Single High-order Vector Mode Fiber Laser And Its Application

As a kind of solid-state laser with high beam quality and power scalability,fiber laser has been widely concerned and recognized in today’s laser research field.In the early days,fiber lasers were mainly focused on single-mode fiber lasers,but in the 21 st century,fiber lasers with high-order modes have gradually attracted the attention of researchers.High-order modes are mainly divided into scalar mode,cylinder vector mode and vortex mode,which are different from the fundamental mode in field strength and polarization distribution,so they have unique advantages in high-power fiber lasers,mode division multiplexing,particle capture and manipulation,high-resolution optical microscopy imaging and laser processing.However,the current high-order vector mode fiber laser has some disadvantages,such as unstable output mode,easy to be disturbed by environment and low output power,which seriously limits its performance in practical application.In order to promote the application of high-order vector mode fiber lasers,this paper proposes a variety of mode coupling,mode separation,mode selection and high-order mode power amplification technologies,and builds a variety of single high-order vector mode fiber lasers as stable light sources in high-order vector beam applications.The main research results are as follows:1.A metal-clad fiber is designed and fabricated based on metal ohmic loss and surface plasmon resonance(SPR)characteristics.The metal-clad fiber has very low loss for TE01 mode and high loss for other modes,so it can achieve selective transmission of TE01 mode.In this paper,an all fiber laser with LP11 mode resonance is built based on metal-clad fiber.Through adjusting the polarization controller,a single TE01,TM01 and HE21 modes output is obtained.The LP11 mode purity reaches 97.6%;2.Ring passive fiber and ring ytterbium doped fiber are designed and fabricated to solve the problem of mode crosstalk among TE01,TM01 and HE21 modes,and the stable transmission of high-order vector mode is realized.Combined with metal mode filtering technology,the fiber laser with single TE01 mode resonance and output is realized,and the mode purity reaches 96.5%;3.Based on the ring fiber,the long period fiber grating is written,which realizes the high-efficiency coupling from HE11 mode to HE21 mode.The fiber laser output from single mode HE21 is realized by using the ring fiber Bragg grating as the mode selection device.By adjusting the phase difference between HE21even and H21odd modes,the orbital angular momentum beam with a topological charge of±1 is obtained,and the mode purity reaches 94.4%;4.The long-period fiber grating coupled with vector mode is designed and manufactured.The high efficiency and high purity coupling between the linearly polarized light in polarization-maintainging fiber and azimuthally/radially polarized light in the ring fiber is realized.A fiber laser with an all polarization-maintaining structure which is able to output single TE01 and TM01 mode is built.The output mode is stable and insensitive to external interference.The mode purities are 92.4%and 97.3%,respectively;5.The mode of MOPA is amplified by double-clad polarization-maintaining large mode-field fiber.The single radially polarized light(TM01 mode)is obtained by the principle of intrinsic mode synthesis of polarization maintaining fiber.The maximum output power of the laser can reach 20 W and the mode purity can reach 91.5%;The innovation of this paper is as follows:1.Based on the polarization dependence of metal layer loss,TE01 mode is selected,and a LP11 mode resonant fiber laser is realized;2.The ring passive fiber and ring ytterbium-doped fiber are designed and fabricated to solve the mode crosstalk problem of LP11 mode.The fiber laser with single TE01 mode resonance can output stable high-purity TE01 mode beam without adjusting the polarization state;3.The long period fiber grating(LPFG)is etched based on the ring fiber to realize the directional coupling from HE11 mode to HE21 mode.Combined with the ring fiber Bragg grating,the fiber laser with single HE21 mode output is realized,and the orbital angular momentum beam with topological charge of±1 is obtained by superposition of two degenerate modes of HE21 mode;4.Based on polarization maintaining fiber and ring fiber,a vector mode coupled long period fiber grating is fabricated to realize the efficient and high purity coupling from HE11 mode to TE01 mode and TM01 mode.Based on this,a stable single TE01 mode and TM01 mode all polarization maintaining fiber laser is realized;5.High-purity single mode is generated in large mode field double clad polarization-maintaining fiber,and its power is amplified successfully.At the same time,high-power and high-purity radial polarized light is synthesized by beam splitting and polarization combining technology,and the output power reaches 20 W.