Mid-IR Supercontinuum Noise Reduction Using a Short Piece of Normal Dispersion Fiber - A General Mechanism

Mid-infrared (IR) supercontinuum (SC) lasers are important in applications such as pollution detection, stand-off detection, and non-destructive testing. The performance in many applications is limited by the noise level of the supercontinuum laser. High noise typically results in low sensitivities or a need for long integration times. In this paper, a simple technique to reduce the noise of high noise soliton-based SC sources is introduced by adding a short piece of normal dispersion fiber to force the spectrally distributed solitons to spectrally broaden through self-phase modulation and thereby overlap to average out the noise. The noise reduction is demonstrated experimentally and numerically using a ZBLAN fiber based mid-IR SC source and adding a short piece of highly nonlinear arsenic-sulfide fiber. However, the method is generally applicable to any soliton-based near-IR or mid-IR SC source. Its efficiency is underlined by experimentally comparing it to SC generation in fibers in which a second zero-dispersion wavelength provides the spectral alignment noise reduction mechanism.