Yao-Tang Chang

Wavelength Division Multiplexing/Spectral Amplitude Coding Applications in Fiber Vibration Sensor Systems

This paper presents a wavelength division multiplexing/spectral amplitude coding system with optical code-division multiple-access, for applications using fiber vibration sensors. The device makes use of fiber Bragg grating (FBG) etching on optical fibers to provide encoding/decoding functionality. According to the orthogonal properties of spectral amplitude coding (SAC) using m-sequence code, the encoding- decoding devices that employ FBG filters provide a considerable reduction in multiple access interference in optical code division multiple access systems. The proposed fiber vibration sensor located between the encoder and optical circulator enables the measurement of multiple points. Experimental results reveal that the proposed sensor detects a variety of vibrational signals.

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.

Performance Analysis of Dual Unipolar/Bipolar Spectral Code in Optical CDMA Systems

This study analyzes and calculates dual unipolar and bipolar coded configurations of spectral-amplitude-coding opticalcode division multiple access (SAC-OCDMA) systems by using simulation methods. The important feature of theSAC-OCDMA systems is that multiple access interference (MAI) can be eliminated by code sequences of a fixed inphasecross-correlation value. This property can be effectively canceled multiple access interference by using balancedetection schemes. This study uses Walsh-Hadamard codes as signature codes for the unipolar and bipolar schemes.The coder and decoder structures are based on optical filters of fiber Bragg gratings (FBGs). The simulation results ofunipolar/bipolar coding structures are first presented by commercial simulation obtained using OptiSystem software.The simulation results show that the bit error rate (BER) through use of the bipolar coding method is superior to theunipolar scheme, especially when the received effect power is large. When the system needs good performance totransmit multimedia data, we can use bipolar scheme in the network. If the users only transmit voice data, the unipolarmethod can be employed. The eye diagram also shows that the bipolar encoding structure exhibits a wider openingthan the unipolar encoding structure. The flexible implementation of codewords assigns and integratable hardwaredesigns for the scheme with FBGs to realize dual coding OCDMA system is proposed.

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.

Improved phase noise performance using orthogonal ternary codes over spectral polarization and amplitude coding networks

This study proposes an improved hybrid scheme of spectral polarization coding SPC and spectral amplitude coding SAC based on a specified orthogonal ternary sequence. In a previous SPC scheme, the entire wavelength was assigned either a vertical or a horizontal state of polarization. However, this study assigns positive, negative, or null chip values to individual wavelengths to create an orthogonal ternary sequence based on the bipolar Walsh-Hadamard matrix. This approach reduces the number of wavelength collisions at the photodetector and hence reduces the phase-induced intensity noise PIIN. Neglecting the effects of shot noise and thermal noise, we consider only PIIN with a degree of polarization P=0. The proposed scheme improves the bit error rate by 40% and 100% over SPC and complementary unipolar SAC schemes. The number of simultaneous active users supported by the hybrid scheme for the worst case P=1 is improved by 41.3% over the complementary unipolar SAC coding scheme for the ideal case P=0.

Packets Buffering Enhancement with Hybrid Coding Labels for Virtual Optical Memory

Abstract For the practical deployment of optical packet switching (OPS) system, realizing all-optical buffering is a critical issue. In this paper, we present a hybrid labelling scheme based on optical code-division multiplexing (OCDM) over generalized multi-protocol label switching (GMPLS) network. The virtual optical memory is implemented by assigning queuing packets with different coded-WDM labels. The proposed hybrid labels combine the advantages of wavelength-division multiplexing (WDM) with spectral-amplitude-coding (SAC) OCDM. Due to the cyclic-shift property of arrayed-waveguide grating (AWG) and maximal-length sequence (M-sequence) codes, blocks of label generating and processing in node organization can be built in low complexity. Furthermore, utilizing hybrid coding technique in the buffering node increases the efficiency of label generating and processing. Derivation of the probability of packet missing is done to quantify the buffering performance of virtual optical memory. Simulation results show that the hybrid-coded labels, as compared to the conventional OCDM labels, are able to buffer the data packets with a relatively low probability of packet missing under similar label length.

Performance analysis of new optical matrices for constructing two-dimensional temporal/spatial optical code-division multiple-access networks

This study presents designs for developing two-dimensional optical matrices exhibiting low cross correlation and excellent orthogonality. The key scheme is to use original one-dimensional temporal codes and a particular mapping technique. A two-dimensional temporal/spatial optical code-division multiple-access network using the proposed optical matrices was also constructed. This study subsequently analyzed the effect of multiuser interference on code performance. The analysis result reveals that some families of optical codes applied to the network theoretically provided a favorable code performance level.

Waveguide-Grating-Routers-Based Realization of Time-Spreading and Wavelength-Group-Hopping over Fiber-to-the-Home Networks

Exploiting the inherent cyclic and periodic free-spectral- range (FSR) properties of arrayed-waveguide grating (AWG) routers, the time-spreading and free-spectral-range (FSR) group hopping code, which is embedded by maximum length sequences (called TS/GH embedded M-sequence code) is configured over a fiber-to-the-home (FTTH) network. For constructing the proposed code, we use the same prime code for generating the time code (time-spreading code) and the spectral domain code (group hopping code). Therefore it is referred to as a two-dimensional (2-D) optical code. Importantly, for the proposed broadband light source (BLS), the total number of available wavelengths is partitioned into G different groups according to the length of the M-sequence code. Every group is referred to as a hopping pattern and characterized by the FSR interval of the AWG router. Improving the prime-hop code (PHC) and the modified prime-hop code (MPHC) with cascading one additional AWG router, the cardinality of the proposed scheme is significantly increased by a factor of 15 under the optimum arrangement for a group hopping number of G=7. Moreover, the correlation property and bit error rate (BER) of proposed scheme is evaluated and the result reveals an improvement of the BER compared to MPHC and PHC.