distributed feedback laser abbr., DFB laser (rus. лазер с распределенной обратной связью abbr., РОС лазер) — injection semiconductor laser, in which the feedback is produced by light waves reflection from a periodic lattice generated in the active medium.

Description

In the injection heterolasers with distributed feedback (DFB lasers) to create a feedback one of the heterointerfaces is corrugated, which creates a periodic variation in the refractive index and leads to an interference reflection (see Fig.). The lattice period  is selected so as to ensure satisfaction of the Bragg condition for the reflections in the opposite direction:

,

where is the wavelength of light in vacuum, is the effective refractive index of the active region, is the lattice period. The lattice period is of the order of 100 nm (in gallium arsenide laser, for example, it is 130 nm).

The condition of reflection from the periodic structure is satisfied for the beams propagating in both directions. Thus, the periodic lattice creates feedback in both directions, distributed along the entire length of the laser. Since the feedback produced by the periodic lattice is selective, the DFB laser operates in the single-mode generation regime.

DFB lasers can be placed directly onto the surface of a semiconductor substrate and connected to waveguides on the surface of the substrate to create photonic integrated circuits.

The most effective alignment between a DFB laser and a channel waveguide is achieved in DFB lasers with separate optical and electron confinement in double heterostructures (SCDH DFB lasers).

DFB lasers are characterised by temperature stability of the oscillation frequency, which is uniquely determined by the optical lattice period. The temperature dependence coefficient of the emission wavelength in a typical DFB laser is 0.1 nm/deg; it is determined by the temperature dependence of the refractive index. This makes it possible to tune the radiation frequency by adding a temperature control unit to the laser. Such simplicity of design is a very significant advantage of tunable DFB lasers. Yet, the major drawback of these lasers is the limited frequency tuning range.

Integrated one-piece designs containing a grid of multiple DFB-lasers combined in one unit allow the tuning range to be increased. Thus, a block of eight parallel DFB lasers integrated by a multi-mode waveguide coupler (MMI) enables a tuning range of up to 60 nm. To increase the power output of the tunable laser it is equipped with an amplifier. Various designs of multi-element tunable lasers with the number of elementary DFB lasers in the lattice ranging from 2 to 8 have already been developed and studied.

Illustrations

Optical arrangement of a distributed feedback semiconductor laser. HR — high reflection ratio mir

Optical arrangement of a distributed feedback semiconductor laser. HR — high reflection ratio mirror; AR — antireflection coating.


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. Ackerman D. A. et al. Telecommunication lasers / Ed. by I. P. Kaminow, T. Li. — Optical fiber telecommunications, IV A, 2002. P. 587–665.
  3. Pikhtin A.N. Optical and Quantum Electronics (in Russian) — Мoscow: Vysshaja shkola, 2001. — 573 pp.
  4. Zvelto O. Principles of lasers. — New York: Plenum, 1982. — 720 pp.
  5. Nanijj O. E. Optical transmitters with tunable wavelength for DWDM-networks. P. 2 (in Russian)// Lightwave Russian Edition. 2006. №3. 53–56 pp.

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