Whalen, M.S.; Divino, M.D.; Alferness, R.C.: 'Demonstration of a narrowband Bragg-reflection filter in a single-mode fibre directional coupler', Electronics Letters, 1986, 22, (12), p. 681-682, DOI: 10.1049/el:19860465
IET Digital Library, https://digital-library.theiet.org/;jsessionid=2gj7j4j6717i1.x-iet-live-01content/journals/10.1049/el_19860465