Phase jump in an optical directional coupler

The phase jumps in a linear coupler and a nonlinear coherent coupler are de monstrated analytically. The theoretical results show that slight changes i n the ratio of input powers or a mismatch in the linear coupler slight chan ges in the input power in the nonlinear coupler can lead to a phase shift o f pi. This characteristic of the coupler may lead to electro-optical switch ing with an ultralow switching voltage or to all-optical switching with low switching power. (C) 2001 Optical Society of America.