Low-loss directional couplers utilizing single-mode fiber-optic waveguides

A new design of Y-type directional couplers with end matching and utilizing single-mode fiberoptic waveguides is proposed. The optimal parameters required to attain losses of ~0.5–1 dB are determined. A method is described for making such couplers by welding single-mode waveguides with a partially retained cladding in an electric-arc apparatus. The additional losses of the couplers when used for splitting a signal between two channels are 1–3 dB, in good agreement with numerical calculations. The decoupling of the counterpropagating channels is better than 60 dB, indicating a high directivity. It was found experimentally that the polarization state of radiation propagating in these couplers is conserved.