Quantum-Enhanced Signal-to-Noise Ratio Fiber Bending Sensor Utilizing Intensity Correlated Pulse Twin Beams

We have experimentally proposed and implemented a fiber bending sensor with quantum-enhanced signal-to-noise ratio (SNR), which stems from the combination of single-mode fiber (SMF) taper and intensity correlated pulse twin beams. One beam from pulse twin beams is coupled into the SMF taper to obtain a bending-induced loss, while the other beam is also attenuated correspondingly by a variable optical attenuator to ensure maximum noise cancellation. Along this line, intensity-difference noise power between pulse twin beams is always reduced below standard quantum limit (SQL), and thus a higher SNR value compared with the corresponding double-channel light source can be realized. In this work, the three different SMF tapers with the waist diameters of $85.1~\mu \text{m}$ , $74.9~\mu \text{m}$ , and $67.3~\mu \text{m}$ , respectively have been prepared by a fusion splicer. The experimental results show that in the bending range of 0–20 m⁻¹, the SMF taper with $67.3~\mu \text{m}$ waist diameter shows the highest sensitivity of 0.105 dB/m⁻¹, the resolution of 0.095 m⁻¹, and its SNR value is enhanced by a maximal factor of 2.84 dB compared with the corresponding classical counterpart. The present bending proposal may find potential applications in monitoring the bending deformation of building structure, roadbed settlement, medical and health, etc.