Bending loss in optical waveguides for nonplanar laser array applications

Abstract

The optical transmission loss in dielectric waveguide bends is investigated using the finite-difference time-domain approach. An absorbing boundary condition, applied to reduce the size of the mesh, is proven to work very well for the waveguide structure. The desired modes are excited using the solution of a one-dimensional waveguide structure. The bending loss is then obtained using the methods of overlap integral and least-square fit. The structures of multiple-bend waveguides are analyzed. It is shown that the coupling between neighboring bends leads to direct transmission to the waveguide section on the aligned plane in addition to the transmission through the zigzag path. The bending loss in nonplanar laser arrays is investigated in detail. The possibility of having a shallow groove depth laser array is then discussed. Lateral lasing is prohibited by the radiation loss due to the bend. It is observed that the optical coupling between neighboring emitters is enhanced by the shallow groove depth, implying that phase-locked array modes can be obtained.