MODE COUPLING EVALUATING DEVICE

摘要

PURPOSE:To measure the lengthwise distribution of the degree of mode coupling with high resolution by detecting the amplitude of an interference signal between light in one propagation mode and light in the other propagation mode which is generated by mode coupling in a transmission path to be measured as a function of an optical path length difference set by an optical path length varying means between both propagation mode light beams. CONSTITUTION:Projection light from a light source 1 is made incident on the optical fiber 6 to be measured as one propagation mode by a polarizer 5. Then a prism 7 splits luminous flux which is projected from the optical fiber 6 and has two propagation mode components into light beams in the two propagation modes. Further, an optical path length varying device 3 varies and sets a necessary optical path difference between both split light beams and a frequency shifting device 8 gives a constant frequency difference between the two split pieces of luminous flux. A half-mirror 10 is a multiplexing means and an analyzer 11 operates to put two orthogonally deflected pieces of luminous flux together. Then the amplitude of the interference light is detected as a function of the optical path length difference by a photodetector 4, an intermediate frequency filter 12, an amplifier 13, and a waveform storage device 14.