DFB Fiber Laser Sensors

Distributed feedback (DFB) Fiber Lasers and Distributed Bragg Reflector (DBR)Fiber Lasers, including strain sensing, temperature sensing are used as acoustic sensors withoptical frequency interrogation, alternative to passive Bragg grating sensors. They areattractive high resolution devices because of their high performance and small size. Remotepumping and interrogation of such laser sensors without the use of an optical isolator near thesensing point may be required. Their demodulation schemes are normally done using anoptical spectral analyzer, or based on optical fiber interferometer and Phase Generated Careermethod, or observing the beat frequency of the fiber laser. The laser may also experiencediscrete external reflections from the end of the lead fiber. However, this will introduceRayleigh back-scattering into the laser from lead fiber.People tried to eliminate the influence of the extra feedbacks of DFB and DBR fiberlasers because they introduce an extra intensity and frequency noise. Here, we propose to usethe weak feedback effect as the sensing principle. This approach is verified with simulationand real-world tests. We will also test the DFB fiber laser as a head sensor and use MZI forsensing applications. These architectures can act in real-time and has good robustness.We will introduce fiber laser sensing systems and fiber laser hydrophone systems. Anoverview about hydrophone development systems and their applications is presented. It alsoincludes the motivation behind undertaking the thesis work and thesis objectives.Then, the background theory of the distributed fiber lasers is presented. The rateequations are used after simplifying considering adequate assumptions.Next, we present a numerical analysis of the distributed feedback fiber laser, applyingmethods such as the transfer matrix method (TMM), and then experimental use of thedistributed feedback fiber laser as an acoustic sensor. Several analysis will be presentedexperiencing the MZI and Intensity modulation.After that, we introduce the weak feedback effect to the DFB fiber laser. Theoreticaland numerical analysis are presented. In the simulation, different aspects of the fiber laser withfeedback are explained.Finally, we provide a comprehensive evaluation of the principal of the DFB fiber laserwith feedback. The performances of a DFB fiber laser sensor with weak feedback are experienced. The performances include the acoustic or vibration measurements based on theweak feedback and intensity modulation.