1. K. Iga, Y. Kokubun, M. Oikawa: Fundamentals of Micro—optics (Academic Press, Tokyo 1984), Chap. 1
2. R.K. Luneburg: Mathematical Theory of Optics (University of California Press, Berkeley 1964), Chaps. 3–4
3. E.W. Marchand: Gradient Index Optics (Academic Press, New York 1978), Chap. 5
4. M.S. Sodha, A.K. Ghatak: Inhomogeneous Optical Waveguides (Plenum Press, New York 1977), Chap. 9
5. A. Fletcher, T. Murphy, A. Young: Proc. R. Soc. London, Ser. A 223, 216 (1954) 6.6 D.W. Hewak, J.W.Y. Lit: Appl. Opt. 28, 4190 (1989)