| As a highly sensitive technology,fiber loop ring down spectroscopy can measure the refractive index and concentration of the sample,and it has received extensive attention from researchers in recent years.For the pulsed fiber loop ring down system,the pulse is generally composed of the intensity modulator,the laser source and the signal generator.Because the frequency and width of the pulse need to be compromised,the length of the fiber loop needs to be considered and the narrower pulse width also has a greater impact on the ring down time,chaos laser technology can solve this problem well.In this study,the fiber sensor based on the chemical etching method is used to realize the chaotic correlation fiber loop ring down sensing,and the chaotic fiber laser is used as the laser light source.The formation and performance of fiber tapers was monitored by combining chaotic fiber ring down technology on line and in real time.The chaotic autocorrelation fiber loop ring down system obtains the measured change through the change of the auto-correlation ring down time.Due to the extremely narrow nature of the half-height autocorrelation function of the chaotic signal,a very short fiber loop length can be used to improve the sensitivity of the sensing system.This article has mainly introduces the following five parts from theory and experiment:(1)Introduce the advantages of fiber loop ring down sensing technology and different fields of application are comprehensively explained.The research progress and application of chaotic laser technology are further analyzed on the basis of analyzing the advantages and disadvantages of pulsed fiber loop ring down technology.(2)The taper fiber based on evanescent potential field sensing was fabricated by chemical etching method based on the theory of the evanescent potential field sensor.The basic principle of the fiber sensor was analyzed by wave optics theory,and analyze the chaotic laser related ring down sensing technology.The analytical relationship among the parameters of the chaotic correlation fiber loop ring down refractive index sensing was derived.(3)According to the sensing principle of chaotic correlation fiber loop ring down technology,the chaotic fiber loop ring down sensing system and a chaotic signal processing system are built.The chaotic fiber loop ring down sensing system includes an chaotic erbium doped fiber laser,an erbium-doped fiber amplifier,and an experimental device for chaotic fiber loop ring down technology.The chaotic signal processing system realizes data acquisition and processing functions through serial communication technology,achieving the purpose of real-time monitoring.(4)A more sensitive etched fiber is used for refractive index sensing,and the effect of etched fiber of different lengths and diameters on the performance of the sensor are studied experimentally.The results show that the sensitivity and detection limit of the chaotic correlation loop system can reach 0.0682 ns-1RIU-1 and 3.45×10-4 RIU.As the length of the fiber loop decreases,the sensitivity of the experimental system gradually increases.Compared with pulsed fiber loop ring down system,chaotic light has stronger anti-interference ability and wide bandwidth,which makes its noise floor lower and detection limit smaller.The sensitivity and detection limit of the sensing system can be further improved by increasing the coupling ratio of the coupler or adding amplification compensation in the fiber loop.(5)The chaotic correlation fiber loop ring down sensing system realizes the sensing of hemoglobin solutions of different concentrations.The designed sensor system is applied to the measurement of bovine hemoglobin concentration.Experiments have proved that it can distinguish lower bovine hemoglobin concentration,the concentration sensitivity is 7.9ns/(mg/m L),and the minimum detection limit is 1.25×10-2 mg/m L.Compared with other biosensors,the sensing system has the advantages of simpler structure,cheap experiment cost,sensitive detection,insensitivity to light source fluctuations,and real-time response. |
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