Abstract
Grating couplers for side coupling of the light from a high-power laser diode
array (LDA) into the inner cladding of a double-clad fiber were studied theoretically
and implemented experimentally. In the experiments, two types of grating couplers were
designed and fabricated: a gold-coated surface relief grating coupler and a
gold-embedded silica grating coupler. A suitable design for heat dissipation for each
grating coupler was employed to minimize thermal expansion due to the heat accumulated
from the light absorption by the metal part of the grating coupler. The experimental
results show that the gold-embedded silica grating coupler is superior to the surface
relief gold grating coupler, because of its higher resistance to thermal expansion and
better heat removal capability. In addition, the grating pitch and groove width were
optimized for the highest overall coupling efficiency by taking account the backward
diffraction loss and the groove wall nonverticality due to fabrication distortion. The
experimental results show that the gold-embedded silica grating coupler is capable of
coupling light power up to 21 W from a 976-nm continuous-wave LDA into the inner
cladding of a 400-μm-diameter double-clad fiber with an overall coupling
efficiency of 50%.
© 2012 IEEE
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