Analysis of the Coupling Mechanism in Asymmetric Fused Fiber Couplers

We investigated experimentally and numerically the coupling mechanism in asymmetric fused fiber couplers consisting of different single-mode fibers with unequal core diameter and numerical aperture. We increased the maximum coupled power by pretapering one of the fibers achieving a nearly complete power transfer at a specific pretaper length. Experimental results are compared to numerical results obtained by using our own 3-D FFT-based beam propagation method (BPM) algorithm. The numerical model explains qualitatively the coupler performance and allows to gain insight into the coupling mechanism. We discuss the influence of the fiber cores on the excited super-modes of the cladding structure. A modal decomposition of the light field is carried out in order to analyze the evolution of the super-modes and to discuss the influence of pretapering on the excitation of these modes.

[1]  K S Chiang.  Effects of cores in fused tapered single-mode fiber couplers. , 1987, Optics letters.

[2]  K. Hill,et al.  Biconical-taper single-mode fiber coupler. , 1981, Optics letters.

[3]  K. Okamoto,et al.  Theoretical investigation of light coupling phenomena in wavelength-flattened couplers , 1990 .

[4]  Suzanne Lacroix,et al.  Refractive index profile of fused-fiber couplers cross-section. , 2004, Optics express.

[5]  Kenneth O. Hill,et al.  Fabrication of fused twin biconical taper singlemode fiber splitters: effect of unequal cladding diameters , 1985 .

[6]  D. B. Mortimore.  Wavelength-flattened fused couplers , 1985 .

[7]  Richard J. Black,et al.  Core-mode cutoff for finite-cladding lightguides , 1986 .

[8]  S. Lacroix,et al.  Refractive index profile of fused-tapered fiber couplers. , 2004, Optics express.

[9]  S. Lacroix,et al.  Analyse d'un coupleur bidirectionnel a fibres optiques monomodes fusionnees. , 1983, Applied optics.

[10]  Jörg Neumann,et al.  Matching of the propagation constants in an asymmetric single-mode fused fiber coupler for core pumping thulium-doped fiber at 795 nm. , 2012, Optics letters.

[11]  W. Burns,et al.  Parabolic model for shape of fiber taper. , 1985, Applied optics.

[12]  S. Lacroix,et al.  Modeling of symmetric 2 × 2 fused-fiber couplers. , 1994, Applied optics.

[13]  C. D. Hussey,et al.  Control of power-splitting ratio in asymmetric fused-tapered single-mode fiber couplers. , 1988, Optics letters.

[14]  Bishnu P. Pal,et al.  Fabrication and Modeling of Fused Biconical Tapered Fiber Couplers , 2003 .

[15]  K. Hill,et al.  Tuned-port twin biconical-taper fiber splitters: fabrication from dissimilar low-mode-number fibers. , 1985, Optics letters.