High Order Mode Supercontinuum Generation In Fiber Amplifier

Supercontinuum have ultra-broad spectral coverage,high brightness and good coherence,they are widely used in optical spectroscopy,optical fiber communication,metrology and biological science.One of the most popular way to get high power supercontinuum is to generate directly from the ytterbium doped fiber amplifier.With the development of high-power fiber devices and large mode fiber,the output power of supercontinuum generated directly in fiber amplifier can reaches hundred watts range.However,the schemes of high-power supercontinuum generated in fiber amplifier are using large mode fiber which support several fiber modes,but there is little research on mode control and selection.High order modes have special dispersion and mode field distribution compared with the fundamental mode,they play a different role in supercontinuum generation.We propose a scheme to explore the nonlinear effect of high order mode in passive fiber and generate high power LP₁₁1 mode supercontinuum in fiber amplifier.The main contents are follows:1?Use a mechanical long period grating as mode converter to analyze the difference caused by mode field distribution,dispersion,cut-off wavelength and loss property of different modes in 15/130 and 25/250 passive fiber.The experiment results show that LP₁₁ mode is unsuitable for transmission in 15/130 passive fiber,which indicates that we cannot get high power LP₁₁ mode supercontinuum in 15/130 fiber.However,25/250 passive fiber is suitable for LP₁₁ mode transmission and we get 5.27W LP₁₁ mode supercontinuum in 200m 25/250 passive fiber with spectral range from850-1700nm.2?An all-fiber master oscillator power amplifier?MOPA?was demonstrated to generate high power LP₁₁ mode supercontinuum.By changing the seed pulse repetition and width,we explore the output beam profiles of LP₁₁ mode under different pulse peak power and get hollow beams output when the LP₁₁ mode pulse is of high peak power.According to the experiment results,we restrict the supercontinuum spectral range beyond the cutoff wavelength of LP₁₁ mode and get 103.6W LP₁₁ mode supercontinuum with spectral range from 900 nm to 1850 nm.