To accurately obtain aimed optical attenuation quantity with a simple configuration.
A variable optical attenuator 10 is equipped with a polarization direction adjusting element 14 and a ferroelectric prism 13. The polarization direction adjusting element 14 emits a first light beam Bm1 and a second light beam Bm2 derived from an incident light beam Bm by aligning the polarization direction thereof to S direction toward the ferroelectric prism 13. When a voltage is applied to the ferroelectric prism 13, its refractive index is lowered, optical paths of the first and second light beams Bm1, Bm2 are changed and they are made incident on a second collimate lens 12 in this state. As a result, coupling efficiency of an optical fiber 22 for outgoing light is lowered and optical attenuation is increased. Because the first and second light beams Bm1, Bm2 with their polarization directions aligned by the polarization direction adjusting element 14 are made incident on the ferroelectric prism 13, birefringence concomitant with optical anisotropy of the ferroelectric prism 13 is not generated, the aimed optical attenuation quantityis more accurately obtained.
YOSHIHIRO MASASHI
SHIMAZAKI KATSUSUKE
SEKINE MASAKI
HIETA HARUMI
TAKEUCHI TERUAKI
