| The structure design of photonic crystal fiber(PCF)has many controllable dimensions and large degrees of freedom.It can achieve unique characteristics that cannot be achieved by traditional optical fibers,such as endless single-mode characteristics,high birefringence characteristics,low nonlinear characteristics,etc.Its porous structure also provides a natural channel for filling and modifying materials such as gases,liquids and metals,which has become a vigorous research direction in the field of optical fibers and optical devices.The PCF-based filter presents the advantages of high thermal stability,high extinction ratio,compact structure,etc.,and provides new solutions for solving many problems in optical fiber devices based on traditional optical fiber filters.This dissertation is supported by the National Natural Science Foundation Program and the research is based on new PCF filters.A variety of continuous wave multi-wavelength fiber lasers,vector curvature fiber sensors and strain fiber sensors with high performance are proposed and developed.For the measurement requirements of body fluid p H and respiratory ammonia concentration in the biomedical field,a new type of biocompatible fiber optic biosensor has been developed.The main innovations achieved in the thesis are as follows:1.A tunable erbium-doped multi-wavelength laser based on a tapered three-core PCF filter is proposed and developed for the first time.The theory and experiment are combined to study the strain tuning characteristics of the tapered three-core PCF filter.Based on the tapered three-core PCF filter,a ring cavity erbium-doped multi-wavelength laser is constructed,which realized tunable single-,dual-,and three-wavelength lasing outputs with the tunable range of 22.22 nm,14.36 nm,and 8.08 nm,respectively.The side mode suppression ratio of the dual-wavelength lasing output is as high as 52 d B.And the dual-wavelength lasing outputs with the wavelength intervals of twice,three times and four times the free spectral width are realized.Compared with most reported lasers based on special fiber filters,the proposed laser has better tunable characteristics and higher side mode supress ratio,which has broad application prospects in the fields of optical communications and microwave photonics.2.A switchable multi-wavelength laser based on four-leaf clover PCF filter is proposed and developed.The theoretical model of the four-leaf clover PCF interferometer is established.The theory and experiment are combined to analyze the mode interference characteristics and transmission characteristics of the filter.On the basis of analysis results,a switchable erbium-doped multi-wavelength laser by using the four-leaf clover PCF filter is constructed.Switchable six-wavelength laser with a side mode suppression ratio of 50 d B and the peak power fluctuation of less than 1.5 d B is realized.Compared with the lasers with similar structures,the side mode suppression ratio is increased by 10 d B,and the peak power fluctuation is reduced by 2 d B.By applying axial strain to the four-leaf clover PCF filter,a dual-wavelength laser output with a tunable wavelength interval can be achieved,with a tuning range of 41 nm,which is nearly double that of most reported multi-wavelength lasers with similar structures.3.A dual-parameter sensor for mesauring curvature and strain based on the tapered dual-core PCF is designed and developed.By tapering at the splice point,the mode interference is strendthed.The dual-core PCF with an asymmetric structure is used to achieve vector curvature sensing in the two bending direction,and the sensing sensitivity reaches 18.29 nm/m-1 and-18.13 nm/ m-1.At the same time,the sensor also has a good linear response to strain changes,and the highest strain sensitivity is-10.65 pm/??.Using the matrix analysis method,the influence of temperature in vector bending measurement and strain measurement can be eliminated.Compared with other vector bending sensors,the proposed sensor has the obvious advantages of simple structure,high sensitivity,low temperature cross-sensitivity and the ability of multi-parameter sensing.4.A high-sensitivity strain sensor by using three-core PCF based Sagnac ring structure is designed and developed.The sensing principle is that the mode coupling characteristics between the three cores change with applied strain.The proposed sensor can achieve the sensitivity of-29.8 pm/??,which is higher than most PCF-based strain sensors reported in recent years.Since the three-core PCF is made of pure quartz,the sensor exhibits an extremely low temperature cross-sensitivity of 0.05 ??/?.In order to further improve the sensitivity of the sensor theoretically,the influence of the mode coupling characteristics of three-core PCF on the sensor sensitivity is systematically studied.The research results show that when the duty cycle of the fiber is 0.84,the sensitivity at the wavelength of 1561.47 nm can be increased by 2 times,which provides theoretical guidance for the subsequent development of high-sensitivity strain sensors.5.A four-leaf clover PCF ammonia sensor with functionalized TPPS sensitive membrane was designed and developed.The theory and experiment are combined to study the response characteristics of TPPS sensitive membrane to ammonia concentration.After that,the TPPS dye is filled into the large air holes of the four-leaf clover PCF by the complete filling method,and a four-leaf clover PCF ammonia sensor with a functionalized TPPS sensitive film was developed.The sensor can realize accurately detection of ammonia gas in the concentration range of 0-10 ppm and the detection accuracy is 0.15 ppm.The response time is 150 s,and it can be reused through hydrochloric acid post-processing.Both TPPS dye and quartz fiber are non-toxic materials to cells,which meet the requirements of biocompatible ammonia gas sensing.This research result breaks the bottleneck that the detection accuracy of current ammonia sensor cannot meet the requirements of biological ammonia detection.And the research has important significance and practical value for advancing the development of ammonia sensors suitable for biological detection.6.A dye-free U-shaped optical fiber p H sensor is proposed and developed.Sol-gel technology is used to wrap ethyl cellulose in a silica matrix to form a dye-free p H-sensitive film.Experimental studies have shown that the prepared sensitive membrane has stable absorption characteristics,uniform composition at room temperature,and no cytotoxicity.The sensitive film is coated on the U-shaped fiber to develop a dye-free U-shaped fiber p H sensor.The sensitivity,measurement range,accuracy,time stability,temperature stability,and measurement consistency of the sensor are experimentally studied.The research results show that the sensor has a good linear response to the solution p H in the range of 4.5-12.5.The sensitivity in the p H range of 7.5-12.5 is-0.42 d Bm/p H,and-0.14 d Bm /p H in the p H range of 4.5-7.5.In addition,the sensor exhibits high temperature stability.The p H value changes in measurement within the temperature range of 21°C-39°C is only 0.12 p H,and the p H values measured in different time periods are basically the same.The measurement range of the sensor is higher than that of most reported dye-free fiber p H sensors.Besides,it is biocompatible and the resolution is reached up to 0.02 p H,which meets the accuracy requirements of most body fluid measurement in the biomedical field.The research results are of great significance and application value for the development of p H fiber biosensors and their applications in the field of biomedicine. |
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