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What is Spectral Width and Central Wavelength? FWHM values

Have you ever thought, that when you every day talk about wavelengths, that are used in your equipment like WDM media converters – 1310/1550 nm or GPON, with 1490/1310 nm, we actually are not too correct to say, they has such single fixed one-only wavelength.



Actually, if you delve into details “under the hood”, you soon see, that light in fiber optic communication systems consist more than of one wavelength. These wavelengths occupy a range, which then is centered over so called “central wavelength.”



That looks schematically something like this:



central wavelenght and spectral width


Figure 1: Central Wavelength & Spectral Width 



As we also know from previous theory articles on our blog, each wavelength also travels at different speeds, and because of that, spectral width is one of the contributing factors that determine also the final distance what we get using our communication systems, be it FTTx PON systems or AHD cameras over fiber.

Spectral width values are given as “full width, half maximum – FWHM”. This value is a range of wavelengths at 50% of the maximum power of wavelength power chart (see Figure 1 above for details).


Lomoveishiy – Finland

I needed those to connect my PC on the third floor to have internet access in that room, and ISP installed their modem on the first floor only. After dropping fiber patch cables, plugged in all cables into these media converters at both sides, and link came up instantly. Was much easier than I thought!

Raymond – USA

Great experience – units worked straight out of the box – just needed plug in cables and we were done. I also like the possibility to enable jumbo frames, while we do not have a need for this feature at the current moment it’s great to have this option.