We all know that DFB laser diode is rarely used in daily life, so do you know what its main function is in optical communication? Let me give you a brief introduction.

The full name of DFB laser is distributed feedback laser. Its biggest feature is that the output wavelength is particularly stable. Why can it do this? The key is that it has a "grating structure" inside, which is equivalent to making a "filter" in the resonant cavity, which only allows light with a specific wavelength to oscillate back and forth. In this way, the output laser is single-mode stable, unlike ordinary FP laser, which is easy to drift or jump modes.

In optical communication, this stability is too important. Because we are always talking about dense wavelength division multiplexing (DWDM), there are dozens or even hundreds of wavelength channels running in an optical fiber. If the laser wavelength is unstable and drifts by a few tenths of a nanometer, the signal will be easy to cross channels and the whole system will be chaotic.

Another advantage of DFB laser is its high modulation speed. Its carrier lifetime is short and it can support high-frequency modulation, so DFB has always been the main player in 10G, 25G and even 100G high-speed communication. Nowadays, many 5G base station backhaul, metropolitan area network transmission and data center interconnection are also inseparable from it.

Of course, DFB laser is not omnipotent, its price is much more expensive than FP laser, and the requirements of packaging, heat dissipation and current control are higher. Especially in high-power applications, if the heat dissipation is not done well, the wavelength will drift fast and the service life will be discounted.