Wavelength-flattened 2 x 2 splitters made of identical single-mode fibers

The fabrication of a new design of fused single-mode-fiber wavelength-flattened 2 x 2 couplers is reported. The device consists of a slightly unbalanced all-fiber Mach-Zehnder interferometer made with identical single-mode fibers; it is compact ( approximately 2 cm) and shows good coupling-ratio uniformity (50 +/- 2.5% over 300 nm) with low excess loss (<0.1 dB.