| 摘要 |
According to an aspect of an embodiment, in a light transmission device for switching a light transmission path for receiving an optical signal from a currently used system to a backup system when the light level of light input from a light transmission path of a currently used system becomes substantially equal to or less than a light input break detection threshold value which serves as a reference for detecting a light input break. The light transmission device includes light level measuring means for measuring the light level of the light input from the light transmission path of the currently used system, and light input break detection threshold value setting means for detecting only the light level of accumulated noise of the light level measured by the light level measuring means and setting the detected light level as the light input break detection threshold value.
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