Optical Fibre very fine, optically pure glass fibre through which light can be reflected to transmit an image or information from one end to the other. In simplest terms, an optical fibre is a conductor of light. In an optical fibre, a thin core of transparent material is surrounded by a material of lower refractive index, known as cladding. Light waves are guided along the core of the fibre by a series of total internal reflections between the core-cladding interface. The principle is inherently simple, yet powerful and elegant. By carefully controlling the impurities in the core, losses of light as low as 0.3 decibels per kilometre of fibre (about 7% per km) can be achieved in practical silica-based fibres. The optical fibre has found many practical applications, such as in communications, in medical imaging systems and as a convenient guide of light from high-power lasers for surgical and industrial applications. Optical fibres are increasingly being used to replace copper wire in telephone cables, the messages being coded as pulses of light rather than a fluctuating electric current. Although expensive to produce and install, optical fibres can carry more data than traditional cables, and are less susceptible to interference. Optical fibre communication is perhaps the most well-known application of optical fibres.

Bangladesh does not yet have any facility for manufacturing optical fibres, but it is increasingly used for telecommunication. For example, bangladesh railways (BR) has installed optical fibre system to meet their telecommunication (including signalling) need. BTTB (Bangladesh Telegraph and Telephone Board) is also using optical fibres in some parts of the telephone network of major cities and towns, and in some local-area networks (LANs). shahjalal university of science and technology and Rajshahi University have optical fibre network backbone, which is used as local area network system of the university. In telephone systems, a single fibre can replace hundreds or even thousands of copper circuits. By using optical fibres, much lower cost per voice channel and more reliable and maintenance-free operation can be realised.

Arrangements have been made to install a large-capacity undersea optical fibre cable under the bay of bengal to connect Dhaka and Chittagong with Singapore. It will connect Bangladesh with the Global Fibre Optic Network and will tremendously improve the overseas connectivity of the country, which at present depends on a number of relatively low-capacity satellite stations. Ultimately, due to larger available bandwidth, the cost of overseas telephone calls should decrease to international levels by using this cable, and the speed of Internet browsing can be expected to increase manifold. [Kazi Monowar Abedin]