Broadband High-Energy All-Fiber Laser at 1.6 μm

A broadband high-energy all-fiber laser at 1.6-mu m window with erbium-doped fiber mode locked by nonlinear polarization rotation technology is demonstrated. The direct output optical spectrum centered at 1.6 mu m has a bandwidth of 52.4 nm. The fiber laser delivers a pulse energy of 3.9 nJ with 9.3-MHz repetition rate at 220-mW 976-nm pump power. Based on it, a wavelength-tunable optical source with a wavelength tuning range from 1.6 to 1.8 mu m is demonstrated through soliton self-frequency shift. To satisfy much longer wavelength demands in some special application scenario, e.g., deep brain imaging with multi-photon microscopy, a chirped pulse amplifier was constructed to boost the pulse energy to 14 nJ, and the wavelength can be tuned from 1.6 to 1.94 mu m with those amplified pulses. These fiber sources at the L-band and a longer wavelength can explore a wider scope in deep biotissue imaging area for lower water absorption.