Figure 1
From: Two-photon interference of polarization-entangled photons in a Franson interferometer
Experimental setup to observe two-photon interference effect. Pump, continuous-wave (cw) single-mode diode laser (406.2 nm, 5 mW); PM, prism mirror; M, mirror; H, half-wave plate; PBS, polarizing beamsplitter; IF, interference filter; FC, fibre coupler; SMF, single-mode fibre; PC, polarization controller; Q, quarter-wave plate; PZT, piezoelectric transducer; P1 and P2, linear polarizers. In particular, we use a double-sided mirror (M1) for simultaneous adjustment of the path-length differences between the two long interferometer arms in the opposite direction, while the relative phase differences between them always remain at zero.
