Efficient phase-sensitive compensation in lossy interferometry using optical amplification

Optical interferometers, as precision measurement tools, inevitably experience optical path losses in practical applications, which introduce unavoidable vacuum noise and reduce the sensitivity in the phase estimation. To mitigate the effects of losses on sensitivity, we propose an enhanced interferometer scheme that integrates a Raman amplifier. This amplifier is strategically positioned within the lossy interference arm to counteract the reduction in phase sensitivity caused by losses. Our research highlights the crucial role of amplifier positioning, revealing that pre-amplification (PRA, placing the amplifier before the lossy section) significantly outperforms post-amplification (POA, placing the amplifier after the lossy section). PRA effectively enhances sensitivity by increasing the number of phase-sensitive particles and minimizing noise amplification. As the loss increases, the superiority of PRA in mitigating loss effects becomes increasingly evident. To validate our approach, we conducted experimental demonstrations. When the losses reach 90%, PRA experimentally achieves a sensitivity improvement of 4.6 dB compared with the case of only loss without the amplifier, equivalent to increasing the input laser power by over 8 times. PRA can effectively improve the robustness against losses for the practical application solely through the use of a coherent amplifier, with a simple technical implementation yet remarkable enhancement effects. We believe that current PRA-enhanced interferometry facilitates the practical implementation of phase measurement in environments characterized by significant loss.