Parametric Frequency-conversions Using Nonlinear-Optical Fibers

在光通信系统而不是电信系统中，正在安装石英玻璃光纤，而在局域网中，出于性价比考虑，将使用塑料光纤(POF)。然而，这两种光纤的互连并不容易，因为它们的透明波长范围和纤芯半径是不同的，本研究是一种利用非线性光纤和轴棱镜同时解决这两个问题的方案。以非线性光学有机晶体为芯的光纤将提供用于石英光纤和POF的1.32和0.66μm或1.55和0.775μm波长的参数相互转换，而轴棱镜或圆锥棱镜可以转换这些光纤辐射的光束半径。其中，切伦科夫辐射型相位匹配被用于互转换，即二次谐波产生(SHG)和简并光学参数产生(OPG)。我们努力实现了这一建议，并取得了以下成果。我们成功地进行了1.064~0.532μm倍频和1.32~0.66μm倍频的初步实验，利用1 mm长的光纤对10s mW的基波功率进行了效率约为1%的实验。对于OPG，我们选择了包层玻璃对非线性光纤进行了优化，并根据我们的理论计算了增益系数，虽然我们还没有得到OPG信号。利用轴棱镜将辐射的二次谐波与圆锥波前准直，通过改变非线性光纤与轴棱镜之间的距离来控制二次谐振环的半径，从而论证了石英光纤与塑料光纤实现光互连的可能性。

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.