The Research Program of Robert W. Boyd


1. Squeezed light generation through use of electromagnetically induced transparency

Our goal is to make use of the concept of electromagnetically induced transparency (EIT) to produce squeezed light and other quantum states of light. EIT is a powerful concept that can be used to render an otherwise opaque, resonant material transparent to optical radiation while maintaining the large nonlinearity associated with a resonant response. The ability to minimize unwanted absorption is particularly important for studies of squeezed light generation, because squeezing is badly degraded by absorption processes and because absorption often leads to fluorescence which can itself add noise to the signal field. While EIT has been shown to enhance the properties of many different nonlinear optical processes, it has not previously been shown to lead to enhance the properties of squeezed light generation. The implications of this work include the establishment of techniques for performing measurements with unprecedented sensitivity.

This project is being pursued jointly with Prof. C. R. Stroud and is funded by ONR.

2. Research in Biophotonics

Biomedicine is an important research area in which optical techniques hold great promise. Our primary research venture in this area is the design of optical biosensors. Our technique is to fabricate optical resonators that can be exposed to the presence of biological pathogens. The presence of a pathogen on the active area of the sensor can lead to an increased optical absorption. For a high-finesse optical resonator, even the small absorption resulting from the presence of several tens of biological molecules can produce a large change in the power circulating within the resonator. Fabrication in glass, in gallium arsenide, or and polymers are being pursued as parallel efforts. Other current projects in the area of biophotonics include the design of nonlinear optical microscopes with increased sensitivity for detecting weak phase objects. This work is supported by DARPA

3. Nanocomposite materials for nonlinear optics

This work is aimed at the development of new materials and structures for use in nonlinear optics. The research program is predicated on the realization (which originated with Boyd and Sipe) that composite materials can be fabricated in a manner such that the nonlinear response of the composite exceeds those of its constituent materials. Our previous work has established that at least a three-fold enhancement of the nonlinear optical response is possible through use of this procedure. Some particular topics presently under investigation include (a) the determination of what sort of nanostructures optimally produce an enhance nonlinear optical and electrooptic response, (b) the investigation of photonic bandgap structure to provide additional enhancement to the nonlinear optical response, and (c) the investigation of how fs optical pulses propagate through these materials. Structured materials give rise to strong dispersive effects as well as to NLO effects, which can lead to effects such as optical soliton formation, self-steepening, and shock wave formation. This research is supported by AFOSR.

4. Research in quantum imaging

This research is motivated toward the development of laboratory techniques to generate multimode squeezed and entangled states of light and the use of these quantum states of light in the development of imaging systems with enhanced imaging characteristics. One application to be studied entails the development of techniques for the detection of weak phase and amplitude objects with a sensitivity that exceeds the standard shot-noise limit. We are also developing techniques for the construction of imaging systems that can achieve a transverse resolution that exceeds the classical Rayleigh criterion. This approach is based on the unusual interference phenomena that can be observed from highly entangled light fields. Much previous work on the development of quantum states of light has utilized second-order nonlinear optical interactions. As part of our research, we are determining the utility of using third-order nonlinear optical interactions for this purpose. Such interactions hold particular promise for quantum imaging for reasons including the fact that they can produce quantum states of light without producing a large wavelength shift on the generated beam.

5. Development of ultrafast switching devices

This research is aimed at the development of a new class of high-speed photonic switching devices with dramatically reduced switching energies. These devices utilize the enhanced nonlinear response of a high-finesse optical ring resonator. Theoretical arguments show that the nonlinear phase shift acquired by a pulse of light in passing through the resonator scales as the square of the resonator finesse. This finesse-squared dependence occurs because the intensity of the light within the resonator is enhanced by the resonator finesse, and in addition the effective interaction path length of the light is increased by the same factor. However, the transit time through the resonator increases only linearly with the finesse. Thus by constructing resonators with small linear dimensions but large finesse it is possible to construct devices with both highly nonlinear and temporally fast response. The design goal of our research is to produce devices with nJ switching energies and Tb/s switching rates. The broad-term significance of this research is as follows: The development of high-speed, low-energy all-optical switching devices has important implications for telecommunications and more generally for optical information technology. More generally, our studies of nonlinear optical interactions involving whispering gallery modes of highly nonlinear glass micro-structures have broad implications both for fundamental aspects of optical physics and for optical technology. For instance, as part of this research we are studying the noise characteristics of light confined in a microcavity, where cavity quantum electrodynamics (QED) is expected to play an important role. Moreover, the system of a light wave light interacting with one or more high-finesse optical resonators is expected to exhibit strong nonlinear and dispersive effects, which can lead to new understandings of nonlinear pulse shaping and ultrafast pulse dynamics as a consequence of nonlinear space-time coupling.

6. Ultrafast nonlinear optics

This research project is aimed at developing new techniques and understanding of nonlinear optical phenomena when excited by ultrashort laser pulses. Nonlinear optical phenomena display new phenomena when excited with ultrashort pulses, including transient optical response, the importance of higher-order nonlinear optical effects including plasma formation, and space-time coupling effects such as pulse self-steepening and shock-wave formation. Our research involves both laboratory studies and intensive numerical modeling. One topic of interest is the characterization of standard and exotic photonic materials and nano/micro structures. Some specific material systems to be examined include chalcogenide glasses, photonic bandgap materials, nano-composite materials, and especially materials with enhanced nonlinear response as a consequence of the presence of both metal and dielectric components. We are also interested in studying fundamental ultrafast interactions. This portion of our research program is aimed at exploring new fundamental interactions that are enabled by ultrafast techniques. One aspect of this work is to perform time-resolved measurements of the turn-on time associated with various nonlinear optical processes, and especially to determine how fast the process of electromagnetically induced transparency develops. Another aspect of the work involves studies of advanced aspects of ultrashort pulse propagation, including the time-development. polarization dependence, and the possibility of chaotic behavior of the filamentation process, and the different behavior that become possible when light beams propagate through nano- and micro-structured materials. Parts of this research are being conducted jointly with Prof. Ian Walmsley.

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