Coupling characteristics of three-guide tapered coupler for integrated optical isolator with semiconductor guiding layer

The characteristics of the three-guide tapered coupler for an integrated optical isolator with a semiconductor guiding layer (GaInAsP) were experimentally studied. By the experiment for measuring power branching ratio, the unbalance of the ratio smaller than 2% was confirmed for wavelengths ranging between 1.50 and 1.58 /spl mu/m. The coupling to the central waveguide occurred when two light waves in the side waveguides were in phase. No output was coupled to the central waveguide when they were 180/spl deg/ out of phase. The isolation of more than 17dB will be achieved when the coupler is employed in the isolator.