Germanate Glass Fiber Lasers for High Power

The research reported here details a fundamental investigation of two modified germanate based glasses with a specific focus on glass stability during thermal-cycling which is representative of the steps required to fabricate a doped micro-structured germanate fiber. The investigations revealed for germanate fibres, surface crystallisation is the dominant loss mechanism, and may explain the poor performance of all published germanate fiber lasers. The research team have found a composition of this glass which shows minimal evidence of crystallisation after thermal cycling, and is of a low enough loss to realize a fiber laser. The glass stability is demonstrated by successful fabrication of a small-core rare-earth microstructured fibre fabricated from an extruded germanate preform. The glass bulk loss is measured to be 1 dB m at 1.5 m, and 7 dBm for the microstructured fiber. Also reported a measurement of the non-linearity of the fibre which indicates its potential suitability for non-linear application such as supercontinuum generation and four-wave mixing. The research team is confident that germanate based fibers will make substantial impact on the field of heavily doped microstructured fiber lasers operating in the 1.5 to 2.7 m spectral region, if 2low-loss fiber can be realized.