Tracking light

22 April 2016

Since 1994, Wallace C. H. Choy has been working in the field of optoelectronics as a researcher and educator. His work contributes to improve our quality of life through evolving optical electronic devices for high-speed data transmission and green energy applications. He also trains professionals to serve as scientists in technical companies and research units, as well as teachers in various institutes.

Having grown up in a poor family living in an old public housing estate with very basic facilities, Wallace understood that working hard in his studies was important for create opportunities for his future. With help from the Croucher Foundation, Wallace completed his PhD program at the National Ion Implantation Centre of the UK at Surrey University, working on optical devices for high-speed data transmission.

In 2001, Wallace took the opportunity to work at Fujitsu in the Silicon Valley to develop new products for optical communication. His work on semiconductor nanostructural devices such as a new class of real-time wavelength-tunable lasers at Fujitsu and grating-based multiplexer (MUX)/demultiplexer (DEMUX) at the National Research Council have been developed and adopted in many industries.

MUX and DEMUX serve to increase the amount of data that can be sent over a network with certain time and bandwidth constraints. On the input end, multiplexers combine multiple inputs into a single data output. On the other side, the demultiplexer takes the single data stream created by the MUX and splits it back up into its original form. By merging multiple inputs into a single stream, more information can be shared across a single channel, streamlining transmission and saving valuable transmission time and bandwidth.

Mitel stock price rose by 46% after the MUX/DEMUX-breakthrough announcement and a start-up launched the technology. Wallace received outstanding an achievement award from NRC, the first Croucher Fellow to join the NRC and receive the award.

After joining the University of Hong Kong, Wallace has had the chance to work with some of the top scientists in his field. He cites the interaction and knowledge exchange as an invaluable opportunity to sharpen his ability to identify challenging issues in optoelectronic devices for green energy applications.

This experience has been important for him to conduct pioneering work on metal nanostructures for inducing abnormally strong electromagnetic fields known as plasmon resonances for solar cell applications. Plasmon resonance is the resonant oscillation of conduction electrons at the interface between a negative and positive permitivity material stimulated by incident light. It forms the basis of many adsorption measuring techniques and is used in many colour based biosensors to detect molecular adsorption, such as polymers, DNA or proteins.

Mechanism of surface plasmon resonance technology

In Hong Kong, Wallace led a team of PhD students and postdocs to invent the first dual plasmonic nanostructures for high-performance organic solar cells with power conversion efficiency (PCE) approaching 10%; the state-of-art PCE for plasmonic organic solar cells at the time. He also proposed the new concept of plasmon-electrical effects to manipulate the electrical properties of semiconductor devices and to break the space charge limit (SCL) in semiconductors. SCL is a fundamental electrostatic limit of paramount importance for photocurrent degradation in optoelectronic devices. It arises when several conditions are met, including unbalanced electron/hole mobility, high-density electron/hole generation, a thick semiconductor layer, and a moderate reverse bias.

Recently, by using monolayer graphene as a novel nanoscale spacer of metal film-metal nanoparticles coupling/resonance systems, Wallace has also worked on light emitting devices. He has optimised the emission of fluorescence nanomaterials and has achieved surface-enhanced Raman spectroscopy (known as SERS) with the highest enhancement ratio of 1700 reported at that time for sensor applications. 

Raman scattering describes the inelastic scattering of photons released from an atom or molecule. Through spectroscopy, much information about the identity and bonds of atoms and molecules can be obtained by observing the vibrational information revealed by the scattering pattern of the photon. In a way, the vibrational information of a scattered photon acts as a sort of fingerprint for identifying a molecule. SERS is a technique which offers orders of magnitude increases in Raman intensity, overcoming the traditional drawbacks of Raman scattering so that the technique may detect and identify single molecules.

His work has drawn the attention of Nobel Laureates and pioneers from many different fields, and has been further studied and adopted. In 2014 and 2015 Wallace was recognized as Top 1% of most-cited scientists in Thomson Reuter's Essential Science Indicators and as prolific researcher on organic solar cells in Nature Index 2014 Hong Kong published by Nature.

After gaining valuable experience in field, Wallace now takes opportunities to serve the community. He has taken up volunteer jobs as an Editorial Board Member for Nature Publishing Group of Scientific Reports in the field of electronics, photonics, and device physics and the journal of Applied Physics D of the Institute of Physics (UK) in device physics and organic devices, a Topical Editor of OSA JOSA B in experimental nano-optics, and an Associate Editor of IEEE Photonics Journal.

Wallace Choy is currently an Associate Professor in the Department of Electrical and Electronic Engineering, the University of Hong Kong. He was the recipient of Croucher Fellowship, Croucher Scholarship and Sir Edward Youde Postgraduate Fellowship. He received Outstanding Achievement Award from NRC in 2001 and overseas visiting fellowships from HKU to take sabbatical leaves for visiting George Malliaras's Group, Cornell University in 2008, Yang Yang's group, UCLA in the summer of 2009 and 2011, Karl Leo's group, IAPP, Dresden, Germany in the summer of 2010, as well as Kido's group in Yamagata University, Japan in the summer of 2012. 

To view Wallace's personal Croucher profile, please click here.