Fourier Domain Mode Locking Swept Laser Technology And Its Application In Fiber Sensor System

With urgent demanding for high-speed optical frequency-swept source by OpticalFrequency Domain Imaging (OFDI) technology in biomedical science, Fourier DomainMode Locking (FDML) frequency-swept laser has come into our sight. As researchprogressed, people not only focus on how to improve the performance of the laser itself,but also begin to explore its new applications. Some of its features, the ability toimprove sensors’performance and to solve problems of huge difficulty in demodulatingsensor signals and expensive cost, make it have great potential practical value in thefield of optical fiber sensor.In this paper, firstly, the present development of FDML lasers and fiber Bragggrating (FBG) sensor is researched, the basic conception of FBG and its measurementprinciples are briefly introduced, the theories of the standard frequency-swept laser andthe FDML frequency-swept laser also are discussed by comparison and the interrogationprinciple in time domain of the FBG sensor system based on FDML frequency-sweptlaser was explained.Secondly, after theoretical analyses, the FDML frequency-swept fiber laser is builtwhich consists of a fiber Fabry-Perot tuned filter (FFP-TF), a semiconductor opticalamplifier(SOA), fiber delay lines, isolators and a coupler. In the experiment, the outputof frequency-swept laser and laser pulse are got by changing parameters of the filter’sdriving signal and then the paper further qualitatively analyze every factor influencingthe output. Spectrograph with a resolution of0.01nm and oscilloscope with a samplerate of100M are used to receive the output of the whole system and LabVIEW is usedto observe and record data.Finally, the FBG sensor system based on the built laser is got with the FDMLfrequency-swept fiber laser as light source and the FBG as sensing element. Then thesensing system is tested in the temperature and stress experiment and demodulation oftime domain of this sensor is accomplished. In the experiment, the signal-noise ratio ofthe system is about25dB, temperature sensing sensitivity is7.98pm/℃, stress sensingsensitivity is1.16nm/N and11.426μs/N in time-domain。At the same time, advantagesand disadvantages of the experiment are analyzed and another improved proposal ismade in which the sensing element FBG as a frequency selection device was put intothe laser cavity, and this sensing system can be called as a spectrum-limited FDMLfiber laser.