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We report design optimization in terms of index-profile parameters of a dual-core dispersion-slope-compensating fiber suitable for broadband dispersion compensation in standard G.655 and G.655b single-mode fibers over the C and L bands of fiber amplifiers and additionally over the S band for the G.655b fibers. It takes into account profiles that can be achieved with state-of-the-art fabrication techniques such as modified chemical-vapor deposition. Relatively high mode effective areas ensure the reduced sensitivity of the fiber to detrimental nonlinear effects when the fiber is integrated into a dense wavelength-division-multiplexed network. The theoretical figures of merit of these DCFs were found to be [greater than or equal to] 700 (ps/dB)/nm; furthermore, the estimated bend losses were also quite low, even for bend radii as small as 16 mm. OCIS codes: 060.0060, 060.2310, 060.2280, 060.2330, 060.2400, 060.2430.

A detailed analysis of the trajectory of an electron injected axially in a free-electron laser (FEL), having a circularly polarized wiggler and ion-channel focusing, has been carried out using single particle dynamics. We show that along with transverse oscillations at the wiggler frequency, betatron oscillations due to the ion-channel field are also setup. This leads to axial oscillations in the electron motion. It is found that spontaneous emission is possible at the upshifted ion-channel betatron frequency and its odd harmonics. Further, we evaluate the gain in radiation at these frequencies with the help of the pendulum equation, in the low-gain-per-pass limit. Index Terms - Free-electron laser (FEL), harmonic generation, ion-focusing.