Reduction of zero baseline drift of the Pound–Drever–Hall error signal with a wedged electro-optical crystal for squeezed state generation

Abstract

We report an electro-optic modulator (EOM) with a wedged MgO: LiNbO₃ as the modulation crystal to reduce the zero baseline drift (ZBD) of the Pound-Drever-Hall (PDH) error signal. When the input linear polarization is not along the modulation direction, the wedged design can separate the two orthogonal polarizations in space after the EOM and eliminate the interference between the carrier and the two orthogonal sidebands. Therefore, the residual amplitude modulation (RAM) of phase modulation process caused by the input polarization misalignment and the etalon effect can be significantly reduced. The noise power spectrum of phase-modulated light with wedged crystal EOM is suppressed from -24 to -69 dBm, which is much lower than that with conventional EOM. The peak-to-peak value of the ZBD of the PDH error signal is reduced effectively to +70/-50 ppm during the 10 h, which meets the requirements for stable squeezed light generation.

Shot-noise-limited Doppler-broadened noise-immune cavity-enhanced optical heterodyne molecular spectrometry

“…There are two main causes of such signals; one is interference between various optical surfaces, usually termed etalons, while the other is residual amplitude modulation (RAM), which in particular can appear from EOMs [25,26]. Numerous efforts have been made to suppress these types of effects, e.g., antireflection coating, alignment of optical components, active feedback control of EOM [25], usage of proton-exchanged EOMs [20] and wedged crystal EOMs [27], application of etalon immune distance (EID) [28], and implementation of a differential NICE-OHMS strategy [24]. However, despite all this, background signals are notoriously difficult to eliminate completely, and the remaining are often the main cause for the restricted performance of the NICE-OHMS system.…”

Rydberg-atom based radio-frequency electrometry using frequency modulation spectroscopy in room temperature vapor cells

“…Recently, an alternative method has also been proposed to passively control RAM. A wedged electro-optic crystal was used to reduce RAM caused by the input polarization misalignment and the etalon effects [52]. This method is useful for the reduction of baseline drift of the Pound-Drever-Hall (PDH) error signal for stable squeezed light generation.…”

Low-noise, transformer-coupled resonant photodetector for squeezed state generation

“…Small variations δL in cavity length can influence the squeezing angle and increase the optical losses, leading to a drop in the level of squeezing. 10,11 Referring to the analysis in Refs. 10 and 11, we present a numerical analysis of the influence of the OPO cavity length variation δL on the squeezing level, which is shown in Fig.…”