  Lithium niobate photonic chip could realize diverse optical engineering for
various applications benefiting from its excellent optical performances. In
this letter, we demonstrate monolithic photonic chips for multi-channel
sum-frequency conversion based on reverse-proton-exchange periodically poled
lithium niobate waveguides, with the different channels showing uniform and
excellent conversion efficiencies. To obtain a robust device and provide a
convenient interface for applications, the integrated chip is fiber coupled
with two fiber arrays. The packaged chip then forms the core of a multi-channel
up conversion single photon detector. In each channel the input signal
interacts with a 1950-nm single frequency pump laser and the sum frequency
output is spectrally filtered and detected by a silicon avalanche photodiode.
Average detection efficiency (DE) of 23.2 % and noise count rate (NCR) of 557
counts per second (cps) are achieved, with a standard deviation of 2.73 % and
48 cps over the 30 channels, as well as optical isolation (OI) between nearby
channels of more than 71 dB, which are excellent for the extensive applications
of monolithic photonic chips in fields including deep space laser
communication, high-rate quantum key distribution and single-photon imaging.
