  Photonic waveguides with triangular cross section are being investigated for
material systems such as diamond, glasses and gallium nitride, which lack easy
options to create conventional rectangular nanophotonic waveguides. The design
rules for optical elements in these triangular waveguides, such as couplers and
gratings, are not well established. Here we present simulations of elements
designed to couple light into, and out of, triangular waveguides from the
vertical direction, which can be implemented with current angled-etch
fabrication technology. The devices demonstrate coupling efficiencies
approaching \unit{50}{\%} for light focused from a high numerical aperture
objective. The implementation of such couplers will enable fast and efficient
testing of closely spaced integrated circuit components.
