Distributed Mixer Engineering with Molecular-Scale Accuracy: Breaking the Stochastic Barrier

Stojan Radic
University of California, San Diego

Thursday, June 24, 2010 at 3:00pm
Engr IV Maxwell Room 57-124

Abstract

Parametric wave mixers have been used to demonstrate a 20THz-wide sampling gate, frequency conversion over 100THz and real-time analysis of ultrafast signals. In contrast to traditional wave exchange in crystalline, centimeter-long devices, distributed mixer utilizes long, high-confinement fibers transparent enough to support parametric interaction over hundreds of meters. Such device possesses five-orders-of-magnitude longer effective length than that of a crystalline device and high figure of merit, even for the case in which a low-nonlinearity material is used.

Unfortunately, long device lengths also impose basic limitations on mixer performance. Small axial fluctuations in fiber cross-section, inherent to any fabrication process, vary the phase-matching condition drastically along the mixer length. Indeed, high-confinement fibers must be manufactured with sub-nanometer radial precision to synthesize spectrally equalized responses beyond 10THz. While recent fabrication has led to new types of silica fibers approaching this target, the fundamental physical limits must be recognized: the glass building block has a diameter of only 0.6nm, as defined by the Si-O molecular ring. In practical terms, this means that a 100m-long mixer would require a drawing process possessing molecular-scale accuracy along kilometers of fabricated fiber. This requirement, recognized as a stochastic parametric barrier, is a fundamental limitation preventing the synthesis of arbitrary-bandwidth distributed mixers.

Rather than demanding unattainable fabrication tolerances, distributed parametric synthesis can be achieved by mapping the nanometer-scale fiber fluctuations. By obtaining exact, molecular-scale knowledge about fiber transverse geometry, it is possible to either select a set of unique fiber segments or alter the fiber geometry in a localized manner.

To accomplish this goal, a new method based on localized four-photon mixing (FPM) was developed. The approach enabled the first construction of distributed mixers capable of 20THz bandwidth and 100THz frequency conversion. New localized FPM physics has basic implications for nanometer-scale, non-destructive measurements, sensing and device fabrication and will be briefly outlined.

Biography
Stojan Radic graduated from The Institute of Optics in 1995 and has subsequently served in Corning and Bell Laboratories. He is presently a Professor and a Director of Systems Laboratory at University of California San Diego and California Institute for Telecommunications and Information Technology. Dr. Radic is a Fellow of the Optical Society of America and serves as editor with IEEE Photonics Technology Letters and Optics Express Journals. He chaired committees with Parametric Processing (IEEE), OFC (OSA/IEEE), OAA (OSA), APOC (OSA) conferences and has founded Coherent Optical (OSA) conference.