Estimating and mitigating the phase noise (PHN) in orthogonal frequency-division multiplexing (OFDM) greatly improves the system performance. Recently, a PHN mitigation method using the best match trajectory (BMT) method was proposed, and it outperformed the conventional inter-carrier interference (ICI) compensation methods in both bit error rate and computational complexity. The authors propose a modified version of the BMT method in order to further improve the computational performance when mitigating the PHN in coherent optical OFDM systems. Their simulations show that the proposed linear PHN trajectory achieves better PHN estimation than the conventional PHN trajectory, and the proposed scheme reduces the computational complexity compared with the BMT method.

Optically induced electron–hole plasmas in silicon are used to perform radiation pattern tuning. The antenna is a slot loaded microstrip patch and the effect of illumination is shown to produce beam switching in the radiation patterns of certain modes while other modes are left unaffected. The structure is specifically designed to make the best use of currently available miniature laser sources to form a compact tunable package. Modelled and measured results for tuning of the radiation patterns and frequency response are presented. The effect of the losses incurred by the plasma along with the losses in the optically transparent ground plane are quantified in both simulation and measurement. This forms the basis for designing other types of optically tunable miniature antennas based on the structure presented.

An existing ternary pulse-coding scheme for bandpass signals, whereby a timing code specifies positive and negative rectangular pulses as well as a third zero state formed by skipping pulses, is adapted to transmission and reconstruction of narrowband RF signals over inexpensive fibre-optic links. The main feature of this technique is that reconstruction of the narrowband analog signal is particularly simple, requiring only a bandpass filter. Simulations using a complex band-limited Gaussian baseband input to represent a 20-MHz LTE-A signal establish the ideal theoretical performance, which is then compared to experimental results obtained by transmission on a 1.6-GHz carrier over a fibre-optic link consisting of an electro-absorption modulated laser, 10 km of standard single-mode fibre (SSMF), and avalanche photodiode detector. The experimental results are only slightly impaired from ideal performance, even for only 6 dB signal-to-noise ratio, thereby demonstrating the viability and robustness of the proposed technique.

In this paper, the authors investigate the optical reflection phenomena of the periodic nanostructure of a Morpho butterfly wing under the oblique-incident light condition. Also, they discuss the simulation of butterfly wings under the view of an optical grating and photonic crystal by using rigorous coupled-wave analysis method and plane wave expansion, respectively. The simulation results show that the displaced lamella is the foremost condition of the reflection light having strong frequency stability under oblique incidence. Moreover, the modified photonic density of state is proposed to evaluate the reflection feature under oblique incidence.

In this study, an optical fibre magnetic field sensor is experimentally demonstrated using chemical etched multimode fibre sandwiched between two single mode fibres. The obtained result of the magnetic field and refractive index response shows that the decreasing fibre diameter in the sensing region plays an important role to enhance the sensitivity of the device. The magnetic field sensing is based on a tunable refractive index (RI) property of magnetic fluid infiltrated into the capillary tube. The sensing system is verified by testing RI of different concentrations of sodium chloride (NaCl) solution before sealing in capillary tube. Experimental results show that the sensor with taper fibre diameter of 45 µm has relatively high magnetic field sensitivity of ∼0.993 dB/mT ranging from 0 to 6 mT. The proposed devices find potential applications in magnetic field sensing.

Recently, double generalised gamma (GG) distribution has been proposed as a generic model, to describe the irradiance fluctuations in free-space optical (FSO) communication systems. In this study, first the authors derive an approximate analytical expression for the distribution of the sum of independent but not necessarily identically distributed double GG random variables (RVs), considering the effects of the turbulence and pointing errors. Using well-known Beaulieu series, the authors describe the probability density function (pdf) and the cumulative distribution function (cdf) of the sum of double GG RVs in the form of a convergent series. The authors derive novel, exact closed-form expressions for the coefficients of the series in terms of the Meijer's G-function, which makes it possible to calculate the pdf and cdf of the sum of double GG variates under different turbulence conditions. In the next step, based on the presented results, the authors derive approximate analytical expression for the outage probability of the system and investigate the outage performance of the FSO link with equal-gain combining (EGC) receivers over double GG fading channels with pointing errors. Numerical results are further demonstrated to confirm the analytical results and also to show the good accuracy of the derived expressions.

The visible light communication (VLC) utilising the light emitting diodes (LEDs) as transmitters has gained much interest for the indoor wireless access due to its abundance of unregulated spectrum. However, the LED non-linearities cause a detrimental non-linear distortion especially for the adoption of optical orthogonal frequency-division multiplexing (O-OFDM), which is known to suffer high peak-to-average power ratio (PAPR). Specifically, the authors consider the direct current biased O-OFDM (DCO-OFDM) to realise the O-OFDM signals. This study aims to develop the mitigation techniques for LED non-linearities at transmitter through the combined advantages of PAPR reduction and the technique of linearising the non-linear LED characteristics. The orthogonal cover code sequence is exploited to design a transform precoding to reduce the PAPR. An uncomplicated pre-distorter at transmitter is adopted to linearise the LED non-linearity. In addition, the authors propose a dynamic DC biasing method to avoid the clipping noise in DCO-OFDM. As a whole, the proposed techniques at VLC transmitter can improve the LED non-linearities even for large input signals.

A novel low-loss photonic crystal fibre (PCF) has been suggested for THz spectral applications. The proposed PCF contains five layers cladding with three layers core. The cladding and core region of the fibre are arranged in the octagonal and porous manner, respectively, where both the core and cladding vicinity are constituted by circular air cavities. The optical properties of the PCF are investigated by utilising the full vectorial finite-element method along with the perfect match layers boundary condition. All numerical outcomes show the ultra-low effective material loss of 0.049 cm⁻¹ and large effective area of 3 × 10⁻⁷ m² at 1 THz operating frequency. The power fraction is also considered as another significant parameter to design a low loss fibre. The almost more than half of the useful power (about 53.78% at f = 1 THz) goes through the core over the wider operating frequency. In addition this, the proposed single-mode PCF can be fabricated using the sol–gel method and is useful not only for high data traffic transmission applications but also for THz waveguide applications.

This study presents a method to improve the efficiency of semiconductor optical amplifier (SOA)-based optical network units (ONUs). The method is based on the combination of remote seeding and self-seeding schemes, which is referred to as the feedback seeding (FBS) scheme. In the proposed method, a centralised laser source provides a coherent light wave at the optical line terminal. At the ONU, a fibre Bragg grating is positioned to reflect a small percentage of the SOA output to increase seeding power. Consequently, the instauration issue is overcome by achieving coherent light power and a higher data rate. A colourless FBS-ONU is also demonstrated in this research. Simulation results demonstrate that the proposed FBS scheme can operate sufficiently with a low seeding power from the central office. In the remote seeding scheme, sensitivity increases as seeding power increases. On the other hand, in the FBS scheme, sensitivity is high and constant at seeding power values of −30 dBm and above. In this study, sensitivity is −23  dBm. The results show that the proposed scheme provides significant improvement in bit error rate performance and optical signal to noise ratio.

In this study, a novel plasmonic waveguide structure consisting of two mutually positioned V-grooves for using as an electro-optic phase modulator has been designed. The key challenge in designing an active plasmonic channel is that the bias field distribution should properly overlap the plasmonic field distribution. The active performance of the waveguide structure has been studied in a single electro-optic phase modulator and also in an all-plasmonic Mach–Zehnder structure. A new plasmonic splitter has been also proposed and analysed for using in the Mach–Zehnder structure. A high overlapping of bias field and plasmonic field along with low loss of 0.22 dB/µm, low value of U_πL_π  = 0.1 V mm, high bandwidth and high extinction ratio of 32 dB has been achieved simultaneously through the authors' new proposed plasmonic waveguide structure.