Second-order interference of two independent photons with different spectra
Zhou Yu1, Liu Jian-Bin2, 3, †, Zheng Huai-Bin2, Chen Hui2, Li Fu-Li1, Xu Zhuo2
       

Two-photon interference in an HOM interferometer. A and B are two independent single photons with different spectra. BS is a 50:50 non-polarizing beam splitter. D1 and D2 are two single photon detectors. CC is a two-photon coincidence count system.