| The two orthogonally polarized modes of birefringent optical fiber can be coupled by allowing a travelling acoustic wave to induce stress in the fiber. This coupling can be used to produce a wide variety of modulators in all-fiber form. Among the types of modulators which can be constructed are single-sideband frequency shifters, tunable optical filters, and broadband amplitude modulators. The first demonstration of such devices is described in this dissertation, as is a simple theory predicting their performance.; In the case of frequency shifters, properties of the fiber limit the useful frequencies of devices using a collinearly propagating acoustic wave to a few megahertz. Techniques have been developed to overcome these limitations and extend the usable range of such devices to several tens of megahertz. Experimental demonstration of two such concepts is included in this dissertation. In the first, an acoustic wave impinges on the fiber at an angle; in the second, the acoustic wave makes periodic contact with the fiber.; Also discussed are the use of similar techniques for making narrowband, tunable optical filters. In these devices, the interaction between the acoustic wave and the fiber takes place over a very long length, making the device narrowband. By changing the acoustic frequency, the center of the optical passband can be tuned. Techniques for making broadband amplitude modulators are also described. In these devices, the optical power in each of the two polarizations is made to vary in accordance with an input electrical signal. Because the acoustic wave is no longer involved in phase-matching in these devices, the bandwidth is limited only by the design of the acoustic transducer.; Future directions for this work are examined. The possibilities of using acoustic waves guided by the fiber itself and the use of monolithic, deposited transducers are also considered. |
