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 (ASE) 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.

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We propose a novel design of a photonic crystal fiber made of praseodymium (Pr 3+)-doped chalcogenide glass with single mode operation beyond 4 µm. Our design has an enlarged Pr 3+doped core diameter of 60 μm. The field area of the emitted fundamental mode is about 3160 μm 2 at 4.5 μm and 2050 μm 2 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 Pr 3+-doped chalcogenide glass fibers. The proposed design also increases the laser efficiency by using the overlap of the emission cross-sections of Pr 3+ in the transitions (3 F2, 3 H6 → 3 H5 and 3 H5 → 3 H4) 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 work presents a numerical study of a W-type index chalcogenide fiber design for Mid-Infrared (MIR) supercontinuum (SC) generation beyond 10µm. Our fiber design consists of a Ge15Sb15Se70 glass core, a Ge20Se80 glass inner cladding and a Ge20Sb5Se75 glass outer cladding. These chalcogenide materials have the advantages to broaden the spectrum to 12µm, due to their low material absorption. The optical mode distribution of the chalcogenide fiber is simulated by a finite element method based on edge elements. With a 6 µm core diameter and a 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). The position of the second zero-dispersion wavelength (ZDW) can be easily and precisely controlled by the inner cladding size and should be shifted to around 7µm for a 18 µm inner cladding diameter. This design is more suitable for a pump wavelength at 6.3µm which is in the anomalous dispersion regime between two ZDWs and can broaden the spectrum due to the soliton dynamics. Our fiber design modelling shows that the nonlinear parameter at 6.3µm is 0.1225W −1 m −1 , when using a nonlinear refractive index nNL=3.44 ×10 −18 m 2 W −1 , and the chromatic dispersion is D = 3.24ps/(nm.km). Compared to previously reported step-index fibers, the proposed W-type index chalcogenide structure ensures single mode propagation, which improves the nonlinearity, flattened dispersion profile and reduces the losses, due to a tight confinement of the mode within the core.

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