vertical cavity surface emitting laser abbr., VCSEL (rus. лазер с вертикальным резонатором otherwise поверхностно-излучающий лазер) — injection semiconductor laser, whose cavity mirrors in the form of one-dimensional photonic crystals are located above and below the active region of quantum-well heterostructures.

Description

Large gain values (see semiconductor laser) achievable in quantum heterostructures make it possible to create lasers with a very short length of the active medium, in which radiation is emitted not from the end of the heterojunction, but from its surface. Such lasers were called “vertical cavity lasers” because of the arrangement of their main elements (see Fig.). In contrast to traditional geometry lasers, in vertical cavity lasers the cavity axis is perpendicular to the plane of the heterostructure, and the length of the active region, which is equal to the thickness of the heterostructure, is very small (usually several micrometres). The cavity mirrors are applied on the radiating surfaces, through which passes the electrical current. They are made in the form of alternating quarter-wave layers with different refractive indices.

In vertical cavity lasers the maximum gain should be provided in the direction perpendicular to the heterojunction, and in the junction plane it should be suppressed. Since the effective gain of the active medium should exceed 1,000 cm-1, double heterostructure containing a set of quantum wells, quantum wires or quantum dots are used in the active region. The use of quantum wires is potentially very promising because they can provide high gain in the direction of their axes. However, the technology of obtaining active media based on quantum wires of the required quality has not yet been fully developed. Therefore, the active region of vertical cavity lasers usually contains either a set of quantum wells or quantum dots that are often grouped into vertically coupled quantum dots.

By reducing the aperture of the work area in vertical cavity lasers it is possible to select a single transverse mode with a coefficient of suppression of side modes exceeding 20 dB. However, reducing the work area limits the achievable output power, whose typical values lie in the range of tenths of a milliwatt.

The cavity in vertical cavity lasers is only several wavelengths long. The distance between the longitudinal modes is large, which facilitates the operation of the laser in the single frequency mode.

A major advantage of these lasers is the possibility of mass production and testing, because several hundred lasers can be manufactured simultaneously on a single semiconductor chip.

Illustrations

Vertical
  cavity surface emission semiconductor laser [1].
Vertical cavity surface emission semiconductor laser [1].

Authors

  • Nanii Oleg E.
  • Pavlova Elena G.

Sources

  1. Nanijj O. E. Optical transmitters (in Russin) // Lightwave Russian Edition. 2003. №2. 48–51 pp.
  2. Pikhtin A.N. Optical and Quantum Electronics (in Russian) — Мoscow: Vysshaja shkola, 2001. — 573 pp.

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