Optical Fibre Communication Feature Analysis and Small Sample Fault Diagnosis Based on VMD-FE and Fuzzy Clustering

To solve the problems of a few optical fibre line fault samples and the inefficiency of manual communication optical fibre fault diagnosis,this paper proposes a communication optical fibre fault diagnosis model based on variational modal decomposition(VMD),fuzzy entropy(FE)and fuzzy clustering(FC).Firstly,based on the OTDR curve data collected in the field,VMD is used to extract the different modal components(IMF)of the original signal and calculate the fuzzy entropy(FE)values of different components to characterize the subtle differences between them.The fuzzy entropy of each curve is used as the feature vector,which in turn constructs the communication optical fibre feature vector matrix,and the fuzzy clustering algorithm is used to achieve fault diagnosis of faulty optical fibre.The VMD-FE combination can extract subtle differences in features,and the fuzzy clustering algorithm does not require sample training.The experimental results show that the model in this paper has high accuracy and is relevant to the maintenance of communication optical fibre when compared with existing feature extraction models and traditional machine learning models.

Fibre Optic Protection System for Concrete Structures

The design concepts, modelling and implementation of various fibre optic sensor protection systems for development in concrete structures were investigated. Design concepts and on-site requirements for surface-mounted and embedded optical fibre sensor in concrete were addressed. Finite element （FE） modelling of selected sensor protection systems in strain-transfer efficiency from the structure to the sensing region was also studied. And experimental validation of specified sensor protection system was reported. Results obtained indicate that the protection system for the sensors performs adequately in concrete environment and there is very good correlation between results obtained by the protected fibre optic sensors and conventional electrical resistance strain gauges.

Construction monitoring of lock head base plate using distributed optical fibre sensing technique

The concrete hydration heat release process of the base plate is monitored using Roman optical time domain reflectometry（ROTDR） sensing sensors. The monitoring data shows that the internal maximum temperature of the base plate is about 54 ℃ after the concrete was cured for 120 h. The fiber Bragg grating （FBG） temperature sensors are adopted to measure the surface temperature of the concrete and the temperature results are used to compensate the data measured by the pulse-prepump Brillouin optical time-domain analyzer （PPP-BOTDA） to obtain the real concrete surface strain of the base plate. The monitoring data is analyzed to obtain a clear understanding of the strain state of the base plate under the effect of concrete hydration heat release. The monitoring results demonstrate the potential of distributed optical fibre sensing techniques as a powerful tool in real-time construction monitoring, and also provide an important insight into the design, construction and maintenance of large hydraulic structures.

Design and analysis of a kind of large flattened mode optical fibre

In this paper, a refractive index profile design enabling us to obtain a flat modal field around the fibre centre is investigated. The theoretical approach for designing such multilayer large flattened mode （LFM） optical fibres is presented. A comparison is made between the properties of a three-layer LFM structure and a standard step-index profile with the same core size. The obtained results indicate that the effective area of the LFM fibre is about twice as large as that of the standard step-index fibre, but the LFM fibre has less effective ability to filter out the higher order modes than the standard step-index fibre with the same bending radius.

Generation of W_n state with three atoms trapped in two remote cavities coupled by an optical fibre

We propose two schemes for the generation of the Wn state with three atoms separately trapped in two distant cavities coupled by an optical fibre. One is implemented by controlling the interaction time, the other is implemented via the adiabatic passage. The influence of various decoherence processes, such as spontaneous emission of the utoma and photon leakages of the cavities and the optical fibre, on the fidelity is also investigated. It is found that the Wn state can be generated with high fidelity even when these decoherence processes are present.

Electrical crosstalk-coupling measurement and analysis for digital closed loop fibre optic gyro

The phase modulation and the closed-loop controller can generate electrical crosstalk-coupling in digital closed- loop fibre optic gyro. Four electrical cross-coupling paths are verified by the open-loop testing approach. It is found the variation of ramp amplitude will lead to the alternation of gyro bias. The amplitude and the phase parameters of the electrical crosstalk signal are measured by lock-in amplifier, and the variation of gyro bias is confirmed to be caused by the alternation of phase according to the amplitude of the ramp. A digital closed-loop fibre optic gyro electrical crosstalk-coupling model is built by approximating the electrical cross-coupling paths as a proportion and integration segment. The results of simulation and experiment show that the modulation signal electrical crosstalk-coupling can cause the dead zone of the gyro when a small angular velocity is inputted, and it could also lead to a periodic vibration of the bias error of the gyro when a large angular velocity is inputted.

Stimulated supercontinuum-radiation generation of carbon disulfide by all-trans-β-carotene fluorescence enhancement effect in liquid core optical fibre

We demonstrate stimulated supercontinuum-radiation of carbon disulfide （CS2） influenced by biological molecules all-trans-stimulated Raman scattering, stimulated Brillouin scattering, all-trans-β-carotene, liquid core optical fibre-carotene in liquid core optical fibre （LCOF）. By virtue of the broad fluorescence characteristics and large third-order optical nonlinearities of all-trans-β-carotene, the high-order Stokes lines of stimulated Raman scattering （SRS） and the multi-order Stokes lines of stimulated Brillouin scattering （SBS） excitated by SRS are observed at low input-laser energies. The results indicate that the fluorescence not only enhances the SRS, but also the SBS. These Stokes lines generate the SRS-SBS supercontinuum radiation （RBSR）. A flat-amplitude bandwidth of 110 nm from 515 nm to 625 nm is observed when a frequency-doubled Nd：YAG laser at 532 nm with an energy of 0.86 mJ is used. This result is expected to be useful for the multi-wavelength fibre laser.

Space radiation effect on fibre optical gyroscope control circuit and compensation algorithm

The process of a γ-irradiation experiment of fibre optical gyroscope （FOG） control circuit was described, in which it is demonstrated that the FOG control circuit, except for D/A converter, could endure the dose of 10krad with the protection of cabin material. The distortion and drift in D/A converter due to radiation, which affect the performance of FOG seriously, was indicated based on the elemental analysis. Finally, a compensation network based on adaptive neuro-fuzzy inference system is proposed and its function is verified by simulation.

Signal Processing for Fibre-optic Distributed Sensing Techniques Employing Brillouin Scattering

As fibre optic distributed scattering sensing systems are providing innovative solutions for the monitoring of large structures,Brillouin-based distributed scattering sensing techniques represent a new physical approach for structures health monitoring,which seems extremely promising and is receiving most attentions.This paper comprehensively presents some methods of signal interrogation for fibre optic Brillouin-based distributed scattering sensing technology,especially establishes an accurate Pseudo-Voigt model of Brillouin gain spectrum and gives some results on spectrum analysis and data processing.

Comprehensive research on self phase modulation based optical delay systems

This paper comprehensively investigates the properties of self phase modulation based optical delay systems consisting of dispersion compensation fibre and highly nonlinear fibres. It researches into the impacts of power level launched into highly nonlinear fibres, conversion wavelength, dispersion slope, modulation format and optical filter bandwidth on the overall performance of optical delay systems. The results reveal that, if the power launched into highly nonlinear fibres is fixed, the time delay generally varies linearly with the conversion wavelength, but jumps intermittently at some conversion wavelengths. However, the time delay varies semi-periodically with the power launched into highly nonlinear fibres. The dispersion slope of highly nonlinear fibres has significant influence on the time delay, especially for the negative dispersion slope. The time delay differs with modulation formats due to the different combined interaction of nonlinearity and dispersion in fibres. The bandwidth of the optical filters also greatly affects the time delay because it determines the bandwidth of the passed signal in the self phase modulation based time delay systems. The output signal quality of the overall time delay systems depends on the conversion wavelength and input power level. The optimisation of the power level and conversion wavelength to provide the best output signal quality is made at the end of this paper.

A STUDY OF INTERFACES OF COMPOSITES BY MEANS OF OPTICAL FIBRE SENSING TECHNTIQUE

Fibre stress of glass fibre reinforced polymeric copmosites on load is determined by using optical fibre as model fiber and by means of laser interference method. In addition, the origination of fibre stress during moulding process of composites and the relation between fiber stress of loaded composites and external stress are examined. The experiments show that fibre stress is related to molecular structure of inter facial materials and structure of inter facial layers. When stress is transferred from matrix to fibre, each inter facial layer has different stress gradient and deformability. This property can be characterized by introducing an inter facial stress transfer coefficient k to the two-phase model.

Effect of structure random disturbances on characterizations of microstructured optical fibres

A method is presented to analyse the effect of structure random disturbances on the confinement loss and the chromatic dispersion characterizations of microstructured optical fibres, which combines multipole methods with the random statistics process. Some useful results to the fabrication of microstructured optical fibres have been obtained.

Propagation of bright femtosecond pulses in a nonlinear optical fibre with the third-and fourth-order dispersions

We solve the generalized nonlinear Schr6dinger equation describing the propagation of femtosecond pulses in a nonlinear optical fibre with higher-order dispersions by using the direct approach to perturbation for bright solitons, and discuss the combined effects of the third- and fourth-order dispersions on velocity, temporal intensity distribution and peak intensity of femtosecond pulses. It is noticeable that the combined effects of the third- and fourth-order dispersions on an initial propagated soliton can partially compensate each other, which seems to be significant for the stability controlling of soliton propagation features.

High-speed chaotic communication using an optical fibre ring as a key

A chaotic communication scheme with a fibre ring inserted in the optical ~eedback of the transmitter laser as an additional key is proposed under anticipating synchronization. The numerical results show that the key can enhance the communication security effectively. It is theoretically safe for the communication scheme to transmit messages with a frequency beyond the relaxation oscllation frequency.

Quantum logic operations on two distant atoms trapped in two optical-fibre-connected cavities

Based on the coupling of two distant three-level atoms in two separate optical cavities connected with two optical fibres, schemes on the generation of several two-qubit logic gates are discussed under the conditions of △ = δ- 2v cos πk/2 〉〉 g/2 and v-g. Discussion and analysis of the fidelity, gate time and experimental setups show that our schemes are feasible with current optical cavity, atomic trap and optical fibre techniques. Moreover, the atom-cavityfibre coupling can be used to generate an N-qubit nonlocal entanglement and transfer quantum information among N distant atoms by arranging N atom cavity assemblages in a line and connecting each two adjacent cavities with two optical fibres.

Photoluminescence of an Yb^(3+)/Al^(3+)-codoped microstructured optical fibre

An Yba＋/Al3＋-codoped microstructured optical fibre is prepared based on photonic crystal fibre technology. The characteristic spectra of preforms and fibres are experimentally investigated. The results show that under a 971 nm excitation, besides the known infrared fluorescence luminescence around 1050 nm, a blue luminescence peak at 486 nm is obtained. Moreover, an unexpected emission peak at 730 nm is also observed. The photoluminescence mechanism of an Yba＋/Al3＋-codoped microstructured optical fibre is discussed. The emission peak at 486 nm is attributed to the cooperative upconversion resulting from pairs of Yb3＋ ions, and the emission peak around 730 nm is ascribed to the stimulated Raman scattering because of nonlinear effects of microstructured optical fibre. The Yba＋/Al3＋-codoped microstructured optical fibre is promising for varieties of applications from laser printing and optical recording to cancer treatments, such as photodynamic therapy.

Numerical Simulation of Radial and Angular Distribution of γ-Ray's Energy Deposition in Scintillation Optical Fibre

Angular and radial distributions of the energy deposition of γ-ray radiation in scintillation optical fibres are simulated and analysed using the Geant4 system. The results show a linear relation between the energy deposition and the radius of the fibres. The deposition is roughly inversely proportional to sinθ with θ the incident angle relative to the fibre axis. The results could provide corrections to the measurements of the scintillation fibres used in monitoring the γ-ray radiation.

Phenomena of optic-bound effect on fibre optic gyro

The optic-bound effect on fibre optic gyro （FOG） precision is analysed theoretically, and formulas describing the change of FOG light power under the action of optic-bound effect are given. It is confirmed that optic-bound effect is a main instantaneous non-reciprocity effect of FOG in addition to the Sagnac effect and can lead to a dynamic error of FOG in practical environments. An approach to suppressing or eliminating the error due to the optic-bound effect is presented and verified experimentally. The result shows that the approach is valid and the precision of FOG is improved observably.

Design of a Reflective Intensity Optical Fibre Bundle Displacement Sensor

Optical fibre sensor has the advantages of small size,light weight,anti⁃electromagnetic interference,and high measurement accuracy,which has important applications in research and industrial production.To design an optical fibre displacement sensor(OFBDS)with simple structure and high measurement accuracy,the unified model of the commonly used OFBDS structures was proposed and the feasibility of the intensity⁃modulation of multi⁃structural optical fibre bundles was analysed based on the arrangement characteristics of the fibre bundle end⁃face.The intensity⁃modulation characteristic of different fibre bundles was analysed,and the single coil coaxial fibre bundle was chosen as the fibre probe in this study.The sensor hardware system was designed.Lastly,the calibration experiment,temperature interference experiment,changes of measured plane surface area,and the dynamic experiment were conducted.Results showed that the sensor linear measurement range was about 3 mm,and the sensor system had excellent static and dynamic characteristics.

Joint nonlinearity and chromatic dispersion pre-compensation for coherent optical orthogonal frequency-division multiplexing systems

This paper introduces a joint nonlinearity and chromatic dispersion pre-compensation method for coherent optical orthogonal frequency-division multiplexing systems. The research results show that this method can reduce the walk- off effect and can therefore equalize the nonlinear impairments effectively. Compared with the only other existing nonlinearity pre-compensation method, the joint nonlinearity and chromatic dispersion pre-compensation method is not only suitable for low-dispersion optical orthogonal frequency-division multiplexing system, but also effective for high- dispersion optical orthogonal frequency-division multiplexing transmission system with higher input power but without optical dispersion compensation. The suggested solution does not increase computation complexity compared with only nonlinearity pre-compensation method. For 40 Gbit/s coherent optical orthogonal frequency-division multiplexing 20 × 80 km standard single-mode fibre system, the suggested method can improve the nonlinear threshold （for Q 〉 10 dB） about 2.7, 1.2 and 1.0 dB, and the maximum Q factor about 1.2, 0.4 and 0.3 dB, for 2, 8 and 16 ps/（nm.km） dispersion coefficients.