A늌W

2009 Seminar

20090613(Stanford, CA)

                                   High Contrast Gratings and Their Applications in Optoelectronics 

Abstract:

Broadband mirrors with very high reflectivity are the fundamental building block for numerous device applications, including lasers, modulators, detectors, sensors and imaging, ranging from 0.7mm to 12mm wavelength regimes. Semiconductor-based distributed Bragg reflectors (DBRs) have been used to achieve high reflectivity required for devices such as vertical cavity surface emitting lasers (VCSEL), detectors and filters. Because of the very short gain length in VCSELs, a very high reflectivity (>99%) is required in the DBRs.  Hence, the DBRs are typically very thick, consisting of 20-40 pairs of alternating index materials.  This has been the most critical bottleneck for the realization of VCSELs in wide wavelength regimes. 

Recently, we reported a novel mirror to replace the DBRs.  This mirror consists of a single layer of one-dimensional subwavelength grating made of materials with a large refractive index contrast, and hence the name high-contrast grating (HCG).  The results in this seemingly extremely simple geometry are a wealth of unexplored and unexpected properties.  In this tralk, we review experimental and simulation results demonstrating many desirable attributes in HCG and HCG-based devices.  First, we will discuss the concept of two designs of HCGs as broadband reflectors to provide lithographically defined polarization control, transverse mode control and large fabrication tolerance.  The HCGs have been incorporated into a tunable micro-electro-mechanical (MEM) VCSEL structure. With a drastic reduction of the mirror thickness by 40 times, the mass of the entire MEM structure is reduced by 10,000 times.  This resulted in a >100 times increase in tuning speed in 60 ns range. 

We will discuss HCG as a high-quality (Q) factor optical resonator with in-plane resonance and surface-normal emission. The simulated Q factor of the resonator is as high as 500,000. A HCG-resonator was fabricated with an InGaAs quantum well sandwiched in-between AlGaAs layers showed a Q factor of >14,000.

Finally, we will discuss the use of HCG as a guiding medium for a novel ultra-low loss single-mode hollow-core waveguide. We analyzed and simulated the propagation loss of the waveguide to be as low as 0.006dB/m, three orders of magnitude lower than the lowest loss of the state-of-art chip-scale hollow waveguides

Biography:

Connie Chang-HasnainA

263M Cory Hall, University of California, Berkeley, CA 94720

cch@eecs.berkeley.edu

 

Prof. Connie Chang-Hasnain is John R. Whinnery Chair Professor in the Electrical Engineering and Computer Sciences Department at the University of California, Berkeley, where she also serves as Director of the Center for Optoelectronic Nanostructured Semiconductor Technologies (CONSRT) and Chair of Nanoscale Science and Engineering Graduate Group.  She received a B.S. degree (1982) from UC Davis, and her M.S. (1984) and Ph.D. (1987) degrees from UC Berkeley, all in Electrical Engineering.  Prior to joining the Berkeley faculty, Dr. Chang-Hasnain was a member of the technical staff at Bellcore (1987C1992) and an Associate Professor of Electrical Engineering at Stanford University (1992C1996).  Since January 1996, she is Professor of Electrical Engineering at UC Berkeley.

 

Her research interests have been in vertical cavity surface emitting lasers and MEMS tunable optoelectronic devices and, most recently, nanostructured materials and nano-optoelectronic devices.  Prof. Chang-Hasnain co-authored over 300 research papers in technical journals and conferences, six book chapters and 31 patents. Prof. Chang-Hasnain was named a Presidential Faculty Fellow, a National Young Investigator, a Packard Fellow, a Sloan Research Fellow, and Outstanding Young Electrical Engineer of the Year by Eta Kappa Nu. She received the 1994 IEEE LEOS Distinguished Lecturer Award, the 2000 Curtis W. McGraw Research Award from the American Society of Engineering Education 2003 IEEE William Streifer Scientific Achievement Award, the 2005 Gilbreth Lecturer Award from National Academy of Engineering, the 2007 OSA Nick Holonyak Jr. Award, and the 2008 National Security Science and Engineering Faculty Fellowship, and 2009 Guggenheim Memorial Fellowship. Prof. Chang-Hasnain is a Fellow of the IEEE, OSA and IEE. She is elected an Honorary Member of A.F. Ioffe Institute in 2005. Since 2007, she is the Editor-in-Chief of the Journal of Lightwave Technology.