A fiber SPR sensor with high comprehensive evaluation indicator based on core mismatched U-Shaped and tapered arm

•A core mismatch type optical fiber SPR refractive index sensor is proposed, which has both a tapered structure and a U-shaped structure.•Parameters such as resonance valley depth and comprehensive evaluation indicator are defined.•The valley depth influence law is found.•A high comprehensive evaluation indicator SPR sensor refractive index test is realized.