Enhancement of the photon pair generation rate by spontaneous four-wave mixing in bent waveguides

Enhancing nonlinear optical effects is critical to improving the performance of many functional devices for nonlinear and quantum optical applications. Here, we study the possibility of bending a waveguide to enhance the photon pair generation rate in a spontaneous four-wave mixing process. Whereas intuition might suggest that bending makes the process less efficient because the waveguides are more lossy when bent, we show that the increase in the effective nonlinearity outperforms the loss disadvantage for moderate bending radii. That can be explained by a better localization of the guided eigenmodes, leading to a reduced mode area. By studying selected waveguide devices with a fixed length, we demonstrate an improvement in the photon pair generation rate between 5% and 210% for an optimal bending radius. These findings have implications for the future design of integrated photonic devices for quantum optical applications, especially in cases where the chip estate tends to be a limiting factor.