Ourmazd, A.; Birch, R.D.; Varnham, M.P.; Payne, D.N.; Tarbox, E.J.: 'Enhancement of birefringence in polarisation-maintaining fibres by thermal annealing', Electronics Letters, 1983, 19, (4), p. 143-144, DOI: 10.1049/el:19830101
IET Digital Library, https://digital-library.theiet.org/;jsessionid=25as6u3oq8d4j.x-iet-live-01content/journals/10.1049/el_19830101