Investigation of efficient pump scheme for Pr/sup 3+/-doped fluoride fiber amplifiers

Analysis of gain and noise performance of bidirectionally pumped Pr 3+ -doped fluoride fibre amplifier configurations with unbalanced pumping

“…Our analysis is based on a general PDFFA model [3], which assumes a steadystate ampli® cation regime. The rate equations include the following transitions: pump ground-state absorption (GSA) 3 H4± 1 G4, signal transition used for ampli-® cation 1 G4± 3 H5, pump ESA 1 G4± 3 P0, signal GSA 3 H4± 3 F4, signal ESA 1 G4± 1 D2, and the corresponding non-radiative multiphonon decay processes (see the sim-pli® ed energy level diagram for Pr 3+ in [3]).…”

“…The rate equations include the following transitions: pump ground-state absorption (GSA) 3 H4± 1 G4, signal transition used for ampli-® cation 1 G4± 3 H5, pump ESA 1 G4± 3 P0, signal GSA 3 H4± 3 F4, signal ESA 1 G4± 1 D2, and the corresponding non-radiative multiphonon decay processes (see the sim-pli® ed energy level diagram for Pr 3+ in [3]). Because of these processes, the upper laser level 1 G4 is repopulated from the 3 P0 and the 1 D2 levels.…”

“…The relative refractive index di erence D n is 2.5%and the cut-o wavelength 0.9m m. The pump and signal wavelengths are 1.047m m and 1.3m m respectively. The optical parameters (lifetimes of the levels, branching ratios, pump absorption, emission and cross-sections at the pump wavelength and signal emission, signal ESA, and GSA cross-sections) are those given for Pr 3+ ions in ZBLAN glass in [3].…”

“…In order to improve the pump e ciency, e orts are being made to search for new suitable host materials for laser operation, and new ampli® er con® gurations have been proposed. In particular, bidirectional pump schemes were demonstrated to be more e cient than the unidirectional schemes, by decreasing the degradation of the 1 G4 level population due to pump excited-state absorption (ESA) and cooperative up-conversion [3]. Among the bidirectional pump schemes, the double-path con® guration which incorporates an optical circulator and an endface re¯ective mirror stands out.…”

“…In [6] it was demonstrated for a speci® c set of parameters that the ratio of the forward to the backward pump powers can be optimized according to the incident signal power without any noticeable noise ® gure degradation. Although the performance di erences between PDFFA with unidirectional and bidirectional pumping schemes have already been numerically investigated [3], no detailed analysis has been made of the in¯uence of unbalanced pumping for bidirectionally pumped single or double-path schemes. This paper presents this analysis based on the changes induced on the upper laser level population density distribution along the ® bre and explains how the achievable gain improvement depends on the ® bre parameters or on the ampli® er's working conditions.…”