New design of variable X-coupler optical waveguide passive device

A new design of a variable passive X-coupler optical waveguide device is proposed and its geometry and application are discussed. This device differs from other conventional 2/spl times/2 directional couplers and fixed X-couplers, as the device functionality is based on the principle that it is symmetrical, with variable parameters, and that the power in each excited mode can be directed unambiguously into one of the output channels by varying any of its parameters. The geometry and relative position between the input waveguide and the second waveguide of these symmetrical X-shaped channels determines the power splitting ratio. The device has excellent features compared to other passive optical couplers, due to the flexibility of the design parameters such as the off-set distance in the z-direction and the waveguide spacing in the y-direction.