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Recent advances in developing nonlinear optical techniques for processing serial digital information at high speed are reviewed. The field has been transformed by the advent of semiconductor nonlinear devices capable of operation at 100 gigabits per second and higher, well beyond the current speed limits of commercial electronics. These devices are expected to become important in future high-capacity communications networks by allowing digital regeneration and other processing functions to be performed on data signals "on the fly" in the optical domain.

We report the high-frequency modulation of individual pixels in 8×8 arrays of III-nitride-based micro-pixellated light-emitting diodes, where the pixels within the array range from 14 to 84 µm in diameter. The peak emission wavelengths of the devices are 370, 405, 450 and 520 nm, respectively. Smaller area micro-LED pixels generally exhibit higher modulation bandwidths than their larger area counterparts, which is attributed to their ability to be driven at higher current densities. The highest optical -3 dB modulation bandwidths from these devices are shown to be in excess of 400 MHz, which, to our knowledge, are the highest bandwidths yet reported for GaN LEDs. These devices are also integrated with a complementary metal-oxidesemiconductor (CMOS) driver array chip, allowing for simple computer control of individual micro-LED pixels. The bandwidth of the integrated micro-LED/CMOS pixels is shown to be up to 185 MHz; data transmission at bit rates up to 512 Mbit/s is demonstrated using on-off keying non return-to-zero modulation with a bit-error ratio of less than 1×10 −10 , using a 450 nmemitting 24 µm diameter CMOS-controlled micro-LED. As the CMOS chip allows for up to 16 independent data inputs, this device demonstrates the potential for multi-Gigabit/s parallel data transmission using CMOS-controlled micro-LEDs.

Gallium-nitride (GaN) based light-emitting diodes (LEDs) are highly-efficient sources for general purpose illumination. Visible light communications (VLC) uses these sources to supplement existing wireless communications by offering a large, licence-free region of optical spectrum. Here we report on progress in the development of micro-scale GaN LEDs (micro-LEDs), optimized for VLC. These blue-emitting micro-LEDs are shown to have very high electrical-to-optical modulation bandwidths, exceeding 800 MHz. The data transmission capabilities of the micro-LEDs are illustrated by demonstrations using on-off-keying (OOK), pulse-amplitude modulation (PAM) and orthogonal frequency division multiplexing (OFDM) modulation schemes to transmit data over free space at rates of 1.7, 3.4 and 5 Gbps, respectively.

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