Bhag, I am trying to answer your question:|
Currently, due to explosive internet usage, ISP all have big problem to meet data capacity problem. However, deploying new optical fiber line is very very expansive. So people invented DWDM technology. It can transmit multiple data channels in a fiber line. More channel means more data can be transferred. Since DWDM can use the existing fiber line so there is a great cost advantages.
APAT is shipping 50 Ghz DWDM filter. It is the most advanced DWDM device on the market. 50 Ghz means that the channel spacing is 50 Ghz which mean higher channel density. For optical fiber, there are only very small range is linear, only this linear range can be used for data transmit. Therefore, a smaller channel spacing means packing more channels in this linear range. What is the difference between 200 Ghz and 50 Ghz? a 50 Ghz device means that it can pack 4 times more of channels(data too) comparing to the 200 Ghz one. For example, if the bandwidth for the optical fiber is 3000 Ghz, then by using 50 Ghz DWDM device, one fiber can transmit 3000/50=60 channels of data but for 200 Ghz DWDM device, it can only transmits 3000/200=15 channels of data. Assume that the data capacity for each channel is the same then the 50 Ghz DWDM device can transmit 4 times more of data comparing to the 200 Ghz DWDM device for the same fiber line. Currently, 50 Ghz DWDM device could pack 64 channel into one fiber. It is selling very very hot and very few people can make it.
Hope it helps