Fabrication And Sensing Characteristics Of Liquid-Filled Fiber Microcavities

In recent years,a new type of optical fiber sensing structure based on the integration of the liquid material and fiber microcavity has been widely concerned.As the liquid material can modulate the light signal in the fiber microcavity directly,it can improve the sensitivity of the fiber sensing structure obviously.The new optical fiber sensing structures also have other advantages,such as flexible design,tunability and ease of integration.As a result,the combination of the liquid material and fiber microcavity is significant for the future development of the fiber sensing field.In this dissertation,efficient methods of liquid filling and packaging were proposed.By using the efficient methods,the new fiber sensing structures were fabricated by integrating the liquid materials and sensitized bubble structure with the fiber microcavities.The main work is as follows:A kind of temperature sensing structure based on a liquid-filled fiber microcavity was proposed against the low sensitivity of the all-fiber temperature sensing structure.A packaging method of arc-discharge caused taper was proposed to solve the problem existed in the process of encapsulating the liquid-filled fiber microcavity.A high-performance fiber temperature sensing structure based on a liquid-filled Fabry-Perot(FP)microcavity was fabricated by the method of liquid-filling together with arc-discharge tapering.The relationship between the temperature sensitivity of the liquid-filled fiber microcavity and the thermal optical coefficient of the medium in the microcavity was studied theoretically.Through experimental investigation,a sensitivity as high as-429 pm/? was achieved in the range between-5 ? and 30 ?.The fiber temperature sensing structure also had other advantages,such as rapid response time,good repeatability,and stability.A composite and sensitized microcavity structure based on the cascaded polymer-microbubble was fabricated by polymer-filling and subsequent heat-curing process.The theoretical study on the sensitizition mechanism of the fabricated fiber composite microcavity showed that,the sensitivity of the polymer microcavity and that of the microbubble microcavity were opposite in sign when the temperature rised.Through a subtraction between the two temperature sensitivities,an overall temperature sensitivity of the fabricated fiber composite microcavity structure was improved.Experimental results showed that the sensitivity of the temperature sensing structure was as high as 5.013 nm/? in the measurement range between 20 ? and 55 ?.A femtosecond laser micropump was used to deliver quantitative liquid to a fiber microcavity efficiently and a spirit level was fabricated.The analysis of the mechanism of the femtosecond laser micropump showed that,when the femtosecond laser was focused in the vicinity of the microchannel in the side wall of the fiber microcavity,a high-speed jet formed in the process of the collapse of the produced cavitation bubble will flow into the fiber microcavity through the microchannel,and the liquid-filling of the fiber microcavity was achieved.The experimental results showed that the amount of the pumped liquid can be controlled by adjusting the irradiation time of the femtosecond laser pulses.Such a method of delivering the liquid to the fiber microcavity based on the femtosecond laser micropump has potential for the fabrication of fiber functional devices and the rapid injection of analytes into a lab-in-fiber for chemical and biological analysis.A fiber tilt angle sensing structure based on a mobile microbubble in a fiber microcavity was fabricated by arc-discharge micromaching and liquid injection.When the fiber was tilted at a certain angle,the microbubble moved along the arc-shaped inwall of the fiber microcavity.The theoretical study showed that,in the process of motion,the arc-shaped inwall will affect the motion state of the microbubble by changing its forced direction,and the microbubble will eventually stop at the vertex of the arc-shaped inwall corresponding to the specific tilt angle.The movement of the microbubble caused the shift of the interference spectrum.Therefore,the tilt angle can be detected by monitoring the shift of the interference spectrum.The experimental results showed that the sensitivity of the fabricated tilt angle sensing structure was as high as 160.21 nm/deg.Moreover,such a fiber tilt angle sensing structure was capable of distinguishing the tilt direction,since the movement of the microbubble was tilt direction dependent.