Abstract: A method of permanently joining or splicing optical fibers containing a fused silica or fused quartz fiber as a main component and having a high softening temperature by using a CO.sub.2 -laser with TEM.sub.oo mode in such a manner that laser power of about 1 watt may be applied to the optical fiber per unit area thereof. Two or more optical fibers are joined together through fusion with the end portions being positioned in opposition to one another, resulting in a joint having a low joint loss and an increased tensile strength.

Abstract: The ends of a length of optical fiber are coupled to each other to form a closed loop so that light wave may propagate freely through the looped optical fiber. At one or more portions of the looped path of light are provided the sections through which the loop is optically coupled to external equipments. A light pulse is injected through the sections into the loop fiber and a part of it is taken out through the sections each time it completes a cycle of travel through the loop fiber, so that a light pulse train with pulses equidistantly appearing on the time base can be obtained.