This project was conceived as the final project of my Bachelor’s studies at the Department of Physics of the University of Trento. The downloadable files are the thesis itself, the LaTex template and also the presentation used for the discussion.
Integrated single photon sources are key building blocks for on-chip quantum computation, quantum information and quantum technologies in general. Single photon states can be produced through a heralding process between correlated photon pairs generated via nonlinear optical processes. On-chip heralded single photon sources based on spontaneous four wave mixing have been already demonstrated. The purpose of this thesis is to show the advantages and potentialities of intermodal four wave mixing in the single photon generation framework. The photon source is developed on a silicon chip, the ideal platform for integrated nonlinear processes and scalable quantum devices, thanks also to its mature and cheap fabrication technology. A heralded single photon source based on a IFWM process in silicon waveguides is here demonstrated. In the first chapter the basics of the formation and propagation of waveguide modes are given, with a focus on optical multimode waveguides. Nonlinear optics is then introduced with a concise overview of the main second and third order nonlinear processes. A particular attention is paid to spontaneous four wave mixing and its inefficiencies in view of a single photon source application. Through this process, in fact, the signal and idler photons are generated close to the wavelength of the pump, thus limiting the generation spectrum. Moreover, narrow spectral post filtering is used to increase the spectral purity, limiting the brightness and the integration of these type of sources. Intermodal four wave mixing can be used to remove the need of tight spectral filtering and to achieve broad band quantum light generation, from the near to the mid infrared. The second chapter initially introduce some elements of photon statistics and deals with the basics of probabilistic single photon sources. A close attention is paid to heralded single photon sources and the experimental metrics necessary in order to characterize their performance. The last part of chapter 2 presents a heralded single photon source based on intermodal FWM on a SOI multimode waveguide. A description of the chip used, which has been fabricated by the Centre for Materials and Microsystems of Bruno Kessler Foundation (Trento, Italy), is initially provided. Next, the experimental set-up for the source characterization is described. The measurements have been carried out by dr. Stefano Signorini and Matteo Sanna (master student) in the Nanoscience Laboratory, in the Department of Physics of the University of Trento. The analysis I carried out on the measurements is presented in the last chapter of this thesis. The experimental demonstration of a silicon integrated source of heralded single photons is reported. The source exploits the intermodal four wave mixing to generate the heralding idler in the near infrared and the heralded signal in the mid infrared.