  In-plane optical anisotropy plays a critical role in manipulating light in a
wide range of planner photonic devices. In this study, the strong anisotropy of
multilayer 2D GeAs is leveraged and utilized to validate the technical
feasibility of on-chip light management. A 2D GeAs is stamped into an
ultra-compact silicon waveguide four-way crossing optimized for operation in
the O-optical band. The measured optical transmission spectra indicated a
remarkable discrepancy between the in-plane crystal optical axes with an
attenuation ratio of ~ 3.5 (at 1330 nm). Additionally, the effect of GeAs
crystal orientation on the electro-optic transmission performance is
demonstrated on a straight waveguide. A notable 50 % reduction in responsivity
was recorded for devices constructed with cross direction compared to devices
with a crystal a-direction parallel to the light polarization. This
extraordinary optical anisotropy, combined with a high refractive index ~ 4 of
2D GeAs, opens possibilities for efficient on-chip light manipulation in
photonic devices.
