Published online by Cambridge University Press: 05 June 2014
When the laser was first invented, it was described as “a solution looking for a problem.” This comment did not long survive scrutiny, and nowadays lasers are ubiquitous in many aspects of daily life, with many technological, artistic, and educational applications. This chapter highlights some of the important application areas where lasers have become essential.
Optical communication systems
Introduction
Optical communications systems have a long history. Ancient man signaled with smoke and fire, often relaying messages from mountain top to mountain top. However, this optical communication scheme had limited transmission capacity. Such messages could serve as a warning, as Queen Elizabeth the First of England planned when she had a network of bonfires erected to be set in the event of a seaborne invasion from Spain. The smoke signals transmitted by native Americans had the capacity to transmit various messages. Since the end of the eighteenth century,messages have been passed by semaphore – the use of flags to indicate the transmission of one letter at a time. This form of communication could transmit information at a rate of about one letter per second over a direct line of sight, although messages could be relayed over long distances. Such means of communication were not very secure: anyone in the line of sight to the message sender could read the information (if he or she knew the code).
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