提出了一种由U型反馈波导、跑道谐振腔和敏感环组成的反馈式跑道型光学微环传感器.采用耦合模理论推导了该传感器的归一化输出光强公式, 数值分析了传输损耗因子、自耦合因子和敏感环尺寸对归一化输出光强的影响.分析表明: 敏感环的损耗因子对归一化输出光强的调制作用明显, 只要损耗因子发生微小变化, 输出光强即发生较大变化；敏感环工作在弱耦合状态时传感灵敏度较高；敏感环的尺寸对传感灵敏度影响较大, 适当地调整敏感环的大小可得到陡峭的输出光强谱线.对结构参数进行优化后不仅可以输出尖锐陡峭的非对称法诺谐振光强谱线, 而且具有较高的法诺谐振光谱斜率, 能更好地增强传感灵敏度.在信噪比为30 dB的测量系统中, 优化的反馈式跑道型光学微环传感器的探测极限达4.48×10-8单位折射率.

A racetrack micro-ring sensor with feedback loop was proposed,which make up of a U feedback waveguide,a racetrack cavity and a sensitive ring. The normalized transmission formula of the sensor was derived by Coupled-Mode theory.The effects of the transmission loss factor,the coupling factor and sensitive ring size of sensor on the normalized optical intensity were numerically analyzed. The results show that the normalized optical intensity is very sensitive to the transmission loss factor of the sensitive ring. As long as the transmission loss factor changes tinily,the normalized optical intensity changes greatly. When the sensitive ring works on the condition of weak coupling,the sensor may obtain high sensitivity. And the size of sensitive ring has great influence on sensing sensitivity,adjusting the size of sensitive ring properly,the sharp normalized optical spectra were got. Based on the results,the optimized structural parameters were given. The optimization of micro-ring structure can not only output sharp steep asymmetric Fano resonance spectral lines,but also obtain a high Fano resonance spectral slope,which was better to enhance the sensor sensitivity. For a measurement system of 30 dB signal-to-noise ratio,a detection limit can reach to 4.48×10-8 refractive index units in the optimized feedback racetrack micro-ring sensor.