| 摘要 |
<p>A first optical attenuation filter (2) is arranged in a predetermined optical path and attenuates light to be attenuated with a first variable attenuation amount. A second optical attenuation filter (3) is arranged in the predetermined optical path and attenuates, with a second variable attenuation amount, the light which has been transmitted through the first optical attenuation filter. The first and second optical attenuation filters (2, 3) can be driven in the forward and reverse directions and each has an attenuation amount characteristic which changes monotonously in both the forward and reverse directions. An attenuation amount setting section (1) sets a desired attenuation amount to the light to be attenuated. First and second drivers (4A, 5A, 9A, 4B, 5B, 9B) are coupled to drive the first and second optical attenuation filters (2, 3) in the forward and reverse directions, respectively. A controller (13A, 13B) controls driving directions and driving amounts of the first and second optical attenuation filters (2, 3) through the first and second drivers (4A, 5A, 9A, 4B, 5B, 9B) in accordance with the desired attenuation amount so that an algebraic sum of the first and second attenuation amounts finally becomes equal to the desired attenuation amount and a variation in attenuation amount is decreased as a whole, thereby providing a smooth attenuation characteristic. <IMAGE></p> |
