Abstract

The standard method for generating biphotons and photon number correlated twin beams is parametric down conversion in a crystal at low and high gain, respectively. These states of light can however be also produced via four-wave mixing in optical fibres [1]. Such systems are beneficial because signal and idler radiation can be generated in a single spatial mode, high values of parametric gain can be achieved due to long-lasting light-matter interaction, and efficient integration into fibre optical systems is possible. However, photon correlations in solid-core fibre systems are masked by unavoidable Raman scattering and ultrafast twin-beam generation is normally prevented by a large group velocity mismatch [2]. Here we present an elegant way to circumvent these issues and generate ultrafast bright twin beams by using a hollow-core photonic crystal fibre filled with noble gas. We exploit the unique properties of kagomé-style PCFs (Fig. 1a), which offer broadband guidance at moderate losses of ~1 dB/m. The weak, anomalous group-velocity dispersion (GVD) of this fibre type can be balanced with the normal dispersion of noble gases, leading to a pressure tunable zero-dispersion wavelength which permits large tunability of signal and idler wavelengths (Fig. 1b) [3]. Pumping in the anomalous GVD regime results in the generation of twin beams close to the pump, so that the weak group velocity mismatch allows the creation of ultrafast signal and idler pulses, while noble gas-filling prevents Raman-scattering.

© 2015 IEEE