| RESEARCH HIGHLIGHTS |


method with other software packages used for flow cytometry data analysis and quality control, namely flowJo and flowClean. Among these, flowAI was the fastest, the most stringent toward anomalies and the most intuitive to use. “Scientists who want to look deeper into the cellular complexity often need to distinguish


extremely rare cells, which may be lost with an unreliable quality control. We expect that flowAI will help scientists to remove background noise and achieve a more accurate detection of these rare cells and an easier characterization of the source of ambiguous results. We recommend flow cytometry users


to try flowAI and let us know what they think,” suggests Larbi.


1. Monaco, G., Chen, H., Poidinger, M., Chen, J., de Magalhães, J. P. & Larbi, A. flowAI: Automatic and interactive anomaly discerning tools for flow cytometry data. Bioinformatics 32, 2473–2480 (2016).


Optoelectronics MIX AND MATCH LASERS


COMBINING SILICON WITH AN OPTICALLY ACTIVE MATERIAL ENABLES TINY LASERS COMPATIBLE WITH INDUSTRIAL FABRICATION TECHNIQUES


Combining silicon with a light-producing semiconductor may help develop micro- meter-scale lasers, say Doris Keh-Ting Ng and her colleagues from the A*STAR Data Storage Institute1. Silicon has revolutionized the manufac-


ture of electrical devices. This abundant semiconductor is easily processed into tiny


components, such as transistors, using methods that are scalable to industrial levels, thus enabling the production of hundreds of thousands of elements on a single chip. Electronic engineers would like to further expand the functionality of these integrated circuits by enabling them to create, manipu- late and detect light. These optoelectronic devices could speed


up processing of digital information, and lead to micrometer-scale lasers, for use in barcode scanners for example. The problem, however, is that silicon is not an efficient light generator. Ng’s team designed and produced a laser


compatible with silicon fabrication techniques by combining silicon and another semicon- ductor material that can produce light: indium gallium arsenide phosphide (InGaAsP). “Our results demonstrate a promising approach for efficient and compact active optoelectronic devices on silicon using a very thin III–V semiconductor layer,” says Ng. A crucial consideration in any laser


A microlaser comprised of a cylinder of indium gallium arsenide phosphide (red) on silicon (blue) could enable integrated optical circuits.


22 A*STAR RESEARCH


structure is optical feedback: the ability to trap light within the structure to drive further light generation. In conventional lasers, this is done by placing a mirror on either side of the light-generating region. Instead, Ng and the team used a cylindrical device geometry. This trapped some of the generated light at the walls


of the device and forced it to propagate round inside the cylinder. This is called a whisper- ing-gallery mode because the same effect traps sound waves in a circular room such as a cathedral dome. The team started with a silicon substrate,


onto which they deposited a thin layer of silicon oxide. The optically active InGaAsP film, just 210 nanometers thick, was fabri- cated separately and bonded on top of the silicon oxide. The team then etched through some of the material to create cylinders either 2 or 3 micrometers in diameter. The 3-micrometer devices emitted laser light with a wavelength of 1,519 nanometers, very close to that used in commercial optical communi- cations systems. A unique feature of this device is that


the whispering-gallery mode extends over both the silicon and the InGaAsP regions. The InGaAsP provides light amplification while the silicon passively guides the light. “Next, we hope to apply these ideas to devices operating at room temperature,” says Ng. “Operation at higher temperature will require fine-tuning the laser design and fabrication.”


1. Lee, C.-W., Ng, D. K.-T., Tan, A. L. & Wang, Q. Hetero-core III-V/Si microlaser. Optics Letters 41, 3149–3152 (2016).


ISSUE 6 | JANUARY – MARCH 2017


© 2016 A*STAR Data Storage Institute


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