Kerry J. Vahala - US grants

This effort involves the use of artificially fabricated semiconductors to reduce the frequency width of the radiation emmitted from a semiconductor laser. Not only is this of great importance for the efficient utilization of semiconductor lasers for a variety of applications, it is also of fundamental importance. The limitations on the linewidth of such lasers is not yet clearly understood.

The influence of phase fluctuations on laser linewidth and hence of the influence of such fluctuations on coherent detection systems for communications and signal processing systems is investigated. Multiple quantum well laser will be used.

Dr. Vahala has been selected as a Presidential Young Investigator. He is active in fundamental research on the application of nanostructure physics to solid state devices - either to create novel devices or to improve existing devices. In the research program for the National Science Foundation he will pursue studies to include the following: (1) to create entirely new optical material properties by nanometric patterning of substrates in two dimensions (or three dimensions if a multiquantum well substrate is patterned), (2) to use individual nanometer scale structures such as quantum boxes to study scaling limitations in solid state devices. These new properties result from the onset of carrier quantum confinement effects in two or three dimensions (at room temperature onset requires structures on the order of 100-200 angstrom units in size. The research in this grant will have impact on optical communications and signal processing technology. The interactions with industry which are inherent with Presidential Young Investigator grants will have implications for national competitiveness in the opto-electronics field.

A quantum cluster dot is a compact structure in the 5 to 20 um size range where small scale in three dimensions yields discrete electronic states. This research is an interdisplinary, experimental program for the formation and characterization of monodisperse gallium arsenide (G A ) quantum cluster dots. The clusters will be produced in an aerosol reactor by the vapor phase reaction of an organometallic gallium contains vapor with arsine. Particle size and cluster quality will be monitored by in-situ laser induced luminescence spectra. Clusters from the aerosol reactor will be classified into very narrow size ranges required for applications by an electrostatic classifier. Captured particles will be analyzed as to particle morphology, interval defect structure, and carbon contamination using electron microscopy (TEM and STEM), energy dispersive X-ray analysis (EDAX), and electron energy loss spectroscopy (EELS). Exciting new electronic and optical components would result from the incorporation of large numbers of identical quantum cluster dots into solid state structures. Possible applications include semiconductor lasers several orders of magnitude better than conventional diode lasers and new electroluminescent display technology with convenient adjustment of color. However, to achieve such results, the clusters must be produced to very strict size tolerances, typically with size variations not larger than 0.5 um. Otherwise a device averaging the electronic states of many clusters varying in size would lose the distinctness of states inherent in any individual quantum cluster dot.

In this proposal funding to purchase an Argon laser and certain optical components is requested. This equipment will be used to study a technique for creating lateral modulation of the bandgap in GaAs quantum well material. One goal of this research is to generate nanometer scale structures in two and three dimensions (so-called quantum wire and quantum dot structures) that can be incorporated in semiconductor laser active layers. This method will also be useful in fabricating other optical components, such as waveguides on a similar small scale. In the technique an Argon laser is used to locally melt the sample on a micron scale. Crystal quality of the region is maintained. In a more selective version of this technique we would use a dye laser pumped by the Argon laser to "resonantly" melt the quantum well. By means of a nanometer scale masking techniques or small scale intermixing of the well the principal investigator hopes to observe phenomena associated with this increased lateral confinement of the electron gas. Processing will occur inside a scanning electron microscope already equipped with a cathodoluminescence system so that in stiu processing and diagnostic tests can be run simultaneously.

9412862 Vahala A series of systems level experiments of wide-band, lossless, wavelength converters shall be carried out. These wavelength converters are based on the principles of four wave mixing in quantum well traveling-wave amplifiers. The experiments planned include a measurement of the intensity noise introduced into the converted signal by the conversion process, a single channel system measurement testing the effect of the converter on bit error rate (BER), a two channel measurement to study potential channel cross-talk effects caused by the conversion process, and a feasibility test of semiconductor TWA wavelength converters for dispersion compensation by way of the spectral inversion technique. In addition, mixed-strain amplifiers will be investigated as polarization independent converters. The amplifiers used in this project will be supplied at no charge by AT&T Bell Laboratories. In addition, a 500MB/sec bit error rate tester will be donated to the project b AT&T Bell Laboratories (see letter in proposal). ***

9871850 Atwater This objectives of this project are to develop the synthesis, processing, manipulation and characterization tools to enable and improve novel, emerging silicon nanoparticle memory and logic devices. These devices exploit common approaches for particle synthesis, manipulation, interface passivation and electrical and optical characterization of ordered, passivated arrays of size-classified silicon nanoparticles which are integrated into larger device structures. Device structures to be addressed in this project include: a nonvolatile memory based on discrete charge storage on the nanoparticle floating gate of a field-effect transistor, and a silicon nanoparticle-based implementation for a cellular automata wire/logic gate, in which information is propagated by cell-cell electrostatic interactions rather than by current flow. The nanoparticle engineering and assembly methods developed in this program may enable the first realization of a cellular automata logic gate capable of room temperature operation. Key aspects of the synthesis and processing are engineering of nanoparticle size, shape, dielectric passivation thickness and stoichiometry, and control of nanoparticle position. Control of position is achieved in model device structures using force manipulation by a scanning probe microscope. Another effort is aimed at utilizing fluid and colloidal forces to fabricate ordered linear and planar arrays. Characterization of charge state and morphology at the single particle level is performed using conducting tip atomic force microscopy. %%% The project addresses basic research issues in a topical area of science and engineering having high technological relevance. The research will contribute new knowledge at a fundamental level to important aspects of electronic devices. The basic knowledge and understanding gained from the research is expected to contribute to improving the performance of advanced devices by providing a fundamental understanding and a basis for designing and producing improved materials, and materials combinations. An important feature of the program is the integration of research and education through the training of students in a fundamentally and technologically significant area. This research grant is made under the Nanotechnology Initiative (NSF 98-20), and is co-funded by the Directorate for Engineering, the Directorate for Computer and Information Science and Engineering, and the Directorate for Mathematical and Physical Sciences. The research team is a university/industry/government lab collaboration between Applied Physics and Chemical Engineering faculty at the California Institute of Technology, and technical staff at Bell Labs/Lucent Technologies and the Jet Propulsion Laboratory.

9903127
Vahala

The proposal describes work to investigate the effect of electronics state energy of relaxation, the variation of capture and escape rates with steady state quantum well carrier density, the impact of barrier height and width on transport rate, and the temperature dependence of the capture/escape processes. The proposed studies will utilize the four-wave mixing measurement techniques that have been pioneered by the PI in pass few years. The technique is capable of measuring frequencies ranging from a few GHz to in excess of 100 GHz. For this work the PI will collaborate with Lucent Technologies to obtain samples used in the experiment and analyzing the data for its impact on the laser performance.

This effort is to develop small, low power, robust spectral rulers called frequency combs that astronomers can use to help measure the motion of stars. In doing so, they can identify planets orbiting those stars and gain information about the mass of the planets. This research enables tantalizing discoveries about the existence and nature of other planets, ultimately helping us to search for other worlds like our own.

This research is to advance the instrumental capabilities for Precision Radial Velocity (PRV) observations of exoplanet-hosting stars by creating broad, octave-spanning comb spectra in the 0.8 micron to greater than 2 micron region at GHz repetition rates through soliton formation in silica microresonators. This will be accomplished by balancing Raman and dispersive wave effects in the microresonators, and using pulsed excitation of the microcomb to improve pumping efficiency. The resulting combs will be used as low power, compact calibration sources on high-resolution spectrographs installed at ground-based observatories. Advances in PRV instrumentation can enable the identification of Earth-sized planets in the Habitable Zones of some of the nearest stars to the sun.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.