Efficient power coupling from a 980-nm, broad-area laser to a single-mode fiber using a wedge-shaped fiber endface

Abstract

A theoretical and experimental study of a new, efficient technique to couple a broad-area laser, emitting a highly elliptical beam, to a single-mode fiber without the use of bulk optical components is presented. The technique involves butt coupling the laser to a wedge-shaped fiber endface. Such a n endface approximates a cylindrical lens which corrects for the phase front mismatch between the curved laser beam wavefront and the planar fiber beam. The fabrication process uses a wedge-shaped polishing tool and a simple polishing procedure. A theoretical formula for the coupling efficiency in the absence of both angular and transverse misalignments is derived. Based on the estimated mode field radii of the two-dimensional laser beam and assumed mode field radius of the fiber beam, a maximum coupling efficiency of 46% is predicted by the theory compared to the measured value of 47% (15.2-mW power coupled to the single-mode fiber) obtained by using a well-designed wedge-shaped fiber endface. For the square endface, the measured coupling efficiency was 20%. The technique was further refined by incorporating an uptapered, wedge-shaped endface to decrease the transverse misalignment sensitivity. The transverse misalignment tolerance for 3-dB reduction in maximum coupled power increases from 0.4 pm for the straight fiber wedge shape to 0.7 pm for the uptapered wedge shape. Using this technique, a single 980-nm, 30-pm stripe width, broad-area laser provided enough power to pump an erbium-doped fiber amplifier to obtain 24-dB gain. Richard S. Vodhanel (M'89) received the B.S. degree from the University of California, Irvine, in 1974, and the M.S. and Ph.D. degrees from the University of Illinois, Urbana, in 1976 and 1981, respectively, all in physics. His doctoral dissertation was on nuclear gamma ray spectroscopy.In 1980 he joined Bell Laboratories as a member of the Technical Staff, where he conducted research on the topic of single-mode fiber transmission systems. In 1984 he joined Bellcore, Red Bank, NJ, where he is presently engaged in research on coherent-optical fiber transmission systems. He has over 70 publications in physics and optical fiber communications.Dr.

Choosing a Better Delay Line Medium between Single-Mode and Multi-Mode Optical Fibers: the Effect of Bending

“…Ball lenses and plano-convex micro-lenses have been developed and applied in coupling light into single-mode optical fiber to enhance the coupling efficiency [8,21,37,43]. Different shapes of lens can be employed to achieve better coupling efficiency [28,31,41]. The focused beam characteristics has to match the fiber parameters for excellent coupling efficiency (Figure 4).…”

Optical fiber polishing automation with on-line force sensing

“…The large emission width prevents thermal problems and makes the 980 nm laser diodes output elliptical mode fields with aspect ratios from 3 to 5 at the LD end face [1]. Various techniques for coupling elliptical fields with single-mode fibers (SMFs) have been applied, including the combination of cylindrical lenses [2,3], an uptapered wedge-shaped fiber endface [4], an anamorphic lens [5], and a wedge-shaped graded-index fiber [6,7]. Fig.…”

New Scheme of Hyperboloid Microlens for High-Average and High-Yield Coupling High-Power Lasers to Single-Mode Fibers

“…To improve the mode match between the 980-nm lasers and single-mode fibers (SMFs) in laser module packaging, a common approach is to fabricate the tip of SMF as an asymmetric microlens with wavefront match for them to couple directly. Several structures of asymmetric microlenses for coupling to 980-nm laser diodes had been demonstrated, such as a up-tapered wedge-shaped fiber [1], an asymmetric hyperbolic fiber microlens [2], [3], an anamorphic lens [4], a wedge-shaped fiber [5]- [7], a quadrangular-pyramid-shaped microlens (QPSM) [8], and a conical-wedge-shaped microlens (CWSM) [9].…”