Orbital angular momentum microlaser (Published in Science, 2016, n. 353, pp. 464-467). A semiconductor laser of micrometric size that produces twisted light by exploiting an “exceptional quantum point”: this is the study that won the fifth edition of the Aspen Institute Italia Award for collaboration and scientific research between Italy and the United States. The research stems from the joint work of seven scientists belonging to three different scientific organizations. It represents important progress in the physics and technology of integrated semiconductor lasers. The orbital angular momentum laser conceived and manufactured by the US-Italy team is a key element in the generation of twisted light, which can revolutionize the current optical communication systems and allow the transmission of information at very high speed – something that is necessary to sustain the forthcoming fourth industrial revolution.
The authors of the research project are the following:
Stefano Longhi 1, 2
Liang Feng 3
Natalia M. Litchinitser 3
Pei Miao 3
Jingbo Sun 3
Wiktor Walasik 3
Zhifeng Zhang 3
¹ Department of Physics, Politecnico di Milano, Milan, Italy
2 Istituto di Fotonica e Nanotecnologie, National Research Council (CNR), Milan, Italy
3 Department of Electrical Engineering, The State University of New York at Buffalo, Buffalo, NY, USA
The originality of the research is the ideation and realization of a miniaturized laser. This miniscule laser – of just a few micrometers – operates in a so-called exceptional quantum point, where the emitted light twists rapidly in propagation. The light oscillates at different frequencies (colors), and for each frequency it can be twisted a limited number of times, giving rise to a swirling wave (as in the vortices of water that form in a drain). An optical vortex carries what physicists call the orbital angular momentum of the photon. Vortex light is of a topological nature and is therefore extremely robust. Like the frequency of light, twisted light beams can be used to encode the information to be sent on optical fiber. The possibility of encoding information (bits) in the swirling motion of light, as well as in its color, allows for a significant increase in the amount of information transmitted at each individual frequency. Therefore, it is expected to revolutionize optical communication systems in the near future, with foreseeable outstanding impacts both on the economy and on society. The need for ever faster and higher information flows is in fact essential to sustain the so-called fourth industrial revolution and to strengthen growing connections among physical, digital and biological worlds.
As demonstrated in this research project, the ability to generate twisted light directly from a very small laser device, with semiconductor technology that is compatible with current optical communication systems, represents a fundamental result for the development of the next generation of optical communication systems with a very high bit rate. The laser manufactured by the US-Italy team is a small ring of optically-pumped semiconductor material on which particular corrugations are made. Along the ring, light can propagate in both directions – clockwise and counterclockwise – so that the light extracted from the device is generally free of vorticity. The main idea of the work is to exploit the properties of the quantum exceptional points, which are special mathematical singularities created here by means of suitable metallizations along the ring. At a quantum exceptional point, circulation of light occurs stably in one direction only. The light extracted from the ring, by means of a second corrugation (optical grating), shows a vorticity (topological charge) that can be suitably varied and used to encode information.