单端面透射模式长周期光栅的设计和测试

Design and test of transmission mode measurement device based on long period fiber grating with a single end face

本文设计了一种单端面长周期光栅透射模式折射率传感器。首先,将2×2单模光纤耦合器输入端的一个光纤接头与光源相连接、输出端的两个光纤接头分别与光谱分析仪和长周期光栅的一个光纤接头相连接。然后,在包含长周期光栅的光纤另一个端面溅射反射银膜。最后,以一系列不同折射率的甘油水溶液为待测液体介质研究了直接透射模式与单端面镀银膜模式下长周期光栅的响应光谱的异同。实验结果表明:单端面镀银膜的长周期光栅的响应光谱仍然以透射谱的形式出现。对于同一种液体,单端面镀银膜的长周期光栅与直接透射模式的长周期光栅的响应光谱有着近乎相同的谐振波长值,但它们的光损耗存在一定的差异。在0~80%的甘油溶液中,直接透射模式下的光损耗从-12.92 dB变为-16.28 dB,再逐渐变到-13.22 dB;单端面镀银膜模式下的光损耗从-13.13 dB变为-13.74 dB,再逐渐变到-11.45dB。与直接透射模式相比,单端面镀银膜的长周期光栅的相对光损耗与甘油浓度的线性关系更加良好。本研究设计的长周期光栅测量系统采用单端面探头的方式检测环境介质,因而在测量中操作更加灵活方便,非常适合于远距离、恶劣环境或深层液体环境中的折射率测量。

In this paper,a type of refractive index sensor based on a single end face long period fiber grating(LPFG) with transmission spectra is designed.First,an optical fiber joint at the input end of a 2×2 singlemode fiber coupler is connected with the light source,and the two optical fiber joints at the output end are connected with an optical spectrum analyzer and an optical fiber joint of LPFG respectively.Then,the reflective silver film is sputtered on the other end face of the optical fiber containing LPFG.Finally,a series of glycerol aqueous solutions with different refractive indices are used as the liquid medium to be measured to investigate the similarities and differences between the response spectra of LPFG in direct transmission mode and the single-end silver film mode.The experimental results show that although the single end face is adopted,the corresponding response spectra of LPFG is still in the form of transmission spectra.Moreover,for the same liquid,LPFG with the single end face silver film and LPFG in the direct transmission mode have nearly the same resonance wavelength value.However,there is a certain difference between their optical losses.In the 0~80% glycerol solutions,the optical loss in direct transmission mode changes from -12.92 dB to-16.28 dB and then gradually to-13.22 dB.However,the optical loss gradually changes from-13.13 dB to-13.74 dB and then to -11.45 dB in the case of the single end face silver film mode.Compared with the direct transmission mode,there is a better linear relationship between the relative optical loss and the glycerol concentration of LPFG based on a single end face silver film.The LPFG measurement system designed in this study uses a single end face probe to detect the environmental medium,making it more flexible and convenient in measurement.It is well suited for refractive index measurement in long-distance,harsh environments or deep liquid environments.