Parametric Frequency-conversions Using Nonlinear-Optical Fibers

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In optical-communication systems instead of telecommunication ones, silica-glass fibers are being installed , while in LAN, plastic optical fibers(POF) will be used for considering cost performance. However, interconnection between these two kinds of fibers is not easy, since their tranparent wavelength-range and radii of their cores are different from each other.This research is a propsal to simultaneously solve the above two problems by using a nonlinear-optical fiber and an axicon. The fiber with a core of a nonlinearoptical organic crystal will provide parametric interconversion of wavelengths of 1.32 and 0.66 μm or 1.55 and 0.775 μm which are used in silica fibers and POFs, respectively, while an axicon or a conical prism can convert the beam radii radiated from these fibers. There, the Cerenkov-radiation type phase-matching is used in the interconversion, that is, the second-harmonic generation(SHG) and the degenerate optical parametric generation(OPG) . We have tried to realize the proposal and have obtained the following results.1. We succeeded in the preliminary experiment of SHG from 1.064 to 0.532 μm and also in the experiment of SHG from 1.32 to 0.66 μm with efficiencies of around 1%, for fundamental powers of several 10s mW using one-mm long fibers. As for OPG, we optimized the nonlinear-optical fiber by selecting the cladd glass and evaluated the gain coefficient based on our theory, although we have not yet obtained the OPG signal.2. Using an axicon, the radiated second-harmonic wave with a conical wavefront was collimasted and the radius of the second-harmonic ring could be controlled by changing the distance between the nonlinear-optical fiber and the axicon, by which we demonstrated a possibility of optical interconnection of the silica and plastic fibers.We are now trying to obtain the OPG signal and to realize the opticalinterconnection.