Pair generator

Introduction

There is a problem of creating a narrow band pair generator compatible with telecom and quantum memories. Typical solution includes OPO with periodically poled crystal placed in high-quality optical resonator. The crystal produces pairs via spontaneous parametric down conversion, which bandwidth is limited by optical resonator linewidth. This solution is cumbersome, requires second harmonic generation, resonator frequency stabilization and etc.

Our solution

We propose to generate narrow band pairs by adding an absorber with narrow spectral transmission window (spectral hole) into OPO with bad quality resonator.

OPO Design

We propose nonlinear fiber with shifted dispersion as active medium for pair generation. An example from FORC photonics has zero dispersion around 1550 nm. In contrast to nonlinear crystals with χ⁽²⁾ non-linearity, optical fiber has only χ⁽³⁾ non-linearity, thus the process behind photon-pair generation is four-wave mixing. In this process one pump photon with wave-vector k_p is in-elastically scattered at fiber photon, then the phonon is converted back into photon by absorbing second photon from a pump. If we send pump at frequency ω we would generate frequency-correlated pairs with broadband spectrum, e.g. for a photon at ω-Δ the correlated twin will be at ω+Δ.

It is important to note, that phase matching has to be fulfilled in this process. $2 k_p - k_s - k_i=0$

If the FBG mirrors are placed at wavelength ω-Δ and ω+Δ, the OPO is formed, that will produce pairs within a window set by FBG and formed Fabry-Perot.