We present an effective method for free-space selective excitation of different combinations of LP
and LP
polarization modes in a birefringent optical fiber using a Wollaston prism, rotatable ...polarizer, and achromatic half-wave plate. The method is minimally wavelength-dependent and can be used for high-power sources. The relative coupling efficiencies of different modes can be continuously tuned and the suppression rate of the unwanted modes with respect to the targeted mode exceeds 20 dB. We present input system configurations that allow for the excitation of different individual modes and groups of modes and estimate the maximum coupling efficiencies based on numerical simulations. As example applications, we show the generation of Raman sidebands in different modes, gain tunability of intermodal four-wave mixing, and broadband conversion of a supercontinuum light beam from the fundamental to the LP
mode.
We report for the first time on rigorous numerical simulations of a helical-core fiber by using a full vectorial method based on the transformation optics formalism. We modeled the dependence of ...circular birefringence of the fundamental mode on the helix pitch and analyzed the effect of a birefringence increase caused by the mode displacement induced by a core twist. Furthermore, we analyzed the complex field evolution versus the helix pitch in the first order modes, including polarization and intensity distribution. Finally, we show that the use of the rigorous vectorial method allows to better predict the confinement loss of the guided modes compared to approximate methods based on equivalent in-plane bending models.
We present a rocking filter in a highly birefringent two-mode fiber that enables resonant coupling between different modes in the LP
group. Our simulations and experimental results prove that such a ...filter allows for resonant coupling between orthogonally polarized LP
modes of the same spatial structure, as well as between modes of the same polarizations and orthogonal spatial distributions. Furthermore, we demonstrate that such rocking filters can be used to generate pure TE
, TM
and HE
beams or their coherent superposition.
Nonlinear femtosecond pulse propagation in an all-solid photonic bandgap fiber is experimentally and numerically investigated. Guiding light in such fiber occurs via two mechanisms: photonic bandgap ...in the central silica core or total internal reflection in the germanium doped inclusions. By properly combining spectral filtering, dispersion tailoring and pump coupling into the fiber modes, we experimentally demonstrate efficient supercontinuum generation with controllable spectral bandwidth.
We report on low-loss patch cords composed of a highly reproducible low-loss fusion splicing of photonic crystal fibers (PCFs) with a standard single mode fiber (SMF). Distinct from other papers in ...this area we report on the results for different types of PCFs, including LMA fibers with similar to a SMF core size and a mode field diameter (MFD), as well as polarization maintaining (PM) Bow-Tie PCF with an elliptical GeO 2 doped core and also a suspended-core (SC) PCF with a tiny core. We show that all studied splices between SMF and PCFs exhibit dispersive and non-reciprocal, in view of a light propagation direction, transmission losses. Defined as a larger decrease of a transmitted optical power comparing both propagation directions, achieved splicing losses, are equal to 0.46 ±0.03 dB, 0.34±0.01 dB, 0.67 ±0.17 dB and 3.09 ±0.36 dB at 1550 nm for LMA8, LMA10, Bow-Tie PCF and SC PCFs, respectively. Moreover, additionally to developed low-loss splicing, we report on low-loss patch cords for all mentioned above PCFs spliced on both ends with SMF pigtails ended with FC/APC connectors achieving the total losses at 1550 nm equal to 1.07 ±0.07 dB for LMA8, 0.72 ±0.20 dB for LMA10, 1.30 ±0.06 dB for Bow-Tie PCF, and 9.36 ±0.20 dB for SC PCF.
We analyzed the effect of fiber bending on spectral position and strength of the surface plasmon resonance arising due to the interaction of the fundamental mode guided in the core of the ...microstructured fiber with a metal layer. Fully vectorial simulations were performed using the finite element method with perfectly matched layers boundary conditions. To conduct the simulations, we adopted the concept of an equivalent bent fiber developed recently on the ground of transformation optics formalism. In this approach, the bent fiber with a metal layer is replaced by an equivalent fiber with appropriate spatial distributions of electric permittivity and magnetic permeability tensors. The obtained results explain the mechanisms responsible for the change in the SPR spectrum induced by bending and by the geometry of the microstructured fiber. By modifying the holes layout in the microstructured cladding, we designed the fiber, in which the depth of the surface plasmon resonance is in a high degree tunable by bending.
We propose an improvement of the interferometric method used up to now to measure the chromatic dispersion in single mode optical fibers, which enables dispersion measurements in higher-order modes ...over a wide spectral range. To selectively excite a specific mode, a spatial light modulator was used in the reflective configuration to generate an appropriate phase distribution across an input supercontinuum beam. We demonstrate the feasibility of the proposed approach using chromatic dispersion measurements of the six lowest order spatial modes supported by an optical fiber in the spectral range from 450 to 1600 nm. Moreover, we present the results of numerical simulations that confirm sufficient selectivity of higher-order mode excitation.
We experimentally studied the influence of different constructional parameters on the performance of surface plasmon resonance (SPR) sensors based on a commercially available polymer step-index ...multimode fiber. For the first time, to the best of our knowledge, we experimentally investigated the influence of polishing depth on the characteristics of SPR sensors based on a straight multimode fiber. We also examined the impact of sensing length on the spectral position and strength of the SPR in side-polished straight fibers. To clarify literature contradictions concerning the effect of fiber bending on SPR, we experimentally investigated the performance of U-bent SPR sensing probes based on multimode fibers. We have shown that the SPR can be significantly amplified by bending the polymer fiber with stripped cladding. We also demonstrated that the side-polishing of U-bent sensing probes has little impact on their performance.
We have studied the effect of waveguide alignment on the reflection spectrum of Bragg gratings fabricated using a multiple order phase mask. We have demonstrated that splitting of certain Bragg peaks ...observed in earlier experiments reported in literature is caused by formation of the gratings with different periodicities in the waveguide tilted with respect to the phase mask plane due to the interference of non-symmetrical diffraction orders. Analytical expressions for spectral separation of the split peaks have been derived and verified against the experimental data recently presented in literature. The analytical predictions were also confirmed by numerical simulations of intensity distributions behind the multiple order diffraction grating and its projection on the tilted waveguide.
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