  We demonstrate generation of high-purity photon pairs at 1560 nm in a single
spatial mode from a periodically-poled KTiOPO_4 (PPKTP) waveguide. With nearly
lossless spectral filtering, the PPKTP waveguide source shows approximately 80
% single-mode fiber coupling efficiency and is well suited for high-dimensional
time-energy entanglement-based quantum key distribution. Using high-count-rate
self-differencing InGaAs single-photon avalanche photodiodes configured with
either square or sinusoidal gating, we achieve > 1 Mbit/s raw key generation
with 3 bits-per-photon encoding, and, to the best of our knowledge, the highest
reported Franson quantum-interference visibility of 98.2 % without subtraction
of accidental coincidences.
