PURPOSE: To facilitate the hole size measurement and to increase the accuracy by propagating a millimeter wave or submillimeter wave in the fine-size hole shape part and detecting an interruption frequency determined by a minimum size hole shape having an intrinsic propagation mode.
CONSTITUTION: A measurement system is constituted by connecting a filter 5, a converter 6 for conversion to a circular TE 11 mode, and a waveguide 1 to be measured which consists of tapered waveguides 3 and the interruption waveguide 2 behind an oscillator 4 which generates a desired submillimeter wave, and further dispasing a detector 7 which receives the wave passing through the waveguide 1 behind them. In this case, the transmission loss of the light power which enters the detector 7 through the waveguide 1 is as shown by a straight line (a). When the diameter R 1 of the cutoff part 2 is about 0.1 μm larger than its initial value, a cutoff frequency f c1 is 1.4 GHz lower as shown by a straight line (b). When the diameter is about 0.1 μm smaller, on the other hand, a cutoff frequency f c2 is 1.4 GHz higher as shown by a straight line (c). A slight difference in diameter like this can be read in terms of a frequency GHz at which spectral diffraction is available.