ROCKY MOUNTAIN SECTION OPTICAL SOCIETY OF AMERICA & IEEE LASERS AND ELECTROOPTICS SOCIETY Apr. Meeting IEEE Distinguished Lecturer Double Header Date: Monday, 12 Apr. 1999 Time: 5:30 PM 1st talk, 6:30 PM refreshments, 7:30 PM 2nd talk Place: National Institute of Standards and Technology 325 Broadway, Boulder, CO Auditorium 1st talk Free-Space THz Optoelectronics X.-C. Zhang Physics Department Rensselaer Polytechnic Institute IEEE Distinguished Lecturer Abstract: The recent development of ultrafast technologies is leading to new ways of seeing and understanding the world. Terahertz electro-optic sensors may soon make it possible for us to see images of electric fields, diseased tissue, and the chemical composition of plants that cannot be detected by other imaging systems. With a frequency of more than a trillion cycles per second, terahertz (THz) signals occupy the portion of the electromagnetic spectrum between the infrared and microwave bands. In the past, much of the electromagnetic spectrum has been used to characterize the world around us and for communications. Until recently technology to use the THz portion of the spectrum has not been well developed. However, just as one can use visible light to create a photograph, radio waves to transmit music and speech, and microwave radiation (MRI) or X-rays to reveal broken bones, terahertz radiation can also be used to create images or communicate information. In theory, many biological and organic compounds have distinct signatures within the terahertz region, meaning that their chemical compositions might be examined. Such a capability could be applied to the diagnosis of disease, detection of pollutants, or quality control of food products. It is also quite possible that plastic explosives look very different under terahertz light and could be distinguished from the molecular structure of suitcases, clothing, and common household materials and equipment. Recently developed ultrafast technologies, including the terahertz bandwidth electro- optic sensor technique developed at Rensselaer, allow imaging of electric fields, diseased tissue, and chemicals in plants that cannot be detected by other imaging systems. We have designed and tested several electro-optic sensors for characterization of the temporal and spatial distribution of free-space broadband, pulsed THz beams. This optoelectronic detection system provides diffraction-limited spatial resolution, femtosecond temporal resolution, DC-THz spectral bandwidth, and mV/cm field detectability. The sensitivity and bandwidth of the electro-optic detectors are superior to other terahertz detectors currently available. Advantages intrinsic to electro-optic detection include nonresonant frequency response, large detector area, high scan rate, low optical probe power, and large linear dynamic range. The concept of a free-space electro-optic detection system, similar to local field electro-optic sampling, is based on the Pockels effect in electro-optic crystals where a pulsed microwave signal (DC-THz) acts as a transient bias to induce a transient birefringence which can be detected by a synchronous optical probe. THz field measurements using ZnTe as an electro- optic crystal in a collinear geometry have demonstrated a signal-to-noise ratio (SNR) exceeding 1,000,000. Until now, no technology existed that could use this radiation to rapidly create images. The electro-optic sensor can create real-time images with 250,000 pixels, it is also capable of single-shot imaging. Using an optically chirped pulse in an electro-optic detection system, we demonstrate single-shot THz field imaging of the spatial and temporal distribution of a THz pulse from photoconductive emitters. Unparalleled by other THz sampling techniques, this single-shot method provides what is believed to be the highest possible data- acquisition rate. Biography: Xi-Cheng Zhang received his M.S. and Ph.D. degrees in physics from Brown University, Providence, RI in 1983 and 1986. He was a visiting scientist at MIT in 1985. From 1985 to 1987, He worked in the Physical Technology Division of Amoco Research Center. From 1987 to 1991, he was in the Electrical Engineering Department at Columbia University. Since 1992 he has been in the Physics Department at Rensselaer Polytechnic Institute. Currently he is Professor of Physics and Professor of Electrical Engineering. --------------------------------------- 2nd talk Progress in Femtosecond Semiconductor Optoelectronic Devices Osamu Wada FESTA Laboratories, The Femtosecond Technology Research Association (FESTA) 5-5 Tokodai, Tsukuba 300-2635, Japan Tel: +81 298 47 5181 Fax: +81 298 47 4417 E-mail: owada@festa.or.jp IEEE Distinguished Lecturer Abstract: Ultrafast optoelectronic devices will be a key to the development of telecommunication systems exhibiting a throughput beyond 1 Tb/s. This talk describes the recent progress in semiconductors-based optoelectronic devices for the operation in the sub-picosecond and femtosecond time domain, focusing on the work being carried out in the Femtosecond Technology project. Present status and prospects of ultrashort-pulse light sources and ultrafast all-optical switches are discussed. Recent monolithic mode-locked semiconductor lasers have exhibited a high (200 GHz) repetition rate and a ultrashort (500 fs) pulse width. A variety of ultrafast phenomena and device structures are being studied for ultrafast all- optical switches. They include ultrafast electron spin relaxation and intersubband transition in multi-quantum well (MQW) structures. A different approach using Mach-Zehnder interferometer switch structure has shown femtosecond operation. Prospects of new semiconductor materials and devices including nanostructures and quantum wires and dots are discussed in view of the femtosecond applications. Biography: He was awarded M. Eng. degree from Kobe University, Kobe, Japan in 1971, and Ph. D. from University of Sheffield, Sheffield, UK, in 1980. He joined Fujitsu Laboratories Ltd., Kobe and Kawasaki, Japan in 1971 and worked on GaAs electoron devices. In 1976-78 he was on leave as an S(E)RC Independent Research Worker at University of Sheffield, Sheffield, UK and worked on InP growth, characterization and junction devices. From 1978, he was involved at Fujitsu Labs in reserah and development of III-V semiconductor optoelectronic devices including LEDs, LDs, PIN-PDs, APDs and OEICs. Since 1988, he was Research Fellow and worked on optical interconnections and ultrafast devices. Since 1996, he is Group Leader at The Femtosecond Technology Research Association (FESTA), Tsukuba, Japan and researching ultrafast semiconductor optoelectronic devices for telecommunications and signal processing. He is a Fellow of IEEE for the contribution to OEIC and he works as LEOS Distinguished Lecturer for 1998-99. He is also a Fellow of OSA for the contribution to semiconductor optoelectronic devices for telecommunications and interconnections. He acted as Program Chair in 1995 and Conference Chair in 1998 for the Intern. Conf. on Indium Phosphide and Related Materials (IPRM Ιά98), May 1998, Tsukuba. He edited several books including "Optoelectronic Integration: Physics, Technology and Applications" (Kluwer Academic, 1994), "InP-Based Materials and Devices - Physics and Technology" (Wiley, 1999) and "Femtosecond Technology - From Basic Research to Applications Outlook" (Springer, 1999).