Font Size: a A A

The Study Of Ytterbium-doped Silica Fiber For High Power Laser And Amplifier System

Posted on:2015-07-13Degree:DoctorType:Dissertation
Country:ChinaCandidate:G ChenFull Text:PDF
GTID:1228330428966035Subject:Optical Engineering
Abstract/Summary:PDF Full Text Request
Ytterbium (Yb) doped silica fiber laser and amplifier has developed rapidly in the past15years, but with the fiber system power climbs ever higher, heat management, nonlinear effect and photodarkening (PD) effect become serious issues. Yb fiber as a laser gain medium is the key factor to decide the fiber system performance, such as slope efficiency, maximum output power and beam quality. In this work, Yb doped silica laser fibers are studied, including fiber fabrication, measurement, gain control and PD. The purpose of this research work is to improve and optimize Yb fibers properties, provided an essential guarantee for the high performance fiber laser and amplifier.Firstly, the rare earth doped fiber fabrication technique is introduced. And some key steps in motified chemical vapor deposition technique are illustrated and analysed in detail. Based on the technique with gas phase and solution doping, different composition silica fibers are fabricated. Then optical specifications and laser performance are measured and visivle light luminescence phenomenon is explained.Secondly, by the analysis of the influence of pump wavelength on fiber heat generation and fiber system laser performance, it can concluded that the best pump wavelength is about1010nm to1030nm. In order to realize the special wavelength fiber laser, phosphorous as a codped ion is proposed. The option is verified by experiment:1018nm fiber laser is realized with45dB signal-nosie ratio.Thirdly, air-clad large mode area (LMA) ytterbium doped photonic crystal fibers are investigated. The basic concept of the design is to increase mode area and reduce nonlinear coefficient.37missing-hole super LMA and7missing-hole polarization-maintaining (PM) LMA Yb fibers are developed and manufactured.1m super LMA with~1330μm2foundamental mode-field-area and>0.5clad numerical aperture is used to1064nm continuous-wave (CW) fiber laser experiment, and a hundred watt level output power is reached with a78%slope efficiency. The maximum polarization extinction ratio of the PM LMA fiber is about16dB.1040nm2.95W1.39ps pulses amplifier and1080nm8.12W W amplifiers are generated from a2m and4m PM LMA fiber respectively, with a slope efficiency above50%. Fourthly, research methods on PD are anslyzed and discussed. The test approaches for PD characterized by the additional loss spectrum and fluorescence attenuation spectrum are suggested and the corresponding devices are designed. The factors affected the PD measurement are illustrated. Based on the experimental data analysis, the linear multiple relation of excess loss value at certain visible light wavelengths to the value at1040nm are listed. And dependences of the equibium additional loss and rate constant on the Yb excitation level are concluded.Fifthly, the possibility and way to improve the PD performance are discussed on the basis of color center formation mechanism. Cerbium (Ce) is selected as a co-doped ion for conducting the study of low PD Yb fiber. A series of fibers are fabricated and tested. The results indicate that Ce is a good choise and the appropriate Ce Yb concentration ratio is between0.4and1. A self-bleaching phenomenon is observed in the Ce Yb co-doped fiber. Non-isothermal treatment experiments show almost no PD induced loss increament in the Ce Yb co-doped fiber at elevated temperatures and the minimum temperature of PD complete bleaching is about400℃, lower than the temperature~550℃needed for the Yb fiber. It may reasonably conclude that the intermediate state in PD is almost vanished due to the Ce ion. Ce is not only reduce the formation of color center but also beneficial for the recovery.
Keywords/Search Tags:fiber lasers, rare-earth doped fibers, ytterbium ion, thermal effects, mode field area, photodarkening
PDF Full Text Request
Related items