PURPOSE: To easily detect an insufficient carbon coat layer by a method wherein an optical fiber subjected to hermetic coating is placed in an ambience of hydrogen, an optical pulse having the absorption wavelength of hydrogen is let in from one end and, the scattering echo is monitored from the entering side of the pulse.
CONSTITUTION: An optical pulse from an LD light source 1 is let into an optical fiber 4 subjected to hermetic coating via a condenser lens 2 and a directional coupler 3. A minute scattering light is scattered rearward when the optical pulse advances in the optical fiber 4. The light of the scattering light which returns back to the entering end is received by a photodetector 6 through the directional coupler 3 and measured. Accordingly, the state of loss of the optical fiber 4 due to hydrogen is measured. In order to enhance the measuring sensitivity, response waveforms of a plurality of optical pulses are taken into an electronic circuit and averaged. In this manner, an insufficient part of the carbon coat layer can be easily detected.
WADA AKIRA
SAKAI TETSUYA
| JPS63217252A | 1988-09-09 | |||
| JPS63217257A | 1988-09-09 |