The demand for access to broadband data services in high-speed trains is increasing as more people are travelling to and from work, which is not met by the existing radio frequency technology. Therefore an alternative technology known as free space optics (FSO) could be readily adopted that could overcome the bandwidth bottleneck problem. The study presents a mathematical model of an FSO link for ground-to-train communications link and analyses the system performance in terms of the signal-to-noise ratio and the bit error rate (BER). The authors show that the simulated BER is in good agreement with the predicted results for bit rates up to 50 Mbps. The link budget analysis for the proposed system is also presented showing a link margin of 17.75 dB.

The authors present the impact of asymmetric filtering of strong (e.g. 35 GHz) optical filters on the performance of 42.7 Gb/s 67% (carrier suppressed return to zero)-differential phase shift keying systems. The performance is examined (in an amplified spontaneous emission (ASE) noise-limited regime and in the presence of chromatic dispersion) when offsetting the filter at the receiver by substantial amounts via balanced, constructive and destructive single-ended detections. It is found that with a slight offset (vestigial side band) or an offset of almost half of the modulation frequency (single-side band), there is a significant improvement in the calculated ‘Q’.

This study presents the modelling and experimental characterisation of 980 nm segmented-contact superluminescent diodes designed to produce linear power–current characteristics for applications requiring high output powers and readily reproducible operational characteristics, with adjustable beam width, radiation pattern and spectral width. The maximum measured output power was 160 mW at 4 A pulsed driving current, resulting in 2% wall-plug efficiency per pulse, with ripple-free broad-band output. Coupling into multi- and single-mode optical fibres was achieved with efficiencies of, respectively, 60 and 17%.

In this work the authors investigate the design of an XOR gate based on two-dimensionalsilicon photonic crystals. The XOR gate is formed by two dual-ring resonators placed between two waveguides; each secondary waveguide is united in a vertical waveguide, through a specific Y branch, where the waveguide contains the main output. We use 45° ring resonators, before the output, to improve gate efficiency. The optical properties and the distribution field E_z for the proposed gate have been calculated by the finite difference time domain technique. The response time of our logic ‘XOR’ gate is < 7.2 ps. This photonic gate is of great interest for several applications such as in electronics, in data processing and also in cryptography.

The authors employ the Bloch theorem of periodic structures and transfer matrix method to study the Tamm states supported in the surface of a semi-infinite one-dimensional (1D) metal-dielectric photonic crystal (PC) that is adjacent to an air background. The authors find that the optical properties of the Tamm states are quite different between the transverse magnetic (TM) wave and electric (TE) wave. The Tamm state properties are also sensitive to the stack sequence of the PC. Owing to the surface plasmon resonance on the surface of metal, the Tamm states of 1D metal-dielectric PC take on some unusual properties including the straight dispersion curve, extremely slow group velocity and large range of frequencies.