Research On The Fabrication And Application Of MZI Based On The Side Polished Germanium Core Fiber

Fiber MZI has a wide range of applications in the field of fiber communication and sensing,which has attracted the attention of many researchers.Among them,fiber MZI based on single mode-multimode-single mode(SMS)fiber structure has become the first choice of researchers at home and abroad because of its advantages of flexible structure and easy production.However,the fabrication of fiber MZI still face a number of obstacles,such as,poor robustness,large sensor size and so on.In order to solve these problems,this article based on Ge-doped fiber(GDF)manufactured SMS fiber structure,through side polishing GDF and alkali etching side polished GDF,two new types of MZI are designed and manufactured,and use them for refractive index measurement,the sensitivity reaches 623.5 nm/RIU,2622.6 nm/RIU.The detailed work are as follows:First,an auxiliary side polishing method for polishing SMS fiber structure is designed.First,make a smooth glass groove that the middle of it is shallower than the two sides.Then,the SMS fiber structure is fixed in the glass groove with AB glue.Finally,the optical fiber polishing paper is used to polish in the direction parallel to the optical fiber.When polishing SMS fiber structure,it can ensure that the core of single mode fiber is not damaged when polished to the core of multimode fiber.In the whole process of fiber polishing,the precise control of fiber polishing depth is realized by real-time detecting the change of transmission spectrum waveform.In addition,the design has the advantages of good robustness,reusability,and small polishing area.Second,a refractive index sensor based on side polished GDF is designed and implemented.First,prepare and side polish the SMS fiber structures with different GDF length,and stop polishing when the deepest interference fringes are reached.Then,the refractive index of the formed sensor is measured.The experimental results show:(1)the refractive index measurement sensitivity increases with the increase of GDF length when the length of the GDF is short.When the GDF length is 70 ?m,the sensitivity can reach 623.5 nm/RIU.(2)an excessively long GDF leads to a decrease in refractive index measurement sensitivity.When the length of GDF is 2 mm,the cladding mode will be excited during polishing,which resulted in complex and unstable transmission spectra.Third,a refractive index sensor based on alkali etched side polished GDF is designed and implemented.The GDF to expose its core to the surrounding environment by side polishing SMS fiber structure.Then,using the unique alkali etching characteristics of the GDF,the core is etched to half of the entire core with a 5% concentration alkaline solution to form a split-wavefront fiber MZI.The fabricated fiber MZI has the characteristics of relatively low insertion loss,high material-efficiency,and high quality transmission spectrum.Moreover,fiber MZI also has better linear correlation and refractive index sensitivity.When GDF is 105 ?m in length,the refractive index sensitivity is 2622.6 nm/RIU,and the linear correlation coefficient is 0.9993.It can be seen that the sensitivity of the sensor is significantly improved,which is about 4 times of that of the sensor manufactured only by the side polishing method.