British Telecommunications Public Limited Company

British Telecommunications Corporation

James D Rush

Benjamin J Ainslie

Keith J Beales

Stephen N Oliver

Clive R Day

Callum A Hill

Christoper S Winter

Allan E Underhill

##STR1## The specification identifies dithiolenes which give good performance as the critical region of an optical switch. The dithiolenes have the formula shown in FIG. 1 wherein: (A) the R groups, any two of which may be the same or different, are selected so as to tune the absorption bands of the molecule for use at the operational wavelength and/or to act as bridges to join molecules together: (B) the X groups, any two of which may be the same or different, are selected from S and Se: (C) M is selected from Ni, Pt, Pd and Cu: (D) C=-1 or 0: and (E) (i) when C=-1, Y is a cation to render the molecule electrically neutral: preferably Y is selected from ammonium, substituted ammonium, Na.sup.+, Li.sup.+ and K.sup.+, (ii) when C=0, Y is absent (since the molecule is neutral there is no change to balance). The dithiolene may be diluted with an organic polymer selected from polyacrylates, polymethacrylates, such as polymethymethacrylate, polycarbonates, polyisobutylene, polyethylene terephthalate, polystyrene and polysiloxane.

Optical switches

An optical fibre capable of monomode transmission in, and having a wavelength of zero dispersion in, the 1.55 .mu.m window and having a core comprising silica and germanium dioxide and a cladding comprising silica is drawn from an appropriate preform at a temperature in the range from 1900.degree. C. to 2000.degree. C. Fibres thus produced have low loss compared with fibres drawn at higher temperature.

Optical fibres

Growing community of inventors

Ipswich, United Kingdom

James D Rush