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Study Of SBS Suppression In Narrow-linewidth Fiber Amplifiers Based On Spectral Manipulation Technology

Posted on:2012-03-09Degree:MasterType:Thesis
Country:ChinaCandidate:W B DuFull Text:PDF
GTID:2218330362960385Subject:Optical Engineering
Abstract/Summary:PDF Full Text Request
Fiber amplifiers have lots of advantages, including compact configuration, high reliability, excellent beam quality, high conversion efficiency and convenient heat management. Recently, with the development of high power laser diode (LD) pumping technology and fabricating craft of double cladding fiber lasers, output powers of fiber amplifiers are promoting ceaselessly. However, the output lasers of those high power fiber amplifiers employ large linewidth making them unsuitable for applications such as coherent beam combination, spectral beam combination and frequency transition where narrow-linewidth lasers (less than 0.1 nm in general) are welcomed. The most important obstacle toward high power narrow-linewidth fiber amplifiers is stimulated Brillouin scattering (SBS) effect. When the output power of a narrow-linewidth fiber amplifier reaches SBS threshold, the backward scattered light will grow dramatically in a nonlinear way. Once the backward light is strong enough, it will cause damage to the pumping LDs and even seed lasers in preamplification parts,thus suppressing SBS is especially important for high power narrow linewidth fiber amplifiers. A number of approaches such as designing large mode area fibers, changing dopant distribution of gain fibers and the use of temperature or stress distribution in fibers have been demonstrated to suppress SBS in some extent. However, when coming into real application, those approaches are limited by various factors, seeking more effective SBS suppression technology is very necessary.SBS effects in all-fiber narrow-linewidth fiber amplifiers with MOPA configurations are well studied in the present paper. Theoretical and experimental researches are carried out to study two kinds of SBS suppression technologies based on spectral manipulation—multi-tone amplification and phase modulation of single frequency seed laser. The main contents are as follows:Firstly, theoretical models of multi-tone fiber amplifiers are set up. Theoretical analysis and numerical simulations are carried out to study the effectiveness of SBS suppression in two kinds of multi-tone narrow-linewidth fiber amplifiers including two-tone amplification with gain competition and multi-frequency multi-wavelength amplification. The influences of seed power ratio, pumping configuration and length of gain fiber on SBS suppression effect are analyzed and discussed in datil.Secondly, experiments on multi-frequency multi-wavelength narrow-linewidth fiber amplifiers are carried out. SBS suppression effectiveness and potential feasibility of coherent beam combination are validated in the low power experiments. In the high power experiment, 334 W narrow-linewidth fiber laser which is in advance in recent domestic reports is attained. Thirdly, Theoretical analysis and numerical simulations on generation of multi-frequency lasers based on phase modulation of single frequency seed laser are carried out. Theoretical model of narrow-linewidth fiber amplifiers based on phase modulation of single frequency seed laser is set up and numerical simulations are performed showing that technology based on phase modulation of single frequency seed laser can suppress SBS effectively.Finally, experiments of SBS suppression in narrow-linewidth fiber amplifiers based on phase modulation of single frequency seed laser are carried out to validate effectiveness of SBS mitigation. Experimental researches are demonstrated to study influences of amplifier parameters, frequencies and amplitudes of modulation signals on SBS mitigation. SBS is well suppressed by phase modulation of single frequency seed laser and the 275 W narrow-linewidth high power fiber amplifier is set up in the high power experiment.
Keywords/Search Tags:fiber amplifiers, stimulated Brillouin scattering, narrow-linewidth, multi-tone amplification, phase modulation
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