  We design, fabricate and characterize integrated photonic routing manifolds
with 10 inputs and 100 outputs using two vertically integrated planes of
silicon nitride waveguides. We analyze manifolds via top-view camera imaging.
This measurement technique allows the rapid acquisition of hundreds of precise
transmission measurements. We demonstrate manifolds with uniform and Gaussian
power distribution patterns with mean power output errors (averaged over 10
sets of 10 inputs) of 0.7 and 0.9 dB, respectively, establishing this as a
viable architecture for precision light distribution on-chip. We also assess
the performance of the passive photonic elements comprising the system via
self-referenced test structures, including high-dynamic-range beam taps,
waveguide cutback structures, and waveguide crossing arrays.
