1. Kapany, N.S., Burgwald, G.M., and Burke, J.J.: ‘Light amplification and switching using fiber optics and laser’, Tippett, J.T., Berkowitz, D.A., Clapp, L.C., Koester, C.J., vanderBurgh, A., Optical and electro-optical information processing, (MIT Press 1965), p. 305–320