Optically powered radio-over-fiber remote units have been designed and constructed for distributed antenna system applications using separate fibers for power and signal transmission. The feasibility of this approach has been investigated through a series of transmission measurements, based on the IEEE 802.11g wireless local area networking standard at a frequency of 2.5 GHz using 64-QAM OFDM modulation at 54 Mb/s. These measurements show that high-quality multilevel signal transmission is possible with modest levels of optical power at the central unit. For example, an EVM of around 3% has been achieved for an RF output power of 0 dBm using a central unit optical power of 250 mW over a link length of 300 m.

${\mathrm{Er}}^{\mathrm{3+}}$ doped aluminosilicate thin films were prepared on silica and silica Si substrates by the sol-gel method. The Er ion concentration was varied from 0.25% to 1%. Fluorescences of Er ions in the visible and infrared regions were characterized. Green and red up-conversion fluorescences centered at 548 and 655 nm for, respectively, the ${(}^2{H}_{\text{11/2}}{+}^4{S}_{\text{3/2}}{\mathrm{)\to }}^4{I}_{\text{15/2}}$ and ${}^2{F}_{\text{9/2}}{\to }^4{I}_{\text{15/2}}$ were observed. A broadband peak was observed at 1531 nm corresponding to the ${}^4{I}_{\text{13/2}}{\to }^4{I}_{\text{15/2}}$ transition, with the full width at half-maximum of 47 nm comparable to those prepared by other methods. The fluorescence lifetime of the ${}^4{I}_{\text{13/2}}$ excited state was found to be constant and equal to 3.5 ms until a high Er doping of 0.5 at. %.

Stable microwave oscillators are realized based on high-quality factor resonators, which in turn are realized using acoustic, electromagnetic, and optical technologies. This article provides an overview of close-in carrier phase noise and temperature stability of various oscillators