We report measurements of intrinsic dissipation in micron-sized suspended resonators machined from single crystals of galium arsenide and silicon. In these experiments on high-frequency micromechanical resonators, designed to understand intrinsic mechanisms of dissipation, we explore dependence of dissipation on temperature, magnetic field, frequency, and size. In contrast to most of the previous measurements of acoustic attenuation in crystalline and amorphous structures in this frequency range, ours is a resonant measurement; dissipation is measured at the natural frequencies of structural resonance, or modes of the structure associated with flexural and torsional motion. In all our samples we find a weakly temperature dependent dissipation at low temperatures. We compare and contrast our data to various probable mechanisms, including thermoelasticity, clamping, anharmonic mode-coupling, surface anisotropy and defect motion, both in bulk and on surface. The observed parametric dependencies indicate that the internal defect motion is the dominant mechanism of intrinsic dissipation in our samples.

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jNTRODUCTIONWith the telephone trunk lines in place, the telephone operating companies and CATV corporations are intending to bring fiber optic technology directly to the home using a singlemode bidirectional fiber network. The obvious advantages are the enhanced services that could be provided by the enormous information capacity available using optical fiber. Such services include: a. Video phone. b. Home banking and shopping. c. Automated utilities recording. d. Home security systems. e. CATV. f. High definition TV (HDTV).Many systems configurations have been put forward and several trials are presently underway. The most typical configuration is shown in Figure 1 and uses a single fiber to the home in a bidirectional format. This system can provide POTS ( Plain Old Telephone Service) and with a WDM overlay, could provide video and other services. Remote Electronics Site DistributionThe "last mile' Singlemode bidirectionalCoupler or WVDM Xmit Receive Module Figure 1. Schematic of single fiber -to-the -home system, In order for a fiber -to -the -home system to be economically competitive with respect to coaxial and twisted -pair approaches, low -cost active and passive components such as transmitters, receivers, couplers, connectors and WDMs are required. In this paper, we show that the wavelength dependence of passive fiber optic couplers strongly affects system performance and ultimately system cost. The utilization of Wideband couplers with their minimal wavelength dependence1-4 will be addressed in terms of improved system performance and reduced system cost through the relaxation of laser wavelength tolerances. As system innovations such as the utilization of Wideband couplers improve the economics of the fiber-to -thehome services, we shall see considerable market penetration by the technology over the next 2 to 3 years.