculated normalized phase-sensitivities of the HC-1550-02 fiber to strain and acoustic pressure are respectively 1 epsilon(-1) and -331.6 dB re microPa(-1) without considering mode-index variation, and 0.9797 epsilon(-1) and -333.1 dB re microPa(-1) when mode-index variation is included in the calculation. The latter matches better with the experimentally measured results.
In this paper we present an analytical formula for bending loss oscillations in photonic crystal fibers (PCFs). We follow the approach originally adopted for conventional double-clad fibers and show that it can be applied to PCFs by substituting the structural parameters of the conventional fiber by their PCF counterparts. We then examine the spectral dependence of the critical bending radius and the position of the first order loss peak as a function of structural parameters of the PCF cladding such as the fill factor and the number of hole rings. Finally, we evaluate the precision of the analytical model by comparing the results to finite element calculations for a selection of PCF geometries.
Because in an air-core photonic-bandgap fiber the fundamental mode travels mostly in air, as opposed to silica in a conventional fiber, the phase of this mode is expected to have a much lower dependence on temperature than in a conventional fiber. We confirm with interferometric measurements in air-core fibers from two manufacturers that their thermal phase sensitivity is indeed ~3 to ~6 times smaller than in an SMF28 fiber, in agreement with an advanced theoretical model. With straightforward fiber design changes (thinner jacket and thicker outer cladding), this sensitivity could be further reduced down to ~11 times that of a standard fiber. This feature is anticipated to have important benefits in fiber optic systems and sensors, especially in the fiber optic gyroscope where it translates into a lower Shupe effect and thus a greater long-term stability.
Photonic crystal fibers guide light by corralling it within a periodic array of microscopic air holes that run along the entire
fiber length. Largely through their ability to overcome the limitations of conventional fiber optics—for example, by permitting
low-loss guidance of light in a hollow core—these fibers are proving to have a multitude of important technological and scientific
applications spanning many disciplines. The result has been a renaissance of interest in optical fibers and their uses.
A photonic crystal fiber (PCF) with circular air holes in the fiber cladding and elliptical air holes in the fiber core is proposed. According to calculation, both ultrahigh birefringence (larger than 0.01) and ultralow confinement loss (less than 0.001dB/km) can be achieved simultaneously over a large wavelength range for a PCF with only four rings of circular air holes in the fiber cladding. The confinement loss in this PCF can be effectively reduced while the birefringence almost remains the same. The proposed design of the PCF is a solution to the tradeoff between the birefringence and the confinement loss for the originally reported highly birefringent elliptical-hole PCF. Moreover, an approach to modify the effective index of fiber core is also suggested in this letter