We all know that DFB narrow linewidth laser diode is not common in daily life, so do you know what its main working principle is? Let's take a look at it together

The narrow linewidth of DFB laser can be achieved because a grating is buried inside the chip, which allows only one specific wavelength to oscillate, and all other wavelengths are suppressed for you.

You can understand it as: a "sieve" is placed in the laser cavity, and only the "laser line" you want passes through, and everything else is stopped. This is DFB.

Why is the line width of common FP laser wide?

The common FP (Fabry-Perot) laser relies on a cavity formed by two front and rear reflecting surfaces, in which multiple modes are reflected back and forth.

Eventually, there will be many laser wavelengths.

The key structure of DFB: Bragg grating

The core of DFB laser is a grating with periodic structure buried near the gain region (MQW).

This grating can only give feedback to a certain wavelength, and give no feedback to other wavelengths, so that the laser can only oscillate at the selected wavelength.

These are the working principles of DFB narrow linewidth laser diodes, and I hope you will have a clear understanding after reading them.