Reflected intensity noise owing to offset coupling in case of excitation of triangular index fiber through upside down tapered cylindrical microlens on the end face of the fiber

Abstract In optical communication technology, the coupling efficiency (CE) remains a big challenge. The slight misalignment between the fiber and the lens causes light to bounce back from the fiber end, which creates reflected intensity noise (RIN). This research presents a theoretical framework for estimating RIN in the case of laser diode (LD) excitation of triangular index fiber (TIF) through a single-mode upside down tapered cylindrical microlens (UDTCML) on the circular core fiber tip. The analysis takes care of different RIN values based on possible lateral misalignments in case of two wavelengths, 1.3 µm and 1.5 µm, and TIFs with three different V numbers in the coupling system. Using the ABCD matrix formalism, we analytically evaluate the CE when there is a lateral mismatch and thereof RIN as well. It deserves mentioning in this connection that increase of lateral mismatch causes both increase of loss due to RIN and decrease of coupling efficiency as well. The results given are useful for reducing RIN and improving CE. This information will benefit the designers and packagers concerned with optical couplers.