Measurements of beat length in short low-birefringence fibers

We describe a new experimental method of determining low birefringence in fibers, based on adjusting the fiber twist in a fiber-optic loop mirror. The method allows simple birefringence measurement in fibers with beat length within the range 0.05-100 m.     

Measurement of birefringence correlation length in long, single-mode fibers

Measurements of birefringence correlation length performed on long single-mode telecommunication fibers are reported. The proposed technique relies on the statistical properties of the backscattered-field polarization, which was measured by means of a polarization-sensitive optical time-domain reflectometer. Experimental results are reported that show good agreement with the underlying theory based on stochastic differential equations.     

Stimulated Raman amplification characteristics in long span single-mode silica fibers

Spectral Raman amplification characteristics have been measured directly for a tunable pumping source, taking the relative polarization states of pump and signal waves into consideration. Raman amplification has been observed, even with an orthogonal polarization pump, in a long span single mode fiber. Raman amplification causes significant crosstalk in wave-length-multiplexed systems.     

Cutoff wavelength of single-mode fibers: Definition, measurement, and length and curvature dependence

The cutoff wavelength λ_c as defined by the CCITT can be defined equivalently as that wavelength for which the attenuation of the second-order LP₁₁ mode is 19.34 dB higher than the attenuation of the fundamental mode. This equivalent definition of λ_c does not depend on the length and curvature of the fiber. Both measuring methods for λ_c, the bending method and the multimode reference method, are analyzed and the measurement conditions that lead to the CCITT cutoff wavelength are indicated. The bend attenuation of the second-order mode of a typical matched-cladding, step-index fiber is calculated numerically, and methods are described to determine the length and curvature dependence of the cutoff wavelength from the bend loss data.     

单模光纤中的脉冲展宽

本文给出了光源频谱是洛仑兹分布的高斯脉冲,在单模光纤中传输时因一阶色散而展宽的近似理论.得到了在光纤中传输的脉冲光功率的系综平均值和输出脉冲宽度的均方根值的近似解析公式.数值分析的结果表明,所给出的公式与数值解的最大偏差小于5%.     

Microchannels in conventional single-mode fibers

Microchannels are fabricated into conventional single-mode fibers by femtosecond laser processing and chemical etching. Fabrication limitations imposed by the fiber geometry are highlighted and resolved through a simple technique without compromising fabrication flexibility. A microfluidic fiber device consisting of a 4 microm wide microchannel that intersects the fiber core for refractive index sensing is further demonstrated.     

Electrostrictive response in single-mode ring-index-profile fibers

We have theoretically investigated, for what is to our knowledge the first time, the electrostrictive response in a single-mode ring-core fiber. We found that the electrostrictive response function differs strongly from those of standard fibers with a Gaussian light-intensity profile.     

单模光纤的磁光效应

本文利用琼斯(Janes)矩阵叙述了单模光纤磁光效应的理论,导出了既具有双折射又具有法拉第效应的琼斯矩阵形式,并利用Mueller矩阵导出电流传感器系统输出光强与法拉第旋转角之间的关系.     

Small-stokes-shift frequency conversion in single-mode birefringent fibers

We report experimental observation of nondegenerate four-photon mixing (FPM) via a new phase-matched process in birefringent fibers. This phase-matching process is characterized by relatively long coherence lengths, and by small pump-to-Stokes frequency shifts (of the order of 100 cm^-1 in high birefringence fibers) that are directly proportional to the fiber birefringence. Pump-to-Stokes energy conversion efficiencies of over 40 percent have been obtained with moderate pump powers (≈1 kW) from a visible cw mode-locked dye laser coupled into single-mode polarization-preserving high-birefringence fibers of a few meters length. In addition, we report the first observation of a totally non-degenerate phase-matched four-photon process in a fiber; this invokes mixing of the original FPM Stokes component with the pump and stimulated Raman radiation.     

A study of the propagation characteristics of W-type single-mode fibers using variational fields of single-clad single-mode fibers

A number of single and two parameter scalar variational fields approximating the fundamental mode of single-clad fibers are available in the literature. The present work aims at checking if these fields can also explain the propagation characteristics of W-type or double-clad single mode fibers with similar accuracies. To assess the accuracies, numerical solution of scalar wave equation is required. A method for solving the scalar wave equation numerically has also been proposed. Investigation shows that the single parameter fields are not very suitable for the W-type fibers. At least a two parameter variational field should be used.     

Polarization mode coupling in long single-mode fibres

In this paper we look at the polarization state evolution of light propagating in long, birefringent, single-mode fibres in the presence of mode coupling. We show first that there always exist two orthogonal linear input polarizations which lead to linear output polarization for monochromatic light. The applicability of the coupled power equations is discussed and it is shown that they cannot be used with only two propagating modes. A more detailed analysis is then carried out for a uniform coupling and the effect of the spectral width of the source is investigated. Some insight into the time-dependent propagation is also given. Experimental results illustrate the theoretical considerations.     

Accuracy of scalar approximation for single-mode fibers

Total dispersion in single-mode fibers has been computed from the exact numerical solution of scalar and vector wave equations and the accuracy of the scalar approximation has been discussed. It has been shown that for larger values of relative index difference between core and cladding, although the values of total dispersion obtained by the two approaches differ appreciably in the vicinity of zero dispersion, the optimum core radii and the zero dispersion wavelengths obtained by the two methods differ negligibly for all practical purposes.     

Coupling of single-mode Ti-diffused LiNbO3 waveguides to single-mode fibers

We report on measurements of the near-field intensity distribution of single-mode T-diffused LiNbO₃ waveguides and on the alignment tolerances when coupled to a single mode fiber. Coupling efficiencies of typically 77 to 87% are calculated and a value as high as 80% has been measured experimentally for a y-cut substrate and TM-like polarisation. The total insertion loss of 1 cm long single-mode Ti-diffused waveguides (c-cut) inserted between single-mode fibers was typically 10 dB.     

Operation of Brillouin dynamic grating in single-mode optical fibers

The first (to our knowledge) observation of Brillouin dynamic grating in conventional single-mode fibers is reported, and the characterization is demonstrated with respect to the external parameters for the grating generation. When a 100 m single-mode fiber is used, a reflectance of 8% with a spectral bandwidth as low as 2.4 MHz is achieved, which is less than 10% of ordinary Brillouin gain bandwidth.     

Reflectometric measurement of birefringence rotation in single-mode optical fibers

We present a novel reflectometric technique for the measurement of orientation and modulus of the linear birefringence vector in single-mode optical fibers. The technique provides information also on circular birefringence, although this component, if present, appears as a rotation of the linear birefringence. A detailed theoretical analysis is reported and validated by experimental results.     

Fusion splicing small-core photonic crystal fibers and single-mode fibers by repeated arc discharges

We demonstrate a novel method for low-loss splicing small-core photonic crystal fibers (PCFs) and single-mode fibers (SMFs) by repeated arc discharges using a conventional fusion splicer. An optimum mode field match at the interface of PCF-SMF and an adiabatic mode field variation in the longitudinal direction of the small-core PCF can be achieved by repeated arc discharges applied over the splicing joint to gradually collapse the air holes of the small-core PCF. This method is simple and offers a practical solution for light coupling between small-core PCFs and SMFs.     

Photopolymer microtips for efficient light coupling between single-mode fibers and photonic crystal fibers

A novel method for light coupling between single-mode fibers (SMFs) and small-core photonic crystal fibers (PCFs) is demonstrated. The method is based on growing photopolymer microtips directly on the end faces of SMFs. The shape and size of the tips can be controlled by adjusting the laser power and the exposure time for polymerization to match the mode field to the small-core PCFs. A 5 dB improvement in coupling efficiency between a SMF and a commercial small-core, highly nonlinear PCF is experimentally demonstrated. This compact and efficient butt-coupling method is particularly suitable for PCF gas sensor applications.