Optical fiber up-tapers with high beam expansion ratios for component fabrication

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Abstract
Optical fibre up-tapers with beam expansion ratios of 10, about twice the previously achieved value for the same taper outer diameter, have been fabricated and characterized. The increased beam expansion is achieved with a near step-index profile for the core of the taper. The excess coupling loss between two tapers is less than 0.1 dB. A lateral offset of more than 20 mu m or an axial displacement of 4 mm between tapers caused an excess loss of 1 dB. The angular tolerance for this loss is a manageable 0.3 degrees . These tapers permit, for a given beam expansion ratio, the manufacture of smaller outer diameter, more compact structures of self-aligned beam expansion. They also permit the insertion of optical elements into the expanded beam for the fabrication of inline single-mode passive fiber components.