  In this work, we report on the preparation of an ultra-broadband
continuously-tunable, highly polarization-entangled photon-pair source covering
the C+L telecom bands using a single type-II phase-matched bulk PPKTP crystal.
Over 60 nm turning band of the down-converted photons is achieved
experimentally. The broad tuning ability is due to operating near an extended
phase match point in this crystal. The S parameter value of CHSH inequality is
in the range between 2.60+/-0.04 (minimum) and 2.72+/-0.07 (maximum), which
clearly demonstrates the high entanglement of the source over the whole tunable
range. This is the first realization of such a broadband tunable degenerate
polarization entanglement pair source in the telecom band. Combined with dense
wavelength-division multiplexing technique, our source could be used to improve
the transmission capacity of a single communication channel in the field of
quantum communication.
