There is an increased interest in developing mid-infrared (mid-IR) laser sources in the region of 3–4 µm because of their huge potential in spectroscopy[1–3]. Since overlapping with the stretching frequency of C-H bonds with different forms (i.e., alkane, alkene, and alkyne) in the range of (i.e., 3.03–3.57 µm)[4], the laser sources in this region can find direct applications in lidar for gas detection and processing polymer, where C-H bonds are rich [including methane, ethane, propane, polypropylene, poly(methyl methacrylate), polyethylene, etc.][5–8]. Among them, short pulsed rare-earth-doped fiber laser with tunable wavelengths is a competitive option, owing to its potential compactness and robustness (compared to external nonlinear wavelength conversion[9]), higher peak power than continuous wave (CW), and flexible wavelength. To cover this band, - and -doped fiber lasers operating on the transitions of and , respectively, have been developed to be the two most common platforms for realizing short pulses based on switching[10–13] or gain switching[14–16]. Despite 10 W CW output from a 2.83 µm pumped all-fiber -doped laser[17], near-infrared pumping at 1.69 µm has enabled continuous wavelength tuning from 2.71 to 3.42 µm[18]. By employing an InAs saturable absorber (SA), -switched pulses tunable across the range of 2.76–3.34 µm have been achieved[11]. Based on the dual-wavelength pumping scheme at 980 and 1.976 µm, the maximum CW power of 14.9 W[19] and tunable wavelength from 3.33 to 3.78 µm[20] have been obtained from an -doped fiber laser (not simultaneously). By switching with a crystal SA[13], continuously tunable short pulses in the range of 3.4–3.7 µm have been generated. All these results are the current records of the two systems in this band. However, it is quite challenging for a - or -doped system alone to entirely cover the absorption band of C-H bonds mentioned above. Recently, we proposed a new laser scheme (i.e., red-diode-clad-pumped codoped fiber laser), which can excite the emissions of the transition of and the transition of simultaneously, via the energy transfer between them and in-band absorption of around 2.8 µm, thus extending the emission band in this spectral region[21]. Continuous tuning in the range of 3.05–3.7 µm has been enabled, almost entirely covering the strong mid-IR absorption band of C-H bonds. This provides not only a promising platform for widely tunable pulse generation, but also an opportunity to accurately assess the long wavelength edges (in terms of pulse generation) of widely used commercial InAs quantum-well-based SA, which has a nominal direct bandgap of 0.36 eV (i.e., 3.444 µm) and has been frequently employed in -switched and mode-locked fiber lasers around 3 µm[22].