Lehigh University
Lehigh University


Diligence vaults optics student to the top

Chee-Loon Tan

Chee-Loon Tan had only a passing acquaintance with optical technologies when he enrolled as a Ph.D. student in electrical engineering at Lehigh in the fall of 2006.

At the University of Malaya in Malaysia, where he had just earned a bachelor’s in electrical engineering, Tan had focused on wireless communications. Among other projects, he had built a wireless ECG (electrocardiogram) monitoring system and fashioned a walking stick that warns the visually impaired about obstacles.

Today, Tan has an international reputation in lasers and semiconductors, having published 35 journal articles and conference papers in less than three years. He has traveled to California, Singapore and England to give presentations at conferences of the major optics professional societies.

This summer, Tan will receive one of the top honors in his new field, the D.J. Lovell Scholarship from SPIE, the International Society for Optical Engineering. The $11,000 scholarship, the largest given by SPIE, will be presented in August in San Diego at SPIE’s annual Optics Photonics conference.

How does one change scientific fields so quickly and so successfully? Tan, who has published 35 journal articles and conference papers in less than three years, cites several factors: preparation, systematic effort, clear direction from a mentor and long hours.

Mathematics is the foundation of engineering, says Tan, who took four years of calculus at a high school that is based on the British education system and located on the Malaysian island of Penang.

“Mathematics is a must,” he says. “Without it, you will be afraid to tackle a problem. Your motivation will be undermined.”

The change from wireless communications to optical technologies, says Tan, required him to gain a firmer grasp of quantum mechanics, the branch of physics that seeks to describe the behavior of light and matter at the atomic and subatomic scales.

Step by step

“Quantum mechanics is the basis of what I do now. It is totally different from the electronics that I learned at the University of Malaya. But if the knowledge is different, the approach to it is the same. When I came to Lehigh, I took courses in quantum mechanics, quantum electronics, semiconductors and lasers. To learn how to apply quantum mechanics, I had to keep building, step by step.”

Tan’s adviser at Lehigh is Boon Ooi, associate professor of electrical and computer engineering and a member of Lehigh’s Center for Optical Technologies, where Tan conducts his research. Tan has also worked with several other professors in the electrical and computer engineering department, including James Hwang, who directs Lehigh’s Compound Semiconductor Technology Laboratory, and Yujie Ding, director of Lehigh’s Terahertz Nonlinear Optics Laboratory. IQE Inc. helps the group grow semiconductor nanostructure materials, while the Army Research Laboratory helps with materials processing. The group receives funding from the National Science Foundation.

Tan says Ooi, who also hails from Penang, helped him get off to a fast start at Lehigh.

“When you start in a new field, you need a distinct problem, a clear target to aim at. Professor Ooi provided this for me. Without a clear problem, you get sidetracked. You go off in too many directions at once.”

Much of Tan’s research at Lehigh has focused on developing broadband semiconductor lasers, which emit light simultaneously along multiple wavelengths, thus achieving greater spectral range than conventional lasers, which emit light along a single wavelength.

“Chee-Loon’s diligence in picking up essential knowledge enables him to perform his research in a very short time,” says Ooi. “By the end of his first year at Lehigh, he had already begun to develop a new theoretical model to analyze broad optical gain semiconductor quantum dot media."

Tan is working on a laser made of two semiconducting materials that emits light from quantum dashes packed at a density of 1 billion per square centimeter. (A quantum dash is a variation on a quantum dot, which is a nanoscale semiconductor that spatially confines electrons and hole pairs.) The laser developed by Ooi’s group, says Tan, has an inhomogeneous structure that enables it to emit light along a broader band of the spectrum.

Ooi’s laser is several orders of magnitude smaller and less expensive than other broadband semiconductor lasers, giving it potential applications in optical telecommunications, biosensing, and biomedical imaging and diagnosis.

In Lehigh’s Center for Optical Technologies, Tan and the other members of Ooi’s group utilize semiconducting materials that self-assemble into quantum dashes, and then monitor the dashes’ mechanical, material and optical properties.

The work requires long hours, says Tan, as experiments cannot be shut off until they are completed. Tan also creates mathematical models to explain experimental results. This work can be halted in midstream, but Tan prefers not to do so.

“I don’t like to go home until I get the results I want. I spend most of my time in the lab. I come in at 8 in the morning and usually leave at 10 or 11 at night or later. That kind of schedule is not unusual for an engineering student.”

Tan hopes to complete his Ph.D. later this year and seek a career as an entrepreneur.

“I would like to start up a company that develops and commercializes broadband semiconductors,” says Tan. “That will require a very different approach from what I do now. It will be very challenging.”

--Kurt Pfitzer

Posted on Thursday, May 14, 2009

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