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Jfopt Location: Jfopt > News > Fiber knowledge > The Differences between FP and DFB

The Differences between FP and DFB

Edit:   Date: 16-06-23


FP Laser

FP (Fabry-perot) laser puts FP cavity to cavity, multi-longitudinal mode coherent light emitted semiconductor light emitting device. FP laser is mainly used for low-speed short-distance transmission, such as transmission distance is generally less than 20 kilometers, the rate is generally less than 1.25G, at the two wavelengths of the FP-1310nm / 1550nm.

Some manufacturers want to reduce the production cost, so they making Gigabit 40km module with FP devices so as to achieve the appropriate transmission distance, it will turn up the power of the emitted light on the market for a long time to make the product work devices premature aging, shorten life. The recommendation of the engineer's 1.25G 40km of dual-fiber modules, applications DFB device more reliable!


FP laser performance parameters:

1) Wavelength: center wavelength emitted by the laser spectrum.

2) spectral width: multi-longitudinal-mode laser rms spectral width.

3) Threshold current: When the operating current of the device exceeds the threshold current laser emits coherent laser well.


4) output optical power: laser output power port optical power emitted


Typical parameters as following:

DFB lasers

DFB lasers is based on FP lasers using grating-optical device consider the device has only one longitudinal mode output. DFB (Distributed Feedback Laser) generally use two wavelengths 1310nm, 1550nm, divided into refrigeration and no refrigeration, mainly for high-speed long-distance transmission, the transmission distance of 40 km.


DFB laser performance parameters:


1) Wavelength: center wavelength emitted by the laser spectrum.

2) side-mode suppression ratio: the main mode laser operating with maximum side mode power ratio.

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


4) threshold current: When the operating current of the device exceeds the threshold current laser emits coherent laser well.

5)output optical power: laser output power port optical power emitted

Typical parameters as the following :

From the above tables we can see that the main difference between FP and DFB laser is the different spectral width , the DFB spectral width is generally narrower than the FB laser ,which  is a distributed single-longitudinal-mode negative feedback. The FP laser spectral width is relatively wide, is a multi-longitudinal mode lasers. Their operating wavelength, threshold current and forward voltage are also different.

 

In summary, FP and DFB lasers working principles are different; DFB laser is with higher  production cost  and  suitble for long-distance transmission.

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