Glass optical Fibres - How was it even thought ?

 

Optic Fibers

Glass Optic Fibers : Thought process behind it

Communication started with the invention of the telephone by Alexander Graham Bell. The communication established used point to point wire communication and DC signals (near 0 Hz) for transmission which was intensity modulated by the vibration of carbon particles in the microphone. However the rate achievable was too low. With the invention of vacuum tubes, the use of AC carriers started which boosted up the concept of data rates.  They used 12 carriers spaced apart by 4kHz. It was discovered that we could achieve higher bandwidth with a higher AC carrier frequency. Higher carrier frequency implies higher information carrier capacity. But at carrier frequencies higher than 1MHz the impedance of metal wires increases abruptly. This was overcome with the invention of wireless transmission of microwaves by SSB modulation during World War 2. With the line of sight propagation the bandwidth of 10 GHz was achievable. With the increase in applications, the frequency use was increased. However the frequency band was limited. So, the focus was shifted back to the development of co axial cables. 

Coaxial cables were developed using copper cables. They were used in trunk lines. Yet the signal loss was high and the amplification was required very frequently. This was solved by using mm waveguides which were transmitted through steel pipes buried in the ground lined with copper and polyethylene covered by steel sheath. However the capacity wasn’t used completely.

The idea of optical communication grew. The optical signal offered bandwidth in the range of terahertz. However the optical signals faced extensive absorption and attenuation by atmospheric factors such as smoke, fog etc. So the transmission in the controlled atmosphere was attempted through pressurized aluminum pipes. A clean atmosphere provides transparency but in a controlled atmosphere we needed to use lenses to prevent divergence. The development of a gas lens was attempted. But the deployment of the same in large scale was not economical.

So the search for the material continued and they needed the material which offered transparency and low losses. The glass was one such material which was initially considered. The transmission of light through thin composite glasses created a new type of communication in optic fibers communication.