Dr. Takeru Amano et al. of the Ultrafast Optoelectronic Device Group in the Photonics Research Institute (Director: Masanobu Watanabe) of the National Institute of Advanced Industrial Science and Technology (AIST, President: Hiroyuki Yoshikawa) have produced the highest density and most uniform quantum dots in the world. Using these quantum dots they have manufactured a communication semiconductor laser which has a large modal gain due to the high density.
Semiconductor lasers using quantum dots with high quantum efficiency have been thought to have promise as a new light source. However, because of their low dot density conventional quantum dot lasers do not have sufficient modal gain, and special structures such as high-reflection film mirrors and long resonators are necessary. This has made practical use of the quantum dot lasers difficult.
In this work, using As2 molecular beams developed at AIST, and gradient-composition strain relaxation layers, the world's first manufacturing of high density (1 x 1011 cm-2) and high uniformity (half width: 23 meV) quantum dots has been made possible. By applying the quantum dots to semiconductor lasers, we have succeeded in inducing laser oscillation at the 1.3 µm waveband without special laser structures. Furthermore, we have attained a modal gain characteristic of over 40 cm-1, the best in the world, using five stacked layers, which is less than half the conventional number of stacked layers (Fig.1). Hereafter, we will aim at high-speed operation. If, using the high density and high uniformity quantum dots we have developed, high-speed operation beyond 40 GHz, which is currently the fastest in the world, is theoretically possible.
Our invention is a breakthrough in techniques for developing quantum dot lasers capable of high-speed operation. We expect that if such high-speed quantum dot lasers can be made practicable, we will be able to enjoy high quality images, which need high speed communication to be delivered, at home.