微纳光纤环形腔海水温度的谐振光谱分析

微纳光纤环形腔作为传感器件，具有灵敏度高、响应快的优点，因而越来越广泛地应用在传感领域。环形腔的谐振光谱直接反映外界环境的变化，因此谐振光谱分析对探测环境参数至关重要。从理论和实验研究了微纳光纤环形腔谐振光谱与海水温度的关系。首先，数值计算了基模(HE₁₁)两个垂直偏振态的传播常数随光纤直径和探测波长的变化关系，计算结果表明传播常数随光纤直径增大而增大，随波长增大而减小，同时计算了传播常数随海水温度的变化，海水温度越高，传播常数越大，表明海水温度的变化会影响到模式的传播常数，因而可以通过测量谐振光谱的变化得知海水温度的变化。其次，搭建了海水温度传感实验系统，获得了微纳光纤环形腔海水温度的谐振光谱，实验发现同时存在两套谐振峰，分别对应基模的TE模和TM模，两个偏振模式的传感灵敏度分别为5.54和5.24 pm·℃-1。最后，探讨了基模两个偏振态谐振光谱的产生原因，由于结型耦合区的扭曲耦合使得两个偏振态分离，并对两个偏振模式的谐振强度进行了分析。两个模式的谐振强度不同，而且随着波长的增加，一个模的谐振强度不断增强，另一个模的谐振强度逐渐减弱。这是由于不同耦合态的耦合系数和衰减决定的，而且他们随着波长而改变。实验结果与理论计算相吻合。

Analysis of Microfiber Knot Resonator Spectrum for Seawater Temperature

As a sensing device,microfiber knot resonator (MKR)has been widely used in sensing field due to its advantages of high sensitivity and fast response.It is important to analyze the spectrum of MKR for detecting environmental parameters in that the spectrum can reflect the change of ambient environment.In this paper,the relationship between spectrum of MKR and sea-water temperature has been studied theoretically and experimentally.Firstly,the dependences of the propagation constants of fundamental mode (HE1 1)on the fiber diameter and the probing wavelength are studied theoretically in this paper,including two orthogonal polarization states of fundamental mode.The calculated results show that the propagation constant increases with the increasing fiber diameter and the decreasing probing wavelength.Simultaneously,the dependence of propagation constant of fundamental mode on seawater temperature is studied.The results show that the larger propagation constant corresponds to the higher seawater temperature,which indicates that the seawater temperature affect the mode propagation constant.Thus,the seawater temperature can be obtained by detecting the resonant spectrum.Secondly,the experimental system for seawater tem-perature sensing is set up,with which the resonant spectrum of MKR for seawater temperature sensing are obtained.The exper-imental results show that two sets of resonant peak exist on the spectrum,which are corresponding to TE and TM modes of fun-damental mode.The sensing sensitivities of the two polarization modes are 5.54 pm/°C and 5.24pm/°C,respectively.Finally, the reason for resonant spectrum of the two polarization states is discussed,which is that the separation of the two modes resul-ting from the twisted coupler of the knot zone,and the resonant intensity of the two polarization modes is analyzed.The resonant intensities of the two modes are different and one increases while the other one decreases with the increasing probing wavelength. It is determined by the coupling coefficients and attenuations of the two coupled states,which are affected by the probing wave-length.The experimental and theoretical results agree well.