Abstract: Fiber-based gain elements, such as fiber lasers, fiber amplifiers, and the like, that have higher power and better frequency stability than can be achieved in the prior art are presented. Embodiments include a fiber-based gain element having a first portion in which anti-Stokes fluorescence (ASF) reduces its temperature below that of an ambient environment and a second portion whose temperature is not reduced below that of the ambient environment, which are thermally coupled so heat can flow from the second portion into the first portion, thereby reducing the average temperature of the gain element. In some embodiments, a core configured to provide optical gain is thermally coupled with a first cladding configured to exhibit ASF cooling via an intervening cladding layer that acts to confine a first pump signal to the core.

Abstract: A fiber optic switch module that can be incorporated into switch designs characterized by negligible crosstalk. The switch module is capable of operation over two wavelength bands. A 2.times.2 switch module has an open or bar state in which polished portions of the fiber segments are separated from each other and a closed or cross state where the polished portions are in optical contact with each other. The module has arbitrarily low crosstalk in the bar state, but typically some crosstalk in the cross state. In one embodiment, the third port of a first 2.times.2 module is coupled to the first port a second 2.times.2 module while no connections are-made to the second ports of the modules or to the third port of the second module.