1. Kapany, N.S.: Fibre optics, (Academic Press 1967),chap. 2, p. 36
2. Snyder, A.W., Mitchell, D.J., and Pask, C.: The failure of geometric optics for analysis of long optical fibres, (to be published)
3. Marcuse, D.: Light transmission optics, (Van Nostrand Reinhold 1972), p. 398