Generation of broadband polarization-orthogonal photon pairs via the dispersion-engineered thin-film lithium niobate waveguide

Broadband photon pairs are highly desirable for quantum metrology,quantum sensing,and quantum communication.Such sources are usually designed through type-0 phase-matching spontaneous parametric down-conversion(SPDC)that makes the photon pairs hard to separate in the frequency-degenerate case and thus limits their applications.In this paper,we design a broadband frequency-degenerate telecom-band photon pair source via the type-II SPDC in a dispersion-engineered thin-film lithium niobate waveguide,where the polarization modes of photon pairs are orthogonal and thus are easily separated deterministically.With a 5-mm-long waveguide,our design can achieve a bandwidth of 5.56 THz(44.8 nm),which is 8.6 times larger than that of the bulk lithium niobate,and the central wavelength can be flexibly adjusted.Our design is a promising approach towards high-quality integrated photon sources and may have wide applications in photonic quantum technologies.