Rayleigh backscattering enhancement (RSE) of optical fibers is an effective means to improve the performance of distributed optical fiber sensing. Femtosecond laser direct-writing techniques have been used to modulate the fiber core for RSE. However, in-core modulation loses more transmission light, thus limiting the sensing distance. In this work, a cladding-type RSE (cl-RSE) structure is proposed, where the femtosecond laser is focused in the fiber cladding and an array of scatterers is written parallel to the core. The refractive-index modulation structure redistributes the light in the cladding, and the backward scattered light is recovered, which enhances the Rayleigh backscattered signal with almost no effect on the core light. Experimentally, it was demonstrated that in an effectual cl-RSE structure, the insertion loss was reduced to 0.00001 dB per scatterer, corresponding to the lowest value for a point scatterer to date. The cl-RSE structure accomplished measurements up to 800°C. In particular, the temperature measurement fluctuation of the cl-RSE fiber portion is only 0.00273°C after annealing. These results show that the cl-RSE structure has effective scattering enhancement, ultra-low loss, and excellent high-temperature characteristics, and has great potential for application in Rayleigh scattering-enhanced distributed fiber sensing.

中文翻译：

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通过光纤包层中的光回收增强超低损耗瑞利散射


光纤瑞利后向散射增强（RSE）是提高分布式光纤传感性能的有效手段。飞秒激光直写技术已用于调制 RSE 的纤芯。然而，芯内调制会损失更多的传输光，从而限制了传感距离。在这项工作中，提出了一种包层型RSE（cl-RSE）结构，其中飞秒激光聚焦在光纤包层中，并且散射体阵列平行于纤芯写入。折射率调制结构对包层中的光进行重新分布，并恢复后向散射光，增强了瑞利后向散射信号，而对纤芯光几乎没有影响。实验证明，在有效的 cl-RSE 结构中，每个散射体的插入损耗降低至 0.00001 dB，相当于迄今为止点散射体的最低值。 cl-RSE 结构可实现高达 800°C 的测量。特别是，退火后cl-RSE光纤部分的温度测量波动仅为0.00273℃。这些结果表明，cl-RSE结构具有有效的散射增强、超低损耗和优异的高温特性，在瑞利散射增强分布式光纤传感中具有巨大的应用潜力。