Great progress has been made in fiber laser technology especially the high power fiber laser. One of the key techniques to acquire higher output power is coupling more pump laser into the double-cladding fiber using the fiber combiner. Fiber splices exist in both manufacture of the combiner and integration of the fiber components. The optical waveguide structure of the splice point has great effect on the insertion loss and modal content for the fiber laser system. Thus it is important to use proper method to compute the insertion loss of the splice points. This is also vital in the manufacture of fiber combiner because the structure must be precisely controlled in order to acquire low insertion loss for the signal arm of the combiner to ensure the capability of sustaining high power laser. Generally speaking, there are two common methods to compute the insertion loss of splice points: the mode field diameter (MFD) and the modal overlap integral (MOI). The MFD method is simple but its accuracy is relatively lower, while the MOI is more accurate than the MFD but also more complicated. We use both two methods to compute the insertion loss of the signal arm of a (6+1) ×1 fiber combiner. The result shows that the MFD method is appropriate when there is only fundamental mode at the splice point. At the mode field matched point, the insertion loss is 0dB when using the MFD method while 0.29dB when using the MOI method. This indicates that the MOI method is more accurate than the MFD method to predict the minimum insertion loss and the optimal structure. Meanwhile, the MOI method can explain the different insertion loss for the co-propagating situation and the counter-propagating situation for the fiber combiner which cannot be explained by the MFD method. If there are higher order modes passing through the splice point, the MFD method is also inappropriate.

Date Published: 17 September 2013
PDF: 10 pages
Proc. SPIE 8904, International Symposium on Photoelectronic Detection and Imaging 2013: High Power Lasers and Applications, 890416 (17 September 2013); doi: 10.1117/12.2034473

Published in SPIE Proceedings Vol. 8904:
International Symposium on Photoelectronic Detection and Imaging 2013: High Power Lasers and Applications
Andreas Tünnermann; Zejin Liu; Pu Wang; Chun Tang, Editor(s)