A segmented-cladding fiber (SCF) has a uniform core of high refractive index and a cladding consisting of alternating high and low refractive-index angular segments. It is known that such a fiber can be designed to provide effective single-mode operation with an ultra-large core size. In this paper, we analyze a SCF that is doped with erbium ions in its high-index regions (i.e., the core and the high-index cladding segments). The core of the fiber has a diameter of 20 &mgr;m and the cladding consists of 8 segments of equal size. The concentration of the erbium ions is 1×10<sup>26</sup>. We calculate the mode-field distributions in the fiber at the signal (1530 nm) and the pump (980 nm) wavelength with the finite-element method. We obtain the gain characteristics and the pump efficiency of the fiber by solving the propagation rate equations. Assuming an initial signal power of 1 μW, the threshold pump power required is 102 mW for a 30-cm long fiber. The optimal gain of the fiber is 25 dB, which can be achieved with a fiber length of 26 cm and a pump power of 150 mW. Our results confirm that a properly designed SCF can provide highly efficient optical amplification with a short length.
Optical absorption, excitation and emission spectra of Nd<sup>3+</sup> in PLZT ceramics have been studied. Based on the Judd-Ofelt (J-O) theory, the J-O intensity parameters are calculated to be Ω<sub>2</sub>=0.7199x10<sup>-20</sup> cm<sup>2</sup>, Ω<sub>4</sub>=1.045x10<sup>-20</sup> cm<sup>2</sup>, Ω<sub>6</sub>=0.9234x10<sup>-20</sup> cm<sup>2</sup> from the absorption spectrum of Nd<sup>3+</sup>-doped PLZT. The J-O intensity parameters have been used to calculate the radiative lifetime (0.385 ms) of the excited <sup>4</sup>F<sub>3/2</sub> level. The stimulated emission cross-sections and the fluorescence branch ratios for the <sup>4</sup>F<sub>3/2</sub> -> <sup>4</sup>I<sub>J</sub> transitions are also evaluated. We have also measured 1.068 mm fluorescence lifetime (0.168 ms) and calculated its Quantum efficiency (0.44). Under 807 nm excitation, the green and red upconversion luminescence from Nd<sup>3+</sup> centers in the ceramic was observed at room temperature. Analysis reveals that Nd<sup>3+</sup>-doped PLZT is promising for the use as efficient optically amplifying or zero-loss electro-optical devices in telecommunication networks.