Mid-IR supercontinuum generation in Tm/Ho codoped fiber amplifier

We demonstrate all-fiber-integrated mid-IR supercontinuum generation in a Tm/Ho codoped fiber amplifier, where the codoped fiber is both nonlinear and a gain medium. The observed supercontinuum spectrum ranges from 1760 to 2600 nm and has an extremely high spectral flatness, with a 3 dB bandwidth ∼635 nm (from 1845 to 2480 nm). In the Tm/Ho codoped fiber, as well as the nonlinear optical processes, the Tm 3+ and Ho 3+ ions also play important roles in mid-IR supercontinuum generation. The 3 F 4 – 3 H 6 transition for Tm 3+ radiates a laser in the 1.8–2.1 μm spectral region, the 5 I 7 – 5 I 8 transition for Ho 3+ radiates a laser around 2.1 μm and the 3 H 4 – 3 H 5 transition for Tm 3+ radiates a laser in the 2.2–2.5 μm spectral region. All of these energy level transitions contribute towards supercontinuum generation.