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无芯光纤(NCF)干涉仪以所处外部介质作为NCF段包层,对外界环境折射率变化极为敏感。本文对以NCF为基础构建的多模干涉仪(MMI)传输特性进行了详细的理论分析,并对其在丙三醇溶液中的浓度传感特性进行了实验研究。实验接入自制的长为4.4mm、直径为104μm的NCF,干涉仪单峰深度超过20dB,波形清晰,辨识度好。理论与实验的一致性说明,实验制作的MMI中,单模光纤(SMF)与NCF之间的渐变区域对干涉仪传输特性没有明显影响。在丙三醇水溶液质量分数由7%逐渐升高到70%的过程中,传输谱峰值波长移动范围达到26.5nm,峰值波长与溶液浓度的变化符合三次函数关系。研究表明,基于NCF的MMI对NCF外界溶液浓度变化能够做出连续实时的显著反应,并具有较高的分辨率。
The coreless fiber (NCF) interferometer uses the external media as the NCF cladding, which is extremely sensitive to changes in the refractive index of the external environment. In this paper, the NCF-based multimode interferometer (MMI) transmission characteristics of a detailed theoretical analysis, and its concentration in glycerol solution sensing characteristics of an experimental study. Experimental access to the homemade length of 4.4mm, diameter of 104μm NCF, single-peak depth of the interferometer over 20dB, clear waveform, good recognition. The agreement between theory and experiment shows that in the experimentally produced MMI, the graded area between single mode fiber (SMF) and NCF has no obvious influence on the transmission characteristics of the interferometer. In the course of increasing the mass fraction of glycerol aqueous solution from 7% to 70%, the wavelength range of the transmission spectrum reaches to 26.5 nm, and the change of the peak wavelength and the solution concentration conforms to the cubic function. The research shows that the NCF-based MMI can make a continuous real-time and significant response to the change of concentration of NCF solution and has high resolution.