Optical microfiber coupler for broadband single-mode operation

We present a broadband single-mode bi-conical microfiber coupler (MFC) with a specifically designed transition region that effectively suppresses any higher-order modes present at the input fiber and provides efficient power splitting into the fundamental mode at the two output ports. As a practical example, single-mode 3dB splitting operation over a broad spectral window (400~1700 nm) was demonstrated for a very thin taper waist (~1.5µm) MFC made from conventional telecom optical fibers