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Common Semiconductor Laser Types for Optical Modules
Time: 2019-02-26
There are three common types of lasers used in optical modules: Vertical-Cavity Surface-Emitting Laser (VCSEL), Fabry-Perot Laser (FP), and Distributed Feedback Laser (DFB).
Figure 1: Laser Classification
1. VCSEL Laser
VCSEL is a surface-emitting laser with relatively low manufacturing costs. At the same output power, it boasts higher efficiency than DFB and FP lasers, requiring only a small driving current (usually just a few milliamps). This results in lower power consumption of the optical module, along with a narrow emission spectrum—all of which are key advantages of VCSEL. However, current mature manufacturing processes can only produce VCSELs operating at a wavelength of 850 nm, which are specifically designed for multi-mode fiber (MMF) applications.
Figure 2: VCSEL Laser
2. FP Laser
The FP laser is a semiconductor light-emitting device that uses a Fabry-Perot cavity as its resonant cavity, emitting multi-longitudinal-mode coherent light. FP lasers are available in two typical wavelengths: 1310 nm and 1550 nm. With well-established manufacturing processes, they have been widely adopted in various applications. Nevertheless, FP lasers suffer from poor spectral characteristics, including issues such as multiple side modes and chromatic dispersion. For this reason, they are only suitable for low-to-medium rate applications (below 1–2 Gb/s) and short-distance transmissions (less than 20 km).
Figure 3: FP Laser
3. DFB Laser
The DFB laser is an edge-emitting semiconductor laser. It integrates a Bragg grating into the gain medium inside the laser, forming a mode-selective structure within the resonant cavity and thus enabling pure single-mode operation. Thanks to its excellent spectral characteristics, it can avoid the impact of chromatic dispersion during long-distance transmission. Therefore, DFB lasers are widely used in long-distance and high-speed transmission scenarios. For instance, products designed for 40–120 km transmission all utilize DFB lasers; 10 Gb/s optical modules for 10 km transmission also use DFB lasers, as do some products for 40 km transmission.
Figure 4: DFB Laser
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