The static behavior of a thulium-doped fiber amplifier (TDFA) operating around 2 μm region at different pump wavelengths is investigated in this paper. A theoretical model is built up by solving a set of rate and propagation equations with considering the effect of cross relaxation mechanism. The developed model provides the influences of the amplified spontaneous emission noise, seed wavelength, and the thulium-doped fiber length into the TDFA performance. Simulation results indicate that the TDFA performance with pump at 1570 nm is more efficient than pump at 793 nm for core pumped thulium-doped silica fiber. Our findings show that the maximum gain reaches up to 30 dB with a 27 dBm pump power when a -10 dBm seed wavelength at 1840 nm is used. In contrast to indirect pumping at 793 nm, only 22 dB maximum gain is achieved under the same conditions. The model is also validated with previous experimental work. Our simulations are consistent with the experimental findings with small variations.

This paper presents the design of a W-type index chalcogenide fiber for mid-infrared beyond 10μm. The main advantages of the W-type index fiber are the possibility to control the chromatic dispersion with a larger possible core area for single-mode operation compared to a common step-index fiber and to enhance the fiber nonlinearity. Our fiber design consists of Ge15Sb15Se70 glass core, Ge20Se80 glass inner cladding and Ge20Sb5Se75 glass outer cladding. The optical mode distribution of the chalcogenide fiber is numerically calculated by employing edge-based finite elements. With 6-μm core diameter and 12-μm inner cladding diameter, the proposed fiber design exhibits flat anomalous dispersion in the wavelength range (4.3-6.5μm) with a peak of about 7ps/(nm.km). It also offers a high nonlinear coefficient of 0.12 $W^{-1}m^{-1}$ at a pump wavelength of 6.3 μm. The simulation results show that our proposed fiber design provides a highly coherent Mid-IR SC extending from 3.7 to 12 μm pumped at low peak pump power of 1kW.

We propose a novel design of a photonic crystal fiber made of praseodymium (Pr3+)-doped chalcogenide glass with single mode operation beyond 4 μm. Our design has an enlarged Pr3+-doped core diameter of 60 μm. The field area of the emitted fundamental mode is about 3160 μm2 at 4.5 μm and 2050 μm2 at a pump wavelength of 2.04 μm. This large mode field area not only reduces the nonlinear effects but also increases the possible pump power before the damage threshold. The selected laser layout avoids fabrication difficulties associated to cascaded Fiber Bragg Gratings in Pr3+-doped chalcogenide glass fibers. The proposed design also increases the laser efficiency by using the overlap of the emission cross-sections of Pr3+ in the transitions (3F2, 3H6 → 3H5 and 3H5 → 3H4) to enable both transitions to simultaneously produce a single coherent mid-infrared wavelength. The simulation results reveal that more than 64% of slope efficiency could be achieved at 4.5 μm for a fiber loss of 1dB/m.

This letter describes the design of a medium infrared laser based on a double clad structure of praseodymium (Pr³⁺)-doped chalcogenide glass. The overlap of the emission cross sections of Pr³⁺ in the transitions (³F₂, ³H₆ $\to $ ³H₅, and ³H₅ $\to $ ³H₄) enables both transitions to simultaneously produce a single coherent wavelength in the range between 3.7 and $4.6~\mu \text{m}$ . A single pair fiber Bragg grating at the overlapping transition wavelengths is used to avoid fabrication complexity of a cascade pumping scheme. In addition, the proposed design takes advantages of the fact that one excited ion will radiate two photons in the overlapping transition wavelengths. In this letter, the laser performance is tested as a function of fiber length, pump power, signal wavelength, fiber background loss, and Pr³⁺-doped concentration. The modeling results reveal that 48% of slope efficiency could be produced when the fiber losses are about 1 dB/m.