Novel lensed-fiber offset coupling scheme to reduce reflected intensity noise in optimizing carrier-to-noise ratio

Fiber-coupled laser diodes are indispensable for optical fiber communications. The design of laser-fiber coupling is often guided by maximizing the optical power coupled into fiber, and by relaxing the fiber-laser alignment tolerances. Many of those fiber-optic designs are susceptible to optical back-reflections from the fiber resulting in not only a reduced coupling efficiency but also an increased optical noise of the signal. For many optical fiber communications, the most important parameter is not necessarily the coupling efficiency, but the quality of optical signal coupled into the fiber characterized by the carrier-to-noise ratio (CNR). This paper reports a novel laser-fiber coupling design for the purpose of optimizing the CNR. This new design involves the use of an intentional offset between the lensed fiber and laser. Though such offset has been studied previously in the context of coupling optics, it is never studied in the context of RIN and CNR. The results enable one to optimize the design of any laser-fiber coupling with respect to CNR. (C) 2001 Elsevier Science B.V. All rights reserved.