Fig. 2: Squeezing-assisted interferometer with parametric amplification at the output.
From: Overcoming detection loss and noise in squeezing-based optical sensing
a A HWP as a Mach-Zehnder interferometer: left- and right-circularly polarized states play the role of the two arms and linear polarization states, input and output modes. b Vertically polarized squeezed vacuum (SV) is produced in nonlinear crystal BBO1 and the horizontally polarized coherent state is fed through beamsplitter BS2. Vertically polarized output of the interferometer is amplified in the second crystal BBO2, cleaned from the pump by dichroic mirror DM, selected by Glan polarizer GP, and finally detected with photodetector PD1. Lens L and pinhole P provide spatial filtering, while bandpass filter BF, spectral filtering. Beamsplitters BS1, BS2 tap off parts of the pump and coherent beams to monitor intensity fluctuations and lock the phase. c The output intensity of unseeded BBO2 versus the pump power.
