Four-wave interaction in a multimode waveguide with a thermal nonlinearity in a circuit with codirectional pumping waves

The spatial selectivity of a four-wave radiation converter in a multimode waveguide with thermal nonlinearity in a circuit with incident pump waves is analyzed. It is shown that the half-widths of the modulus of the point spread function, which characterizes the image conversion quality, are mainly determined by the transverse dimensions of the waveguide. With an increase in the angle of incidence of the pump waves on the front face of the waveguide, it decreases both the maximum value and the half-width of the modulus of the point spread function. The recording of two temperature gratings in the waveguide leads to a modulation of the point spread function with a period inversely proportional to the angle of incidence of the pump waves.