Research On Narrow Linewidth Tunable Fiber Laser Based On Stimulated Rayleigh Scattering

The National Key Scientific Instrument and Equipment Development Project in the 13 th Five year clearly proposed the requirement for the design and measurement of narrow linewidth laser, based on the high and new technology’s dependence on high-end instruments. In optical fiber communication system, the high demand of information transmission throughput and light utilization efficiency leads to the stringent requirement of narrow linewidth tunable laser. While in the field of interferometric spectral measurement, for fm and higher measurement resolution, the demand for linewidth of k Hz and even k Hz below are put forward. But there is still difficult to get the linewidth below k Hz in the field of narrow linewidth tunable fiber laser.Aiming at this problem, this thesis proposes a method to achieve narrow linewidth tunable fiber laser based on stimulated Rayleigh scattering. This method using the narrow linewidth feature of stimulated Rayleigh scattering narrow the linewidth of fiber laser through the special tapered fiber in ring cavity. Combining with the thermal tuning of fiber Bragg grating, we achieve the narrow linewidth tunable fiber laser with the linewidth below k Hz. The main research contents of this thesis are following:1. Studying the stimulated Rayleigh scattering in the fiber. The narrow linewidth features of stimulated Rayleigh scattering have been proved and the related parameters which influenced the threshold of stimulated Brillouin scattering have been determined through the studying of the related theory about stimulated Rayleigh scattering and stimulated Brillouin scattering. Design scheme for improving stimulated Brillouin scattering’s threshold to utilize the narrower stimulated Rayleigh scattering to narrow the linewidth of fiber laser. Calculate the design parameters of the special tapered fiber used in the scheme by Beam PROP.2. Improving the linewidth measurement theory of fiber laser. Analyze the theory of laser linewidth. Aiming at the problem of accurate measurement of narrow linewidth, considering the noise of laser itself and the delay fiber, fit the final beat spectrum with the more accurate Voigt spectrum on the basis of the delayed self-heterodyne method. Achieve a more accurate measurement of the linewidth of k Hz and k Hz below with shorter delay fiber.3. Designing narrow linewidth tunable fiber laser. By the analysis of different resonant cavities of fiber laser and tune methods of fiber Bragg grating, determine the cavities and tune scheme of this thesis. Use Opti System to simulate the basic ring cavity fiber laser and determine the parameters of the equipment used.4. Building and testing the narrow linewidth tunable fiber laser: firstly, a special tapered fiber is designed and manufactured, in which the threshold of the SBS is improved by 1.9 dB than conventional single mode fiber; then a fundamental fiber laser system with 1570 Hz linewidth and 48.2 m W is set up; based on this, the special tapered fiber is added to the laser system, and as the experimental results suggest, the output power of the improved system(with a 260-millwatt pump) could be 3.52 m W, while the output linewidth, side-mode suppression ratio and threshold is 550 Hz, 60 d B and 54.5 m W respectively, and fluctuation of central wavelength is below 2 pm within half an hour; at last, a temperature controlled tank is applied to the system and a tunable output spectrum is achieved, the experimental analysis has also demonstrated that the tuning range of the laser is 1.61 nm(with a temperature tuning factor of 14.8 pm/℃), while the minimum tuning step is 4 pm, furthermore, the instability of the output power can be kept below 2.1% and the linewidth is narrower than 650 Hz during the tuning process, which have satisfied all the design requirements.The research of this thesis solve the problem of achieving k Hz below extremely narrow linewidth in the field of narrow linewidth tunable fiber laser. It provides a new way to realize higher efficiency fiber communication and high-precision interference spectrum measurement.