Polarization-correlated narrowband photon pair generation in a fiber-pigtailed MgO:ppLN ridge waveguide

Spontaneous parametric down-conversion (SPDC) based waveguide sources are widely used to generate heralded single photons or paired photons of lower frequency for various applications in quantum technology. In this work, we present a narrowband spectral and polarization-correlated photon-pair source around telecom wavelength 1560 nm based on type II quasi phase-matched, fiber-pigtailed, MgO-doped periodically poled lithium niobate (MgO:ppLN) ridge waveguide module of length ~1.69 cm. Waveguide-based SPDC sources have gained popularity as they offer better confinement of spatial modes, thus enhancing the degree of nonlinear interactions leading to an increase in the brightness of generated photons. Fiber-pigtailing such sources offer compact solutions and can increase the commercial viability of quantum systems. A type II phase-matched waveguide generates narrowband orthogonal photon pairs thus, fiber coupling such sources can be complicated compared to other types. Hence, photon pair generation using type II fiber-pigtailed waveguides has not been explored sufficiently to the best of our knowledge. We have demonstrated an efficient photon-pair source with the following characteristics: a measured phase-matched bandwidth of 0.6nm, a spectral brightness of ~7.79×10⁴ pairs/sec/mW/nm and a coincidence-to-accidental ratio (CAR) of ~246. This source can be potentially used in commercial long-distance quantum communication systems owing to its compact, narrowband and reliable nature.