基于聚合物微球腔的高灵敏温度传感器（特邀）

提出了一种基于聚合物微球腔的温度传感器，该温度传感器利用微球腔谐振波长漂移量测量外界环境温度变化量，兼具结构紧凑和高度灵敏的特点。首先利用有限时域差分法对拉锥光纤耦合聚甲基丙烯酸甲酯(PMMA)微球的谐振结构进行了仿真分析，验证了拉锥光纤激发聚合物微球腔中回音壁模式的可行性。实验结果表明，束腰直径为1.8 μm的拉锥光纤与直径为数十微米的聚合物微球之间通过消逝场耦合的方式能够激发品质因子为104量级的回音壁模式。利用点式封装和全包裹封装相结合的方式将拉锥光纤和聚合物微球封装一体，一方面可保持两者之间稳定的耦合状态，另一方面保护拉锥光纤和微球腔免受外界污染。由于聚合物微球腔的负热光系数大于其热膨胀系数，其谐振光谱随外界温度降低发生红移。当外界环境温度在20~30 ℃范围内变化时，聚合物微球腔温度灵敏度为68 pm/℃。与传统光纤温度传感器相比，该传感器的高品质因子使其具有更低的探测极限，在受限空间内的原位温度精密测量中具有潜在的应用前景。

Highly sensitive temperature sensor based on polymer spherical microcavity (invited)

A temperature sensor based on polymer microsphere cavity is proposed, which measures the change of external temperature through the resonant wavelength shift and demonstrates the characteristics of high compactness and sensitivity. The finite-difference time-domain method is firstly employed to simulate the structure of tapered fiber coupled polymethyl methacrylate (PMMA) microspheres to verify its feasibility of whispering gallery mode excitation. Experimental results show that whispering gallery mode with a quality-factor on the order of 104 can be excited by evanescently coupling a polymer microsphere with a diameter of tens of micrometers through a tapered fiber with a diameter of 1.8 μm. Packaging the device by combining spot and complete coating can keep a stable coupling state between the tapered fiber and the microsphere and protect them from external contaminant. Red shift happens in the resonant spectrum of the microsphere cavity as the external temperature decreases since its negative thermo-optic coefficient is larger than the thermal expansion coefficient. When the external temperature varies in the range of 20-30 ℃, the polymer microsphere demonstrates a sensitivity of 68 pm/℃. In comparison with the conventional optical fiber sensors, lower detection limit can be achieved by the proposed temperature sensor with a higher quality-factor, which can be potentially used in the in-situ temperature precise measurement in a limited space.