In this paper, we present a design of an all-fiber source of correlated photon pairs based on standard telecommunications tapered fibers. We examine the generation of correlated photon pairs using parametric process χ ( 2 ) in silica tapered optical fibers. This nonlinear process is ensured thanks to surface dipole and bulk multipole nonlinearities. The process of photon creation is modeled by taking into account the vector aspect of the propagation of the optical field in a silica nanofiber. The phase matching is provided by propagating the pump field in one spatial mode while generating a photon pair in another spatial mode. The generation efficiency of photon pairs depends on diameter uniformity of the nanofiber after the manufacturing process. We size this nanofiber for a good optimization of photon pair generation efficiency, and we report that the tolerance in diameter uniformity is Δ d = 2 n m for a generation rate of photon pairs estimated to N ph ≈ 22 000 p a i r s / s , for 1 W power pump and a nanofiber length of 1.1 mm. Deposits on the nanofiber can be used in order to relax the manufacturing constraints on diameter to maximize the generation rate of photon pairs. As an example, the use of polytetrafluoroethylene on the nanofiber applied as a cladding whose thickness is infinite makes it possible to relax the constraints on the nanofiber diameter. For the same Δ d = 2 n m , a generation rate of photon pairs estimated to N ph ≈ 78 000 p a i r s / s for 1 W power pump and a nanofiber length of 2.4 mm is predicted.
Entangled quantum states generation is crucial for quantum cryptography, particularly in quantum key distribution (QKD). While optical fibers enable low-loss photon transmission, standard silica fibers exhibit weak nonlinearities for spontaneous parametric processes. This paper proposes an optimized scheme for entangled quantum states generation in subwavelength silica nanofibers, leveraging effective second-order nonlinearities χ(2)induced by surface inversion symmetry breaking. Unlike bulk silica, tapered silica nanofibers exhibit significant second-order responses via surface dipole and bulk quadrupole nonlinearities, enabling spontaneous parametric down-conversion (SPDC). Our key innovation is a second-order nonlinear coating (PMMA/DR1 encapsulated with Teflon), enhancing
χeff(2) and boosting the spectral density efficiency of entangled quantum states generation by a factor of 103. This approach optimizes phase matching while maintaining optical stability and minimizing scattering losses. Additionally, the proposed source inherently avoids spontaneous Raman scattering (SRS) noise, which is a major limitation in fiber-based SPDC systems, ensuring high-purity entangled quantum states generation. Our results demonstrate that silica nanofibers, with tailored nonlinear coatings, offer a scalable platform for integrated quantum light sources in fiber-based quantum networks.