Fourth - Sixth Generation

Fourth generation (from 1984) 
- Initiate research and development into a coherent system, modularity but not the intensity modulation frequency modulation, so that the signal is weak intensity, can still be detected, the distance that can be taken, also the transmission capacity, expand participate. 
- In 1984 capacity is equal to the capacity of direct detection system (intensity modulation). 
- Hampered its development since the technology tools and resources frequency modulation detection is still lagging behind. 

Fifth Generation (starting 1989) 
- Developed a brace that replaces the function of optical Repeater on the previous generation. 

- In the early development capacity transmission only achieved 400 Gb.km / s but a year later the transmission capacity is 50,000 penetrate Gb.km / s 

Sixth generation

- In 1988 Linn F. Mollenauer pioneered optical soliton communication system. Soliton waves are charging that consists of many components of long waves that are only slightly different, and also vary in intensity. 

- The length of soliton only 10-12 seconds and can be divided into several components near each other, so that the signals in the form of soliton is information that consists of several channels at once (Wavelength division multiplexing). 
- Eksprimen shows that the soliton can bring at least 5 channels, each carrying information with a rate of 5 Gb / s. The transmission capacity has reached 35,000 tested Gb.km / s. 
- How the system is the soliton Kerr effect, namely-ray diffraction long gelombangnya same will be spread with a different pace in a material intensity, if the price exceeds a limit. This effect is then 
menetralisir used to dispersi effects, so that the soliton is not the time to widen the Receiver. This is beneficial because the level of error is very small ditimbulkannya can even be ignored.