Contacts:
Søren Stobbe, ssto@fotonik.dtu.dk, building 345A/170, tel. 4525-6383
Babak Vosoughi Lahijani, bala@fotonik.dtu.dk, building 345A/172, tel. 4525-3642
Background:
Optical confinement can be distinguished into two figures of merit: temporal confinement and spatial confinement. By confining photons for a long time to a very compact spatial region, the interaction between light and matter may be greatly enhanced, which is required for next-generation electronic-photonic integrated circuits. Until recently, it was believed that extreme spatial confinement could only be realized in metallic nanocavities but they suffer from losses and thus poor temporal confinement. On the other hand, dielectric cavities can have excellent temporal confinement but their spatial confinement was believed to be bound by the diffraction limit.
Recently, a new type of optical cavity has been invented that seems capable of getting the best of both worlds. They work by a novel mechanism that combine conventional cavity concepts with nanoantennas [1, 2]. Such an extreme confinement of light leads to a strong interaction of light with matter, which can open up a new variety of applications in generating, manipulating, and detecting light [3, 4]. Although the temporal and spatial confinement of light under a sole confinement mechanism have been studied thoroughly and understood very well, their interplay is not clear yet and many interesting aspects are surely still to be discovered. For example, a fundamental limit to the light-matter interaction in the optical near-field was recently discovered [5] and it would be of great interest to locate where the new optical cavity resides within those theoretical boundaries.
Project:
The purpose of this project is to study this new type of extremely confining cavities and to develop an understanding of the interplay between the two types of confinement. Finite-element numerical method will be used to calculate the temporal and spatial confinement of the cavity as well as to disclose the interplay between them. The developed understanding will be applied to design novel cavities. Depending on the progress and interests, the designed devices can be fabricated in the cleanroom and you can get access to our optical laboratories to carry out optical measurements. This is a challenging project that will allow you to get very close to cutting-edge research (the new cavities were first demonstrated in 2018 [3]).
References:
[1] S. Hu, and S. M. Weiss, Design of photonic crystal cavities for extreme light concentration, ACS photonics 3, 1647, (2016).
[2] F. Wang, R. E. Christiansen, Y. Yu, J. Mørk, and O. Sigmund, Maximizing the quality factor to mode volume ratio for ultra-small photonic crystal cavities, Appl. Phys. Lett. 113, 241101, (2018).
[3] S. Hu, M. Khater, R. Salas-Montiel, E. Kratschmer, S. Engelmann, W. MJ Green, and S. M. Weiss, Experimental realization of deep-subwavelength confinement in dielectric optical resonators, Sci. Adv. 4, eaat2355, (2018).
[4] H. Choi, M. Heuck, and D. Englund, Self-similar nanocavity design with ultrasmall mode volume for single-photon nonlinearities, Phys. Rev. Lett. 118, 223605, (2017).
[5] H. Shim, L. Fan, S. G. Johnson, O. D. Miller, Fundamental Limits to Near-Field Optical Response over Any Bandwidth, Phys. Rev. X. 9, 011043, (2019).