What is the difference between FP Lasers and DFB Lasers?

Both FP lasers and DFB lasers are common optical communication modules, so what is the difference between them?

DFB lasers

Definition of FP Laser

FP laser (Fabry-perot laser) is a semiconductor light-emitting device that emits multi-longitudinal mode coherent light with an FP cavity as a resonant cavity. FP lasers are mainly used for low-rate and short-distance transmission. For example, the transmission distance is generally within 20 kilometers, and the speed is generally within 1.25G. The FP has two wavelengths, 1310nm/1550nm.

FP lasers have the following performance parameters:

1) Working wavelength: the central wavelength of the spectrum emitted by the laser.

2) Spectral width: the root mean square spectral width of the multi-longitudinal mode laser.

3) Threshold current: When the operating current of the device exceeds the threshold current, the laser emits a laser with good coherence.

4) Output optical power: the optical power emitted by the laser output port.

Definition of FP Laser

Definition of DFB Laser

The DFB laser uses a grating optical filter device based on the FP laser so that the device has only one longitudinal mode output. The characteristics of this type of device are: large output optical power, small divergence angle, extremely narrow spectrum, and high modulation rate, which are suitable for high-speed medium and long-distance communication.

DFB (Distributed Feedback Laser) generally uses two wavelengths of 1310nm and 1550nm, which are divided into cooling and non-cooling, and the transmission distance is generally more than 40 kilometers.

DFB laser performance parameters:

  1) Working wavelength: the central wavelength of the spectrum emitted by the laser.

2) Side mode suppression ratio: the power ratio of the main mode of the laser to the maximum side mode.

  3) -20dB spectral width: the spectral width is reduced by 20dB from the highest point of the laser output spectrum.

4) Threshold current: When the operating current of the device exceeds the threshold current, the laser emits a laser with good coherence.

5) Output optical power: the optical power emitted by the laser output port.

Definition of DFB Laser

The difference between DFB laser and DP laser

As can be seen from the above table, the main difference between FP and DFB lasers is that the spectral width is different. The spectral width of DFB lasers is generally narrow, which is a single longitudinal mode of distributed negative feedback. The spectral width of the FP laser is relatively wide, and it is a multi-longitudinal mode laser. They also differ in their operating wavelength, threshold current and forward voltage.