Mahi R Singh

Mahi R Singh

University of Western Ontario

Title: The study of Acoustic-optical Nano-sensors for space exploration


Professor Mahi R. Singh received both his M.Sc. (1970) and PhD (1976) degrees from Banaras Hindu University, Varanasi, India in condensed matter physics. Consequently, he was awarded an Alexander von Humbold Fellowship in Stuttgart University, Germany from 1979 to 1981. Between 1981 and 1985 he was a Research Associate as well as a Lecturer at McGill University, Canada. During 1982 to 1983 he worked in INSA, Toulouse, France as a visiting scientist. In addition, he worked as a Research Associate at the University of North Carolina, Chapel Hill, USA. Following this he joined the University of Western Ontario, Canada as an Associate Professor in 1985. In 1995 he became a Full-Professor at UWO. He was a visiting professor at the University of Houston, USA from June to November in 1992. He also worked as a chief researcher at CRL HITACHI, Tokyo between November 1992 and May 1993. In the summer of 1993 and 1994, he was a visiting professor and Royal Society Professor at the University of Oxford, UK. Additionally, he was the director of the Centre of Chemical Physics at the University of Western Ontario, Canada. He also served as the director of the Theoretical Physics Program for many years at UWO. Dr. Singh has worked in many research areas of science and technology, He has published approximately 200 papers in international journals and has written several books which are used as text books at UWO. In addition, he has organized several international conferences and has been invited as a plenary and an invited speaker in several conferences around the world.


There is considerable interest in studying the quantum optics of photonic nanofibers due to their potential applications in subwavelength imaging, sensing and as photonic circuit elements. Generally photonic nanofibers are formed by embedding a dielectric material with a high-refractive index within another dielectric material with a low-refractive index. Here we introduce a polaritonic nanofiber fabricated by embedding a nanowire made from polaritonic materials within a dielectric photonic crystal. The polaritonic nanowire is also doped with an ensemble of quantum dots. Photons propagating in polaritonic materials undergo strong coupling with excitations in the material, forming quasiparticles known as polaritons. Two prominent types of polaritons formed are phonon- and exciton-polaritons. Phonon-polaritons are formed when photons couple with transverse optical phonons while exciton-polaritons are formed by the coupling of photons with excitons (electron-hole pairs). Photonic crystals are periodic dielectric structures which have band gaps in their photonic dispersion relations. The nanowire's size is chosen so that polaritonic modes in the nanowire lie within the band gap of photonic crystal. These modes do not propagate into the photonic crystal because there are no propagating states available within the band gap. Therefore polaritons are confined within the nanowire. This means that the nanofiber has localized modes and a very high Q-factor. Polaritonic materials have been widely studied due to their potential for developing new types of optoelectronic nanodevices. Polaritons propagate with frequencies in the range of gigahertz to terahertz (THz). This frequency range lies in an intermediate regime between the operating frequencies of photonic and electronic devices. Thus, the field of polaritonics bridges the gap between electronics and photonics. Currently, there are very few optical devices that operate at THz frequencies. Consequently, the present research in polaritonics will be exceptionally useful for developing new types of nanodevices. Exciton-polaritons have also attracted interest because they possess energies within the visible frequency range. Bose-Einstein condensation phenomenon has also been observed in polaritonic nanofibers. We have studied the acousto-optic effect in polaritonic nanofibers made by embedding a cylindrical polaritonic nanowire within a photonic crystal. The nanowire is doped with an ensemble of quantum dots. It is found that a phase transition occurs where the nanofiber transform to an ordinary dielectric material. It is also found that a quantum dot has a transparent state which can be switched ON or OFF by the external acoustic strain intensity. These results can be used to make new types of nano-sensors for the space applications.