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DDC: 620 × Type: article × Subject: Microstructured fibers × WGL Institute: IPHT ×

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Now showing 1 - 4 of 4
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    Diffusion and interface effects during preparation of all-solid microstructured fibers
    (Basel : MDPI AG, 2014) Kobelke, J.; Bierlich, J.; Wondraczek, K.; Aichele, C.; Pan, Z.; Unger, S.; Schuster, K.; Bartelt, H.
    All-solid microstructured optical fibers (MOF) allow the realization of very flexible optical waveguide designs. They are prepared by stacking of doped silica rods or canes in complex arrangements. Typical dopants in silica matrices are germanium and phosphorus to increase the refractive index (RI), or boron and fluorine to decrease the RI. However, the direct interface contact of stacking elements often causes interrelated chemical reactions or evaporation during thermal processing. The obtained fiber structures after the final drawing step thus tend to deviate from the targeted structure risking degrading their favored optical functionality. Dopant profiles and design parameters(e.g., the RI homogeneity of the cladding) are controlled by the combination of diffusion and equilibrium conditions of evaporation reactions. We show simulation results of diffusion and thermal dissociation in germanium and fluorine doped silica rod arrangements according to the monitored geometrical disturbances in stretched canes or drawn fibers. The paper indicates geometrical limits of dopant structures in sub-μm-level depending on the dopant concentration and the thermal conditions during the drawing process. The presented results thus enable an optimized planning of the preform parameters avoiding unwanted alterations in dopant concentration profiles or in design parameters encountered during the drawing process.
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    Identification of zero density of states domains in band gap fibers using a single binary function
    (Washington, DC : Optical Society of America, 2016) Li, Guangrui; Schmidt, Markus A.
    Here we introduce a new calculation method to find the domains of zero density of states for photonic band gap guiding fibers consisting of arrays of high refractive index strands in a low refractive index cladding. We find an analytic expression that associates any combination of geometric parameter, effective index, material and wavelength with a single binary function which allows direct determination whether the density of cladding states is zero or not. The method neither requires the typically used root finding procedure for dispersion tracking nor simulation volume discretization. We verify the validity of our approach on well-established results and reveal as example that band gap regions are mainly determined by the two lowest order Bessel function orders. Our method allows for extensive parameter scans and evaluation of photonic band gap structures against structural and material inaccuracies with substantially reduced simulation effort.
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    Strain sensitivity enhancement in suspended core fiber tapers
    (Heidelberg : Springer, 2013) André, R.M.; Silva, S.O.; Becker, M.; Schuster, K.; Rothardt, M.; Bartelt, H.; Marques, M.B.; Frazão, O.
    Suspended core fiber tapers with different cross sections (with diameters from 70 μm to 120 μm) are produced by filament heating. Before obtaining the taper, the spectral behavior of the suspended core fiber is a multimode interference structure. When the taper is made, an intermodal interference between a few modes is observed. This effect is clearly visible for low taper core dimensions. Since the core and cladding do not collapse, two taper regions exist, one in the core and the other in the cladding. The cladding taper does not affect the light transmission, only the core is reduced to a microtaper. The spectral response of the microtaper based-suspended core fiber is similar to a beat of two interferometers. The strain is applied to the microtaper, and with the reduction in the transverse area, an increase in sensitivity is observed. When the taper is immersed in a liquid with a different index of refraction or subjected to temperature variations, no spectral change occurs.
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    Micro-structured fiber interferometer as sensitive temperature sensor
    (Heidelberg : Springer, 2013) Favero, F.C.; Becker, M.; Spittel, R.; Rothhardt, M.; Kobelke, J.; Bartelt, H.
    We report on a fast and sensitive temperature sensor using a micro-structured or photonic crystal fiber interferometer with a high germanium doped fiber core. The wavelength sensitivity for temperature variation was as high as δλ/δT= 78 pm/ C up to 500 C, which was 6 times more sensitive than the fiber Bragg grating temperature sensitivity of δλ/δT= 13 pm/ C at 1550 nm. The sensor device was investigated concerning the sensitivity characteristics and response time.