Superfast Photonic and Electronic Device Group

A team at the National Central University, Taiwan, are working on advanced high-power THz photodiodes, avalanche photodiodes and high-speed visible light-emitting diodes and vertical-cavity surface-emitting lasers to develop more advanced, efficient communication and wireless technology.

Professor Jin-Wei Shi, at the National Central University, Taiwan, seeks to develop promising new technology to increase cost effectiveness of wireless technology using high-power, high-bandwidth (DC-300 GHz) photodiodes (PDs) for millimetre wave (MMW) generation. His most recent research investigates the use of high-speed high-power PDs and avalanche photodiodes (APDs) for applications including optical interconnections, fibre communication, radio-over-fibre wireless communication and photonic radar systems as well as high-speed light sources such as vertical-cavity surface-emitting lasers (VCSELs) and visible light-emitting diodes (LEDs) for optical interconnections, fibre communication, visible-light communication and 3D sensing. Shi and his team have achieved unprecedented switching speeds, THz PD O-E bandwidth and high-speed VCSEL E-O bandwidth, revolutionising optoelectrical devices.

Part of Shi's research focuses on high-powered and avalanche PDs, often used in radio-over-fibre wireless communication systems. Able to convert intense modulated light into strong MMW signals for free space radiation, they offer wider bandwidth and higher signal-to-noise (S/N) ratios for the MMW signals than existing solutions. Shi explains, 'The advantage of this is that it can be used to interconnect dozens of cells or base stations to create a synchronised wireless communication system.' APDs, on the other hand, are usually used in extended-reach (40 km or more) or passive optical network (PON) fibre communication systems. He tells us: 'APD-based solutions can offer 8 dB high-sensitivity levels compared to normal PD-based receivers, implying that we can eliminate the need to install optical amplifiers inside fibre channels.'

Furthermore, Shi's recently-developed uni-travelling carrier photodiodes (UTC-PDs) offer amazing power-generation capabilities not found in most PD-containing devices. 'The unique feature of our device is that it can be operated under forward bias and still sustain high-speed performance. This would switch the device from a power-consumption device to a power-generation one. Our device can thus generate electrical power during high-speed optical detection,' he notes. This feature offers impressive benefits to high-power consumption users such as data centres that use millions of PDs.