Study of Raman-free photon pair generation using inter-modal four-wave mixing in a few-mode silica fiber

摘要

-mode and at λ2 = 1550 nm in the LP01mode, respectively, by pumping in the LP11-mode at λ7, = 1064 nm, where laser sources are readily available. The 810 nm photon is detectable with relatively cheap and efficient silicon-based single-photon detectors, and the heralded 1550 nm photon is mode-matched with transmission fibers in the low-loss spectral window. We design a silica fiber that phase matches these modes and wavelengths while it also reduces the impacts of core radius fluctuations (CRF) caused by fabrication imperfections; the fiber design is inspired by B. P.-P. Kuo et al. [3] and a sketch of the refractive index profile is shown in Fig. 1(a). The scalar wave equation is solved using appropriate Sellmeier data for Germanium-doped silica and the calculated effective indexes for the three modes versus wavelength are shown in Fig. 1(b) together with the core and cladding refractive indexes; the inset shows the wavelength configuration of the pump and two side-bands; phase matching is achieved when the effective indexes of the three modes lie on a straight line [2]. The nonlinear overlap of the waves in this configuration is approximately 18% of the corresponding overlap where all waves are in the LP01-mode.