Optical Realizations of Multilayer Perceptrons
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I have shown in section 2.2 that, if a nonlinear decision problem has to be solved, a single-layer perceptron fails to give the right response because of its linear separation of the classes to be distinguished. However, multilayer perceptrons that allow for sigmoidal threshold in combination with the possibility to adapt the slope of this decision function are well suited to solve these problems (see section 2.3 for a detailed explanation). These cascaded systems may be easily realized using optical devices, because cascadability is an inherent feature of most of the simple optical implementations I have discussed up to now. The critical point in realizing all-optical multilayer perceptrons however is to realize the error backpropagation function which has to be the derivative of the forward propagating sigmoid threshold function. Many of the all-optical realizations of the sigmoidal threshold function have derivatives that do not simulate the requirement of the error backpropagation to have its maximum in the region where the slope of the sigmoidal function is steepest.
KeywordsHide Layer Optical Realization Faraday Rotator Spatial Light Modulator Optical Implementation
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