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Edge-emitting Semiconductor Lasers

Definition: semiconductor lasers emitting light along the plane of the wafer

Alternative term: in-plane lasers

More general term: semiconductor lasers

German: kantenemittierende Halbleiterlaser

Category: laser devices and laser physicslaser devices and laser physics


Cite the article using its DOI: https://doi.org/10.61835/3z7

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Semiconductor lasers can be grouped into two classes:

  • Edge-emitting lasers (also called in-plane lasers), where the laser light propagates in a direction along the wafer surface of the semiconductor chip, from which the laser is made. The light is usually reflected or coupled out at a cleaved edge.
  • Surface-emitting lasers, where the light propagates in the direction perpendicular to the semiconductor wafer surface.
broad area laser diode
Figure 1: Edge-emitting semiconductor laser.

Edge-emitting lasers are the original and still very widely used form of semiconductor lasers. Their resonator length is typically between a few hundred micrometers and a few millimeters. This is sufficient for reaching a high gain, so that an edge-emitting laser may lase even if the resonator losses are fairly high, e.g. when the end faces (edges) are not coated and there is only the Fresnel reflection of the semiconductor/air interfaces.

Within the edge-emitting laser structure, the laser beam is guided in a waveguide structure. Typically, one uses a double heterostructure, which restricts the generated carriers (electrons and holes) to a narrow region and at the same time serves as a waveguide for the optical field. Such an arrangement leads to a low threshold pump power and a high efficiency.

Depending on the waveguide properties, particularly its transverse dimensions, it is possible either to obtain an output with high beam quality but limited output power (some hundreds of milliwatts), or (with a broad-area laser diode) an output with high output power (tens of watts or even more than 100 W) but with poor beam quality.

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Questions and Comments from Users


Are ruby lasers edge emitting?

The author's answer:

No – this concept has been developed for semiconductor lasers, not for bulk lasers like ruby lasers.


Are edge-emitting semiconductor lasers polarized?

The author's answer:

Yes, you usually get linearly polarized emission.


I wonder how light can propagate through the semiconductor. Most semiconductors I know are fairly opaque in the optical region. In addition to that, free carriers are generated in the material and they should have a significant screening effect.

The author's answer:

These materials are totally opaque in the visible spectral region, but not in the infrared. Free carriers are hardly generated; most excited carriers are in the valence band, where they are not free.

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