Mid-infrared fiber sources for real-time biomedical sensing

The development of new, compact mid-infrared light sources is critical to enable biomedical sensing applications in resource-limited environments. Here, we review progress in fiber-based mid-IR sources, which are ideally suited for clinical environments due to their compact size and waveguide format. We first discuss recent developments in mid-IR supercontinuum sources, which exploit nonlinear optic phenomena in highly nonlinear materials (pumped by ultrashort pulse lasers) to generate broadband spectra. An emerging alternative approach is then presented, based on broadly tunable mid-IR fiber lasers, using the promising dysprosium ion to achieve orders of magnitude higher spectral power density than typical supercontinua. By employing an acousto-optic tunable filter for wavelength tuning, an electronically controlled swept-wavelength mid-IR fiber laser is developed, which is applied for absorption spectroscopy of ammonia (NH3)|an important biomarker|with 0.3 nm resolution and 40 ms acquisition time.