Coupling of a laser diode to a quadric interface lensed monomode elliptic-core step index fiber: efficiency computation with the ABCD matrix

We report what to our knowledge is the first theoretical prediction of the coupling efficiency of a laser diode emitting two wavelengths either 1.3 or 1.5 μm, to three elliptic core step index fibers with different aspect ratios via quadric interface microlens of three different focal lengths on the fiber tip. Here, quadric interface microlens contains elliptical (hemispherical included), hyperbolic and parabolic microlenses. Instead of considering special ABCD matrix for individual microlens, a simple, accurate, and popular unified transfer ABCD matrix for refraction of quadric microlens under paraxial approximation is utilized to analyze the theoretical coupling efficiency, based on Gaussian beam approximation. The coupling efficiency can reach as high as 98.63 % with optimizing structure parameters of specific lensed fiber. The analysis can give some guidance for fabricating quadric interface lensed elliptic core fiber which are mainly useful in polarisation-maintaining fiber optic sensors and coherent fiber optic communication systems.