Optical-Fiber Laser Amplifier for Ultrahigh-speed Communications

This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANLJ. The project objective was to develop a praseodymium-based 1.31-pm fiber amplifier that can be optically pumped with off-the-shelf semiconductor diode lasers. Development of optical amplifiers for the 1.3 1 -pm communications window is motivated by the push towards "all-optical" networks that will support multigigabits per second communication rates. Our approach exploited radiationless energy transfer from optically pumped Yb3+ ions co-doped with Pr3+ into a fluorozirconate glass (ZBLAN). We obtained a gain of approximately 10 on a 1.31-pm amplifier, a value too low for practical applications. In two spin-off applications, all-solid-state operation at all four output wavelengths was achieved in the development of a four-color visible laser, and laser cooling of a solid material was demonstrated for the first time in the development of a fluorescent cryogenic refrigerator. 1. Background and Research Objectives Next-generation telecommunications systems will be based on the transmission of information-bearing optical signals through silica-glass fiber waveguides. Although signal attenuation in silica fiber is actually less than in free air, optical communications systems still require repeater stations every 50 km to compensate for scattering and absorption losses. Existing optical networks accomplish this task through optical-to-electrical signal decoding, followed by optical regeneration and retransmission over a subsequent fiber link to the next repeater. These optoelectronic regenerators are slow, complex, and sacrifice the greatest advantage offered by optical communications-wavelength multiplexing. There has, therefore, existed strong motivation for the development of all-optical systems in which an appropriate optical amplifier is used to refresh optical signals directly. *Principal investigator, e-mail: gosnell@ lanl.gov