  The entangled photons are crucial resources for quantum communications and
networking. Here, we present an ultra-bright polarization-entangled photon
source based on a periodically poled lithium niobate waveguide designed for
practical quantum communication networks. Using a 780 nm pump laser, the source
achieves a pair generation rate of 2.4 $\times 10^{10}$ pairs/s/mW. This work
has achieved a directly measured power of 17.9 nW in entangled photon
generation with a 3.2 mW pump power. Based on this, we demonstrate the
practicality of the source by conducting quantum key distribution experiments
over long-distance fiber links, achieving the applicable secure key rates of up
to 440.80 bits/s over 200 km with 62 dB loss and reaching a maximum secure key
generation distance of 404 km. These results demonstrate the potential of
wavelength-multiplexed polarization-entangled photon sources for high-speed,
long-distance quantum communication, positioning them as key components for
future large-scale quantum networks.
