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Research On Fiber Laser Source To Generate Single Mode TM01 And TE01

Posted on:2015-03-11Degree:MasterType:Thesis
Country:ChinaCandidate:J L LiFull Text:PDF
GTID:2268330425489076Subject:Electromagnetic field and microwave technology
Abstract/Summary:PDF Full Text Request
Radially polarized mode TM01and azimuthally polarized mode TE01have important research values in nanofabrication, high-resolution imaging, optical trapping, etc. In order to obtain fiber laser sources which can generate pure mode TM01and TE01, two methods have been proposed in the thesis.The main works of the thesis are as follows:A fiber with spoke-like air slits introduced between the fiber core and cladding is proposed to generate pure mode TM01. Theoretical analyses show that the modal birefringence between the mode TM01and the modes TE01, HE21increase to10-4, the values of which are10-5in conventional step-index fiber. The confinement losses of the modes TE01and HE21are greater than that of the mode TM01. The designed fiber is presented as the gain medium of the fiber laser. The simulation results based on the rate equations show that the fiber laser can output mode TM01with the purity of99.9%and the slope efficiency of87.3%.A fiber with a thin metallic layer introduced between the central core and the cladding is designed to obtain the pure mode TE01. Theoretical analyses indicate that the modal birefringence between the modes TE01and TM01and HE21can increase to10-3and10-4respectively over wavelength ranging from1μm to2μm. Meanwhile, the confinement loss for the mode TE01is much smaller than those of the modes HE21, TM01and HE11.Two cases are analyzed on this basis:1) In the case of the active fiber, the fiber is presented as the gain medium of a fiber laser. The gain of the fundamental mode can be much less than that of the mode TE01by adjusting the rare-earth doping profile in the central core. The modes TM01and HE21possess larger confinement losses in the meantime. Thus, the fiber laser output mode TE01with the purity of99.99%2) In the case of the passive fiber, two contrastive cases of the initial laser source are proposed, which are single y-polarized Gaussian laser beam and the x-and y-polarized Gaussian beams with anti-symmetric field distributions. Theoretical analyses show that the mode TE01can be excited when the Gaussian light beam is coupled with suitable shift distance from the center core in the former case, but the axial symmetry of the intensity distribution is poor. The mode TE01with axisymmetric intensity distribution can be obtained in the latter case.
Keywords/Search Tags:Mode TM01, Mode TE01, Fiber laser, Finite element method, Full-vector finite-element beam propagation method
PDF Full Text Request
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