When you focus a light beam down to a small spot in a crystal to the size of a few microns, it then rapidly expands and diverges to a much greater diameter, right? No! Shown in Fig. 1 is a top view picture of a light beam focused to a small size at the entrance face of a crystal. After entering the crystal, it is seen expanding. However, after inducing its own waveguide in the crystal, the second picture demonstrates that moments later the beam is trapped and a small optical wire is created from one end of the crystal to the other. One can envision as an application a set of optical fibers connected to a second set of fibers through a crystal. Each beam can be deflected from any incoming fiber to any outgoing fiber without spreading. A second application will have two electronic chips talking to each other via optical wires. Since these self-induced waveguides are erased as a new optical beam enters the crystal and passes over the same region, the optical interconnects are reconfigurable. Currently we are using semiconductor InP and the ferroelectric insulator SBN as crystals for our investigations. Using our new crystal growth facility we are exploring new materials which can be used as substrates for photonic-electronic circuits using these optical interconnects. This work is in collaboration with Hongxing Meng and Scot Hawkins, graduate students at Arkansas, David Bliss of Hanscom Air Force Base, and Moti Segev of Princeton University.

Is it possible to redesign crystal structure after growth? Yes! Shown in Fig. 2 is a picture of a crystal with microvariation in its ferroelectric domains. The periodic variation in the domain planes, seen below, then results in a crystal behavior with periodic electrical and optical properties. In this case the periodic domain reversed planes were produced starting with a uniform material and then writing optical holographic gratings which created the modulated material. Our vision is to develop micro-structure devices using domain programming written by a laser beam. Using our crystal growth facility and our experience in ferroelectric programming, we have a unique opportunity to develop the next generation of nano-ferroelectric devices. For example, we have recently made permanent 10 micron waveguides in the middle of a large crystal. In fact, we have formed and made permanent 10 micron Y-junctions. This opens up the possibility of a new technology of 3-D optical wiring throughout a crystal. This work is in collaboration with Matt Klotz, a graduate student at Arkansas, and Steve Montgomery of the Naval Academy.

Is it possible to store a library of 3-D images in a small crystal? Yes! Holography is a common technique used to generate realistic three-dimensional (3D) images. Photorefractive crystals are an ideal storage medium for recording holographic images because of the following advantages: real-time exposure and display, a simpler recording process in which no pre- or post-processing is required, low writing beam powers, and a potentially large storage volume. Our recent experiments have clearly demonstrated the potential of photorefractive crystals for storage and retrieval of 3D images. In fact, we have demonstrated the storage and retrieval of 3D color holograms in a photorefractive crystal. The 3D image closely reproduces the actual colors of the object. The 3D hologram is visible over a wide perspective as demonstrated by moving oneÕs head back and forth while viewing the hologram. The wide field-of-view of the hologram is also demonstrated using an imaging lens with a color CCD camera mounted on a goniometer to record various perspectives. The picture below (Fig. 3) shows different perspective views of a hologram stored in a crystal. Our new experiments are aimed at demonstrating angle and wavelength multiplexing of many 3-D color images as well as making the storage permanent. This research is in collaboration with Christy Heid, Brian Ketchel, and Gary Wood of the Army Research Laboratory, and Rich Anderson of the National Science Foundation.

Can we build semiconductors one atom at a time? Yes! Using a new molecular beam epitaxy (MBE) machine, made possible by a grant from NSF-EPSCoR, we are today building semiconductors one atom at a time and watching where these atoms are going using a scanning tunneling microscope (STM). In particular, we are building new broadband infrared sensors by constructing complex quantum well structures and are exploring new condensed matter "two-level atoms" by growing quantum dots. The tiny dots have controllable conduction band energy levels with long dephasing times, allowing us the opportunity to carry out coherent optics type experiments. Fig. 4 shows a typical quantum dot structure. The dot is only 20 nm round and 5 nm high. Because of itÕs small size, the dot structure will make novel optical and electronic devices. This research is in collaboration with Philippe Ballet and Jay Smathers, research associates at Arkansas, and Omar Manasreh of Kirtland Air Force Base.