Direct Digitization of Terahertz Signals
George Valley, Electronics and Photonics Laboratory, The Aerospace Corporation, El Segundo, CA
April 27, 2007
Abstract
Terahertz (THz) electromagnetic radiation is generally defined as radiation in the frequency band between 100 GHz and 10 THz. Using radiation in this band for wireless transmission offers the promise of hugely increased capacity and speed compared to today's cell phone and wireless internet networks-leading to fewer dropped calls, better voice quality, wireless HDTV on demand, etc. THz radiation can also be used for imaging, in biological and medical applications, and in environmental sensing. But development of THz-band components is just beginning and one key component needed for this development is a digital oscilloscope to measure THz signal voltages as a function of time. The best digital oscilloscopes today can directly digitize radio frequency bandwidths up to 20 GHz and incremental improvements can be expected over the next decade, but the maximum input bandwidth and sampling rate of oscilloscopes is directly linked to the maximum speed of the semiconductor technologies used to make them. These speeds, in turn, are linked directly to basic physical properties of semiconductors and the sizes of the devices made from them. Unless a massive technology shift away from silicon occurs, the physical properties will not change and decreasing device sizes also leads to difficult physical issues-hence the claim that there will be only incremental improvement in the input bandwidth and sampling rate of oscilloscopes. Thus one is strongly motivated to develop new methods to digitize THz signals. At The Aerospace Corporation and the University of California, Los Angeles we have been developing a unique optical processing technology that stretches radio frequency signals uniformly in time or equivalently compresses their bandwidth. This technology combined with the latest digital oscilloscopes has demonstrated a sampling rate of 5 terasamples per second and has directly digitized a 90 GHz signal, but it has the potential to reach 10 THz or more. In this talk I will discuss the applications for direct digitization of THz radiation, review the state of the art in analog-to-digital converters, and describe the novel optical processing technology that we use to compress the bandwidth of electronic signals.
Biography
George Valley has an AB in physics from Dartmouth College (Hanover NH) and a PhD in physics from The University of Chicago (IL). He has worked at Cornell Aeronautical Laboratories and Hughes Aircraft Company and is now Senior Scientist at The Aerospace Corp. (El Segundo, CA). He is a member of the American Physical Society and a fellow of the Optical Society of America. Past research work has focused on nonlinear optics, optical solutions, photorefractive materials, free-space laser communication and wave propagation in random media. Current research interests include optical fiber amplifiers, simulation of mixed signal integrated circuits, and photonic analog-to-digital converters.