Broadband 2-µm fiber-laser supercontinuum for high-resolution optical coherence tomography.

We report a compact and stable broadband light source for 2-µm optical coherence tomography (OCT). The source is seeded by a polarization-maintaining (PM)-based mode-locked thulium-doped fiber oscillator with an intracavity spectral filter that suppresses soliton sidebands and provides a stable seed for subsequent nonlinear conversion. After wavelength shifting in a thulium-doped fiber amplifier and spectral broadening in a 5-m highly nonlinear fiber, a supercontinuum (SC) spectrum with a 295-nm 3-dB bandwidth was obtained in the 2-µm region. A fiber-based time-domain OCT system was employed as a broadband characterization platform, yielding an axial resolution of 6.6 µm and a sensitivity of 99.6 dB. Representative OCT imaging results further confirmed the practical performance of the developed 2-µm system. These results demonstrate a practical route toward stable 2-µm SC generation for OCT imaging in highly scattering media.