Polarization-holding single-mode optical-fiber cables

Polarization-holding properties of low-loss and highly birefringent single-mode fibers inserted into two kinds of cable are presented. Variation of the properties and microbending loss during cabling processes were investigated. No degradation in extinction ratio between two orthogonal polarizations was measured in cabling processes for the both cables. Furthermore, length dependence of the extinction ratio was examined theoretically and experimentally by splicing fibers over a 10-km optical transmission line, and the experimental results were found to be in good agreement with those evaluated from the coupled-wave equation.     

A 100-km-long single-mode optical-fiber fault location

A Raman OTDR (ROTDR) fault location for a 100-km-long single-mode optical fiber has been tested. A Ge p-i-n photodiode cooled by liquid nitrogen has been used as a backscattered light receiver. The signal-to-noise ration (SNR) improvement of the cooled Ge p-i-n photodiode from a Ge avalanche photodiode (Ge APD), which operates at room temperature, is 14 dB. Spectral Stokes light power distributions, which have been emitted from a long single-mode fiber, have been measured to estimate the maximum locatable length for a single-mode fiber. It has been shown, from the measurements and calculations, that a 100- km-long and a 30-dB total attenuation at a 1.55-μm wavelength single-mode fiber fault location can be achieved with the aid of an averaging technique. On the basis of these results, a 102-km-long single-mode fiber fault location experiment has been successfully carried out.     

Parametric study of depressed inner cladding single-mode fibers

A parametric study on the depressed inner cladding (DIC) single-mode fibers shows the influence of the inner-cladding diameter on the effective cutoff wavelengths of the first two modes, determining a practical transmission window. The set of curves that is obtained can be considered universal, at least for a value of the inner-cladding/core index differences ratio close to 0.5. The behavior of the effective cutoff wavelengths is explained by studying the effective index of the modes and the fundamental mode diameter, this explanation being confirmed by a bending and microbending sensitivity test. It appears that DIC fibers optimized for long-range transmission should have an inner cladding to core diameter ratio greater than 3 and a relative depth of the inner cladding smaller than 0.5.     

Vibration immunity for optical-fiber current measurement

Optical-fiber measurement of electric current can be rendered immune from the effects of environmental vibration by utilizing the nonreciprocity of the Faraday effect in an arrangement which propagates light simultaneously in the two directions around a fiber loop enclosing an electric current. The system is compared with a back-reflection arrangement. Temperature variations are also suppressed     

Optical microscope observation method of a single-mode optical-fiber core for precise core-axis alignment

A new method is presented for observing a single-mode optical-fiber core by the use of an optical microscope to achieve precise core-axis alignment. The formation mechanism of a core image and its observation condition have been investigated using a ray tracing method. Simulation results show good accordance with practical observed results. Precise alignment of cores can be achieved when the dimension of a core image becomes equal to the core diameter multiplied by the magnification of the observation system. In the core aligning experiment for a single-mode fiber with a large core eccentricity of 3.4 μm, the average misalignment was 0.6 μm.     

Mode coupling loss in single-mode fibers with depressed inner cladding

Single-mode fibers with depressed inner cladding show sharp resonant loss peaks near the fundamental mode cutoff wavelength where the core-guided mode starts to become a leaky mode. The magnitude of the loss peak exceeds 200 dB/km and was found to be extremely sensitive to fiber curvature. The phenomenon is attritubed to mode coupling between the core-guided mode and the discrete modes guided in the outer cladding.     

Evidence of fundamental mode cutoff in depressed inner cladding single-mode fibres

We report experimental evidence of fundamental mode cutoff in depressed inner cladding single-mode fibres. It is characterised by a sharp decrease in the transmission curve and by a local increase of the fundamental mode spot size. Both phenomena are theoretically explained.     

Characterisation of single-mode fibres by near-field measurement

A new technique for the determination of the refractive-index profile of single-mode optical fibres from a simple near-field measurement is proposed. This permits one to deduce accurately all the important parameters of the fibre.     

单模光纤弯曲损耗的测量与分析

提供了弯曲半径从1．7mm到5．8mm，波长从1520nm到1565nm范围内单模光纤弯曲损耗的测试结果。观察到了弯曲损耗呈震荡变化、随着弯曲半径的增加损耗减小，振幅减小，随着波长的增加损耗增加、振幅增大的现象。并利用光纤的耦合模理论对单模光纤弯曲损耗震荡进行了解释。     

Mode field diameter measurement conditions in single-mode fibres

The relationship between the dynamic range and the measurement accuracy of the mode field diameter in single-mode fibre is investigated theoretically. It is clarified that the required dynamic range in which the mode field can be measured within given accuracy depends on the index profiles and operating V value.<>     

Fundamental mode spot-size measurement in single-mode optical fibres

We report a very simple method for measuring the mode spot size in single-mode fibres on the same apparatus as used for attenuation measurements without additional fibre handling. Measurements as a function of wavelength lead to the equivalent step index parameters allowing one to predict directly the splice, microbending and curvature losses.     

Interferometric measurement of dispersion of a single-mode optical fibre

The methods of Fourier transform spectroscopy are applied to the measurement of the dispersion of short lengths of a single-mode optical fibre. The fibres used were one metre or less in length.     

Polarization dispersion measurement on twisted single-mode optical fibers

A new method for measuring polarization dispersion between two eigen polarization modes is presented. It utilizes the measured phase shift corresponding to birefringence difference between two adjacent wavelengths. This method makes it possible to measure small polarization dispersion by using a short test piece even when eigen polarization modes are elliptically polarized. A polarization dispersion of 0.4 ps/km in twisted single-mode fibers can be measured in an approximately 4-m-long fiber by using 1.152- and 1.161-μm lines in a He-Ne laser. Experimental data that polarization dispersion decreases with an increase in fiber twist ate in very close agreement with theoretical results.     

Technique for direct measurement of single-mode fiber chromatic dispersion

A technique for the direct measurement of single-mode fiber chromatic dispersion is presented. The technique uses wavelength modulation to provide a differential fiber chromatic delay signal from which chromatic dispersion is obtained directly. The system is described in detail and practical measurement results shown to illustrate the high accuracy of the technique and its versatility in use with all fiber types.     

一种高灵敏度相位调制单模光纤传感器的信号处理系统

报道一种高灵敏度相位调制单模光纤传感器的信号处理系统。简述了系统的传感原理,讨论了辨向检测电路和信号的计算机处理。     

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.     

The measurement of chromatic dispersion in single-mode fibers byinterferometric loop

A method for chromatic dispersion measurement in long-length fibers (1-10 km) based on the application of an interferometric loop (IL) with phase modulation and lamp/monochromator light source is described. The wavelength region of the measurement is 1.1-1.6 μm and the dynamic range is >15 dB. The reproducibility error of the measured group delay and chromatic dispersion is 40 ps/km and 0.1 ps/km-nm respectively. The results obtained by the IL method and Nd-YAG/Raman laser technique are compared. The measured dispersion agrees with the theoretical results calculated from the refractive index profile of the preform. The influence of the type of phase modulation and the length source spectral width on the accuracy of chromatic dispersion measurements by IL technique is analyzed theoretically     

Distributed beatlength measurement in single-mode fibers with optical frequency-domain reflectometry

The polarization dependence of the coherent detection in optical frequency-domain reflectometry can be exploited to measure the local beatlength along an optical fiber. Reproducibility of the results is given for high and low polarization-mode coupling fibers, and the influence of several effects on beatlength measurement precision, such as spatial reflectometer resolution, fiber twist, and the presence of circular birefringence, is discussed. The experimental results seem to indicate that the typical assumption that the fiber birefringence can be treated as purely linear might not be fully justified. Beatlength overestimates of 10% and more can result.