New Delhi: Indian Railways has covered over 100 cities, nearly 21,000 km of broadband optic fibre cable (OFC), including all metros. Provisioning of electronics on the OFC network, set up under the aegis of RailTel Corporation of India Ltd (RCIL), has been commissioned on about 21,000 route kilometres. The RCIL has laid 25,750 kilometre long OFC, since the year 2000, when Indian Railways had only 5,000 kilometre of OFC network.

As many as 1,925 points of presence (PoP) have been created across the country including remote and backward areas.

Advantage of optic fibres in the railways

• Optic sensors: Sensors based on optic fibre are used to detect flaws in rails and even in wheels of the carriage or bogie. Sensitive optic fibre is attached to the rails using epoxy and tape. The sensor is intelligent enough to feel the changes in its immediate environment — such as the pressure due to weight of a passing train. The weight would cause an obvious strain on the rail — which gets transferred to the attached optic fibre. More importantly, it can sense the strain created by a cracked, broken or buckled rail. In short, such sensors help to protect both freight and passenger trains from derailment. Researchers claim that the speed of the train is not a stumbling factor.
• Light transmission: The intensity of the light that is transmitted through the fibre will depend on the condition of the rail and the amount of induced strain. Light loses its intensity as it traverses farther away from the source along the fibre. This is termed as 'signal loss' and is a function of the distance. The principle involved is a 'time gated' pulse detection technique based on 'optical time domain reflectometry'. The derivative of the accumulated data can give a clue to the speed of the train, its position and of course, the damage to the rail, if any.
• Micro bends: An altered type of sensor uses the micro bending property of optical fibre. It is known that light travels along the core of the fibre by the principle of 'total internal reflection'. When light encounters a bend in the fibre, part of the travelling light 'leaks' out. An interesting correlation can be developed between the applied bending pressure and the intensity of light traversing the fibre longitudinally, minus the leaked out portion of light.
• Flat spots: Wheels have 'flat spot' even though every wheel under the railway carriage is 'seemingly' circular., This is due to wear and tear, as the wheels age by use, wheels develop flat spots. This flattened spot damage the rails while carrying load - a dynamic load acts on the rails whenever the flat spot comes into contact with the rail. This technology also enable in identifying a defective wheel.
• Detection and warning: The rail mishap on the Konkan Rail, last year, was due to boulders sliding on to the rail near a tunnel during heavy rains. The approaching train had no warning when disaster struck. Rock falls, landslides and washouts are also detectable with electromagnetic field. Three components integrate the system — system processor, radio frequency transceiver, cables with protective carrier to transmit and receive.