Crosstalk in directional couplers (DC's) is an important parameter for device and system performance. Although various crosstalk mechanisms have been studied through the course of integrated optics, the fundamental lower limit for crosstalk is still uncertain. In this paper, crosstalk mechanisms are reviewed and fundamental limits are discussed. A new model for optical scattering is presented, and the effect of bending loss variation between the two propagating modes in the taper region on the crosstalk is discussed.
Judith C. Powelson, Wei Feng, Sihan Lin, Robert J. Feuerstein, and Darja Tomic, "Crosstalk of Passive Directional Couplers," J. Lightwave Technol. 16, 2020- (1998)