Towards Watt-Level, Spectrally Flat Supercontinuum from Mid-IR Mode-Locked Fibre Laser

Supercontinuum generation in the wavelength region of 2.5-5 μm is typically obtained by using a passive ZBLAN or InF
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fibre paired with a 1.55 μm or 2 μm seed source [1]–[3]. While this method can produce a broad spectral coverage, the average output power is low and especially suffers towards the longer wavelengths with most of the power concentrated near the pump frequency. In our approach, we utilise the technique of nonlinear amplification to simultaneously amplify and generate a broadband spectrum using a mid-IR seed source at 2.8 μm. Due to the current limitation on average power injection in current mid-IR fibres, we are optimising the design of the nonlinear amplifier using our previously reported numerical model [4] to obtain watt-level supercontinuum by exploring various fibre doping concentrations and core size. Despite limiting the pump power to a relatively low level (20 W), we achieve with our design orders of magnitude higher average power with significantly flatter spectral density.