Cozens, J.R.: 'Propagation in cylindrical fibres with anisotropic crystal cores', Electronics Letters, 1976, 12, (16), p. 413-415, DOI: 10.1049/el:19760316
IET Digital Library, https://digital-library.theiet.org/;jsessionid=2exu01x05c0fq.x-iet-live-01content/journals/10.1049/el_19760316