Abstract:We present a new method for measuring the group dispersion of the fundamental mode of a holey fiber over a wide wavelength range by white-light interferometry employing a low-resolution spectrometer. The method utilizes an unbalanced Mach-Zehnder interferometer with a fiber under test placed in one arm and the other arm with adjustable path length. A series of spectral signals are recorded to measure the equalization wavelength as a function of the path length, or equivalently the group dispersion. We reveal that some of the spectral signals are due to the fundamental mode supported by the fiber and some are due to light guided by the outer cladding of the fiber. Knowing the group dispersion of the cladding made of pure silica, we measure the wavelength dependence of the group effective index of the fundamental mode of the holey fiber. Furthermore, using a full-vector finite element method, we model the group dispersion and demonstrate good agreement between experiment and theory.
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.
Fiber Bragg gratings written in highly birefringent microstructured optical fiber with a dedicated design are embedded in a composite fiber-reinforced polymer. The Bragg peak wavelength shifts are measured under controlled axial and transversal strain and during thermal cycling of the composite sample. We obtain a sensitivity to transversal strain that exceeds values reported earlier in literature by one order of magnitude. Our results evidence the relevance of using microstructured optical fibers for structural integrity monitoring of composite material structures.
We present a white-light spectral interferometric technique employing a low-resolution spectrometer for a direct measurement of the dispersion of the group birefringence of a calcite crystal over the wavelength range approximately from 490 to 780 nm. The technique utilizes a tandem configuration of a Michelson interferometer and a calcite crystal of known thickness to record a series of spectral interferograms and to measure the equalization wavelength as a function of the optical path difference (OPD) in the Michelson interferometer, or equivalently, the wavelength dependence of the group birefringence of the calcite crystal. We confirm that the measured group birefringence dispersion agrees well with that described by the dispersion equation proposed by Ghosh. Furthermore, we determine precisely the thickness of the calcite crystal from the slope of linear dependence of the measured OPD on the group birefringence given by the dispersion equation.
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