| Popis: |
We describe a new configuration for an optical fiber acousto-optic frequency shifter using a section of two-mode fiber where acousto-optic interaction causes mode-convertion accompanied by single sideband frequency translation. A fiexural acoustic wave travels in the stripped section of the two-mode fiber. Because both optical and acoustic waves are confined in the fiber, high efficiencies (close to 100 %) can be achieved with relatively low RF power (< 100mW) applied to the transducer. The acoustic wave is excited in the fiber via an acoustic horn, which focuses the acoustic energy generated by a 5 x 5 mm2 transducer into a fiber-size tip. The new configuration proposed here employs the fiber and the acoustic horn in a collinear assembly, which can reduce excitation of backward acoustic waves in the fiber, contributing to a better image sideband suppression. Moreover, the collinear configuration improves ruggedness of the fiber-to-horn bond as well as device compactness. An improvement of the acoustic bandwidth was also observed. A study of several possible variations of the main configuration was performed and an optimization regarding power requirements, convertion efficiency and acoustic bandwidth is discussed. |
