Integrated optical directional couplers: How much effective are design and modeling for device production?

The performance characteristics of an integrated optical directional coupler are extremely sensitive to both geometrical and optical waveguide parameters: this makes quite difficult the realization of devices complying with the design specifications. The adequacy of currently available design and modeling tools is discussed, starting from the analysis of the measured performance characteristics of directional couplers fabricated in glass substrates by K+-Na+ ion-exchange.