Research On Micro Fiber-optic Sensor And System Fabricated By Deep Ultraviolet Laser

Fiber-optic sensor can offer many advantages such as good harsh environment resistance, passive operation, and easy of remote measurement, which could play important role at meeting significant nation demands including earthquake monitoring, key facilities health monitoring, electrical power industry, medical and chemical fields, etc. It has become one of the main research directions in sensor field. A few innovative achievements have been obtained in respect of micro fiber-optic sensor and system fabricated by deep ultraviolet (UV) laser in this doctor thesis (One of the important parts of the 2008 science award of ministry of education), as below:I. Important breakthrough achieved at new generation of micro Fabry-Perot(1) 157nm laser micromaching technology has been stuied in detail. Experiment results show that such a laser system can be used to realize mirror-like micromaching, which is the basis of fabricating micro fiber-optic sensor.(2) A one-step 157nm laser micromaching method has been used to create a high quality in-line F F-P interferometer with best optical performance and highest operation temperature (800℃), for the first time. It is anticipated that it can be applied into arospace and energy industry with extreme harsh environment, and provide an effective means for long-term existed problem, accuracy strain measurement under high temperature.(3) In order to realize strain and pressure measurement under high temperature, a type of self-enclosed micro Fabry-Perot (F-P) is invented, for the first time, which can be safely operated at 800℃with low temperature sensitivity, and can achieve accurate measurement in normal temperature range without any thermal compensation. As a strain sensor, the static strain sensitivity is ~0.304mrad/με, and dynamic strain resolution is ~20nε/Hz1/2 at frequency of <1.8 kHz. As a pressure sensor, good linearity of 99.9975% is achieved. At the same time, simultaneous high temperature and strain measurement system based on F-P and LPFG (Long-Period Fiber Grating) is also investigated.(4) A micro Fabry-Perot (F-P) optical fiber tip sensor for high-resolution refractive-index measurement fabricated by using 157-nm laser micro-machining, is investigated, for the first time. It can provide temperature-independent measurement of practically any refractive index larger than that of air and offers a refractive-index resolution of ~4×10-5 in its linear operating range. The sensor exhibits many desirable characteristics, including wide RI sensing range, good linearity, high resolution, easy operation, low thermal sensitivity, low fabrication cost, potential for mass production, small size, good reliability (no cavity filling), etc.(5) In order to futher improve the sensitivity of refractive index sensor, A novel miniature fiber-optic Fabry-Perot (F-P) refractive-index (RI) sensor machined by 157nm laser is also proposed. A RI resolution of 1130.887nm/RI unit (RIU) is achieved by experiment. Such a sensor has a number of outstanding advantages when compared with other fiber-optic RI sensors, such as very small, rigid, high resolution, excellent linearity, wide measurement range, et al. It is anticipated that this miniature sensor could find important applications in chemical and biomedical sensing fields.These innovative works not only enriched fiber-optic research system of F-P sensor, but also open a new way to develop novel micro sensing strcture, which is significant from aspect of sensing science. Simultaneously, it could solve the issue of mass production of F-P sensor, and offer basis for the purpose of wide application of F-P sensor, which is also significant from aspect of application.II. Important progress achieved at fiber bragg grating sensors(1)Long-range fiber bargg grating (FBG) sensing system based on Raman/EDFA (Erbium-doped Fiber Amplifier) hybrid amplification lasing is proposed, for the first time. 50km and 100km hybrid raman/EDFA (Erbium-doped Fiber Amplifier) fiber laser FBG sensing system were demonstrated. Within 50km fiber link, a high optical SNR of over 60dB is obtained.(2)Advanced algorithms such as MUSIC or Eginvetor method, have been used to improve SNR of strain signal of FBG.Due to these methods, low-cost quasi distributed fiber sensing network can be obtained, which could be applied in railway, gas or oil pipline, sea bank and borderline monitering when long-distance is essential.