Designing a W-type index praseodymium-doped chalcogenide fiber for strongly-efficient MIR Laser beyond 4 μm

This study is to propose an efficient design based on W-type index praseodymium (Pr 3+ )-doped chalcogenide fiber to enhance the emission of mid-infrared (MIR) wavelength beyond 4 μm. The advantage of the proposed design is to enlarge the core diameter to 32 μm under single mode guidance in order to restrict any impacts of nonlinearity and enhance the applied pumping power before the damage threshold. The effective mode field areas are about 979 μm 2 and 812 μm 2 at 4.5μm emitted MIR wavelength and 2.04μm pump wavelength, respectively. In the considered laser layout within this paper, a single pair of Fiber Bragg Gratings FBGs lay is adopted in the overlapping area of the emitting cross-sections parts of Pr 3+ ions in the transitions ( 3 F 2 , 3 H 6 → 3 H 5 and 3 H 5 → 3 H 4 ). This selected laser layout avoids the difficulties in the fabrication of concatenated FBGs in Pr 3+ -doped chalcogenide glass fibers. In addition, the efficiency of the laser can be also enhanced at this laser layout by emitting two photons in MIR wavelengths from one excited ion. The simulation outcomes indicate the possibility to exceed 61% of slope efficiency at 4.5 μm for 1dB/m loss in the fiber.