Optical Signal Processing Using Nonlinear Optics

摘要

The 2-D correlation/convolution which can be achieved in real time via four wave mixing in nonlinear materials has been investigated in detail to determine the accuracy and signal power possible. This analysis was initiated under other support; the experimental confirmation was completed under this contract. The analysis which is based on Fourier transforms of the equations of nonlinear interactions has resulted in a closed from solution for the output and clearly shows how it differs from the desired 2-D correlation. In the example of a scene that is search for given objects, the accuracy decreases as the ratio of scene to object size increases. The accuracy also decreases as the length of the nonlinear material increases resulting in a trade-off between accuracy, size of the scanned scene, and power or signal to noise ratio in the output. The first result of this analysis is the realization that a non-colinear interaction is considerably less accurate than a colinear. In the typical four wave mixing scheme, the two inputs, B1 and B2, propagate at a small angle to each other within a nonlinear medium; the pump wave is counter to one of the inputs. This angle between the beams results in a lateral translation between the patterns as they propagate through the nonlinear material. The result is a correlation between smoothed versions of the inputs and a considerable error.