Indistinguishability of photon pair in a periodically poled KTiOPO4

We report the two-photon interference properties of a photon pair generated in a type-II collinear periodically poled KTiOPO4 (PPKTP) crystal pumped by a 406-nm diode laser capable of producing a single or dual longitudinal mode (LM). When the Hong–Ou–Mandel (HOM) interference signals in the PPKTP crystal pumped by a dual-mode diode laser were investigated at various crystal temperatures, it was found that the maximum visibility of the HOM interference signal depends on the relative strength of the dual LMs of the pump laser. The HOM interference pattern was numerically calculated considering the dual LM components of the pump laser diode and the crystal temperature, and was found to be in good agreement with the experimental results.