We present an experimental and theoretical study of the optical properties of metal-dielectric-metal structures with patterned top metallic surfaces, in the THz frequency range. When the thickness of ...the dielectric slab is very small with respect to the wavelength, these structures are able to support strongly localized electromagnetic modes, concentrated in the subwavelength metal-metal regions. We provide a detailed analysis of the physical mechanisms which give rise to these photonic modes. Furthermore, our model quantitatively predicts the resonance positions and their coupling to free space photons. We demonstrate that these structures provide an efficient and controllable way to convert the energy of far field propagating waves into near field energy.
The regime of ultrastrong light-matter interaction has been investigated theoretically and experimentally, using zero-dimensional electromagnetic resonators coupled with an electronic transition ...between two confined states of a semiconductor quantum well. We have measured a splitting between the coupled modes that amounts to 48% of the energy transition, the highest ratio ever observed in a light-matter coupled system. Our analysis, based on a microscopic quantum theory, shows that the nonlinear polariton splitting, a signature of this regime, is a dynamical effect arising from the self-interaction of the collective electronic polarization with its own emitted field.
The monolithic integration of novel nanomaterials with mature and established technologies has considerably widened the scope and potential of nanophotonics. For example, the integration of single ...semiconductor quantum dots into photonic crystals has enabled highly efficient single-photon sources. Recently, there has also been an increasing interest in using graphene - a single atomic layer of carbon - for optoelectronic devices. However, being an inherently weak optical absorber (only 2.3 % absorption), graphene has to be incorporated into a high-performance optical resonator or waveguide to increase the absorption and take full advantage of its unique optical properties. Here, we demonstrate that by monolithically integrating graphene with a Fabry-Perot microcavity, the optical absorption is 26-fold enhanced, reaching values >60 %. We present a graphene-based microcavity photodetector with record responsivity of 21 mA/W. Our approach can be applied to a variety of other graphene devices, such as electro-absorption modulators, variable optical attenuators, or light emitters, and provides a new route to graphene photonics with the potential for applications in communications, security, sensing and spectroscopy.
We have studied the coherent intercavity coupling of the evanescent fields of the whispering gallery modes of two terahertz quantum-cascade lasers implemented as microdisk cavities. The electrically ...pumped single-mode operating microcavities allow to electrically control the coherent mode coupling for proximity distances of the cavities up to 30-40 \mu\m. The optical emission of the strongest coupled photonic molecule can be perfectly switched by the electrical modulation of only one of the coupled microdisks. The threshold characteristics of the strongest coupled photonic molecule demonstrates the linear dependence of the gain of a quantum-cascade laser on the applied electric field.
We present the heteroepitaxial growth of wurtzite GaAs nanowhiskers on Si(111)-nanowire trunks forming hierarchical star-like structures with a six-fold symmetry, grown in the 0001 direction ...perpendicular to the Si-NW {112} facets.
A monolithic coupling scheme with two active waveguides merging into a single waveguide is presented for a mid-infrared GaAs/AlGaAs quantum cascade laser. The rapid development of unipolar quantum ...cascade lasers (QCLs) creates a basis for a broad variety of technological applications. Farfield patterns of the identical laser with a truncated mixing region result in a different superposition of the two modes with even and odd symmetry. In conclusion, the fraction of the even mode increases with increasing coupling length. The obtained results allow for designing coherent QCL Y-junctions, which open new possibilities for monolithic interferometric sensing devices.
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