Micro light-emitting diode (micro-LED) arrays based on an AlInGaN structure have attracted much interest recently as
light sources for data communications. Visible light communication (VLC), over free space or plastic optical fibre (POF), has become a very important technique in the role of data transmission. The micro-LEDs which are reported here contain pixels ranging in diameter from 14 to 84μm and can be driven directly using a high speed probe or via complementary metal-oxide semiconductor (CMOS) technology. The CMOS arrays allow for easy, computer control of
individual pixels within arrays containing up to 16×16 elements. The micro-LEDs best suited for data transmission have
peak emissions of 450nm or 520nm, however various other wavelengths across the visible spectrum can also be used.
Optical modulation bandwidths of over 400MHz have been achieved as well as error-free (defined as an error rate of
<1x10-10) data transmission using on-off keying (OOK) non-return-to-zero (NRZ) modulation at data rates of over
500Mbit/s over free space. Also, as a step towards a more practical multi-emitter data transmitter, the frequency response of a micro-LED integrated with CMOS circuitry was measured and found to be up to 185MHz. Despite the reduction in bandwidth compared to the bare measurements using a high speed probe, a good compromise is achieved from the additional control available to select each pixel. It has been shown that modulating more than one pixel simultaneously can increase the data rate. As work continues in this area, the aim will be to further increase the data transmission rate by modulating more pixels on a single device to transmit multiple parallel data channels simultaneously.
In this paper we discuss theoretical modelling methods for the design of photonic crystal and photonic quasi-crystal
(PQC) LEDs - and apply them to the analysis of the extraction enhancement performance and shaping of the emitted
beam profile of PQC-LED structures. In particular we investigate the effect of the pitch of the PQC patterning, and
consider the physical mechanisms giving rise to performance improvements. In addition, we examine the relative
contributions to performance improvements from effective index reduction effects that alter the conditions for total
internal reflection at the device air interface, and from photonic crystal scattering effects that give rise to radically
improved extraction performance. Comparisons are made with the performance of recently fabricated devices.
A very low-loss and low switching energy vertical micro-cavity has been developed for all-optical signal reshaping. This saturable absorber-based device shows insertion loss as low as 0.2 dB and a switching energy of 13 μJ/cm2 while keeping a response time lower than 5 ps. Such a low loss and low switching energy device has high potential applications in 2R regenerated transmission lines.