We report on a flat and broadband thulium-doped amplified spontaneous emission (ASE) fiber source working around 1.85 µm in the eye-safe spectral region. Core-pumped thulium fibers were prepared in-house using the modified chemical vapor deposition method. The amplified spontaneous emission source in a backward direction with respect to the pump and in a single-ended configuration produces stable, non-polarized radiation with an output power of up to 280 mW, corresponding to a slope efficiency of about 36% with respect to the pump power. To the best of our knowledge, the device reported herein is the broadest ASE source based on Tm-doped fiber without internal spectral filtering with an output power exceeding 90 mW and full width at half-maximum of the spectrum greater than 155 nm.