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Learning dynamics of photorefractive neural networks


Qiao, Yong (1994) Learning dynamics of photorefractive neural networks. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/5qwx-ww61.


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This thesis investigates the optical implementation of neural networks utilizing dynamic photorefractive volume holography. The number of accessible degrees of freedom in a general holographic interconnection system is derived, and a cascaded-grating scheme that provides full, nondegenerate interconnections between two unsampled planes is presented. The dynamics of the formation of photorefractive volume holograms is considered. The impact of time-constant asymmetry on multiple hologram recording is evaluated. A basic framework for controlling the dynamics of photorefractive holograms is described and a number of dynamic copying methods for rejuvenating decayed holograms are identified. Experiments of linear dynamic copying using phase conjugation and nonlinear copying using an optical feedback loop are presented. The electrical fixing of photorefractive holograms in [...] crystals is experimentally demonstrated and the physical mechanism is discussed. A number of neural learning algorithms are investigated for optical implementation. An Anti-Hebbian local learning algorithm is proposed to simplify the optical architecture of feedforward multilayer networks. Experimental demonstrations of several optical neural networks are presented. An optical perceptron is trained for face classification, and the use of dynamic copying for improving its performance is demonstrated. A two-layer network based on Kanerva's sparse, distributed memory model is implemented and trained for real-time handwritten character recognition. Finally an optical two-layer network for real-time face recognition, with moderate tolerance to shift, rotation, scale, and facial expression, is presented.

Item Type:Thesis (Dissertation (Ph.D.))
Degree Grantor:California Institute of Technology
Major Option:Electrical Engineering
Thesis Availability:Public (worldwide access)
Thesis Committee:
  • Psaltis, Demetri (chair)
Defense Date:29 June 1993
Record Number:CaltechETD:etd-12042007-084534
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:4781
Deposited By: Imported from ETD-db
Deposited On:06 Dec 2007
Last Modified:19 Apr 2021 22:40

Thesis Files

PDF (Qiao_y_1994.pdf) - Final Version
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