The authors present a new method for determining the optical properties of arbitrary refractive index elliptical core fibres. The method applies the elliptic cylindrical coordinate system to Maxwell's equations and appropriately, using Fourier Transforms, operated on an elliptical core optical fibre waveguide, derives a flexible algorithm, which can be used to determine the optical properties of elliptical fibre waveguides. By dividing the fibre into a series of uniform consecutive thin dielectric layers transversely across the elliptical cross section with suitable transforming functions representing voltage and current themselves based on the electromagnetic field components, leads to transverse transmission line equations. The resonance frequencies of the cascaded matrices determine the mode propagation constants. The analysis leads to a numerical algorithm for calculating the exact modes of propagation constants. The method is analytically exact and computationally accurate, leading to algorithmic implementation, without making use of Mathieu functions which are solutions for step index waveguide. The advantage of this work is also the fact that it can be applied to arbitrary refractive index profiles. They present results of modal diagrams for various fibre ellipticities and also apply this method to determine the birefringence of graded index profile fibres and mode cut-off frequencies.

The growing interest in underwater explorations has stimulated considerable interest in advancing the enabling technologies of underwater wireless communication (UWC) systems. The study presents the design and implementation techniques of a short-range unidirectional UWC system which uses optical camera communication (OCC) principles. OCC systems have light emitting diodes at the transmitter, with the receiver being a camera. Overall system design considerations, synchronisation and frame selection, and a novel spatial position-based image processing algorithm to decode data from frames are discussed. Also, the optimisation techniques used in the image processing algorithm are also elaborated. Importance of few of key features of an OCC system, namely camera quality, transmission distance and the threshold value used for image binarisation are demonstrated through numerical results using simulations via synthetically generated images. Further, the bit error rate (BER) performance of the system is evaluated using the experimental proof of concept setup in clear water, muddy water and under turbulence conditions. Overall BER performance in the order of within the communication distance of 1 m is observed, and it shows that the proposed system design and algorithms can be used to realise an UWC link for short-range applications successfully.

This study has given the investigation for achievable net coding gain (NCG) of optical forward error correction (FEC) coding scheme with convolutional code to control the received sensitivity following a required signal-to-noise ratio in the communication channel. The achievable NCG is obtained from the difference between the upper bound NCG and the power penalty of the optical exclusive-OR (XOR) gate, which is based on a four-wave mixing in highly non-linear fibre. The upper bound NCG was analytically derived by calculating error probability of optimal convolutional code, and the power penalty was numerically derived by comparing bit-error rates between with and without the optical FEC coding. To confirm the feasibility for achieving the highest NCG, the optimal operating condition of the optical XOR gate is experimentally evaluated to minimise their power penalty. A 0.5 dB power penalty was obtained at under the optimised condition with 2²³−1 pseudo-random binary sequence differential phase-shift keying-modulated return to zero signal at 10 Gbps.

In this study, the authors propose a decentralised cooperative transmission in a multiple-input–single-output visible light communication (VLC) system to deal with the co-channel interference (CCI) converting the interference between adjacent light-emitting diode (LED) lamps into the desired signal and to overcome link blockage recovering the data when the obstruction is not severe. VLC uses the LED lamps already installed for illumination and can alleviate the growing data traffic in the existing wireless communications without interfering. However, CCI and link blockage must be considered to improve performance. The proposed scheme decentralises a cooperative transmission employing a randomised coding rule since each LED sends a random linear combination of the columns of a deterministic code matrix whose coefficients are independent and identically distributed and the decoding is performed by ignoring the number of cooperative LEDs that is unknown and time varying at the receiver. Through computer simulations, the proposed scheme outperforms a centralised scheme when the random coefficients are real and positive. Although the performance deteriorates as decreasing the received links, it does not require to exchange information among the LEDs before transmission or receive all data before decoding as in a centralised scheme.

The concept and analysis of a nano-scale multifunctional logic gate based on graphene/hexagonal boron nitride (h-BN) plasmonic waveguides at a wavelength of 7.5 µm are presented. By using graphene as a metamaterial with outstanding electro-optical properties, various logical operations including AND, OR, and XOR are implemented. The proposed multifunctional structure supports surface plasmons (SPs) whose dispersion properties can be controlled by applying an electrical field to graphene. The effects of the incident polarisation and the substrate of graphene on the transmission of SPs are investigated. Simulations by finite difference time domain method show that the extinction ratios for the presented logical operations are higher than 15 dB. Also, the structure has a compact footprint of 1.12 µm² which is suitable for using in integrated photonic circuits. This provides a path for the development of novel nano-scale practical on-chip applications such as plasmonic memory devices.

This study presents a fuzzy neural network based non-linear equaliser to diminish the non-linearities in a coherent optical orthogonal frequency division multiplexing (CO-OFDM) system. The numerical results show that the proposed technique based CO-OFDM system outperforms the CO-OFDM system without non-linear equaliser by 5 and 7.5% EVM performance, and 2.36 and 4.87 dB Q-factor performance after 1000 km transmission and −3 dBm input launch power at a bit rate of 40 and 80 Gbps, respectively. Moreover, it has been generally accepted in statistics that the rank-based Wilcoxon methodology provide more robust results in a contradiction of outliers. Therefore, the aim of this study is to analyse fuzzy neural network based non-linear equaliser and compare the results with that of Wilcoxon approach fuzzy neural network based non-linear equaliser.