Amnon Yariv, Ph.D. - US grants

The following is an award to engage in research aimed at understanding and exploring experimentally the ultra high speed potential of quantum well lasers. The recent advances in quantum layer understanding and growth now make the prospects of subpicosecond pulses at rates greater than 100 GHz a distinct possibility. It is proposed to pursue this goal using our combined crystal growth (MBE, LPE), microwave, picosecond pulse, and simulation capabilities.

Research in semiconductor-based optoelectronics will be conducted, with emphasis on applications to optical communication. Semiconducted laser noise will be analyzed to determine the basic physical limits to the spectral purity of semiconductor lasers. This work will extend the previous results on a self-consistent semiclassical theory of noise behavior to a full quantumtreatment, particularly quantum-well lasers. Detuned loading in coupledsemiconductor lasers will be pursued both theoretically and experimentally. High output power laser arrays which could have considerable impact on the development of optoelectronic processing and devices will be addressed. Several new ideas including fabrication techniques could overcome some of the current lack of success in this area.

This research project is directed to exploring the possibilities of implementing large parallel generic neural network architectures using both silicon devices and optical technology. The underlying principle of the new architectures is to take advantage of the fact that signal processing in silicon ins an advanced and mature technology and to incorporate optics where silicon fails, namely, the interconnectivity problem. These new architectures make possible the construction of fully integrated, alterable networks with 1000 neurons using existing technologies. The next important breakthrough will be to implement a complete learning structure with local memory on a single device. Large, fully parallel architectures that incorporate a simple learning algorithm are delineated and their initial design specified.

Professor Yariv and his co-workers are the innovators of the quantum well laser, a device which has tremendous potential for practical application in opto-electronic systems. NSF supported this early work and the research proposed here is a continuation of this effort. One major contribution will be both the theoretical and experimental study of these devices in order to achieve a major reduction in the threshold current. Because of materials problem associated with fabrication of these systems, Dr. Yariv has devoted considerable commitment, time, money and effort into materials technology to enhance this productive research.

9224604 Yariv This project wil investigate the fundamental noise properties of semiconductor lasers. The need for narrow bandwidth and frequency stabilized semiconductor lasers in coherent lightwave communication networks is crucial. For multi-channel distribution systems it is important that the laser frequency will be known exactly. In addition narrow laser linewidth increases the S/N ratio and the network's channel capacity. Narrow linewidth lasers are also needed for microwave links, precision spectroscopy, time and frequency standards and many other important applications. This research is motivated with the view of a significant, orders of magnitude, reduction of the quantum limited phase noise and increased frequency stability of the semiconductor laser. Another prospect is amplitude noise squeezing below the standard quantum noise limit. These important problems will be pursed using the concept of a semiconductor laser with dispersive loss. This work will continue and expand unfunded, exploratory studies in our group. The early results from these preliminary studies are promising. A subcontract to Professor Shevy at the University of Miami will contribute to the work on frequency stabilization and linewidth reduction ***

0401397
Yariv

This proposal addresses theoretical and experimental investigation of a completely
new type of optical resonators.

Intellectual merit:

The resonator belongs to the class of "Defect" resonators in periodic photonic bandgap structures [13, 14, 17]. The "defect" consists of a controlled departure from the ideal index distribution of a cylindrical Bragg waveguide [3, 4]. The main advantage of such resonator is the fact that the (annular) defect, and therefore the light confinement, can be placed at will at any radial position and not necessarily at the core or the periphery (like whispering gallery resonators).

In addition, the dependence of the modal characteristics on the transverse periodicity (or quasi periodicity) offers a new and major control of the free spectral range which can be increased by, possibly, an order of magnitude. Moreover, by placing the defect, where the light is concentrated, away from the outer boundary, where inevitable scattering due to surface imperfections take place, the new resonator promises to posses, potentially, much higher Q-factor than is possible with the conventional dielectric counterparts. In addition, the interaction of the electrical field with the surrounding medium can be enhanced significantly by the ability to confine the field in an air defect. This is important for applications including optical communication, spectroscopy, detection of chemical and biological agents, quantum communication and encryption which depend on a strong atom (molecule) - light interaction.

The broader impact:

The Caltech educational environment supports and encourages collaborative work and interaction between experienced researchers (senior graduate students, postdoctoral scholars, faculty) and inexperienced researchers. Programs such as the Summer Undergraduate Research Fellowship (SURF) and the Minority Undergraduate Research Fellowship (MURF) enables a diverse group of students, both from within and outside Caltech, to get involved in cutting-edge scientific research under the guidance of faculty and senior researchers. The strong collaborations of their group with industry partners and government laboratories will expose the student to real-world problems and enhance the dissemination of new ideas and technology. Periodically, results from this work will be presented in a research seminar open to all Caltech students who wish to attend, ensuring knowledge transfer to the community.

0438038
Yariv

This project will experimentally investigate the slowing and stopping of light in polymeric, tunable, and nonlinear coupled high-Q optical microresonator waveguides. In principle, a light pulse can be slowed arbitrarily on a chip in ambient conditions. To achieve this goal, the project will target (i) the application of novel tunable and nonlinear optical polymers, (ii) the development of submicron resolution fabrication methods and processes for polymers, and (iii) the study of new device designs and concepts for optical microresonators.

Intellectual Merit: The demonstration of slow light on a chip will be important from a fundamental physics point of view while enabling new classes of optical delay lines, buffers, and memory elements which are important to interferometry, optical telecommunications, and optical computing systems. The development of tunable, nonlinear, and low-loss polymeric optical devices will be generally applicable to optical switches, filters, and modulators. The project will comprehensively address the issues concerning the materials, fabrication and processing techniques, and physical designs for polymeric integrated optical devices.

Broader Impacts: This project primarily supports the research of a female graduate student. Programs such as the summer and minority undergraduate research fellowships enable a diverse group of students to participate in this project. The budget will partially sponsor the student-organized Applied Physics Optics Seminars. Through this project, researchers will interact with collaborators at academic institutions, industry, and government laboratories. The collaborations and the seminar series promote an interdisciplinary cooperation, enhancing the dissemination of new ideas. Through publications and conference presentations, the discoveries from this project will be shared with the scientific community.

Objective
The next major advance in optical communication technology will involve hybrid Si/III-V structures in which the light generation and detection capabilities of III-V semiconductor will join forces with VLSI Si electronics. An important step in this direction is a work described as "electrically pumped hybrid AlGaInAs-silicon evanescent lasers." Our proposal takes the next major step along this direction, we propose another approach to hybrid Si/III-V optoelectronic circuits which combines, with minimal compromise, the advantages of both materials. This is based on the ability to control the mode behavior in the composite waveguide system.

Intellectual Merit
The eigenmodes ("Supermodes") of such a coupled waveguide system can be designed such that the optical energy is confined to either the Si or the III-V waveguide. This can be achieved by controlling the geometry of the waveguides along the propagation direction, e.g., by tailoring the Si waveguide width. Numerical calculations predicted a four-fold enhancement of the modal gain with this design compared with that of the existing Si evanescent lasers.

Broader Impacts
Once experimentally demonstrated, the "supermode coupling" scheme will result in more efficient devices so as to greatly increase the density of integrated components. Through various kinds of exposure, the results and discoveries will be shared with the scientific and technological communities at large. Another goal of this project is to educate and train a group of students to pursue scientific research and to mentor them about the culture of scientific discovery.

"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)."


The project proposes to investigate a new type of amplifying coupled-resonator optical waveguide (CROW). The CROW is to be realized in a waveguide geometry with individual resonators formed by grating "defects". The waveguide will be fabricated on a hybrid Si/III-V platform in which the propagating slow mode will be amplified through the partial modal penetration into the amplifying
III-V layers. The project aims to fabricate a grating CROW with 100 defect resonators thus enabling signal storage of more than 10 bits in a compact semiconductor geometry.

Intellectual Merit
Having initially proposed and analyzed CROWs for the purpose of slow-light waveguides the authors have come to the conclusion that the best way to realize them would be grating defect CROWs. Compared to microring CROWs and 2D photonic crystal defect CROWs, grating CROWs over the advantages of small resonator sizes, smaller footprint, and easier control of the coupling coefficients.Since the major weakness of any slow-light device is the optical attenuation due to inherent losses, the amplifying CROW will compensate for the loss inside the structure. The key technology of current-pumped hybrid Si/III-V waveguides will be the amplifying platform of the proposed work. The demonstration of amplifying CROWs with 100 resonators will enable new classes of optical delay lines, buffers, and memory elements.

Broader Impacts
Another aspect of the project is to educate a diverse group of students to pursue scientific research and to mentor them about the culture of scientific discovery. Programs such as undergraduate thesis research, the Minority and Summer Undergraduate Research Fellowship (MURF and SURF, respectively), enable a multicultural group of students to participate in scientific research.

The objective of this research is to help bring closer to reality the inevitable merger of optics and electronics, or in material terms, the union of silicon and III V materials on a platform for the next generation of information technology. Specifically, it involves the use of some of the more subtle aspects of guided wave optics to realize spatial control of information-bearing optical beams in crystals.

Intellectual Merit

The intellectual merit of the proposed research is to extend the concept of adiabatic transitions to the optics and communications fields. For years, adiabatic transitions have played a key role in physics and, more recently, chemistry. If successful, the proposed work could have a significant impact on the U.S. optoelectronics industry, contributing to both employment and well-being.

Broader Impacts

Carrying out the proposed research requires the training of graduate students in diverse areas such as electromagnetic modal theory and semiconductor device fabrication. Graduate students engaged in this research will be exposed to ahead-of-state-of-the-art theoretical and fabrication tools. Undergraduate students will be incorporated in the project through Caltech's Summer Undergraduate Research Fellowship program. Results and discoveries from this project will be shared with the scientific and technological communities through journal publications, conference presentations, and seminars.

Project Abstract
This project proposes the development and demonstration of a label-free sensing instrument based on the integration of an electronically controlled linear swept-frequency semiconductor laser, a high quality factor (Q) optical resonator with covalent surface functionalization, and a microfluidic cell for analyte delivery. It will address a number of key issues that currently prevent this technology from becoming an accessible, affordable, and useful tool. These efforts will develop the optical cavity sensing platform to a point where it is robust and repeatable, and provides sensitivity and cost-effectiveness that are at least an order of magnitude better than any available alternative biomolecular assay instrument.
The proposed system will combine the results of two major recent developments in the field of optical and laser physics: the high-Q optical resonator and the phase-locked electronically controlled swept-frequency semiconductor laser. The high-Q optical resonator is part of a monolithic unit with an integrated optical waveguide, and is fabricated using standard semiconductor lithography-based methods. Optoelectronic swept frequency lasers will be developed at wavelengths relevant for aqueous sensing, and will replace expensive and fragile mechanically-tuned laser sources whose frequency sweeps have limited speed, accuracy and reliability. The resonator will be functionalized using known techniques providing an adaptable and selective surface chemistry. The sensor will include an integrated microfluidic flow cell for precise and low volume delivery of analytes to the resonator surface.
The proposed instrument represents an adaptable and cost-effective platform capable of various sensitive, label-free measurements relevant to the study of biophysics, biomolecular interactions, cell signaling, and a wide range of other life science fields. It will be capable of binding assays, thermodynamic and kinetics measurements, and has the potential for additional impact through integration into existing instruments to replace less sensitive analytical methods. The sensor also has potential applications in point-of-care medical diagnostics, where it can enable early detection of relevant antigens.
The project is inherently multidisciplinary and will develop expertise in and better understanding of the interplay between such diverse fields as semiconductor lasers, optical nanofabrication, high speed electronics, control systems, fiber-optics, microfluidics, biomolecular binding assays, mass transfer, and integrated instrument design. It affords the opportunity for two graduate students and an undergraduate student to take part in a collaborative research effort under the close guidance of the PIs, educating the students in the culture of scientific discovery, alongside engineering and application considerations. The results obtained during the course of the project will be published in leading scientific journals and conferences.