Mismatch considerations in laser diode to monomode fiber excitation via a hemispherical lens on the elliptical core fiber tip

We present what, as per our knowledge, is the first theoretical investigation of the coupling efficiency of a laser diode to a single-mode fiber via a hemispherical microlens on the elliptical core fiber tip in presence of possible transverse and angular misalignments. Using the ABCD matrix for refraction by a hemispherical lens on the tip of an elliptical core single-mode fiber, we present analytical expressions of such coupling efficiencies and investigate the corresponding losses due to possible transverse and angular misalignments. The concerned calculations involve little computations. Our analysis takes into consideration the limited aperture provided by the hemispherical lens. The results should be useful in optimum launch optics for designing suitable hemispherical microlenses on the tip of elliptical core fibers or circular core fibers which suffer from noncircularity.