The Difference Between FP And DFB Laser

May 06. 2016

Recently some colleagues reflected that many customers want to learn what FP and DFB lasers are and their differences. In order to make them easy to explain to the customer, briefly summarize the knowledge of FP and DFB laser.

FP laser

FP (Fabry-perot) laser is mainly used for low data rate short-distance transmission, the transmission distance is generally within 20 km,the rate is generally within 1.25G. FP is divided into two wavelengths, 1310nm/1550nm.

Some customer in order to decrease the cost , so chose the FP laser to make the 1.25G 40km module. Reason by make the module reach the 40km transmission distance, the engineer must adjust the output power rather bigger to meet the distance, but it will make the laser ageing fastly cause more issue.

The performance parameters of FP laser:

1）Working wavelength: Emitted the center wavelength of spectrum by laser.

2）The width of spectral: RMS spectral width of multi-longitudinal mode laser.

3）Threshold current: The laser send out a very good laser when the working current of the device exceeds the threshold current.

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

The typical parameters are shown in the following table:

DFB laser

DFB ( Distributed Feedback Laser) laser use the grating filter device to make the device have only one longitudinal-mode output based on the FP laser.DFB generally also use two wavelengths 1310nm and 1550nm, divides into refrigeration and No-refrigeration, mainly used for high data rate long-distance transmission.The transmission distance is generally above 40 kilometers, the rate is above 1.25G.

The performance parameters of DFB laser:

1）Working wavelength: Emitted the center wavelength of spectrum by laser.

2）The suppression ratio of side mode: The power ratio of the main mode and the maximum side mode of the laser.

3）Decreased the spectral width of 20dB: Decreased the spectral width of 20dB by the highest point of the laser output spectrum.

4）Threshold current: The laser send out a very good laser when the working current of the device exceeds the threshold current.

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

The typical parameters are shown in the following table:

The main difference can be got by the form between the FP and DFB laser is that the spectral width is different. The spectral width of the DFB laser is generally narrow, is a single longitudinal mode with distributed negative feedback. While the spectral width of the FP laser is relatively wide, it is a multi-longitudinal mode laser. The working wavelength, threshold current and voltage are also different.

Thanks for your reading! Hope these shares will give you some understanding of FP and DFB lasers! Welcome to discuss with the industry’s elite together, also hope to provide your valuable views and suggestion, creating progress together with you！

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