We irradiate the surface of pure fused silica with few-cycle pulses (duration < 10 fs, central wavelength at 800 nm, repetition of 400 kHz and a pulse energy of ca. 1 µJ) focused at a quasi grating incidence and observe a permanent densification in the irradiated region. A translation of the sample in the direction of the laser results in the direct writing of surface waveguides. The eigen modes of such structures exhibit a pronounced sensitivity to the refractive index of the immediate environment which we exploit to demonstrate direct refractive index sensing as well as plasmonic sensing.
Indistinguishable and/or entangled photons propagating in waveguide arrays (WAs) represent a promising platform whose utility ranges from research on fundamental aspects of quantum mechanics all the way to applications in quantum sensing and quantum information processing. Quantum simulators of decoherence reveal that while decoherence processes inevitably destroy single-particle coherence and any form of multiparticle entanglement, quantum correlations based on particle indistinguishability do endure. Further, by judiciously combining multi-photon states with the idea of synthetic dimensions in WAs yields the notion of a synthetic atom and in turn this provides entirely novel perspectives on the dynamics of such multi-photon states. Similarly, simple beam splitters fed with indistinguishable photons, can be used to perform discrete fractional Fourier transforms or can be tuned to realize exceptional points of any order. The latter setup facilitates efficient quantum-enhanced sensors.
Integrated nanophotonic circuits allow for realizing complex optical functionality in a compact and reproducible fashion through high-yield nanofabrication. Typically configured for single-mode operation in a single path, the optical propagation direction in such devices is determined by the waveguide layout which inherently requires smooth surfaces without scattering and restricts the device footprint to the limits of total internal reflection. Yet intentionally introducing disorder and scattering can be beneficial for the realization of novel nanophotonic components to overcome fabrication imperfections. Therefore, the understanding of the underlying physics of randomly disordered nanophotonic systems has gained increased attention. In particular on-chip spectrometers may benefit from random disorder. These devices are widely used tools in chemical and biological sensing, materials analysis and light source characterization. Conventional nanophotonic spectrometer designs are based on concepts using ring resonators, arrayed waveguide gratings or echelle gratings. Those devices are based on careful design and rely on high control of the fabrication and are therefore prone to fabrication errors and exhibit a very large footprint.
Here, as part of the priority program “Tailored Disorder” (SPP 1839), we utilize multi-path interference and the interaction of light with randomly oriented scatterers to realize broadband and narrow linewidth on-chip integrated spectrometers with small footprint. In combination with integrated superconducting nanowire single-photon detectors such devices allow for resolving optical spectra on the single photon level which is of interest for single-photon spectroscopy or quantum wavelength division multiplexing.
An essential device in opto-electronics is the optical waveguide. In the following we present a way to incorporate a waveguide field source into numerical time-domain simulations via the total field/scattered field technique. In particular, we develop a method by which we introduce a Gaussian light-pulse with the real eigenmodes of a slab waveguide into the nodal discontinuous Galerkin time-domain scheme.
Certain plasmonic and derived systems such as hyperbolic metamaterials promise large and broadband enhancements of the photonic density of states which, in turn, lead to corresponding enhancements of light-matter interaction. In this talk, recent theoretical advances regarding the most simple settings, i.e., planar materials and one- and zero-photon effects (spontaneous emission, Casimir-Polder force, and quantum friction) will be discussed with an emphasis regarding the appropriateness of different material models [1,2] and the validity of certain approximation schemes such as the Markov and the local thermal equilibrium approximation [3,4,5].
[1] F. Intravaia and K. Busch, Phys. Rev. A 91, 053836 (2015)
[2] D. Reiche et al., submitted
[3] F. Intravaia et al., Phys. Rev. Lett. 117, 100402 (2016)
[4] F. Intravaia et al., Phys. Rev. A 94, 042114 (2016)
[5] D. Reiche et al., submitted
We describe the treatment of thin conductive sheets within the Discontinuous Galerkin Time-Domain (DGTD) method for solving the Maxwell equations and apply this approach to the efficient computation of the optical properties of graphene-based systems. In particular, we show that a thin conductive sheet can be handled by incorporating the associated jump conditions of the electromagnetic field into the numerical flux of the DGTD approach. This results in a flexible and efficient numerical scheme that can be applied to a number of systems. Specifically, we show how to treat individual graphene sheets on substrates as well as finite stacks of alternating graphene and dielectric layers by modeling the dispersive and dissipative properties of graphene via a two-term critical-point model for its electrostatically doped conductivity.
We prepared thin film opal crystals and studied their angle-resolved transmission spectra in linear and circular polarized light as a function of the incidence angle and the azimuth rotation angle. We also explored the polarization conversion in linear and circular polarized light. Based on the spectra analysis we ascribed the polarization conversion in opal photonic crystal to properties of the Bloch modes of 3-dimensional photonic crystal.
We present a microscopic theory of thermal emission from truncated photonic crystals and show that spectral
emissivity and related quantities can be evaluated via standard bandstructure computations without any approximation.
We then analyze the origin of thermal radiation enhancement and suppression inside photonic crystals
and demonstrate that the central quantity that determines the thermal radiation characteristics such as intensity
and emissive power is the area of the iso-frequency surfaces and not the density of states as is generally assumed.
We also identify the physical mechanisms through which interfaces modify the potentially super-Planckian radiation
flow inside infinite photonic crystals, such that thermal emission from finite-sized samples is consistent with
the fundamental limits set by Planck's law. As an application, we further demonstrate that a judicious choice
of a photonic crystal's surface termination facilitates considerable control over both the spectral and angular
thermal emission properties. Finally, we outline design principles that allow the maximization of the radiation
flux, including effects associated with the isotropy of the effective Brillouin zone, photonic band gap size and
flatness of the band structure in the spectral range of interest.
While plasmonic nano-antennas typically have a rather basic shape, they still present
considerable challenges for numerical simlations. In particular, their small size (compared to the
wavelength) and their strong sensitivity to geometrical changes mandates a highly accurate spatial
discretization. In this work, we employ a nodal discontinuous Galerkin time-domain technique to
investigate the dependence of the fundamental resonance of rod-shaped nano-antennas on a number
of geometrical parameters.
Polarization anisotropy of the zero order forward-diffracted and the off-resonance transmitted light in the 3-dimensional
thin film opal photonic crystals has been numerically computed and experimentally measured. Studies of the
polarization anisotropy as a function of the incidence and azimuth angles of the incoming light have revealed strong
anisotropy changes at diffraction resonances and in the ranges of the multiple-band diffraction. The opposite sign of the
polarization anisotropy for different diffraction resonances has been observed. The cross-polarization coupling has been
measured and identified as one of the reasons for changing the anisotropy sign. The correlation of the lattice ordering and
the magnitude of the light polarization anisotropy has been demonstrated.
We apply the three-dimensional Discontinuous-Galerkin Time-Domain method to the investigation of the optical
properties of V-shaped metallic nanostructures on dielectric substrates. In particular, we study in detail the
possibility of controlling the spatiotemporal localization of radiation via chirped pulse excitations. Even for
rather small structures, we find significant deviations from predictions based on quasi-static theory.
We introduce an efficient Krylov-subspace based operator-exponential
approach for solving the Maxwell equations. This solver exhibits
excellent stability properties and high-order time-stepping
capabilities. The usage of a non-uniform spatial grid facilitates
the realization of a high-order spatial discretization in the presence of discontinuous material properties. This ideally complements the time-stepping capabilities of our solver so that many nonlinear wave propagation phenomena and/or coupled system dynamics in complex nano-photonic problems may be treated with high accuracy and efficiency.
We present a novel approach for the accurate and efficient modeling of photonic crystal-based integrated optical circuits. Within this approach, the electromagnetic field is expanded into an orthogonal basis of highly localized Wannier functions, which reduces Maxwell's equations to low-rank eigenvalue problems (for defect mode and waveguide dispersion calculations) or to sparse systems of linear equations (for transmission/reflection calculations through/from functional elements). We illustrate the construction of Wannier functions as well as the subsequent determination of defect modes, waveguide dispersion relations, and the characterization of functional elements for realistic two-dimensional photonic crystal structures consisting of square and triangular lattices of air pores in a high-index matrix. Moreover, on the basis of our Wannier function calculations we suggest a novel type of broad-band integrated photonic crystal circuits based on the infiltration of low-index materials such as liquid crystals or polymers into individual pores of these systems. We illustrate this concept through the design of several functional elements such as bends, beam splitters, and waveguide crossings.
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