Polymer tapered multimode waveguides were modeled using the finite difference wide-angle beam propagation method to investigate whether tapered input waveguide couplers decreasing in width away from the waveguide entrance give improved tolerance to lateral misalignments of an optical source compared to straight waveguides and whether there is any effect on angular misalignment tolerance for use in optical backplane interconnections. Input tapered couplers having a larger entrance and tapering down in width do indeed improve the lateral misalignment tolerance compared to straight waveguides but do so at the expense of an increased loss. Tapers have no effect on angular tolerance for strongly driven vertical cavity surface-emitting laser (VCSEL) sources although they cause a loss of angular tolerance for single-mode fiber sources and VCSELs at low drive currents.
Finite difference beam propagation modelling (FD-BPM) calculates the effect of thermal gradients in an optical backplane on the optical field propagation in a polymer multimode linearly tapered waveguide. Compared to straight waveguides, tapered entrances offer improved power coupling for a wide range of optical source lateral offset misalignments. However, surface temperature gradients of 0.5°C/μm across the taper were found to degrade this benefit due to the thermo-optic effect of the polymer. Higher surface temperature gradients improve power coupling in two discrete ranges of lateral source offset but the original tolerance to a wide range of source offsets is not recovered.
A finite difference beam prop0agation mode is used in conjunction with laser rate equation simulations to study the inclusion of an intracavity lens in a high-power tapered ridge waveguide laser diode emitting at 980 nm. A parabolic lens is introduced in the top of the ridge near the front facet via a change in the waveguide effective refractive index profile. The inclusion of the lens has led to 13 percent reduction in the threshold current and an improved power slope efficiency from 0.4 W/A up to 0.8 W/A. The lens has caused near field broadening of 2 micrometers at full width half maximum power, indicating more efficient use of the cavity. The far field has narrowed by 1 degree indicating higher brightness. The model uses a mesh for reach of its points the standard carrier rate equation is solved across the active layer. The 2D wave equation is solved for the two counter propagating fields using a finite difference algorithm. The result of the does how good agreement with experiment.