A prism coupler filled with nonlinear Kerr-like material is studied theoret
ically. A simple, approximate analysis is developed to predict its behavior
in both linear and nonlinear optics. In a wide range of incident amplitude
magnitude, optical bistability and multistability are found. As far as fie
ld map not undergo drastic change, the simpler approximate theory is able t
o quantitatively analyze both prism couplers and waveguide in nonlinear opt
ics and to study such effects as nonlinear phase shift, existence of nonlin
ear asymmetric modes in symmetric environments, bi-and multistability. The
predictions of the analytical theory are compared with the results obtained
via numerical integration of Maxwell equations and they agree quite well.