Toward all-fiber supercontinuum spanning the mid-infrared

Broadband laser light sources in the mid-infrared region attract enormous interest due to the plethora of applications they are enabling, including multispecies trace gas detection, free-space communications, and infrared countermeasures. Key to the progress in supercontinuum generation has been the wide availability of fiber-based near-infrared and bulk-optic mid-infrared pump sources and suitably engineered nonlinear media capable of supporting high-brightness supercontinua. A large proportion of the system complexity relates to the pump source itself with free-space systems based on parametric conversion being the most common for the generation of long-wavelength supercontinua. In an effort to realize all fiber and all mid-infrared supercontinuum sources, we combine a recently developed 2.9 µm ultrafast fiber laser based on holmium with an environmentally stable, polymer-protected all-chalcogenide tapered fiber. By launching 230 fs, 4.2 kW peak power pulses into the As2Se3/As2S3 tapered fiber, we demonstrate a spectrum spanning from 1.8 to 9.5 µm at the −20  dB points with an average power of more than 30 mW. This >2 octave-spanning supercontinuum is a crucial step toward robust mid-infrared broadband sources required for future field-deployable instruments.