Hsu-Chih Cheng

The synthesis of multiple parameters of arbitrary FBGs via a genetic algorithm and two thermally modulated intensity spectra

This paper describes the use of a genetic algorithm and two thermally modulated fiber Bragg grating (FBG) reflection intensity spectra to perform the inverse extraction of multiple physical parameters of arbitrary FBGs, including the grating period, grating position, grating length, chirped direction, and refractive-index modulation. The developed numerical approach is applied to synthesize the parameters of uniform and chirped FBGs. The experimental results confirm the ability of the proposed method to recover the grating period, grating length, grating position, refractive-index modulation depth, and apodize factor of a 10-mm-length uniform FBG. The proposed method is suitable for fiber communication applications and smart structure-monitoring systems.

Using a Fiber Loop and Fiber Bragg Grating as a Fiber Optic Sensor to Simultaneously Measure Temperature and Displacement

This study integrated a fiber loop manufactured by using commercial fiber (SMF-28, Corning) and a fiber Bragg grating (FBG) to form a fiber optic sensor that could simultaneously measure displacement and temperature. The fiber loop was placed in a thermoelectric cooling module with FBG affixed to the module, and, consequently, the center wavelength displacement of FBG was limited by only the effects of temperature change. Displacement and temperature were determined by measuring changes in the transmission of optical power and shifts in Bragg wavelength. This study provides a simple and economical method to measure displacement and temperature simultaneously.

The Enhanced Locating Performance of an Integrated Cross-Correlation and Genetic Algorithm for Radio Monitoring Systems

The rapid development of wireless broadband communication technology has affected the location accuracy of worldwide radio monitoring stations that employ time-difference-of-arrival (TDOA) location technology. In this study, TDOA-based location technology was implemented in Taiwan for the first time according to International Telecommunications Union Radiocommunication (ITU-R) recommendations regarding monitoring and location applications. To improve location accuracy, various scenarios, such as a three-dimensional environment (considering an unequal locating antenna configuration), were investigated. Subsequently, the proposed integrated cross-correlation and genetic algorithm was evaluated in the metropolitan area of Tainan. The results indicated that the location accuracy at a circular error probability of 50% was less than 60 m when a multipath effect was present in the area. Moreover, compared with hyperbolic algorithms that have been applied in conventional TDOA-based location systems, the proposed algorithm yielded 17-fold and 19-fold improvements in the mean difference when the location position of the interference station was favorable and unfavorable, respectively. Hence, the various forms of radio interference, such as low transmission power, burst and weak signals, and metropolitan interference, was proved to be easily identified, located, and removed.

Adaptive modified time-spreading and wavelength-group-hopping embedded M-sequence code for improved confidentiality over synchronous networks

An adaptive modified two-dimensional time-spreading/wavelength-group-hopping embedded M-sequence code (TS/WGH embedded M-sequence code) is proposed for enhancing the cardinality, confidentiality, and bit error rate (BER) of synchronous networks. The proposed arrayed-waveguide-grating (AWG)-based modified TS/WGH embedded M-sequence encoder/decoder (codecs) is constructed by using a fine AWG to generate an M-sequence code pattern and then using multiple-coarse AWGs to spread this pattern in the wavelength domain. The signals produced by the coarse AWGs are then spread in the time domain using optical delay lines. In addition, an algorithm based on an anticipative-warning-time mechanism and a degree of weighted load balance (DWLB) policy is proposed for changing the signature address code word of each user on a sufficiently frequent basis in order to thwart synchronous-network attacks by eavesdroppers. Overall, the simulation results show that, compared to conventional two-dimensional prime-hop code (PHC) and modified PHC and previous TS/group-hopping embedded M-sequence code, the proposed adaptive modified TS/WGH embedded M-sequence code proposed in this study yields an effective reduction in the multiple-access interference and BER while simultaneously improving the degree of confidentiality.

Reconstruction of chirped fiber Bragg grating parameters and phase spectrum using two thermally modulated intensity spectra and a genetic algorithm

This study presents a synthesis method for reconstructing the multiple parameters such as grating position, length, period profile, refractive index modulation, and phase response of a chirped fiber Bragg grating (FBG) and its phase spectrum using two thermally modulated reflection intensity spectra and a genetic algorithm. In the proposed approach, the FBG parameters are determined using the genetic algorithm and are then used to reconstruct the phase response. The advantages of the proposed method include its simplicity, low cost, and nondestructive nature. Furthermore, the proposed method does not require a prior knowledge of the sign of the chirp of the grating period distribution of FBGs.

Group-delay-based phase-shifting method for Fourier domain optical coherence tomography

Frequency-domain optical coherence tomography (FD-OCT) has the advantages of an improved sensitivity and a reduced acquisition time since it enables cross-sectional images of the sample of interest to be obtained using a broadband source or a swept source. The phase-shifting method can always be applied to reduce the additional noise within FD-OCT and provide accurate signal processing. We present a phase-shifting method in which a parallel diffraction grating pair is inserted into the reference arm of the OCT system. The gratings separate the spectrum of the illuminating light and stretch the optical pulse in time thereby producing a linear group delay between the adjacent wavelengths in the superluminescent diode light source. The simulation results show that the proposed group-delay-based phase-shifting method improves the precision of the sample parameters extracted using the FD-OCT procedure compared to those obtained using traditional techniques such as the 0/4 phase-shifting method.

Numerical investigation on arbitrary strain distribution sensing with fiber Bragg grating-based Sagnac interferometer and genetic algorithm

This study presents a numerical investigation into a novel approach for the inverse measurement of arbitrary strain distributions using a genetic algorithm (GA) and a fiber-Bragg-grating-based Sagnac interferometer. In the proposed method, a single uniform fiber Bragg grating (FBG) is bonded to the structure of interest such that it encounters the arbitrary strain field. The arbitrary strain distribution is then determined inversely from the transmission intensity spectrum using a GA population-based optimization process. The major advantage of the proposed approach is its use of a single, uniform FBG to sense arbitrary strain distributions. The approach provides a low-cost and computationally efficient means of detecting strain distributions in many smart-structure monitoring applications.

Electric and magnetic properties of Al65Cu20(Fe1-xMnx)15 quasi-crystals with x=0.0, 0.2, 0.4 and 0.6

The authors have prepared the alloys Al65Cu20(Fe1-xMnx)15 with x=0.0, 0.2, 0.4 and 0.6 by the liquid-quenching method. The alloys with x=0.0 and 0.6 are examined by the transmission electron microscopy. Their electron diffraction patterns demonstrate fivefold, threefold and twofold symmetries of the typical icosahedral symmetries of quasi-crystals. The X-ray diffraction patterns of the samples with x=0.0, 0.2, 0.4 and 0.6 can be indexed with six independent Miller indices of the icosahedral structure of quasi-crystals. Thus they can determine the quasi-lattice constant, which was found to increase with increase in the manganese concentration. The differential thermal analysis measurements show that the icosahedral quasi-crystals Al65Cu20(Fe1-xMnx)15 with x=0.0, 0.2, 0.4 and 0.6 are in thermodynamically good stable phases. The room-temperature resistivity of the samples are in the range 15.47-30.93 mu Omega m, which increases with increase in the manganese concentration. The very high resistivities may be caused by the high density of distorted icosahedral structure defects and the possible s-d resonant scattering. The inversed susceptibility versus temperature for x=0.4 and 0.6 can fit the Curie-Weiss formula. The local magnetic moments are 1.64 mu B and 1.27 mu B per Mn atom for samples with x=0.4 and 0.6, respectively. In contrast the samples with x=0.0 and 0.2 do not display a Curie-Weiss-like behaviour.