The Investigation Of Photonic Crystal Fiber Sensors Based On Selectively Filling Technique For Temperature Measurement

Photonic crystal fibers(PCF)are generally formed by pure silica with a core surrounded by a periodic lattice of air-holes running along its propagation axis.The regular morphological microstructure makes the confinement of light possible.Our knowledge of what an optical fiber is and what it does is changing due to the development of this new technology,and a broad range of applications based on these principles are being developed.The PCFs with periodically arranged air channels represent a versatile platform for functional material integration,which can be investigated combining with many other fields such as chemistry,biology,materials.As one branch,the selectively filled photonic crystal fiber sensors are widely applied to sense the strain,electric field and so on,especially in temperature sensing application.However,plenty of investigations are focus on how to get higher sensitivity,smaller size,and larger temperature range.There has no prior investigation concerning the influence of the coupling strength between the liquid filled waveguide and the silica core on its temperature sensitivity.In addition,most PCF sensors are demodulated in wavelength domain by expensive equipment like an optical spectrum analyzer.Few works have been reported on the sensing signal demodulation of those PCF sensors.In this work,the simulation and experiments of directional coupler structures with different separations between the liquid selectively infiltrated channel and the silica core of a large mode area photonic crystal fiber,Assessment of their coupling characteristics and the corresponding temperature sensing capabilities have been investigated.The results reveal that the smaller distance between the silica core and the liquid core does not affect the modes indices,but increases the intensities of modes in the liquid core and thus enhances the temperature sensitivity.This work provides insights into the design and optimization of the liquid-infiltrated PCF for sensing applications.For the second question,an optical fiber sensing system based on low coherence interferometry(LCI)is proposed and demonstrated to interrogate sensors comprised by selectively filled double-core photonic crystal fiber(SFDC-PCF).The sensor used here is made by selectively filling about 1/3 area of air holes in the cladding of photonic crystal fiber with distilled water.So the dual-core in the sensor has different effective refractive indices,resulting in a phase delay between two lights transmitting in the fiber.The phase delay of the sensor can be compensated by a Mach-Zehnder interferometer with a scanning optical tunable delay line in one arm of the interferometer,namely temporal interrogation.By tracking the value of phase delay,the change of the measurand can be detected.Temperature measurement is carried out to test the system performance.An average sensitivity of 0.9 ?m/? is achieved within the temperature range of 29-92?.The experimental results coincide with theoretical analysis.The proposed all-fiber sensing system,with the merits of cost-effective,stability,and flexibility,can demodulate the SFDC-PCF sensor signals well,which is very important for practical sensing applications.This work provides a new thinking for fiber sensing technology based on LCI technique.