This invention embodies an optical medium which consists of polar, multi-monomolecular layers of organic dye molecules with a net polar orientation, considerable second order optical nonlinearity, and excellent thermal stability. The medium is prepared by repeated sequential depositions on a surface of multivalent metal ions, e.g. Zr.sup.4+, and organic dyes terminated with an acidic functionality, e.g. a phosphonic acid, followed by activation of the surface for the next deposition sequence. The monolayers are deposited in the form of a multilayer film containing up to 1000 or more monolayers. The monolayers are deposited from liquid solutions; therefore they may be deposited on substrates having diverse topography and configurations. Second harmonic generation (SHG) analysis establishes that the multilayers have uniform polar order which does not decrease with increasing numbers of monolayers in the film. As determined by SHG, the inorganic interlayers impart orientational stability to the dye molecules up to 150.degree. C. and higher. The optical medium is useful in electrooptical or optical parametric devices comprising an optically nonlinear element and means for providing an optical input to and output from said element wherein said element comprises the nonlinear optical medium supported on a suitable base. When said device is employed in an electrooptic mode, it includes means for applying an electric field and/or optical input to said element for altering an optical property thereof.