MEASURING METHOD OF MINUTE REFRACTIVE INDEX DIFFERENCE BETWEEN OPTICAL WAVEGUIDE LINE AND ITS SUBSTRATE

摘要

PURPOSE:To make it possible to directly compare the refractive index by use of the same optical system and to derive the difference with high precision, by measuring the angle of incidence to the coupler in case the reflected light quantity is extremely a little, and also deriving the refractive index difference by measuring the angle of incidence in case of total reflection critical time. CONSTITUTION:The sample table 5 is rotated in the vicinity of the critical point of total reflection in the boundary between the right angle prism coupler 26 for incidence and the substrate 7, and its rorary angle is detected by the angle detecting element 28, and also the angle variation curve of strength of the folded reflected light is derived by the photodetector 22. The angle thetagz of the table 5 in case strength drops abruptly is derived from the above curve. Subsequently, the angle thetagI of the table 5 in case strength is maximum is derived by deriving the curve of the reflected light strength, which has passed through the pin hole 2 of the reflected light from the beam splitter 14. And the angle of incidence thetagin to the coupler which performs incidence to the phototransmission line 6 is derived efficiently by the aforementioned difference. Subsequently, the angle of incidence thetas to the coupler at the critical time of total reflection in the boundary between the coupler 26 the and substrate 7 is derived. And the refractive index differnece required is obtained by operating the respective regular expressions derived by the rule of Snell.