Hong-Ou-Mandel DIP Measurement of two Independent Weak Coherent Pulses

Due to the simplicity of Hong-Ou-Mandel (HOM) interferometer setup, it becomes very important in various quantum-based applications, especially when the photon indistinguishability is required such as measurement device independent quantum key distribution (MDI-QKD). In the present work, the HOM experiment setup is designed to study the quantum interference between two indistinguishable photons (frequency, time of arrival and polarization should be same for both photons) coming from two independent laser sources (attenuated laser). The aim is to achieve high visibility as it indicates the photon indistinguishability from two independent sources. Theoretically, the visibility is $50 \%$ for indistinguishable photons from attenuated laser sources but in the experiment, due to various devices imperfections and other factors it is less than 50%. The HOM visibility achieved from our setup is $40 \%$ tested for a distance of 20 km over standard single mode fiber (SMF). The main point to be noticed in this work is that, this experiment is performed using single photon avalanche diode.