Experimentally testing the Bell inequality violation by optimizing the measurement settings

Many experiments have been made to test the Clauser-Horne-Shimony-Holt (CHSH)-Bell inequality (CBI). However, the Cirel'son's limit has not been reached yet, due to various practically existing imperfections. In this paper, we experimentally investigate how to select the measurement settings for obtaining the optimal violation of CBI for a mixed entangled state. With the commercialized entangled source, we first determine the entanglement degree of the generated photon pairs by using the tomographic technique, and then numerically optimize the measurement settings. Finally, we experimentally obtain the optimal violation of the CBI with the present commercialized entangled source without the maximal entanglement.