A novel method with M-sequence code in optical code-division multiple-access (OCDMA) network, called pseudo-random number mapping/coding (PRNMC) algorithm, includes chaos equation, HCC/EHCC algorithm, two mapping methods. An approximately symmetric scheme is used to transmit and receive the secret key in private channel from encoder to decoder. By combining those algorithms appropriately, the security of network is increased and reduces the probability of eavesdropping of codeword.

One approach for designing the one-coincidence sequence (OCS) low-density parity-check (LDPC) codes of large girth is investigated. These OCS-LDPC codes are quasi-cyclic, and their parity-check matrices are composed of circulant permutation matrices. Generally, the cycle structures in these codes are determined by the shift values of circulant permutation matrices, and the existence of cycles in the corresponding Tanner graph is governed by certain cycle-governing equations (CGEs). Therefore, finding the proper shift values is the key point to increase the girth of these codes. In this paper, we provide an effective method to systematically find out the CGEs for these codes of girth 6, 8, and 10, respectively. Then, one less computation-intensive algorithm is used to generate the proper shift values for constructing the OCS-LDPC codes of large girth. Simulation results show that significant gains in signal-to-noise ratio over an additive white-Gaussian noise channel can be achieved by increasing the girth of the OCS-LDPC codes.

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.

A new two-dimensional frequency/spatial code for spectral-amplitude coding a optical code-division multiple-access system is proposed. The corresponding coder/decoder pairs are based on the tunable fiber-Bragg gratings cooperating with optical splitters/combiners, and multiple-access interference can be eliminated through the proposed decoding mechanism. For the performance analysis, the effects of phase-induced intensity noise, shot noise, and thermal noise are considered simultaneously. Bit-error rate (BER) performance is compared with that of the former system using M-matrix codes. It is shown that the system using these new code matrices not only maintains most advantages of the former one, but also allows larger number of active users under a given BER

Two codeword families and the corresponding encoder/decoder schemes are present for spatial/frequency optical code-division multiple-access communications. These 2-D codewords have multiple weights per row and can be encoded/decoded via compact hardware. With the proposed decoding mechanism, the intended user will reject interfering users and multiple-access interference is fully eliminated. In addition, the power of the same wavelength contributed by all interfering codewords is split and detected by distinct photodiodes in the decoder. Thus the performance degradation due to the beat noise arising in the photodetecting process is improved, as compared with the traditional 1-D coding scheme, and a larger number of active users is supported under a given bit-error rate.

An optical spectral coding technique in fiber-grating-based optical code-division multiple-access (OCDMA) system has been investigated in our previous work. In this thesis, the same architecture is set up to investigate the reduction of multiple-access interference caused by the overlapping wavelength from undesired users. Furthermore, the reduction of optical beat interference (OBI) induced by those adjacent grating chips is examined. The reduction of multiple access interference (MAI) and OBI induced by those adjacent grating chips. FBG written as M-sequence and Walsh codes is proposed for such MAI and OBI cancellation in spectrally balanced photo-detectors. Theoretically, M-sequence and Walsh codes are characterized by nearly the same number of "on" chips (i.e., logic "1" chips) and "off" chips (i.e., logic "0" chips). It is seen that the differential decoding scheme characterizes a better performance on eliminating the MAI and OBI problem by mutual cancellation in reflected and transmitted branches of wavelength chips. Furthermore, we propose that the wavelength interleaving allocation method can result in a guard band to suppress OBI. It is shown that SIR has 13 dB improvement with the proposed scheme.

A fiber Bragg grating (FBG) encoder/decoder scheme based on correlation subtractions of nearly orthogonal M-sequence codes is presented. With proper coder design, a receiver can reject interfering users and obtain quasi-orthogonality between optical code-division multiple-access (CDMA) users in the network. However, optical CDMA networks may be degraded by multiple-access interference (MAI) due to nonflattened incoherent sources and nonideal FBG coders. A compensating module is therefore proposed to compensate for such MAI effects. As a result, the MAI effects induced by nonideal FBG coders can be perfectly eliminated by the compensating module. With spectral width reduction on the incoherent source, the scheme can partly compensate the MAI effects induced by nonflattened sources and further reduce the average error probability in the system performance.