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FP.VS DFB laser in OPTICAL module

We all know that optical modules have many types of lasers. FP and DFB lasers are common types of lasers. What is the difference between them?


The FP laser FP (Fabry-perot) laser is a semiconductor light-emitting device that emits multi-longitudinal mode coherent light with a FP cavity as a resonant cavity. FP lasers are mainly used for low-rate short-distance transmission. For example, the transmission distance is generally within 20 km, the speed is generally within 1.25 G, and the FP is divided into two wavelengths, 1310 nm / 1550 nm.
Nowadays, some manufacturers have produced Gigabit 40km optical modules for FP devices in order to reduce costs. In order to achieve the corresponding transmission distance, the optical power must be increased. The long-term work will cause the devices of the products to age and shorten the use. life. According to the engineer‘s recommendation 1.25G 40km dual fiber module, the application of DFB devices is more secure!

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:

Parameter Symbol Unit Conditions Min. Typical Max.
Wavelength λp nm IW=Ith+20mA 1290 1310 1330
        1530 1550 1570
Spectral bandwidth Δλ nm IW=Ith+20mA   3 5
Threshold Current Ith mA   5 20  
Pigtail output power Po mW IW, 1310nm 0.3   2.5
      IW, 1550nm 0.3   2
Forward Voltage vf v IW=Ith+20mA   1.1 1.5


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:

Parameter Symbol Unit Test Conditions Min. Typical Max.
Wavelength λp nm IW=Ith+20mA   1310  
          1550  
Spectral bandwidth Δλ nm IW=Ith+20mA   0.3 0.55
Threshold Current Ith mA   15 20  
Pigtail output power Po mW IW, 1310nm 0.3   2.5
      IW, 1550nm 0.3   2
Forward Voltage vf v IW=Ith+20mA      

Organic Solid-State Lasers: Past and Future
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.
The main difference between FP and DFB laser is that the spectrum width is different. The spectrum width of DFB laser is generally narrow, and it is a single longitudinal mode with distributed negative feedback. The FP laser has a relatively wide spectrum and is a multi-longitudinal mode laser. They also differ in wavelength, threshold current and forward voltage.

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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