Quality of radiation conversion under four-wave mixing on thermal nonlinearity with feedback

Quality of radiation conversion under four-wave mixing on thermal nonlinearity with feedback for both signal and object waves has been investigated at high reflection coefficients. It has been shown that the optimal operating mode of a four-wave converter on thermal nonlinearity is the mode in which the pumping waves have equal intensities and there is a compensation for a phase shift arising from the pumping wave self-action. In this operating mode of the four-wave radiation converter, as compared with the case of the absence of feedback for both signal and object waves, a significant increase in the amplitude reflection coefficient is observed with an increase in the pumping waves intensities. In this case, despite the decrease in the bandwidth of spatial frequencies of the object wave with an increase in the pumping wave intensities, the quality of radiation conver-sion with feedback for both signal and object waves is better than in the absence of feedback.

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.