Methods
1.set equipment like this picture
2.shoot laser through BBO crystal
3.align collimator A and B in the way of conservation of momentum law and conservation of energy law
4.measure single photon from detector A at various angles.
5.measure single photon from detector B at various angles.
6.measure single photon from detector A and detector B by fixing the arm of detector A and change angle bet ween the arm of detector B and the blue laser's pathway at various angles