In this study, we have studied the entangled photon source and how the coincident
count rate and visibility could be affected by the optical elements of the system setup. The
profile of the interference dip of the optical elements for Quantum Cryptography (QC)
system is modified by the increase of the second order dispersion parameter (Dp) and lead to
increase of visibility. Non zero chirp parameter (ai) of the pump beam can provide a higher
central peak but on the other hand it reduces the visibility, the peak remains, while the
dispersion in an optical element through which down converted photon propagate leads to
asymmetry in the interference pattern dip , the dip is particularly stretched with larger value
of birefringent material length (20-30)mm. The highest visibility at birefringent material
dispersion (d) equals to zero, and the dip was broader at larger value of (d).