A novel fiber-optic Fabry-Perot resonator with two mode-conversion mirrors: proposal and application

A novel fiber-optic Fabry-Perot resonator composed of a piece of fiber with two LP/sub 01//spl rlarr2/LP/sub 02/ mode-conversion reflectors is proposed and theoretically investigated. The reflective fiber-optic LP/sub 01//spl rlarr2/LP/sub 02/ mode converter is analyzed based on the coupled-mode theory. The resonance characteristics including the transmission, reflection, and circulation of this novel fiber resonator are examined. In addition, we also describe the application of this device as an optical filter which can be used for FDM/WDM communications, etc. In contrast to a conventional Fabry-Perot optical filter with a periodic output spectrum, our proposed optical filter has only one peak in output spectrum, while the bandwidth of the filter spectrum is very narrow, with several Megahertz determined mainly by the cavity length of the fiber resonator. Finally, it is demonstrated that the characteristic of this optical frequency filter can be greatly improved by introducing a gain mechanism using a rare-earth-doped fiber. The tunable performances of this optical filter are also presented.