High modulation depth, fast (megahertz to gigahertz), intensity-modulated light sources of various wavelengths within the 0.7–1.35 µm bio-penetration window are highly desirable for many biophotonic diagnosis systems. In this Letter, we present a novel scheme of a wavelength tunable, ultra-broadband light source which simply consists of a pump laser, a nonlinear fiber, and demodulation circuits. The working wavelength range of the light source is from 0.7 to 1.35 µm which covers a vast part of the bio-penetration window, and its modulation frequencies extends from tens of megahertz to gigahertz. The performances of the proposed light source in either working wavelength range or modulation frequency bandwidth are much superior to any typical laser diodes or solid state lasers currently employed in the frequency-domain or other biophotonic utilization. The wide applicability of this novel light source in diverse biophotonic applications can be observed from our carefully designed diffused optical spectroscopy phantom measurement.