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  • The Teacher

Photonics Spectra
Oct 2009
an Interview with Nader Engheta

David L. Shenkenberg, Features Editor,

After earning a PhD at Caltech, Nader Engheta spent four years at Kaman Sciences Corp. before joining the faculty at the University of Pennsylvania in Philadelphia, where he is now the H. Nedwill Ramsey Professor of Electrical and Systems Engineering. He has won many awards for both research and teaching and is known for his concept of optical lumped nanocircuits.

NaderEngheta.jpgYou spent some time in industry before becoming a professor. What was your industry experience like?

It was a very valuable experience. I learned a great deal from how the industry works, yet I always knew that the academic research university environment is where I wanted to be.

Your work has covered many areas. Why?

They have a common thread. I am very curious about different aspects of fields and waves. I am fascinated by the beauty of electromagnetic theory.

You are not only an electrical engineer, but also a member of the Mahoney Institute of Neurological Sciences. How does an electrical engineer move into neuroscience?

One of my areas of research is toward biological polarization imaging – how we can learn from nature and have better sensors, for example. The human eye has an amazing ability to detect optical signals, but the human eye is essentially polarization-blind. If someone sends a yellow light to our eyes, we can detect if it is yellow, bright or dim, but we cannot detect if it is horizontally or vertically polarized, but some animals can detect polarization. From the engineering and applied science point of view, I wonder how we can exploit these systems. For example, in camera systems, we are exploring algorithms that will enable the combination of polarization with other visual information from the scene.

How can this polarization information be used?

You can see farther away underwater or in any other optically scattering media. We have developed a technique using polarization and lighting that enables detection of the indentations in a flat surface.

Your research has covered nano-antennas. What applications are there for them?

If you look at a circuit inside your cell phone, the circuit could be in the micro regime. Could we have a similar concept in the nano regime? Could we detect an optical signal from the circuit? If you look at a regular antenna and you load a regular antenna with a circuit zone, could we do something analogous to that on the nanoscale? If I have a silver nanowire, imagine you have another nanomaterial, a nanoparticle. That particle would behave as a load on the nanowire “antenna,” changing its resonance. That can open interesting possibilities. Could we have wireless communication using light? If 40 years ago someone had told me that we will have telephone communication without using any landline, I wouldn’t have believed it. What I’m envisioning is wireless photonic communication in different nanocircuitries. We are doing proof-of-concept experiments.

I thought you are a theorist?

By training, I have been a theorist, but more and more I am moving my group toward experiments. That work in my group is experimental work. Most of my work has been theoretical. We have done microwave work, epsilon-near-zero microwave experiments and so on. We are moving to optical microscopy. I just won a proposal to get an NSOM [near-field scanning optical microscope]. It will be here in three months.

Why do experiments?

I see the need to expand my work into some aspect of experimentation to show the proof of concept. That is exciting because I am learning every day.

One of your most recent papers is about transporting an image through a subwavelength hole.

It is a theoretical work to see how the concept of epsilon near zero would work. We show how the subwavelength image can be squeezed through tiny wires through a hole. You are familiar with Thomas Edison’s wonderful work on plasmons through subwavelength holes? In this theoretical work, we have shown a completely different mechanism of energy transport through the hole. We started with an object and found out what would happen if we have a bunch of tiny objects through the wire of this epsilon-near-zero material.

Epsilon is permittivity, correct?

The relative value of permittivity would be near zero. What we have shown is that this material has interesting properties. We call it “super coupling.” If you have waveguide one and want to connect to waveguide two, you get very good coupling with almost no reflection. This is useful if I want to bend the waveguide to fit it within a very small area and get very good transmission.

Have you done anything on quantum computing?

No, I have not done anything on that yet. I have in mind to look into that in the near future, particularly from the point of view of my optical nanocircuits. If you look at this optical nanocircuit concept that I’m developing, an interesting thing is how to connect ideas from one to another. This epsilon-near-zero material could be connected to this concept of optical nanocircuits. One concept that I have been working on in relation to this concept is of moving particles. If you look at optics, that is a displacement current. What I’m quite interested in is how we can control the displacement current. Could we tailor my concept of optical nanocircuits to displacement? We have a paper under review on a nanocircuit board with material of epsilon near zero. If you have something like this, then imagine you cut a groove into this substrate. If there is an optical field in this substrate, then you have a vector in this current. Inside the groove, the epsilon is not zero, so your displacement would not be zero.

Your work has covered metamaterials and cloaking.

There’s a lot of groups working on cloaking. One group is the transformation cloaking. There is another way to achieve cloaking. That is plasmonic. Ours is based on cancellation of the dipole moment. Imagine you have an object and a wave and get some scattering. You induce a dipole moment. Imagine you design a metamaterial layer around the object and induce opposite phase with the original dipole moment of the object. You almost cancel the induced dipole moment. Scattering would be reduced, leading to the invisibility of small particles. We have done an experiment using our own technique in the microwave. It hasn’t been published yet.

Several awards that you have won have been for teaching. Were any of these awards based on student evaluations?

The S. Reid Warren Award for distinguished undergraduate teaching, I won that two times. The Christian F. and Mary R. Lindback Foundation Award, that one is based on letters from both colleagues and students.

What are the characteristics of a good teacher?

I love my job. I don’t see any boundary by the way in departments. If I am interested in a topic, I try to learn about it and see how I can contribute to it. I think one of the most important aspects of the research or the scientist is to be in love with the subject. When you are excited, you can excite other people. In my opinion, teaching and research are intertwined. You cannot separate the two; all are pursuit of knowledge.

What are the biggest challenges in higher education today?

One of the challenges is to educate graduate students such that they can get into any field quickly. Electrical engineering, that field has changed significantly in five years, let alone 10 years. When you get your PhD and get your first job as a scientist or young faculty, it’s very different. Any field you choose is evolving. What’s more important is to teach how to approach any new topic because you have to find ways to solve problems no one has solved before.

What got you interested in math in the first place?

I became very fascinated with how a transistor radio works. Where does this sound come from in the air? I didn’t know anything about this. I was talking to my older brother, and he said if you are interested in this, you should go into electrical engineering. Back in those days, people had in mind civil engineering. Electrical engineering was more of a novelty. One thing led to another. I have a picture of Richard Feynman from my PhD commencement at Caltech. I listened to his lectures. He was an amazing guy at explaining physics. Many students would go to his class.

electromagnetic theory
The theory of propagation of energy by combined electric and magnetic fields included in Maxwell's equations.
An electromagnetic wave lying within the region of the frequency spectrum that is between about 1000 MHz (1 GHz) and 100,000 MHz (100 GHz). This is equivalent to the wavelength spectrum that is between one millimeter and one meter, and is also referred to as the infrared and short wave spectrum.
A small object that behaves as a whole unit or entity in terms of it’s transport and it’s properties, as opposed to an individual molecule which on it’s own is not considered a nanoparticle.. Nanoparticles range between 100 and 2500 nanometers in diameter.  
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