Fiber-coupled laser diodes are indispensable for optical fiber communicatio
ns. The design of laser-fiber coupling is often guided by maximizing the op
tical power coupled into fiber, and by relaxing the fiber-laser alignment t
olerances. Many of those fiber-optic designs are susceptible to optical bac
k-reflections from the fiber resulting in not only a reduced coupling effic
iency but also an increased optical noise of the signal. For many optical f
iber communications, the most important parameter is not necessarily the co
upling efficiency, but the quality of optical signal coupled into the fiber
characterized by the carrier-to-noise ratio (CNR). This paper reports a no
vel laser-fiber coupling design for the purpose of optimizing the CNR. This
new design involves the use of an intentional offset between the lensed fi
ber and laser. Though such offset has been studied previously in the contex
t of coupling optics, it is never studied in the context of RIN and CNR. Th
e results enable one to optimize the design of any laser-fiber coupling wit
h respect to CNR. (C) 2001 Elsevier Science B.V. All rights reserved.