  We show several techniques for using integrated-photonic waveguide structures
to simultaneously characterize multiple waveguide-integrated
superconducting-nanowire detectors with a single fiber input. The first set of
structures allows direct comparison of detector performance of
waveguide-integrated detectors with various widths and lengths. The second type
of demonstrated integrated-photonic structure allows us to achieve detection
with a high dynamic range. This device allows a small number of detectors to
count photons across many orders of magnitude in count rate. However, we find a
stray light floor of -30 dB limits the dynamic range to three orders of
magnitude. To assess the utility of the detectors for use in synapses in
spiking neural systems, we measured the response with average incident photon
numbers ranging from less than $10^{-3}$ to greater than $10$. The detector
response is identical across this entire range, indicating that synaptic
responses based on these detectors will be independent of the number of
incident photons in a communication pulse. Such a binary response is ideal for
communication in neural systems. We further demonstrate that the response has a
linear dependence of output current pulse height on bias current with up to a
factor of 1.7 tunability in pulse height. Throughout the work, we compare
room-temperature measurements to cryogenic measurements. The agreement
indicates room-temperature measurements can be used to determine important
properties of the detectors.
