Middle-IR supercontinuum generations and applications

In this paper, the two different mechanisms of supercontinuum generation in single crystal sapphire fibers according to fiber lengths longer and shorter than dispersion length are theoretically and experimentally investigated. When the fiber length is shorter than the dispersion length, self-phase modulation is the dominant factor for supercontinuum broadening. A broad spectrum ranging from near-IR (1.2 μm) to the lower end of mid-IR (2.8 μm) is obtained. But, when the fiber length is longer than dispersion length, soliton-related dynamics with self-phase modulation is the dominant factor for supercontinuum. We further demonstrate that supercontinuum in a sapphire fiber can extend beyond the range of silica fibers by showing the spectrum from 2 μm to 3.2 μm. Also, we successfully apply the supercontinuum source generated from a sapphire fiber to IR spectroscopy. The spectra of pseudo-TNT chemical measured using our own supercontinuum source is in good agreement with those obtained by FTIR. Supercontinuum generation using a sapphire fiber, which has high damage threshold and broad transmission ranges can be used in many applications such as IR spectroscopy, broadband LADAR, remote sensing, and multi-spectrum free space communications.