Supercontinuum generation from ～1.9 to 4:5μm in ZBLAN fiber with high average power generation beyond 3:8μm using a thulium-doped fiber amplifier

摘要

A mid-IR supercontinuum (SC) fiber laser based on a thulium-doped fiber amplifier (TDFA) is demonstrated. A continuous spectrum extending from ～1:9 to 4:5μm is generated with ～0:7W time-average power in wavelengths beyond 3:8μm. The laser outputs a total average power of up to ～2:6W from ～8:5m length of ZrF_4?BaF_2?LaF_3?AlF _3?NaF (ZBLAN) fiber, with an optical conversion efficiency of ～9% from the TDFA pump to the mid-IR SC. Optimal efficiency in generating wavelengths beyond 3:8 μm is achieved by reducing the losses in the TDFA stage and optimizing the ZBLAN fiber length. We demonstrate a novel (to our knowledge) approach of generating modulation instability-initiated SC starting from 1:55μm by splitting the spectral shifting process into two steps. In the first step, amplified approximately nanosecond-long 1:55μm laser diode pulses with ～2:5 kW peak power generate a SC extending beyond 2:1μm in ～25m length of standard single-mode fiber (SMF). The ～2μm wavelength components at the standard SMF output are amplified in a TDFA and coupled into ZBLAN fiber leading to mid-IR SC generation. Up to ～270nm SC long wavelength edge extension and ～2:5× higher optical conversion efficiency to wavelengths beyond 3:8μm are achieved by switching an Er:Yb-based power amplifier stage with a TDFA. The laser also demonstrates scalability in the average output power with respect to the pulse repetition rate and the amplifier pump power. Numerical simulations are performed by solving the generalized nonlinear Schr?dinger equation, which show the long wavelength edge of the SC to be limited by the loss in ZBLAN.