The design and consideration of an optical coherent two-wave coupling and a self-pumped phase conjugator using totally internal reflection in the photorefractive KNbO_3: Fe are reported. The exceptionally large value of the electro-optical coefficient r_(42) and an optimized geometrical configuration are considered for both cases. The nature of phase conjugation of the retroreflected beam ls demonstrated. Nonlinear optical effects are extended successfully from wavelengths 514.5nm to 632.8nm.