FP laser FP (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-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. In order to reduce the cost, some manufacturers use FP devices to make Gigabit 40km optical modules. In order to achieve the corresponding transmission distance, the transmitted optical power must be increased. Long-term work will cause the product components to age in advance and shorten the use. life. According to the engineer’s suggestion for a 1.25G 40km dual-fiber module, the application of DFB devices is more secure.
The 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. The typical parameters are shown in the following table: DFB laser DFB laser is based on FP laser using grating filter device so that the device has only one longitudinal mode output. DFB (Distributed Feedback Laser) generally also uses two wavelengths of 1310nm and 1550nm, which are divided into refrigeration and no refrigeration. They are mainly used for high-speed, medium- and long-distance transmission. The transmission distance is generally more than 40 kilometers. DFB laser performance parameters: 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 following table: As can be seen from the above table, the main difference between FP and DFB lasers is that the spectrum width is different. The spectrum width of DFB lasers is generally the same. It is relatively narrow and 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.