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Optical fibers with a modified radial profile of acoustic refractive index (ARIP) have been considered. The use of two-component doping of the core in the silica optical fiber makes it possible to create simultaneously various profiles of refractive indices for an optical wave and a hyper-sound wave generated due to electrostriction, which can be applied for efficient reduction of the maximum of the amplification coefficient (gain) of the stimulated Brillouin scattering (SBS). The use of phosphor oxide (P2O5) and fluorine (F) with this purpose, when maintaining optically single-mode operation, makes it possible to realize a high-contrast ARIP by optimizing the shape of it, it is possible to effectively involve a great number of guided acoustic modes to the SBS process. This creates a broad multiband SBS gain spectrum and leads to a reduction of the absolute value of its maximum proportional to the number of acoustic modes. In this work, for the optical fibers with such a step-index profile of optical refractive index (ORIP), we have studied theoretically the dependence of the absolute maximum of the SBS gain at the ARIP parameters providing its ultimately possible reduction owing to the multimode acoustics on the value of the contrast Δn of the optical refractive index between the fiber core and its cladding. Among others, the real technological limitations on the maximum codoping of silica glass with P2O5 and F (in particular, for the method of the modified chemical vapor deposition, MCVD) are considered. In addition, an approximate analytical model of the optimal ARIP (and, respectively, the radial distributions of the P2O5 and F concentrations) is presented. The results have made it possible to come to the conclusion that the maximum SBS gain suppression (up to 15 dB) in the P2O5–F–SiO2 fibers can be achieved at Δn < 0.0045, while at 0.0045 < Δn < 0.0075, these limits are objectively restricted by 6 dB; at Δn > 0.0075, it is necessary to use other glass compositions or methods. [ABSTRACT FROM AUTHOR]

Dip coating technique has the potential to provide a simpler and more cost-effective means of forming an optical fiber microcollimator composed of parabolic Polymethyl methacrylate microlenses for various applications. The effects of dip-coating operating parameters such as withdrawal speed on the thickness of a microlens were investigated in this work. Zemax® software was used to validate the analytical results and to assess the efficiency of the optical coupling. The obtained waist and working distance values, make possible the optimization of the optical coupling between a microcollimator and a laser beam, as well as between a microcollimator and an optical fiber. The simulation results of the coupling between the microcollimator and the laser beam show that the optical coupling efficiency η is about 99% with an optimal microlens radius R = 19.14 μm, a waist size W1 = 2.49 μm and a working distance Zw = 41.78 μm. However, the optimal microlens for the coupling between the microcollimator and the optical fiber has a minimum curvature radius about 28.78 μm. We believe that these results are of a big interest in many applications in optical experiments and laser-optical fibers applications. [ABSTRACT FROM AUTHOR]

In free-space optical communication (FSOC), it is necessary to couple optical fibers for application in optical-fiber technology and devices. However, propagation through atmospheric turbulence degrades the single-mode-fiber coupling efficiency (CE). This degradation can be compensated by an adaptive optics (AO) system. In this paper, we analyze the influence of spatial and temporal characteristics of turbulence on the CE. Experiments along a 1 km urban link demonstrate that the CE increases from 5% without AO to 10%–25% in the AO closed loop at different times of day. We obtain an increase by factor 4 in the CE under weak turbulence conditions. [ABSTRACT FROM AUTHOR]

This paper proposes the theoretical design of a polarized interferometric fiber-optic gyroscope (IFOG). The polarized IFOG utilizes a coherent light source and polarization elements (Faraday rotators and polarizing beam splitter) to obtain maximum visibility of an interference signal and to compensate for the birefringent effect of a single-mode fiber coil in an IFOG. [ABSTRACT FROM AUTHOR]

A new design of all-glass microstructured fibers with a large mode area is presented. The numerical analysis of the fibers was performed using the finite element method. Confinement losses for the fundamental modes and for those of a higher order were calculated in the spectral range of 0.8 to 1.4 microns. Simulation results show that the proposed design allows us to obtain single-mode guidance of these fibers in the spectral range of 0.87 to 1.11 microns for straight and bent fibers with a bending radius of 0.25 m. [ABSTRACT FROM AUTHOR]

An all-vapor phase MCVD process has been proposed for the fabrication of fiber preforms with a Yb2O3-Al2O3-P2O5-SiO2 multicomponent glass core. We have investigated the tubular preform collapse into a rod and demonstrated approaches capable of preventing P2O5 losses in the central part of the core during the collapse process. Preforms with a flat, perfect step-index profile have been fabricated. [ABSTRACT FROM AUTHOR]

A new nonlinear optical laser surface profilometer with micron surface resolution is considered. It is shown that with a resolution of the spectrometer of 0.23 nm the spatial resolution of the proposed method may reach 22.5 μm. [ABSTRACT FROM AUTHOR]

Low-loss splicing of index-guiding microstructured optical fibers (MOFs) and conventional single-mode fibers (SMFs) can be achieved by enlarging the mode field diameter of MOFs, which leads to an optimum mode field match at the joint interface. We study analytically the low-loss fusion splicing between an MOF and an SMF by expanding the modal field of MOF, using the controlled air-hole collapse method. Our method is simple and offers analytical solution for light coupling between MOFs and SMFs. Comparisons with available experimental and simulation results have also been included. [ABSTRACT FROM AUTHOR]

After reviewing three different definitions of mode field diameter of single-mode fibers, coupled efficiency calculation methods associated with lateral offset, longitude separation and wavelength, the effects produced by them, and the influences of splicing defects were discussed in detail. The regularities of the effects were studied according to the first order derivation of couple efficiency formula, and a simplified formula for couple efficiency calculation was presented under the circumstance of slight misalignment, with respect to wavelength, λ, and in a good agreement with the theoretical model. The simplified formula provides a new but simple approach to evaluate wavelength dependent couple efficiency of single-mode fibers. Theoretical analyses and numerical calculations show that, when those defects exist, the wavelength produces additional effects on the couple loss that growth of wavelength causes an increase on the couple efficiency for the lateral offset or longitude separation whereas lessens the couple efficiency due to angular misalignment or mode fields mismatching, and that the wavelength degrades the couple efficiency distinctly when λ ≥ 2.5 μm whereas it distorts the couple slightly in range of λ≤ λ≤2 μm. [ABSTRACT FROM AUTHOR]

Ultrashort optical pulse generation using a fiber FM laser is presented and analyzed in detail. Fiber FM laser operation is realized using a fiber ring with an internal phase modulator and an erbium-doped fiber amplifier. To compress FM laser pulses, an external dispersive single-mode fiber is employed. Furthermore, by external intensity modulation, the pulse background is removed. The background ratio of the generated ultrashort pulse is calculated and compared with the experimental results. The experimental results show an output optical pulse width of 1.77 ps and a spectral bandwidth of 0.5 THz. [ABSTRACT FROM AUTHOR]

Results of the wavelet analysis of an extremely short femtosecond pulse propagating in a single-mode optical fiber with a shifted dispersion characteristic are described. The advantages of wavelet analysis as compared with Wigner analysis are shown. In particular, wavelet analysis allows improving the spectral resolution of the studied pulse in the high-frequency range. [ABSTRACT FROM AUTHOR]

The all-fiber lidar shows exciting prospects in space-borne applications, but the coupling efficiency between the telescope and a single-mode fiber is an important problem in the lidar design. We employ the mode-matching theory to analyze theoretically the coupling efficiency. In practical coupling system design, three position deviations, which are the off-axis deviation, defocus deviation, and angle deviation, exert a substantial influence on the coupling efficiency and must be considered and discussed. Generally it is very difficult for a fiber coupling system based on a single lens to adjust the fiber position deviations and obtain the maximum coupling efficiency. Therefore, a coupling system, based on the GRIN lens combined with the lenses, is designed and employed to decrease the influence of these position deviations. We perform some numerical simulations to verify the feasibility of a coupling system based on the GRIN lens. Our results show that a coupling system based on the GRIN lens can overcome the off-axis deviation and defocus deviation and decrease the adjustment difficulty. [ABSTRACT FROM AUTHOR]

We propose a new, spectral-interferometric, technique of complete characterization of ultrashort pulses. The technique is based on employing, as a reference, a sub-parabolic pulse with a known phase formed in a single-mode fiber from the pulse under study. The proposed method has been tested experimentally with femtosecond pulses. Initial phases and temporal profiles of intensity of tested pulses have been restored. [ABSTRACT FROM AUTHOR]

Based on the numerical and experimental studies, a nonlinear-spectronic character of similaritons formed in a single-mode optical fiber without gain is demonstrated. It is shown that the combined action of the Kerr-type nonlinearity and normal dispersion of the fiber leads to the formation of similaritons. The temporal envelop, spectral and phase profiles of such similaritons have a nearly parabolic shape in their central energy-carrying parts. [ABSTRACT FROM AUTHOR]