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We derive and numerically verify a simple analytical approximation for the calculation of Brillouin gain spectra (BGS) in acoustically antiguiding optical fibers. We use our approximation to find acoustic speed profiles that minimize the peak Brillouin gain. The optimized BGS are top-hat-shaped, regardless of the optical mode distribution, with peak value inversely proportional to the effective area of the optical mode. We further investigate acoustically guiding speed profiles, in which acoustic waveguide modes lead to peaks in the Brillouin gain spectrum. However, for large cores with diameters down to 50 [micro]m, and often even smaller, these Brillouin gain peaks are spectrally dense, and can be smeared out due to broadening in many practical systems. The Brillouin gain spectrum is then similar for waveguiding and antiguiding acoustic profiles. OCIS codes: 060.4370, 190.5890, 060.2320.

We characterize bismuth-doped fibers under different excitation wavelengths. The fiber laser performance at 1179 nm was investigated, incorporating different cooling arrangements. Effective heat extraction can reduce the temperature-dependent unsaturable loss in fiber, resulting in increased laser performance. The operation of a bismuth-doped fiber amplifier at 1179 nm, at both low and high input signals, is also examined. The amplifier efficiency and the saturation power both depend on effective fiber cooling. OCIS codes: 060.2320, 140.3510, 140.4480, 140.3380, 160.2290.

Complete birefringence compensation is demonstrated in plasma-enhanced chemical vapor deposition waveguides by 193-nm postexposure. A single relaxation process dominates the decay in stress anisotropy, indicating that compressive stress from the substrate leads to an elastic stress anisotropy at the core. [C] 2000 Optical Society of America OCIS codes: 050.1950, 050.2770, 130.3130, 130.1750, 230.1950, 230.3120.