| 摘要 |
PURPOSE:To measure a frequency characteristic exactly, by providing a means for coupling an exit light beam of a semiconductor laser, with an optical path to be measured, through a liquid crystal to which an AC electric field has been applied. CONSTITUTION:As voltage of a signal generator 11 is varied, a DSM scattered state is varied, a mode power distribution of a laser beam which is made incident to a fiber cable 4 to be measured, and is propagated is varied in each time, by which a speckle pattern of the section of the fiber is varied. In case when it has been observed by a time constant which is much longer than a period of an applied voltage signal, the speckle pattern of the fiber section is averaged. Accordingly, when a time constant for measuring a frequency characteristic of the optical fiber cable 4 is made much larger than a period of a voltage signal which is applied to a liquid crystal film 9 generated by the signal generator 11, the speckle pattern in case of measuring the frequency characteristic of the optical fiber cable 4 is averaged equivalently. Therefore, the reproducibility is elevated. |
