| 摘要 |
<p>PURPOSE:To eliminate the influence of an alternating-current-wise optical intensity modulation which is caused by the vibration or the like of parts other than a photosensor part, e.g. an optical fiber, in an optical fiber sensor. CONSTITUTION:Instead of a quarter-wave plate in conventional cases, a (1 + or -alpha)/4-wave plate 16 is used, and a direct-current phase bias corresponding to a + or -alpha/4 wavelength is applied in addition to the phase bias of pi/2 in order to optimize sensitivity. As a result, in a photosensor part, the phase difference of direct-current light is added so as to be superposed on the phase difference of alternating-current light lay a signal under test, and a high-order harmonics component is generated in detected signal light. Consequently, when its fundamental-wave component and a second harmonics component are detected and the ratio of the both is found, it is possible to completely eliminate the influence of optical intensity. That is to say, it is possible to eliminate the influence, of an alternating-current optical intensity modulation, which is caused by the vibration of parts other than the photosensor part, e.g. an optical fiber.</p> |
