The characteristics of 155 Mbps optical propagation through atmosphere at the wavelengths of 0.78 and 1.55 m over a 72 m range were measured. Two propagation characteristics were compared to examine the wavelength dependence on the rain rate and the aperture size of a receiver. An enhanced intensity exceeding the signal level measured in the absence of rain was observed at both wavelengths during 7.2 mm/h rain. The resultant bit error rate is shown to be dominated mainly by the rain-induced scintillation rather than the attenuation.

A frequency-tuning method in the microwave region, which maintains a high unloaded Q-factor, was demonstrated using a double-sapphire-loaded cavity which operates on the Whispering Gallery mode, WGH9,1,0. Two adjacent nominally identical sapphire cylinders were positioned in a copper cavity and tuned by changing their relative coupling. A frequency tuning range of 85 MHz and a maximum unloaded Q-factor of 1.3 105 was experimentally measured at room temperature. This is only 13% less than the single resonator Q-factor, which is a small compromise to pay for the increased tuning capacity.

A cryogenic Whispering Gallery sapphire resonator oscillator has been investigated using a 4 K pulse-tube cryocooler. The turnover temperature of the chosen mode in the sapphire crystal was 9.17 K with an unloaded Q-factor of 7108. The prototype sapphire-loaded cavity oscillator was designed to oscillate at 9.195 GHz. A fractional frequency stability of 210-13 was measured at integration times of 10 s.