Optical loss property of silica-based single-mode fibers

The optical loss property of silica fibers has been investigated theoretically and experimentally based on their Rayleigh scattering and absorption losses. The Rayleigh scattering loss for fibers has been estimated using Rayleigh scattering coefficients and power distribution in the fiber. The Rayleigh scattering coefficients are measured for preforms prepared for fiber fabrication and are discussed for GeO₂ -doped and F-doped glasses. The relationship between the optical loss and fiber parameters is clarified. Moreover, the loss increase due to residual stress which occurs during the drawing process is simulated. The optical loss limitations for GeO₂-doped and pure silica core fibers are shown     

Fluorine concentration dependence of viscosity in F-doped silica glass

The fluorine (F) concentration dependence of the viscosity of F-doped silica glass is investigated experimentally. It is confirmed for the first time that the viscosity of F-doped silica glass depends on the F concentration and that the viscosity difference between pure silica and F-doped silica glasses increases as the temperature decreases.<>     

Rayleigh scattering reduction method for silica-based optical fiber

The effect of the thermal treatment of silica-based glasses and glass fibers on their Rayleigh scattering is investigated experimentally. The Rayleigh scattering coefficients of bulk glasses are found to be increased 5-10% by heating them to 1800 °C because the density fluctuation is in proportion to their fictive temperature. Based on these results, we propose a method for reducing the Rayleigh scattering losses of silica-based optical fibers by drawing them slowly at low temperatures. We used this method to obtain a GeO₂ doped silica core single-mode fiber with a minimum loss of 0.16 dB/km at 1.55 μm. As a result, we confirmed that the reduction in the fictive temperature of silica-based glasses and glass fibers reduces their Rayleigh scattering     

Low Rayleigh scatteringP2O5-F-SiO2 glasses

The Rayleigh scattering and infrared absorption losses of P₂ O₅-F-doped silica glass, which is a candidate material for ultra-low-loss optical fiber, were investigated experimentally. The Rayleigh scattering loss of 8.5 wt.% P₂O₅ and 0.3 wt.% F-doped SiO₂ glass is found to be 0.8 times that of pure silica glass. It is also found that the infrared absorption property of P₂O₅-F-SiO₂ glass is almost the same as that of pure silica glass. The minimum loss for the proposed composition is estimated to be 0.11 dB/km at 1.55 μm wavelength, and 0.21 dB/km at 1.3 μm wavelength     

Heavy metal fluoride glasses with low intrinsic Rayleigh scattering

The results of Rayleigh light scattering measurements in bulk multicomponent fluorozirconate glasses are described. We observe for the first time that such materials may be reproducibly prepared with uniformly low scattering levels throughout their volume. In 13 of the 15 specimens studied, the magnitude of the Rayleigh scattering loss was one-third to one-half that typically observed in fused silica glass.     

Brillouin scattering and phonon attenuation in halide glasses: stimulated Brillouin emission

The results of Brillouin light scattering measurements in bulk halide glasses are described. The Brillouin linewidth, intensities and frequency shift measurements allowed the calculation of phonon attenuation, Pockels' elasto-optic coefficients and stimulated Brillouin scattering gain coefficients. The above study shows that the threshold power for stimulated Brillouin scattering in some halide glasses is greater than that for silicate glasses.     

Refractive index and material dispersion interpolation of dopedsilica in the 0.6-1.8 μm wavelength region

An extension of the Claussius-Mossotti interpolation scheme is proposed so that the refractive index and material dispersion of GeO₂- and F-doped silica glasses (with doping concentrations different than those of published data) can be predicted in the 0.6-1.8-μm wavelength region. The new interpolation expression provides a well-behaved functional relationship for use in computer models which analyse propagation in single-mode fibers. The technique proposed is particularly powerful because it can be applied to any glass, whether single or multicomponent, having any other single dopant     

Scattering of acoustic surface waves from periodic grating filters

New data are presented on the scattering of the z-propagating Rayleigh wave on y-cut LiNbO3 by a metallic grating into the x-propagating Rayleigh wave, a pseudo-surface-wave, and bulk shear waves. Estimates of the magnitudes of the scattering coefficients are given     

Viscosity of F and GeO/sub 2/ codoped silica glass

The dopant concentration dependence of the viscosity of fluorine (F) and GeO/sub 2/ codoped silica glass is investigated experimentally. The viscosity of these glasses at various dopant concentrations is measured using the drawing method in the 1700-2000 degrees C temperature range. The change in the viscosity logarithm of F and GeO/sub 2/ codoped silica glass was found to be the linear sum of the changes induced individually by F and GeO/sub 2/.<>     

Thermal effects of Brillouin gain spectra in single-mode fibers

Brillouin gain spectra in two 250-m-long single-mode fibers with GeO₂-doped core/pure-silica cladding (fiber A) and pure-silica core/F-doped cladding (fiber B) were measured at temperatures ranging from -40 to +60°C at a wavelength of 1.32 μm. The temperature coefficients of Brillouin frequency shift were found to be 1.17 and 1.33 MHz/°C for fibers A and B, respectively. Temperature coefficients of Brillouin gain bandwidth were found to be -0.12 and -0.10 MHz/°C. These measurements provide useful information for applications of stimulated Brillouin scattering     

Intrinsic scattering and absorption losses of Ge- and F-doped optical fibres prepared by PCVD

The scattering absorption and profile losses of PCVD fibres are analysed. The Rayleigh scattering increases proportionally to the sum of the F- and Ge-dopant concentrations, the UV absorption is proportional to the Ge concentration, and profiling losses are negligible.<>     

Dispersion of pure GeO2 glass core and f-doped GeO2 glass cladding single-mode optical fibre

The letter investigates the dispersion of GeO2 glass core and F-doped GeO2 glass cladding single-mode optical fibre. It is estimated that the total dispersion goes to zero at about ? = 1.77 ?m. The material dispersions of these glasses are also measured. Material dispersion of GeO2 glass, which contains fluorine of 0.41 wt%, vanished at ? = 1.722?m. This occurs at ? = 1.734 ?m for pure GeO2 glass.     

Rayleigh waves and leaky SAWs in periodic systems of electrodes: periodic Green functions analysis

A new method using periodic Green functions is developed and used to calculate dispersion curves and attenuation coefficients for Rayleigh waves and for leaky waves propagating in periodic systems of thin electrodes on piezoelectric substrates. Such basic parameters as stopband width, centre frequency of the stopband, attenuation in the stopband and resulting bulk-wave scattering are found for Rayleigh waves in YZ-LiNbO/sub 3/ and leaky waves on 36 degrees YX-LiTaO/sub 3/ substrate with shorted or open electrodes.<>     

Temperature-dependent Sellmeier coefficients and chromaticdispersions for some optical fiber glasses

Temperature-dependent Sellmeier coefficients are necessary to optimize optical design parameters of the optical fiber transmission system. These coefficients are calculated for fused silica (SiO₂ ), aluminosilicate, and Vycor glasses for the first time to find the temperature dependence of chromatic dispersion at any wavelength from UV to 1.7 μm. The zero dispersion wavelength λ₀ (1.273 μm for SiO₂, 1.393 μm for aluminosilicate, and 1.265 μm for Vycor glasses at 26°C) varies linearly with temperature, and dλ₀/dT is 0.03 nm/K for aluminosilicate and Vycor glasses, whereas for SiO₂ it is 0.025 nm/K. This study interprets the recently observed experimental value of dλ₀/dT for two dispersion shifted optical fibers; and the dominantly material origin of dλ₀/dT is confirmed here as a fundamental property of the optical fiber glasses     

A theory of wave scattering from an inhomogeneous layer with an irregular interface

Bistatic wave scattering from a layer of Rayleigh scatterers with an irregular interface is investigated by combining the doubling method in volume scattering with the Kirchhoff method in rough surface scattering. Theoretical results are shown illustrating the effect of the rough interface. It is found that for scattered and incident angles near the vertical, the rough interface causes a substantial increase relative to the plane interface in both the like and cross-scattering coefficients over all azimuth angles. However, for large scattered and incident angles, the reverse is true except for azimuth angles around the specular direction. It is interesting to note that while one dominant peak of the like polarized scattering coefficient occurs along the specular direction, two dominant peaks of the cross-polarized scattering coefficient may appear symmetrically with respect to the specular direction. In backscattering, the surface roughness causes a peak to appear in both the like and cross-scattering coefficients at near vertical incidence and also a decrease of these coefficients at large incidence angles.     

Dispersive and scattering properties of a ZrF4 based glass

In a previous letter we presented the material dispersion in a ZrF4 based fluoride glass. The zero crossover wavelength ?c was found to occur between 1.6 and 1.7 ?m. Here, we analyse the refractive index measurements against wavelength data in order to obtain some physical parameters of this material on which ?c is dependent: electronic energy gap E0, electronic oscillator strength ED, lattice oscillator strength E1 and structure factor B. Such values, which are not yet known for fluoride glasses, will be then compared with those corresponding to SiO2 glass. Evaluation of the Rayleigh scattering coefficient will also be made.     

抽运光参数对玻璃中受激布里渊散射光能量提取效率的影响

以K9玻璃与熔石英玻璃代替传统的液体或气体作为纵向受激布里渊散射(LSBS)样品,波长1.064μm,脉宽可调的单纵模电光调Q激光器作抽运光,实验探讨了抽运光脉宽、抽运光能量大小、抽运光脉冲重复频率对纵向受激布里渊散射脉宽压缩效应和散射光能量提取效率的影响。实验结果表明,抽运激光脉冲重复频率高,则散射光能量提取效率高;脉宽小,则散射光能量提取效率高;焦距为500 mm时300 mm长的K9玻璃中得到的散射光能量提取效率比170 mm长的熔石英玻璃高;在抽运光脉冲重复频率为1 Hz时,二者都可以得到90%的散射光能量提取效率。探讨了抽运光为多纵模时,固体介质中受激布里渊散射与光学击穿相伴发生的三种不同情况。实验证明,多纵模情况下固体光学介质中同样可以发生受激布里渊散射;多纵模情况下不一定会对固体光学介质产生光学击穿破坏;光学击穿破坏的发生也不一定会阻止受激布里渊散射的发生,二者可以相伴发生。     

瑞利散射对拉曼光纤放大器性能的影响及抑制措施

瑞利散射是影响拉曼光纤放大器性能的重要因素。本文系统地分析了瑞利散射对拉曼光纤放大器噪声、串扰和功率代价等性能的影响，指出优化选择泵浦功率和泵浦方式以及插入光隔离器等措施可以降低瑞利散射的影响，从而为拉曼光纤放大器的优化设计提供了依据。     

Limitations in fibre Raman amplifiers imposed by Rayleighscattering of signals

A simple method of Rayleigh scattering noise calculation in fibre Raman amplifiers is proposed. Using the method, it is disclosed that the optimal Raman pump power is lower when the Rayleigh scattering of both signal and amplified spontaneous emission (ASE) are considered than when the Rayleigh scattering of ASE only is considered     

合肥上空中层大气密度和温度的激光雷达探测

为研究中层大气分布情况,采用自行研制的532 nm瑞利（Rayleigh）散射激光雷达,对合肥地区（31.90 N,117.170 E）25~40 km高度范围内的大气密度和温度廓线分布进行观测。将瑞利散射激光雷达所测结果与NRLMSISE-00大气模型数据进行对比,以验证瑞利散射激光雷达性能及数据处理方法的可靠性。通过数据对比得出,在25~40 km高度范围内,瑞利散射激光雷达获得的大气密度值与NRLMSISE-00大气模型密度值的比值为0.99~1.03;瑞利散射激光雷达所测温度值与NRLMSISE-00大气模型数据的温度偏差均值约为2.8 K,其中38 km以下两者温度偏差约为1.6 K。数据对比说明,瑞利散射激光雷达观测值与NRLMSISE-00大气模型数据具有较一致的密度分布特征和温度分布特征,瑞利散射激光雷达的观测结果能够较真实地反映合肥上空25~40 km高度范围内的大气密度和温度分布。