Intermodal four wave mixing for heralded single photon sources in silicon

High order waveguide modes are nowadays of great interest for the development of new functionalities in photonics. Because of this, efficient mode couplers are required. In this thesis a new strategy for mode coupling is investigated, based on the interference arising from two coherent tilted beams superimposed in a star-coupler. Handling the high order modes allows to explore new processes within the photonics platform, as the intermodal four wave mixing. Intermodal four wave mixing is a new nonlinear optical process in waveguide, and it is here demonstrated on a silicon chip. Via intermodal four wave mixing it is possible to achieve a large and tunable frequency conversion, with the generation of photons spanning from the near to the mid infrared. The broadband operation of this process is of interest for the field of quantum photonics. Single photon sources are the main building block of quantum applications, and they need to be pure and efficient. Via intermodal four wave mixing, it is here demonstrated the generation of single photons above 2000 nm heralded by the idler at 1260 nm. Thanks to the discrete band phase matching of this nonlinear process, high purity single photons without narrow band spectral filters are demonstrated. Intermodal four wave mixing enables a new class of classical and quantum sources, with unprecedent flexibility and spectral tunability. This process is particularly useful for the developing field of mid infrared photonics, where a viable integrated source of light is still missing.