Abstract
In this dissertation, we introduce the methods of the beamlike polarization-entangled photon pair generation, measurements and analyses. Through these methods, they would be easy to collect the SPDC photon pairs. This dissertation reports two major results about beamlike polarization-entangled photon pair generation. One is polarization-entangled generation via geometrical overlap in a free space. The other is through a 2x2 single mode fiber. We generate the second harmonic light by ultra-short pulse laser. The second harmonic (SH) light was used to pump the Type-II BBO crystal and to generate the beamlike polarized photon pairs under the phase matching condition, which can be imaged by a CCD. The Hong-Ou-Mandel (HOM) dip interference signal was observed when photons were overlapping in the crossing point of a 2x2 single mode fiber. In order to generate beamlike photon pairs with polarization-entanglement and interference, we used a mirror to reflect the SH light back to the BBO crystal. Before reflecting on the mirror, the SH light would generate the beamlike photon pairs as the SH light was passing through the BBO crystal for the first time. The photon pairs are called the first photon pairs in the following. After reflecting, the reflected SH light could also generate beamlike photon pairs called the second photon pairs. The polarization of the first photon pairs were rotated by 90 degrees by inserting a quarter-wave plate into each path of the two photons of the pair. Then the first photon pairs reflected back and had overlapping optical path with the second pairs. We can find the interference signal and the beamlike polarization-entangled photon pairswith the fidelity of 0.90±0.05, indicating that the generated photon pairs were highly polarization-entangled. To overcome the difficulty in the alignment of above method, we developed another method to generate beamlike polarization-entangled photon pairs by a 2x2 single-mode fiber. This method is that two photons of one beamlike polarized photon pair were directly incident to two input ports of the 2x2 single-mode fiber, respectively. Each of the polarized photon could emerge from any output ports of the 2x2 fiber. Therefore, the photon pairs coming out from the 2x2 fiber had polarization entanglement. This approach made it easy to perform the alignment for the experimental system and the generated photon pairs were highly polarization-entangled. Rotating the polarizer, we can analyze the photon polarization by the coincidence measurements. The local measurements estimated the fidelity to be 0.93±0.006. For the Bell-CHSH inequality (S) measurements, we obtained S=2.59±0.08 which is higher than the classical threshold (=2) and seven times the standard deviation of measuring system. It implies that we have generated high quality beamlike polarization-entangled photon pairs by a 2x2 single-mode fiber. Our results indicates that the high quality beamlike polarization-entangled photon pairs can be generated via the overlap of two photon pairs in free space or a 2x2 single-mode fiber. The entangled photon source developed in this study can be utilized in further researches of quantum information science and quantum computation.