Abstract: A wave transmission medium includes an input port 3-1 and an output port 3-2. A field distribution 1 and a field distribution 2 are obtained by numerical calculations. The field distribution 1 is a field distribution of the propagation light (forward propagation light) launched into the input port 3-1. The field distribution 2 is a field distribution of the phase conjugate light (reverse propagation light) resulting from reversely transmitting from the output port side an output field that is expected to be output from the output port 3-2 when an optical signal is launched into the input port 3-1. According to the field distributions 1 and 2, a spatial refractive index distribution is calculated such that the phase difference between the propagation light and reverse propagation light is eliminated at individual points (x, z) in the medium.

Abstract: When plug is fitted to adapter, optical fiber is inserted to an alignment hole for the optical fiber. By providing a taper at the entrance thereof, even if the tip of the optical fiber is deviated from the central position, the deviation is absorbed to make it possible for the optical fiber to be inserted smoothly. When two plugs is fitted to adapter, the tip of one optical fiber is confronted with the other one in the alignment hole, and excessive length L.sub.1 -L.sub.2 is pushed into the two optical fiber-bending spaces with a suitable distribution, thus the optical fiber buckles therein. The end face of the optical fiber is subjected to flat surface-polishing, removal of ripples after being cleaved, or chamfer grinding after being cleaved. The buckling portion of the optical fiber is coated with carbon or the like.