A new laser generation

NEWS4_FIG3 OKLight allows transmitting a great quantity of information on optical fiber nets and, to exploit this potentiality at best, both in terms of speed and of transmission distances, the laser light that generates light signals must be spectrally pure, as much as possible consistent, that is to say close to a single frequency. Current optical nets are still based on lasers of S-DBF (distributed-feedback semiconductor) type, whose development dates back to the Seventies and which today start showing some limits due to the growing demand for broader bandwidth, determined by the exponential development of applications where the multimedia component is increasingly present. The particular longevity of this technology depends on the spectral purity of the generated signal, not overcome by other solutions, yet, despite the efforts of university researchers and corporate laboratories. It finally seems anyway that we can go beyond S-DBF lasers thanks to the recent results achieved by Caltech, the Institute of Technology of California, with an approach where nanotechnology is protagonist. In detail, at Caltech they succeeded in integrating a nanoscale-level ripple into the multilayer laser structure, actually, as researchers explain, the equivalent of the corrugated surface of a board to wash linens, which acts as internal filter against noisy waves that represent a sort of contamination that leads to the degradation of the purity of a single ideal frequency. The current S-DBF lasers provide for several continuous crystalline layers of materials belonging to the category called III-V semiconductor, generally Gallium Arsenide or Indium Phosphide, which convert into light the electrical current that is made to flow through the structure, but these materials absorb also light, phenomenon that is cause of degradation of the spectral purity. In the new lasers based on nanotechnology, still implemented with III-V semiconductors, the phenomenon of the light absorption does not occur but rather its concentration: as final effect, it is possible to obtain a 20 time “stricter” frequency range than what feasible with S-DBF lasers, resulting in a high spectral purity. These results will exert a remarkable impact on the development of the future optical fiber communication nets.

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