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Photonic Crystals - October 2008
Interview Date: December 2008
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Fan Shanhui Fan
From the Special Topic of Photonic Crystals

According to our Special Topics analysis on photonic crystals, the scientist whose work ranks at #9 is Professor Shanhui Fan, with 52 qualifying papers cited a total of 1,747 times. In Essential Science IndicatorsSM from Thomson Reuters, his record includes 222 papers, the majority of which are classified in the field of Physics, cited a total of 3,763 times between January 1, 1998 and August 31, 2008.

Professor Fan is an Associate Professor of Electrical Engineering at Stanford University, where he heads up his own research group.

In the interview below, talks with him about his highly cited work.

 Please tell us a little about your research and educational background.

I was an undergraduate student in Physics in the University of Science and Technology of China, at Hefei, China, from 1988-1992. I obtained my Ph.D. on Theoretical Condensed Matter Physics from the Massachusetts Institute of Technology (MIT) in 1997. I was a Postdoctoral Research Associate and later a Research Scientist at MIT for several years until I joined the faculty of Stanford University in 2001. I am now an Associate Professor of Electrical Engineering at Stanford.

 What first interested you in photonic crystals?

"These days you can find applications of photonic crystals in practical every aspect of optical technology."

After I got into MIT, I needed to find someone to work with. Professor John Joannopoulos was very kind to take me into his group. He wanted a student to work on photonic crystals, so I started. At the time the field was only a few years old. As a young graduate student, it took me a while to gradually realize, and this really was Prof. Joannopoulos’s vision, that the idea of photonic crystals is very powerful, and can have substantial impacts on practically every aspect's of optical technology. Looking back, I am amazed that there are so many things that excite me in this area even after working in it for fifteen years.

 A key paper in your publications is the 1998 Phys. Rev. Lett. paper, "Channel drop tunneling through localized states," (80: 960, 1998)." Would you talk about the significance of this paper for photonic crystals?

This paper dealt with the optimal condition for a frequency-selective transfer between two waveguides. This condition leads to the construction of ultra-compact photonic crystal channel add/drop filters, which is of great importance in wavelength division multiplexing for communication purposes. In addition, the paper provides one of the first theoretical treatments of waveguide-cavity interaction in photonic crystals. Waveguide-cavity interaction has since been very extensively exploited to create many different kinds of functional devices.

 Your most-cited paper in our analysis is the 1999 Phys. Rev. B paper, "Guided modes in photonic crystal slabs," (60[8]: 5751-8, 15 August 1999). Would you talk a little bit about this paper's methods, findings, and conclusions?

In the late 1990s, experimentalists were starting to explore the photonic crystal slab structures. These structures typically consist of two-dimensional array of air holes introduced into a high-index guiding layer. This paper, together with an earlier paper (Phys. Rev. Lett. 78: 3294, 1997), and a subsequent paper (Phys. Rev. B 62, 8812, 2000), represented some of the foundational analysis of these slab structures. In this set of papers, in addition to Professor John Joannopoulos, I have mainly collaborated with Steven Johnson and Pierre Villeneuve.

At the time these papers were published, there were substantial confusions in the community on whether such a structure can guide light or not. These papers showed that in spite of the large in-plane index contrast, as long as the index of the guiding layer is much larger than the surrounding regions, there exist exact guiding modes that are intrinsically lossless.

These papers also provided many detailed considerations on designing these slab structures for various purposes, including, for example, the structures that achieve a large in-plane band gap. These days, most of the photonic crystal devices are based on exactly the kind of slab structures that were analyzed in these papers.

 One of your more recent papers is the 2008 Appl. Phys. Lett. article, "Aligning microcavity resonances in silicon photonic crystals with laser pumped thermal tuning," (92: Art. no. 103114, 2008). Would you discuss the findings of this work?

"...the idea of photonic crystals is very powerful, and can have substantial impacts on practically every aspect's of optical technology."

Starting in 2004, together with M. F. Yanik, who was then a Ph.D. student in my group, we started to explore dynamic photonic crystal for the purpose of stopping, storing, and time-reversing optical pulses. (Phys. Rev. Lett. 92: 083901; Phys. Rev. Lett. 93: 173903; Phys. Rev. Lett. 93: 233903) All these applications, and many others, rely upon the capability to create coherent interaction and interference between two different cavities. For that purpose, two cavities need to have the same frequency, to an accuracy much smaller compared with the cavity linewidth. This is difficult to accomplish by nanofabrication alone. This paper shows a thermal tuning scheme to align two cavity resonances, which is very effective in overcoming fabrication inaccuracy.

 What are the practical applications (or hoped-for applications) for photonic crystals?

These days you can find applications of photonic crystals in practical every aspect of optical technology. A few examples include communication, sensing, solid-state lighting, and energy applications.

 What should the "take-home" lesson be about your research?

In this area, those theorists that ultimately have had impacts were almost always those who understood the experimental reality, and yet at the same time were not constrained by what the experimentalists could do at that particular moment. Instead, they always sought to think deeper and to look beyond. Theory matters a lot, even, and perhaps, in particular in a field like this that is strongly influenced by many practical considerations.

Shanhui Fan, Ph.D.
Stanford University
Stanford, CA, USA

Shanhui Fan's current most-cited paper in Essential Science Indicators, with 382 cites:
Fink Y, et al., "A dielectric omnidirectional reflector," Science 282(5394): 1679-82, 27 November 1998. Source: Essential Science Indicators from Thomson Reuters.

Keywords: photonic crystals, waveguides, waveguide-cavity interaction, photonic crystal slabs, optical pulses.

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Special Topics : Photonic Crystals : Shanhui Fan