optical communication and networking by gayatri pdf reader

This allowed transmission of whole sentences over long distances. 8.1 to represent the entire alphabet through different positions of two needles. Chappe called his invention optical telegraph and developed a coding scheme shown in Fig. Figure 8.1 shows the inventor and his basic idea schematically. A major advance occurred in 1792 when Claude Chappe came up with the idea of transmitting mechanically coded messages over long distances through the use of intermediate relay stations (10–15 km apart) that acted as repeaters in the modern-day language. In spite of such clever schemes, the distance as well as the rate at which information could be transmitted using semaphore devices was quite limited even during the eighteenth century. This idea is not too far from our modern schemes in which information is coded on the light emitted by a laser by modulating it at a high speed . Similarly, shutters were used inside lighthouses to turn the beacon signal on and off at predetermined intervals. For example, the North American Indians changed the color of a smoke signal for this purpose. Attempts were made throughout history to increase the amount of transmitted information. The chief limitation of such a scheme is that the information content is inherently limited and should be agreed upon in advance. a 500-km-long line of fire beacons to convey the news of the fall of Troy . For example, it is claimed that the Greeks constructed in 1084 b.c.

Most civilizations have used mirrors, fire beacons, or smoke signals to convey a single piece of information (such as victory in a war). The use of light for communication purposes dates back to antiquity if we interpret optical communication in a broad sense, implying any communication scheme that makes use of light.

Optical communication and networking by gayatri pdf reader