The optical performance of nanostructured gradient index vortex phase masks (VPMs) in various external media was investigated. We utilized a modified stack-and-draw technique to fabricate the ...microscopic-size masks. Its structure contains spatially distributed sub-wavelength rods made of two thermally matched glasses with high and low refractive indices. Measured optical characteristics of the generated vortices with azimuthal phase distribution are presented. The numerical and experimental study shows that such VPMs with the same designed structure but varied thickness can convert fundamental light beam into optical vortices with different charges. Furthermore, we found that the mask performance is unaffected by the refractive index of the surrounding media making it an excellent candidate for microfluidic applications.
We experimentally studied axial stress distribution in recently developed optical all-solid fibers with nanostructured cores. In this type of fiber, the core is composed of thousands of low and high ...refractive index glass rods with individual diameters of a few hundred nanometers. A distribution of nanorods determines the effective distribution of the refractive index in the core. A structure of nanorods may introduce unrevealed axial stress distribution after fiber drawing, which may induce change of the expected refractive index value. We studied stress in a custom made nanostructured silica fiber with parabolic refractive index distribution in the core and compared it with the reference SMF-28 fiber. For nanostructured fibers we proved that the axial stress is purely thermal with negligible contribution of mechanical stress. This results in the presence of tensile stress in the fiber core, which is in contrary to a standard telecom fiber, where a compressive stress in the core exists. We showed that measured axial stress has negligible impact on refractive index distribution of nanostructured fibers, thus it does not affect its performance.
A method for the continuous detection of heart rate (HR) in signals acquired from patients using a sensor mat comprising a nine-element array of fiber Bragg gratings during routine magnetic resonance ...imaging (MRI) procedures is proposed. The method is based on a deep learning neural network model, which learned from signals acquired from 153 MRI patients. In addition, signals from 343 MRI patients were used for result verification. The proposed method provides automatic continuous extraction of HR with the root mean square error of 2.67 bpm, and the limits of agreement were -4.98-5.45 bpm relative to the reference HR.
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 demonstrate that higher order rocking filters coupling energy between polarization modes at several wavelengths can be fabricated in a birefringent photonic crystal fiber using a fusion arc ...splicer. Three resonant couplings were identified, respectively at 855, 1271, and 1623 nm for the filter with a pitch distance of 8 mm characterized in this work. We also measured the filter response to temperature, elongation and hydrostatic pressure at the first and the second resonance. Our results show that the fabricated filter has very low sensitivity to temperature 1.77 and 1.38 pm/K, moderate sensitivity to elongation 1.35 and 1.12 nm/mstrain, and extremely high sensitivity to hydrostatic pressure 6.14 and 3.30 nm/MPa, respectively at the first and the second resonance.
Determined polarization state of light is required in nonlinear optics applications related to ultrashort and single-cycle light pulse generation. Such short time scales require up to full octave of ...spectral width of light. Fiber-based, pulse-preserving and linearly polarized supercontinuum can meet these requirements. We report on the development - from linear simulations of the fiber structure, through fabrication of physical fibers to their versatile characterization - of polarization maintaining, highly nonlinear photonic crystal fibers, intended for femtosecond pumping at a wavelength of 1560 nm. Full octave of linearly polarized light around this wavelength would enable to cover amplification bandwidths of the three major fiber amplifiers from ytterbium doped systems up to thulium and holmium doped fiber amplifiers, with a coherent, linearly polarized seed signal. At the same time, an all-normal chromatic dispersion profile over an entire transmission window, and small dispersion of nonlinearity in the developed fibers, would facilitate use of commercially available femtosecond fiber lasers as pump sources for the developed fibers.
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