FOCUS RESEARCH NEWS
Researchers at Caltech have developed a new semiconductor laser that could transmit data at higher speeds along an optical fibre. The work could pave the way for faster broadband internet and other optical fibre communications. The new laser design has a much higher spectral purity than the semiconductor distributed-feedback (DFB) laser that is at the heart of today’s fibre optic communications. The new laser has more than 10 times the linewidth improvement compared to commercial semiconductor lasers, the researchers state, with a possibile further increase in coherence. The study, led by Dr Christos Santis and carried out in the laboratory of Amnon Yariv, a professor of electrical engineering at Caltech, was published in the online edition of the Proceedings of the National Academy of Sciences. The laser design incorporates a high-Q optical resonator as part of the laser cavity, which reduces noise. Some of the noise in commercial semiconductor lasers is due to spontaneous emissions from the semiconductor material, as the photons are both generated and stored in the same material. In the new design, the stored optical energy is removed by concentrating it in a passive low- loss material and incorporating the high-Q resonator in the laser cavity. The higher spectral purity of the
New laser design promises faster fibre optic broadband Although such quantum dot lasers
Currently, so-called ‘quantum
have been grown on silicon before, their performance has not equalled that of quantum dot lasers grown on their native substrates, which are platforms made of similar materials as the quantum dot lasers.
well’ lasers are used for data transmission. They consist of nanometre-thick layers of light- emitting material, representing the quantum well, sandwiched between other materials that serve to guide
both the injected electrical current as well as the output light. A quantum dot laser is similar, but the sheets of quantum well materials are replaced with a high density of smaller dots, each a few nanometres high and tens across.
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new Caltech laser design increases the data carrying capacity of fibre optic cables . Other work into using quantum dot lasers for high bandwidth data transmission is underway. At the OFC conference in March in San Francisco, researchers from the University of California at Santa Barbara discussed results from growing novel quantum dot lasers on silicon, which could be an important step towards making photonics compatible with the existing silicon microelectronics industry.
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www.lasercomponents.co.uk 26.02.2014 11:40:31
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