digital optical switches with asymmetrical wave guides and an electro - optically controllable adiabatic coupling in a central region must have a degree of crosstalk suppression of better than 20 db for use in transparent optical networks . with x or y arrangements , the invention provides for this purpose a grid device in the central region which affects the wave guide &# 39 ; s inherent modes as the main cause of the crosstalk , i . e . amplitude and phase matching of the wave guide &# 39 ; s inherent modes at the output . the result of the solution of the invention takes the form of a &# 34 ; cascade &# 34 ; of two different physical effects , each of which , of at least 20 db , contributes to the overall result crosstalk suppression of better than 40 db .