Optical directional coupler switch.

摘要

An optical directional coupler switch is fabricated from a semiconductor substrate having a (111) plane. Thus, refractive indexes are changed for TE and TM modes by electrooptic effect, although the change amount is different between TE and TM modes. Therefore, a switching operation is realized for an incident light having any polarization. A device length L is preferrably set to meet an equation of "LTE </= L </= LTM" (LTE and LTM are coupling lengths for TE and TM modes) to decrease a cross-talk, even if the coupling lengths are different between TE and TM modes, considering that the difference is small.