In this study, the performance of optical code-division-multiple-access (OCDMA) systems using 2D optical codes, taking into account an optical channel in local area network context is investigated. The authors demonstrate that one can enhance the 3-dB multi-mode fibre baseband bandwidth up to 4 GHz by exciting only two mode groups with the optimal axial launching. It has been demonstrated, that the OCDMA system performance can achieve a very low bit-error-rates in the range of −9 dBm. Furthermore, a large number of simultaneous users can be supported. In the authors’ treatment, the effect of both multiple access interference and modal dispersion are considered. Nonetheless, an OCDMA successive interference cancellation receiver is used to foster a better system performance.

In this study, the authors present a numerical study of the dynamics of a non-linear optoelectronic oscillator (OEO) based on the resonant tunnelling diode (RTD) oscillator incorporating a photo-detector and coupled to a non-linear electrical circuit. In the first part, it is found that the RTD-OEO oscillator presents periodic and quasiperiodic behaviours depending on the values of the parameters of a pulse-like optical signal. In the second part where the RTD-OEO is coupled to the Van der Pol oscillator, the dynamics present a variety of states including bursting, relaxation and sinusoidal oscillations.

Developing a perfect absorber based on metamaterials (MTMs) is a promising technique towards improving the efficiency of solar photovoltaic cells. In this study, a novel MTM-based perfect absorber (MPA) is proposed for solar cell applications, which exhibits an excellent single-band with high absorption rate of 99.7% in visible frequency regime (resonance frequency of 614.4 THz) with an outstanding absorption bandwidth of 15.5%. The proposed design presents a high symmetry flexibility which makes it easy to fabricate. Besides, the simulation results for the defined different incident angles and different polarisation (transverse electric and transverse magnetic) confirm the quality of the proposed design by showing how insensitive it is to both the defined incident angles (normal and oblique incident) and different polarisation angles of electromagnetic wave. The parametric study on dielectric spacer shows the tunability characteristic of an intended MPA structure. The proposed MPA design is a good candidate for fabrication of high-efficiency solar cell operating in a visible frequency range.

Holographic lithography has been widely used to the realisation of complex photonic structures such as photonic crystal and quasi-photonic crystals. Dual-beam multi-exposure holographic technique was adopted for the fabrication of 18-fold and 36-fold sub-microscopic rotational symmetric structures; the fabricated photonic quasi-crystals examined by laser diffraction pattern, optical and scanning electron microscopes. Here, the authors have fabricated photonic quasi-crystals in photoresist and the structure was transformed into metal, the transferred structure in metal could act as a substrate/or back reflector for the thin film solar cell. Further work on concentration of solar light by photonic quasi-crystals is progressing.

Variable weight optical code division multiple access system (VW-OCDMA) is developed to provide service differentiation in optical metro networks where different applications demand for different quality of services. In VW-OCDMA, different number of wavelengths carries the data for different services. Hence, the fibre impairment effects vary for different services. In this study, the performance of a VW-OCDMA is analysed under the impact of fibre impairments including chromatic dispersion, self-phase modulation, four wave mixing and stimulated Brillouin scattering. It is shown that how higher weights which are supposed to deliver higher quality are more affected by fibre impairments. At last, the experimental results of three users with different weights are demonstrated.

A suitable decoding technique for spectral amplitude coding optical code division multiple access (SAC-OCDMA)-based secured distributed vibration sensor is investigated. The study is carried out to identify the most appropriate techniques for receiving the transmitted vibration signal in SAC-OCDMA-based system. The techniques which are direct decoding, complementary and logical AND decoding are compared based on the level of crosstalk, number of components used and supported transmission distance in multiplexed vibration sensing using both simulation and experiment. The results show direct decoding capable of supporting 55 km unlike the other two which are 44 and 38 km, respectively. Aside that, direct decoding techniques could be implemented with less number of components and has optimal signal-to-noise ratio while still preventing the system again the ‘man in the middle’ attack.