Composite optical interference in non-unitary and unitary beam-splitter systems

摘要

In this paper, we theoretically propose and demonstrate a non-unitary beam-splitter (BS) by introducing coupling losses at the interface of the plasmonic waveguide and multimode dielectric waveguide (DW). The coupling losses enable us to modify the reflection and transmission factors, which can result in arbitrary shift of interference curves of two outputs. Specially, the lossy non-unitary BS can tune the amplitudes and phases of two outputs, even making them change synchronously, regardless of input phase differences. After a pi/2 phase delay in one arm, these two outputs are fed into another multimode DW. This DW is a normal unitary BS, working like the Michelson interferometer, where anti-synchronous interference can take place. At last, the whole device outputs an invariant zero energy state in one port, exhibiting a phase-insensitive performance. Our study provides a versatile design platform to realize non-unitary/unitary BS and construct more multi-functional devices.