Low-loss fiber-optical directional couplers

A method was developed for the fabrication of directional couplers for multimode quartz glass fiber waveguides. These couplers were made by electric-arc welding without preliminary etching away of the cladding. Couplers with branching into two or three channels were characterized by average additional losses of 1.4 and 2.5 dB, respectively. The return-channel isolation of 50-60 dB was evidence of a high directionality of these couplers. The mode composition of the radiation was also determined.