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SEL
SEL (Surface-Emitting Laser) emits laser beams parallel to the semiconductor surface while enabling optical coupling in the perpendicular direction.
Key Features:
- Low threshold current
- Easy single-mode output implementation
- Facilitates 2D array integration
Primary Applications: Short-range communications and parallel optical signal processing systems.
EEL
EEL (Edge-Emitting Laser) is currently the most widely used type of semiconductor laser.
Key Features:
- Edge-emission parallel to the semiconductor surface
- Optical coupling capability at both ends of the chip
- Superior beam quality and higher output power
Dominant Applications: Long-haul fiber optic communications and fiber sensing applications.
VCSEL
VCSEL (Vertical Cavity Surface Emitting Laser) is the most prevalent surface-emitting laser type employs Distributed Bragg Reflector (DBR) resonator structures.
Key Features:
- Low threshold current
- Stable single-wavelength operation
- Simplified two-dimensional array integration
Technical Specifications:
- Primary Wavelength: 850nm band
- Material System: GaAs/AlGaAs composition tuning
- Manufacturing: Mature and cost-effective, suitable for large-scale mass production
- Multi-junction cascade structure design: higher output optical power can be achieved at the same drive current, enhancing optical power density
In fiber optic communications, VCSELs offer significant advantages including high coupling efficiency, low power consumption, high transmission rates, and low manufacturing costs. While VCSELs cannot yet fully replace EELs in high-power applications, they are increasingly becoming the mainstream choice for low-power, low-cost scenarios.
FP
Fabry-Perot Laser (FP Laser) operates based on the Fabry-Perot resonator, where light reflects between two partially reflective mirrors (high-reflectivity and low-reflectivity coatings). Lasing occurs when the round-trip optical path length matches an integer multiple of the wavelength.
Spectral Characteristics:
- Multi-longitudinal-mode output: Weak wavelength selectivity results in broad spectral width (~1–5 nm).
- Lower coherence: Less suitable for applications requiring precise wavelength stability.
Advantages:
- Cost-effective: Simple structure enables low manufacturing costs.
- High output power: Suitable for power-sensitive applications.
Applications:
- Fiber-optic communications: Primarily used in 1G/10G optical modules for medium-distance transmission (≤40 km).
- Industrial sensing: Where spectral purity is less critical.
DFB
DFB (Distributed Feedback Laser) incorporates a Bragg grating within the active gain region, enabling wavelength-selective feedback. Only light satisfying the Bragg condition undergoes constructive interference, producing single-longitudinal-mode output.
Spectral Characteristics:
- Narrow linewidth (~0.1 nm or less).
- High side-mode suppression ratio (SMSR) (>40 dB).
Advantages:
- Wavelength stability: Ideal for dense wavelength-division multiplexing (DWDM).
- Low chirp: Critical for high-speed modulation.
Applications:
DFB lasers are widely used in fiber optic communications, gas sensing, lidar, atomic clocks, and medical equipment. Within the optical communications industry, DFBs are typically employed in high-speed single-mode optical modules, suitable for medium-to-long-distance transmission applications.
EML
EML (Electro-Absorption Modulated Laser) integrates a DFB laser (continuous-wave source) and an electro-absorption modulator (EAM).
Modulation Mechanism:
- The DFB section operates under a constant bias current and provides stable, low-chirp light.
- The EAM modulates light intensity via the Franz-Keldysh effect (voltage-dependent absorption).
Advantages:
- High-speed modulation (up to 100 Gbps+).
- Low power consumption compared to externally modulated lasers.
Applications:
- Long-haul/coherent communications (e.g., 400G ZR modules).
- 5G fronthaul/data center interconnects (DCI).
