On-going research activities

Here is listed the current research activities in the SEM group.

[1] 2D materials for integrated photonics

Silicon based optical interconnects offer a promising solution to solve the communication bottleneck faced by the electric interconnects, and intensive efforts have been devoted to developing compact integrated photonic elements including laser source and photodetector. However, due to indirect bandgap of silicon, these devices are often realized by integrating other gain materials, e.g., germanium or III-V compound semiconductor, thus leaving us a big challenge for reducing the fabrication cost and direct monolithic integration with CMOS technology. Two dimensional (2D) layered materials, such as graphene and transition-metal dichalcogenides (TMDC), have shown great potential to realize components that can easily be integrated with Si devices. This project is to explore and develop a novel class of lasers and photodetectors relying on two-dimensional materials integrated with silicon photonic chip, which is CMOS-compatible, and suitable for chip-level integration.            

Contact Person: Sanshui Xiao, saxi@fotonik.dtu.dk;

Related publications:

[1] Y. Ding, et. al., Ultra-compact integrated graphene plasmonic photodetector with bandwidth over 110 GHz, Nanophotonics, accepted (2019).
[2] Y. Ding, et. al., Efficient electro-optic modulation in low-loss graphene plasmonic slot waveguides, Nanoscale, 9, 15576 (2017).
[3] S. Yan, et. al.,  Slow-light-enhanced energy efficiency for graphene microheaters on silicon photonic crystal waveguides
, Nature Communications, 8, 14411 (2017).
[4]Y. Ding, et. al., Effective electro-optical modulation with high extinction ratio by a grapheme-silicon microring resonator, Nano. Lett., 15, 4393 (2015).  

[2] Graphene plasmonics
grapheneThe field of graphene plasmonics is a novel, emerging research field at the intersection of condensed matter physics and photonics or more precisely, at the intersection between graphene physics and plasmonics. This field offers the promise of tunable plasmonic excitations - a tunability that is unavailable in the e.g. the widely studied field of metal plasmonics. In this project, we aim to study the properties of graphene plasmons theoretically in a range of finite and semi-infinite structures and to investigate potential applications in nanosensing and optoelectronics.

Contact Persons: Sanshui Xiao, saxi@fotonik.dtu.dk, Martijn Wubs, mwubs@fotonik.dtu.dk

Related publications:
[1] X. Zhu, et. al., "Bends and splitters in graphene nanoribbon waveguides", Opt. Express, 21, 3486 (2013). 
[2] X. Zhu, et. al., "Experimental observation of plasmons in a graphene monolayer resting on a two-dimensional subwavelength silicon grating", Appl. Phys. Lett., 102, 131101 (2013).

[3] Quantum effects in nanoplasmonic metal structures 
quantum plasmonicsMiniaturization of photonic and plasmonic circuits is inevitable in the future, and there is therefore a need for a deeper understanding of the interaction between electromagnetic waves and matter, when objects are much smaller than the wavelength of the waves, i.e. on the order of 10 nm. The appearance of quantum mechanical effects in plasmons are anticipated at these size scales, and therefore the ability to experimentally probe and theoretically explain these quantum effects is of increasing importance. To this end, we use the superb spatial resolution capabilities of transmission electron microscopes at DTU Cen to probe the metallic nanostructures, while we theoretically include quantum effects in a semiclassical treatment based on the so-called hydrodynamic Drude model for the free electrons in metals. With this perfect combination, we are capable of calculating and measuring quantum mechanical effects in plasmons.

Contact Persons: Nicolas Stengers, niste@fotonik.dtu.dk.

Related publications:
[1] S. Raza, et. al., "Unusual resonances in nanoplasmonic structures due to nonlocal response", Phys. Rev. B, 84, 121412 (R), 2011. 
[2] G. Toscano, et. al., "Modified field enhancement in plasmonic nanowire dimers due to nonlocal response", Opt. Express, 20, 4176 (2012).
[3] G. Toscano, et. al., , "Surface-enhanced Raman spectroscopy (SERS): nonlocal limitations", Opt. Lett., 37, 2538 (2012).
[4] G. Toscano, et. al.,, "Nonlocal response in plasmonic waveguiding with extreme light confinement", Nanophotonics, 2, 106 (2013). 
[5] S. Raza, et. al., "Nonlocal response in thin-film waveguides: loss versus nonlocality and breaking of complementarity", Phys. Rev. B 88, 115401 (2013).

[4] Quantum optics of metamaterials
QOMetamaterials are engineered materials with optical properties often not occurring in nature. They have unit cells much smaller than an optical wavelength. Their optical properties can be described by effective parameters such as the effective refractive index. Most metamaterials are designed to interact with classical light. We study the use of metamaterials to transport and modify quantum states of light, for example squeezed light or single photons, and ask questions like: (1) Are the metamaterials also useful in quantum optics? (2) Do we need to modify the effective description of the metamaterial? (3) Are there new fundamental limits in the use of metamaterials in quantum optics?

Contact person: Martijn Wubs, mwubs@fotonik.dtu.dk

Related publication:
[1] E. Amooghorban, et. al., "Quantum optical effective-medium theory for loss-compensated metamaterials", Phys. Rev. Lett., 110, 153602 (2013).