How to classify laser diodes
Laser diodes are classified based on emission direction, cavity structure, mode operation, and wavelength control, with major types including edge-emitting, VCSEL, DFB, and external-cavity lasers.
Classification by Emission Direction
- Edge-Emitting Diode Lasers (EELs): Emit light from the edge of the semiconductor chip, parallel to the surface. They typically use materials like GaAs, InP, or GaN and are suitable for high-power applications .
- Vertical-Cavity Surface-Emitting Lasers (VCSELs): Emit light perpendicular to the chip surface. They feature a vertical cavity with distributed Bragg reflector mirrors and often include quantum wells in the active region. VCSELs have low threshold currents, circular beam profiles, and are ideal for fiber-optic coupling .
Classification by Cavity and Feedback
- Distributed Feedback (DFB) Lasers: Incorporate a grating within the cavity to provide wavelength-selective feedback, producing narrow linewidth and stable single-mode operation. Common in telecommunications .
- External-Cavity Diode Lasers (ECDLs): Use an external optical cavity with mirrors or diffraction gratings to control wavelength and linewidth. They offer high tunability and spectral purity for precision applications .
Classification by Mode Operation
- Single-Mode Lasers: Emit a single spatial or longitudinal mode, providing high coherence and narrow beam divergence. Used in spectroscopy, metrology, and optical communications .
- Multi-Mode Lasers: Emit multiple modes, producing higher output power but lower coherence. Suitable for applications like laser printing, scanning, and illumination .
Classification by Pumping Method
- Electrically Pumped Laser Diodes: Most common type, using a p–n or p–i–n junction to inject carriers into the active region, generating light through stimulated emission .
- Optically Pumped Semiconductor Lasers (OPSLs): Use another laser as a pump source to excite the gain medium. OPSLs allow flexible wavelength selection and stable beam parameters .
Other Considerations
- Quantum Well and Heterostructure Designs: Modern laser diodes often use double-heterostructures or quantum wells to confine carriers and photons, improving efficiency and lowering threshold currents .
- Wavelength and Power Classification: Diodes are also categorized by emission wavelength (visible, near-infrared, mid-infrared) and output power, which are determined by material choice, junction design, and cavity structure . In summary, laser diodes are classified by emission geometry, cavity design, mode structure, pumping method, and material properties, with each classification tailored to specific applications ranging from telecommunications and data storage to medical and industrial uses .
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