The Difference Between SFP Optical Module Transceiver FP And DFB Laser

- Nov 12, 2020-

The Difference Between SFP Optical Module Transceiver FP And DFB Laser

 

Regarding the technical knowledge of optical module FP and DFB laser, what is the difference between them. On the front, briefly summarize the knowledge of FP and DFB lasers.


SFP transceiver lasers difference

FP laser:

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

There are also some manufacturers in the market that use FP devices to make Gigabit 40km modules in order to reduce costs. In order to achieve the corresponding transmission distance, the emitted optical power must be increased. Long-term work will cause the product components to age in advance and shorten the service life. . According to the engineer’s suggestion for a 1.25G 40km dual-fiber module, the application of DFB devices is more secure!


The typical parameters are shown in the table below:

sf spec performance

Performance parameters of FP laser:

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

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

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

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

 

sfp transceiver module structure

DFB laser

The DFB laser is based on the FP laser and uses a grating filter device to make the device have only one longitudinal mode output. DFB (Distributed Feedback Laser) generally also uses two wavelengths of 1310nm and 1550nm, which are divided into cooling and no cooling. They are mainly used for high-speed, medium- and long-distance transmission. The transmission distance is generally more than 40 kilometers.


Performance parameters of DFB laser:

1) Working wavelength: the center 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 highest point of the laser output spectrum is reduced by 20dB.

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

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

 

The typical parameters are shown in the table below:

dfb spec performance

The main difference between the optical module SFP transceiver FP and the DFB laser is that the spectral width is different. The spectral width of the DFB laser is generally narrow, and it is a single longitudinal mode with distributed negative feedback. The FP laser has a relatively wide spectral width and is a multi-longitudinal mode laser. Their operating wavelength, threshold current and forward voltage are also different.


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