Cascaded Double Cavity Optical Fiber Temperature Sensor Sensitized By Vernier Effect And PDMS

Temperature plays a very important role in human daily life and industrial production.High-precision temperature measurement has always been the goal pursued by researchers.Because optical fibers have many advantages such as small size,light weight,and anti-electromagnetic interference,optical fiber temperature sensors have received extensive attention from researchers.In recent years,the optical vernier effect has been widely used to improve the sensitivity of optical fiber temperature sensors,that is,two optical fiber interferometers are cascaded.When the free spectral ranges of the two interferometers are close but not equal,the cascaded interference spectrum will appear enveloped.The network presents a cursor phenomenon,which greatly improves the temperature measurement sensitivity.In addition,in recent years,researchers have combined PDMS with fiber-optic sensors and used the high thermo-optical and thermal expansion characteristics of PDMS to improve temperature measurement sensitivity.Based on the current research progress of temperature optical fiber sensing technology,this paper designs and studies several new types of optical fiber temperature sensors based on the cursor effect and PDMS sensitization.The specific research contents are as follows:A fiber optic temperature sensor based on PDMS filling film is designed and prepared.Firstly,single-mode fiber-quartz tube(SMF-HCF)with a length of about175?m was prepared by fiber fusion and precise cutting.Then,the liquid PDMS was injected into the quartz tube by capillarity to form a film in the fluorescent tube,and the cured length was about 25?m,thus realizing the air cavity and PDMS membrane cascade structure.In this structure,due to the relatively thin PDMS film,the combined cavity composed of air cavity and PDMS film and a single air cavity will produce a vernier effect.The experimental results show that the interference spectrum of the sensor has an envelope,and the envelope presents a vernier phenomenon,with a magnification rate of 4.9 times.With the increase of temperature,the interference spectrum envelope gradually redshifts and the sensitivity reaches 0.73nm/?.This result is consistent with the theoretical calculation results.Designed and prepared an optical fiber temperature sensor based on a quartz tube package SMF-PDMS-Air-SMF structure.First,the SMF is welded to a section of HCF with a length of 165?m;then,the PDMS is filled with the HCF to form the PDMS cavity;then,in the quartz tube,another SMF is aligned with the HCF to ensure the air between the PDMS and the SMF The length of the cavity is about 290nm,forming the structure of SMF-PDMS-Air-SMF;finally,the SMF-PDMS-Air-SMF is encapsulated in a quartz tube with UV glue.The PDMS cavity and the air cavity in the SMF-PDMS-Air-SMF structure are cascaded to realize the cursor effect.The experimental results show that the temperature sensitivity of a single PDMS cavity is 0.89 nm/~oC,and the sensitivity of the SMF-PDMS-Air-SMF structure is-1.9856 nm/~oC,which is 2.23times higher than that of a single cavity.The experimental results are consistent with the theoretical results.An optical fiber temperature sensor based on the SMF-PDMS-Air-PDMS structure encapsulated by a quartz tube is designed and prepared.Different from the single-sided PDMS of the SMF-PDMS-Air-SMF structure,the two sides of the air cavity in the SMF-PDMS-Air-PDMS structure are PDMS,and the thermal expansion of the PDMS on both sides will squeeze the air cavity and change its cavity length.Therefore,its temperature sensitivity is higher than the SMF-PDMS-Air-SMF structure.The sensor is also composed of a PDMS cavity and an air cavity.The length of the PDMS cavity is 165?m and the length of the air cavity is 200 nm.Experimental results show that the temperature sensitivity of a single PDMS cavity is 0.89nm/~oC,and the temperature sensitivity of the SMF-PDMS-Air-PDMS structure is-20.127nm/~oC,which is more than 10 times higher than that of the SMF-PDMS-Air-SMF structure,The experimental results are consistent with theoretical analysis.