(19)

(11)

EP 0 542 799 A1

(12)

(43) Date of publication: 26.05.1993 Bulletin 1993/21 (21) Application number: 91913913.0 (22) Date of filing: 31.07.1991

(51) International Patent Classification (IPC):  G02B 6/ 38( . ) G02B 7/ 02( . ) G02B 6/ 42( . ) (86) International application number: PCT/GB1991/001301 (87) International publication number: WO 1992/002837 (20.02.1992 Gazette 1992/05)

(84) Designated Contracting States: DE FR GB IT (30) Priority: 02.08.1990 GB 19900017015 (71) Applicant: BRITISH TELECOMMUNICATIONS public limited company London EC1A 7AJ (GB)	(72) Inventors: FATAH, Rebwar Acton, Sudbury CO10 0BT (GB) CAMERON, Keith, Henderson Felixstowe, Suffolk IP11 9HP (GB) BIRD, David, Michael Kirton, Suffolk IP10 0PF (GB) COX, Maurice, Kevin Ipswich, Suffolk IP5 7UA (GB) (74) Representative: Pratt, David Martin, et al  BT Group Legal Services Intellectual Property Department 151 Gower Street London WC1E 6BA London WC1E 6BA (GB)