Common types of semiconductor lasers in optical modules

        There are three types of lasers commonly used in optical modules: Vertical Cavity Surface Emitting Lasers (VCSEL), Fabry Perot Lasers (FP), and Distributed Feed Back Lasers (DFB).

Figure 1 Classification of laser

1. VCSEL laser
        VCSEL is a surface emitting laser with relatively low production and manufacturing costs. At the same output power, it has higher efficiency than DFB laser and FP laser, and the driving current is very small, usually only a few milliamperes. The power consumption of the module is relatively small, and the spectrum is relatively narrow, all of which are the advantages of VCSEL; However, currently mature processes can only produce 850 nm wavelengths for multi-mode fibers.

Figure 2 Laser of VCSEL

2. FP laser
      FP laser is a semiconductor light-emitting device that emits multi longitudinal mode coherent light using an FP cavity as the resonant cavity. FP laser has two wavelengths, 1310nm/1550nm. The process is very mature and widely used. However, the spectral characteristics of FP are not good, with multiple edge modes and dispersion issues. Therefore, it can only be used for medium to low speed (speeds below 1-2G) and short distance applications (less than 20 kilometers).

Figure 3 FP Laser

3. DFB laser
        DFB belongs to a side emitting semiconductor laser, which integrates a Bragg grating into the gain medium inside the laser, forming a mode selection structure in the resonant cavity , and can achieve complete single mode operation. The spectral characteristics are very good, which can avoid the influence of dispersion in length transmission, so it is widely used in long-distance and high-speed applications; For example, products that transmit 40-120KM use DFB lasers, products that transmit 10KM at 10G speed also use DFB lasers, and a part of 40KM products also use DFB lasers.

Figure 4 DFB laser

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