Miniaturized Fiber Modal Interferometers And Their Applications As Fiber Sensors

Nowadays miniaturized fiber modal interferometers(MMIs)are more and more popular,and compared with electrical sensors they have many inherent advantages,such as low cost,small size,easy to fabricate,immunity to electromagnetic interference,etc.,especially,they are widely used in measurement of various parameters,such as temperature,Refractive Index(RI),strain,displacement and humidity.In this thesis,three types of MMIs are proposed and demonstrated.They are single mode fiber(SMF)up taper-down taper-up taper(UDU)-based MMI,SMF up taper-core offset-up taper(UCU)-based MMI and Er-doped-fiber(EDF)-based MMI.And they are briefly introduced as following.The first type is a SMF UDU-based MMI.It's sensitive to refractive index(RI)and strain.Experimental results show that,this kind of MMI can realized the measurement of RI and strain.The sensitivity of RI is-22.437 dBm/RIU with a linear fitting of 0.997(the range of RI is 1.326-1.352)and the sensitivity of strain is 0.0008 dBm/?? with a linear fitting of 0.996(the range of strain is 0-400 ??).The second type is a SMF UCU-based MMI.It can achieve simultaneous measurement of RI and strain.The sensitivity of RI is-102.76 nm/RIU with a linear fitting of 0.998(the range of RI is 1.319-1.351)and the sensitivity of strain is 12.4pm/?? with a linear fitting of 0.997(the range of strain is 0-423.529 ??).The third type is a SMF-EDF-SMF-based MMI.It can achieve simultaneous strain and temperature measurement.The sensitivity of strain is 0.025 dB/?? with a linear fitting of 0.9938(the range of strain is 0-94.118 ??)and the sensitivity of temperature is 0.223dB/? with a linear fitting of 0.990(the range of temperature is 29.6-38.4?).All the three types of MMI are fabricated by a commercial fiber splicer,and experimental results show that they all have good performances with easy fabrication,good reproducibility and low cost.