High-speed wavelength-swept source at 20 μm and its application in imaging through a scattering medium

We report a high-speed wavelength-swept source operating at 2.0 μm through advanced time-stretch technology. It sweeps over 30 nm at a speed of 3.3×109  nm/s and a repetition rate of ∼19  MHz. To the best of our knowledge, this is the first time that a megahertz-stable swept source has been implemented at such a long wavelength. A wide bandwidth is enabled by a simple mode-locked fiber laser that covers a wavelength range of ∼60  nm. The all-optical wavelength sweeping is realized by a chirped fiber Bragg grating (CFBG), which shows a superior temporal stability and power efficiency, compared with commonly used dispersive fibers, particularly in the 2.0 μm wavelength window. To showcase its specialties, here we employ it to perform high-speed spectrally-encoded microscopy (i.e., time-stretch imaging) through a scattering medium at a line-scan rate of up to ∼19  MHz. Better image quality is achieved, compared with a conventional imaging window at 1.0 μm. It is believed that the potential applications of this new high-speed swept source will benefit the transient diagnosis that requires deep penetration through a scattering medium.