High Efficiency Cascade Fiber Laser at 2.8 µm (original) (raw)
2017
Diode-pumped erbium-doped fluoride glass (Er:FG) fiber lasers operating near the water absorption peak have a potential use in medical [1] and spectroscopy [2] applications. However, their efficiency is generally limited to the maximum Stokes efficiency limit of ~35%. Until now, the only way demonstrated to exceed this limit takes advantage of an energy transfer upconversion process (ETU). Nonetheless, such ETU processes are only efficient in heavily doped fibers which lead to high heat load per unit length of the fiber, thus limiting the power scaling potential of such an approach. To date, the highest slope efficiency of 35.4%, slightly exceeding the Stokes limit, was reported through ETU with a 7 mol. % Er 3+ :FG fiber laser emitting near 2.8 µm [3]. In this work, we present a diode pumped passively-cooled Er:FG cascade fiber laser operating at 2.8 µm and 1.6 µm with a maximum slope efficiency of 40% at 2.8 µm with respect to the absorbed pump power at 980 nm. The schematic of the laser setup is shown in Fig. 1a. A 7 m length of 1 mol. % Er +3 doped FG fiber was used as an active medium and pumped by two combined 30W multimode diodes operating around 980 nm. As an input coupler for both wavelengths, a highly reflective dichroic mirror (HR-DM) having a reflectivity of 80% at both 1.6 µm and 2.8 µm and a transmission of 90% around 980 nm was used. Fresnel reflection from a straight cleaved end face was used as the output coupler (OC) for the 2.8 µm wavelength. As for the 1.6 µm OC, a fiber Bragg grating (FBG) centered at 1.613 µm and having a maximum reflectivity of 87% µm was written directly in the core of Er:FG fiber using a femtosecond laser. A residual pump stripper (RPS) was made near the end of the cavity by recoating a section of the fiber. In order to evaluate the effect of the 1.6 µm OC reflectivity on the 2.8 µm transition efficiency, experiments were performed at different decreasing OC reflectivities by thermally annealing the FBG.
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Diode-pumped mid-infrared fiber laser with 50% slope efficiency
Optica, 2017
Until now, the field of mid-infrared fiber laser research has been constrained by the limitation imposed by the Stokes efficiency limit. The conversion of high-power diode light emission operating at near-infrared wavelengths into mid-infrared light invariably results in the deposition of significant amounts of heat in the fiber. This issue is compounded by the fact that mid-infrared transmitting glasses are thermomechani-cally weak, which means scaling the output power has been a longstanding challenge. In this report, we show that by cascading the adjacent transitions of the erbium ion at 2.8 and 1.6 μm in combination with a low-loss fluoride fiber, the slope efficiency for emission at 2.8 μm can reach 50%, thus exceeding the Stokes limit by 15%. We also show that by highly resonating the 1.6 μm transition, a highly non-resonant excited-state absorption process efficiently recycles the excitation back to the upper laser level of the mid-infrared transition. This demonstration represents a significant advancement for the field that paves the way for future demonstrations that will exceed the 100 W power level.
Eect of Incorporating A FBG In L-Band Erbium-Doped Fiber Laser
The eect of incorporating a fiber Bragg grating (FBG) in long wavelength band erbium-doped fiber laser (L-band EDFL) is investigated. The EDFLs with and without the FBG operate at wavelength of 1579.3 and 1591.9 nm, respectively. At low pump power, the system without the FBG shows a lower threshold and a better slope eciency compared to that of the system with the FBG. However, the out- put power is reduced at higher pump power due to the mode competition in the cavity. By incorporating the FBG in the laser cavity, the side mode suppression ratio (SMSR) of the laser is significantly improved and a higher output power can be obtained at high pump power. At pump power of 99 mW, the EDFL with the FBG has output power of 11.9 dBm, a 3 dB bandwidth of 0.06 nm and a SMSR of 59 dB.
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