LAUSR

This paper presents a fabrication method for 2 × 2 twisted fiber-optic directional couplers based on biconical low-loss tapered optical fibers using a two-step wet-etching technique with hydrofluoric acid-based droplets and surface tension-driven flows. The droplet-based wet etching of optical fibers allows us simple and cost-effective fabrication of tapered fibers and multiports directional couplers. The simulation results agree well with the experimental observations on the propagation losses, which can be monitored in real-time by measuring the transmitted optical powers during the chemical etching process. The fabricated 2 × 2 fiber-optic directional coupler shows wavelength-insensitive operation within the telecommunication C-band with an excess insertion loss of less than 0.5 dB.