Direct measurement of electrostriction in optical fibers

The electrostriction contribution to the nonlinear refractive index in optical fiber was theoretically calculated and measured. Nonlinearity was induced directly by insertion of the optical fiber into an intense external electric field. With this technique both the Kerr and the electrostrictive contributions to the intensity dependence of the nonlinear refractive index in a step-index fiber were measured. Good agreement between calculated and measured values was observed. These results should confirm and explain the differences observed in measurement of n(2) at different bit rates.     

Residual stress profiles in optical fibers determined by the two-waveplate-compensator method

Stress-induced birefringence impacts the performance of many optical devices. Techniques are needed to measure accurately stress profiles in optical fibers. The two-waveplate-compensator (TWC) method allows the accurate measurement of small retardations. The full-field TWC method is applied here to measure the two-dimensional retardation distribution of single-mode fibers with a spatial resolution of 0.45 μm and a sensitivity of 0.07 nm. Axial stress profiles are hence determined along the axis of the fiber. The stress profiles determined with the TWC method are in good agreement with profiles previously reported in the literature while containing less noise and resolving more details.     

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.     

基于光纤光栅技术的船体横扭角测量方法研究

简要介绍了常见的船体横扭角测量方法,与传统的船体横扭角测量方法相比,光栅技术具有精度高、体积小、测量通道多等优势。建立了从应变量到横扭角的转换模型,设计并完成了与测量船现有变形测量系统的对比测量试验。试验结果表明:在较短测量时段内光栅测量数据与现有船载变形测量系统的测量数据吻合度高,误差在5″范围内,满足船体变形测量的要求;在长时间测量过程中,外界振动干扰对测量结果影响显著。     

Attenuation measurement of optical fibers for sensor technology

Abstract

Generally the attenuation of optical fibers used for sensor technology is higher than that of fibers for telecommunications. This is difficult to measure by the optical time domain reflectometry (OTDR). This paper presents a simple method that employs an integrating sphere. The total and scattering attenuation coefficients can be calculated and discriminated by the measured power of the light scattered out of the optical fiber and collected by the integrating sphere.     

Attenuation measurement of optical fibers for sensor technology

Generally the attenuation of optical fibers used for sensor technology is higher than that of fibers for telecommunications. This is difficult to measure by the optical time domain reflectometry (OTDR). This paper presents a simple method that employs an integrating sphere. The total and scattering attenuation coefficients can be calculated and discriminated by the measured power of the light scattered out of the optical fiber and collected by the integrating sphere.     

Velocity measurement by the laser speckle method using optical fibres

An optical device for in-plane velocity measurement is described. Laser light is focused by the use of an optical fibre onto the object, and the device utilizes the dynamic sparkle effect for velocity determination. The influence of different optical fibres on the speckle formation is investigated with special respect to fibre movement, and as the diameter of the aperture used for speckle detection also affects the measuring signal, an optimum value is found. A simple electronic circuit processes the measuring value proportional to the object velocity.     

Distribution measurement of Raman-gain and optical-loss characteristics in optical fibers

We propose a test method with which to measure the longitudinal distribution of Raman-gain characteristics in connected optical fibers. We describe a technique for obtaining the pump-loss distribution, knowledge of which is necessary for deriving the Raman-gain efficiency distribution, by the bidirectional measurement of Raman amplification. Based on this technique, we performed experiments and demonstrated that the Raman-gain efficiency distribution can be evaluated with the same equipment.     

Nonlinearity in holey optical fibers: measurement and future opportunities

Holey fibers combine two-dimensional microstructuring with one-dimensional longitudinal propagation, resulting in fibers with tailorable dispersive and nonlinear properties. We measure the effective nonlinearity of a typical holey fiber. The small effective area that is possible in this type of fiber significantly enhances its effective nonlinearity relative to standard fiber.     

Spectral-resolved backreflection measurement of polarization mode dispersion in optical fibers

An improved backreflection technique is proposed to perform the spectral-resolved measurement of polarization mode dispersion (PMD) in optical fibers. This technique is based on the PMD dynamical equation and realized by measuring the polarization state evolutions of the reflected signal in both frequency and time domains. Two experimental setups, employing the far-end Fresnel reflection, are constructed to verify this technique. The agreement between the results of the proposed backreflection technique and the conventional forward technique is observed.     

Three-dimensional FDTD method for optical pulse propagation analysis in microstructured optical fibers

We propose a three-dimensional (3D) finite-difference time-domain (FDTD) method to analyze the pulse propagation characteristics in microstructured optical fibers (MOFs). The computation domain size is greatly reduced by adopting the technique of moving problem space. The propagating pulse is virtually held in the buffer cell of the problem space as simulation continues. This method is capable to investigate the temporal evolution of the propagating pulse. Spectral information can be obtained by Fourier analysis. As an example, the influence of the kerr nonlinearity on the optical pulse propagation in a Lorentz dispersive MOF is demonstrated. The model is also used to simulate the nonlinear interactions between the pump spectral broadening and third harmonic generations in a highly nonlinear fused silica nanowire with good agreement with the generalized nonlinear envelop equation (GNEE) model.     

A novel measurement method for the photosensitivity of fibers

An online measurement method for the photosensitivity of fibers is proposed. This method is simple and useful. Theoretical and experimental studies have been carried out. This method is based on the Mach-Zehnder interferometer (MZI). One arm of the MZI is externally exposed to UV light at 248 nm originating from a KrF excimer laser. Then the output optical spectrum is measured, by some relevant analysis, and the photosensitivity of the fiber can be obtained. The relationship between the refractive index increment of fibers and the exposure time is in accordance with the absorbing model that is brought forward by H. Patrick, which shows that this method has high precision.     

Spectral interference measurement of nonlinear pulse propagation dynamics in optical fibers

Ultrafast pulse shaping and ultrafast pulse spectral phase-retrieval techniques are used in the spectral interference measurement of nonlinear pulse propagation dynamics in dispersion-shifted optical fiber. Nonlinear responses in both amplitude profile and phase profile of the pulses at zero-dispersion wavelength as well as at nonzero-dispersion wavelength are directly measured. A numerical simulation that uses a third-oder-dispersion-included nonlinear Schr?dinger equation gives excellent agreement with the experimental data.     

Simple and highly accurate technique for time delay measurement in optical fibers by free-running laser configuration

A novel and simple technique for the measurement of time delay in the optical fiber by a free-running laser is proposed and demonstrated. The fiber to be measured was spliced to an erbium-doped fiber so as to form a ring-cavity laser. The mode beating frequency of the laser was measured to determine the round-trip time delay. This precise and efficient technique has an accuracy of 10(-8) for a fiber length of 100 km and of 10(-6) for a several-meters-long one.     

Power measurement of noise-initiated Brillouin scattering in optical fibers for sensing applications

We discuss the measurement of noise-initiated Brillouin scattered power in optical fibers and its application to distributed sensing systems. In particular, we consider the use of Brillouin scattering in the nonlinear regime, demonstrating a novel processing technique that compensates for the nonlinear growth of the scattered signals. The signal-to-noise ratio performance of this technique is evaluated, highlighting the importance of the noise contributed by the random statistics of the scattered field and yielding the conditions for optimum system operation.     

Weak mode coupling measurement with EMD-based method in polarization-maintaining fibers

The intensity and position of coupling points in polarization-maintaining fibers (PMFs) caused by force and twist can be effectively detected by Polarization Coupling Measurement (PCM). The sensitivity of detection will decrease due to the movement of scanning Michelson interferometer. To detect the weak coupling point, an EMD-based method is proposed in this paper. The experimental results illustrate that the EMD-based method can suppress the noise and improve the SNR effectively. The DWT method is also performed for a comparative study. The results show that the EMD-based method is effective and applicable for PCM and the coupling point can still be detected when the intensity is as weak as ? 70 dB.     

New method for strength improvement of silica optical fibers

The reliability and the expected lifetime of optical fibers used in telecommunication technologies are closely related to the chemical environment action on the silica network. To ensure the long-term mechanical strength of the optical fibers, a polymer coating was applied onto the fiber surface during fiber fabrication. This external coating is vital to ensure a long optical fiber lifetime. Its protective action includes several functions, such as to protect glass fiber from any external damage, to limit chemical attack, in particular that of water, and finally to ensure fatigue protection and bending insensitivity, especially during handling and in-service installation. Since the mechanical strength of the fiber is controlled by its surface characteristics, we propose a new method for increasing fiber strength.The silica optical fibers used were 125 μm in diameter, with a 62.5 μm thick epoxy-acrylate coating. Fibers were rolled up around two similar cylinders. Using a screw, these cylinders moved away from one another and thus subjected the fibers to stretching. Submitted to this mechanical loading, the distended fibers were plunged into hot water at 65 or 85 °C and aged for several days. Then, the fibers were removed from the water and various weights were suspended on the fiber ends. Thus, the fibers were subjected to a tensile loading in static fatigue for several days. Just before fiber rupture, the fibers were unloaded and subjected to dynamic tensile tests at different velocities.Result analysis proved that the aging in hot water increased the fiber strength. The Weibull's diagram study shows a bimodal dispersion of defects on the fiber surface and the important role of polymer coating.     

Interference method of measuring the extinction coefficient of birefringent optical fibers

The extinction coefficient of a birefringent optical fiber (the ratio between the radiation power output of the polarization mode and the radiation power transferred from this mode to another one) characterizes the capability of a birefringent fiber to retain the polarization state of the radiation. In relatively short birefringent fibers (1–100 m), the extinction coefficient may reach 10⁴–10⁶. Such high values of the extinction coefficient are difficult to measure by standard techniques (excitation of one polarization mode by an incoherent source with subsequent recording of the light intensity at the output of the analyzer). An interference method of measuring the extinction coefficient of birefringent fibers is suggested. It is based on using a coherent source and measuring interference oscillations caused by an additional phase modulation at the input of the fiber. This method does not require precise polarization matching between the laser source and fiber and considerably loosens requirements for the polarizer-analyzer extinction and resolution of the photodetector. As a result, using simple standard components (semiconductor laser, film polarizer, and photodetector), one can measure extinction coefficient as high as 10⁶. The suggested interference method of measuring the extinction coefficient of birefringent fibers receives a theoretical analysis, and experimental data obtained for 2- to 1000-m-long fibers are presented.     

Optical Kerr coefficient measurement at 1.15 μm in single mode optical fibers

We have measured the optical Kerr coefficient n_2B in a SiO₂-GeO₂ birefringent single mode fiber at 1.15 μm. We have observed experimentally a 100% modulation depth with a low pump power of 390 mW launched into a 580 m long single mode optical fiber.     

Photon-pair generation by four-wave mixing in optical fibers

We present a theory to quantify a fundamental limit on correlated photon pairs generated through four-wave mixing inside optical fibers in the presence of spontaneous Raman scattering (SpRS). Our theory is able to explain current experimental data. We show that if correlated photon pairs are generated with polarization orthogonal to the pump the effect of SpRS is significantly reduced over a broad spectral region extending from 5 to 15 THz.