Photonic crystal optical parametric oscillator (Nature Photonics, December 2020)
Authors: Gabriel Marty, Sylvain Combrié, Fabrice Raineri and Alfredo De Rossi
Teams at Thales and C2N have developed a new miniaturized source of light called Photonic Crystal Optical Parametric Oscillator. An Optical Parametric Oscillator (OPO) is similar to a laser as it generates coherent light, namely photons having the same frequency, direction and polarization, except that here photons are emitted in pairs. These pairs are correlated, meaning that their perturbations (e.g. fluctuation of their frequency) are not independent. This property is exploited in many ways, in particular to decrease the noise in sensitive measurements (quantum sensing), to encode and encrypt information (quantum communication) and also to perform computing.
Optical Parametric Oscillators used to be bulky and expensive and by no means suitable for integration on a “photonic chip”. In the last year, however, optical parametric oscillator have been miniaturized using optical resonators where light circulates many times inside tiny rings or disks. As a consequence of the tight confinement, less power is required to attain the large intensity of the field required by an OPO to operate.
These miniaturized devices footprint is as small as the cross section of a human hair. Thales and C2N have managed to decrease their size and also their power consumption even further using a radically different concept to “trap” light in semiconductor materials, which is called “Photonic Crystal”. In these wavelength scale structures, light bounces many times against nanometric holes drilled in an ultra-thin membrane instead of circulating. This results in a huge enhancement of light matter interaction causing super-efficient generation of photons.
Because these OPO are so small and consume very little power, they could be put on a single photonic chip and operate simultaneously to generate non-classical light necessary to feed a quantum photonic circuit. Novel quantum sensing devices will be possible exploiting the small scale of these sources.