The Nano & Quantum Optics group at the Institute of Applied Physics targets to explore and understand the properties of nanoscale matter and objects and their interaction with photons. Some of the most recent research highlights are:

 SPDC_spectroscopy_250x250   Waveguides for integrated SPDC spectroscopy

Spontaneous parametric down-conversion (SPDC) spectroscopy using photon pairs is a promising avenue towards affordable mid-infrared (MIR) spectroscopy. Here, we experimentally investigate the feasibility of using periodically poled waveguides in lithium niobate for SPDC spectroscopy applications. We find the waveguides suitable to generate wavelength non-degenerate photon pairs with one photon in the MIR spectral range with high fluence. We use this to determine the cutoff wavelengths of the waveguide mode in the MIR by performing only measurements in the near-infrared spectral range.

Published in APL Photonics 3, 021301 (2018) >>>more
Featured in Nature Photonics 12, 189 (2018) >>>more
 image_telecom_nano_250x250   Routing of telecom signals with waveguide-integrated nanoantennas

Optical nanoantennas are uniquely suited to control the propagation of light. Here we show together with collaborators from the Australian National University, that a single gold nanoantenna integrated on a silicon waveguide can be used to sort optical signals into different output modes and propagation directions based on the input polarization. We demonstrate, that this is even possible for modulated signals used in telecom applications without measurable impairment of the signal quality.

Published in Science Advances 3, e1700007 (2017)>>>more
 SPDC_backward_Bell   Path-entangled photon pairs from periodic waveguides

Photon pairs entangled in the path degree of freedom are uniquely suited for qubit encoding in integrated optical platforms. In our work, using the unique properties of Bloch modes, we propose a general scheme for direct and fully integrated generation of counterpropagating photon pairs in a single periodic waveguide, entangled in the propagation direction. We numerically demonstrate the Bell state generation with a design in a lithium niobate photonic crystal slab waveguide.

Published in Physical Review Letters 118, 183603 (2017)>>>more
 SPDC_coupler_web250x250    Tunable source of entangled photon states

For the practical implementation of on-chip integrated quantum light sources for quantum information applications, it is crucial to develop sources delivering entangled quantum photon states with on-demand tunability. Together witch co-workers from Australia we developed and experimentally demonstrated an integrated all-optically tunable source based on spontaneous parametric down-conversion in two coupled waveguides. We experimentally demonstrated the control of entanglement and spatial shape of the generated two-photon states.

Published in Laser & Photonics Review 10, 131 (2016) >>> more


Nonlinear coupling in optical waveguide arrays

We experimentally demonstrate nonlinear coupling between optical waveguides, where the rate of energy exchange between neighboring waveguides depends nonlinearly on the optical power. Using discrete waveguide arrays, i.e. regular chains of weakly coupled waveguides, we show the profound impact of such nonlinear coupling on second-harmonic generation. In particular, we find a peculiar dependence of the generated second-harmonic power on the symmetry and the propagation direction of the exciting beam.

Published in Phys. Rev. A 92, 043832 (2015) >>> more

Radially polarized SPP in plasmonic tip_web250x250

Superfocusing of radially polarized conical surface plasmon polaritons

By employing superfocusing of surface plasmon polaritons (SPP) a sharp metallic tip enables efficient detection of optical nearfields and nano-objects with ultrahigh spatial resolution. We demonstrated experimentally the excitation and superfocusing of radially polarized SPP in a fully metal-coated conically tapered M-profile fiber (concentric double-core fiber) tip. In this structure, the radially polarized waveguide mode, propagating inside the fiber, resonantly excites the radially polarized SPP on the metal surface that consequently superfocuses at the apex generating strong field oscillating longitudinally along the tip axis.

Published in ACS Photon. 2, 1468 (2015) >>> more


Enhanced second-harmonic generation from gold nanorings filled with lithium niobate

Lightsources localized in nanometer volumes are important for several applications ranging from fluorescence spectroscopy to quantum communications. A flexible way to generate light at almost any desired frequency is by parametric nonlinear effects as e.g. second-harmonic generation. We experimentally demonstrate enhanced second-harmonic generation in gold nanorings filled with lithium niobate. We make use of the plasmonic resonances of the gold, which concentrate the fields inside the nanorings where it efficiently interacts with lithium niobate and achieve enhancement factors around 20 with respect to unpatterned lithium niobate.

Published in Nano Lett. 15, 1025 (2015) >>> more

Huygens nanosurfaces_web

All-dielectric Huygens' nanosurfaces

Resonant optical nanosurfaces tailored to impose a spatially variant phase shift onto an incident wavefront have developed as a breakthrough concept for advanced wave-front engineering. However, reflection and/or absorption losses as well as low polarization-conversion efficiencies pose a fundamental obstacle for achieving the high transmission efficiencies that are required for practical applications. We showed that all-dielectric nanosurfaces with high efficiency and full phase coverage in transmission can be realized at NIR frequencies using arrays of silicon nanodisks with crossed electric and magnetic dipole resonances. If these resonances are brought into spectral overlap, the nanodisks emulate the behavior of the forward-propagating elementary wavelets known from Huygens' principle. All-dielectric Huygens' nanosurfaces offer unique opportunities for flat optical devices, including beam-steering, beam-shaping, and focusing, as well as holography and dispersion control.

Published in Adv. Mater. 24, 813 (2015) >>> more


Realization of lithium niobate nanowaveguides

Nanoscale nonlinear waveguides are fundamental building blocks for high density integrated optics. For applications making use of frequency conversion, lithium niobate is an ideal substrate material. We fabricated mm-long waveguides with cross-sections below 1 µm² in lithium niobate using the potassium hydroxide-assisted ion-beam enhanced etching technique. Waveguide widths as low as 200 nm were realized, demonstrating precise control over the geometrical parameters of the waveguide, which is crucial to achieve modal phase-matching. We experimentally demonstrated efficient second-harmonic generation for a phase-matched waveguide.

Published in Opt. Lett. 40, 2715 (2015) >>> more


Nonclassical biphoton generation via quantum walks in a nonlinear waveguide array

Nonclassical quantum states of several photons with strong entanglement are a key to the optical realization of quantum phenomena which can be used for unbreakable cryptography and powerful computational algorithms. The practical implementation of such complex applications requires stable quantum interference as well as the minimization of coupling losses. We experimentally demonstrated a nonlinear optical chip based on an array of coupled waveguides as a flexible integrated platform that achieves these requirements. Using nonlinearly driven quantum walks our approach allows for the generation of entangled photon pairs with reconfigurable nonclassical correlations.

Published in Phys. Rev. X 4, 031007 (2014) >>> more


Plasmonic near-fields explored by two SNOM tips

A long-standing issue of nanooptics lies in the fact that the electromagnetic near-fields around subwavelength structures are fully vectorial in nature. In consequence, the classical notion of polarization of electromagnetic radiation is generally not applicable in the near-field. In our most recent work we have studied the polarization characteristics of light emission and collection in the near field by a unique setup consisting of two scanning near-field optical microscopes (SNOMs). For the first time, the mapping of different polarization components of a plasmonic dipole pattern emitted by an aperture probe was demonstrated.

Published in Nano Lett. 14, 5010 (2014) >>> more


Order-disorder-transitions in photonic metasurfaces

Understanding the impact of order and disorder is of fundamental importance to perceive and to appreciate the functionality of modern photonic metasurfaces. Together with coworkers from Europe and Australia, we have investigated photonic metasurfaces with different lattice arrangements and uncovered the influence of lattice disorder on their electromagnetic properties at the full angular spectrum.

Published in Sci. Rep. 4, 4484 (2014) >>> more


Vortex Light Bullets - Self-trapped Light with a Twist

In a recent series of breakthrough experiments researchers from Jena have observed the most complex spatiotemporally self-confined solitary wave. In their experiments light, which propagates through a fiber array, was found to withstand linear broadening due to dispersion and diffraction and at the same time rotate around a center of symmetry in a cohesive manner. These nonlinear wavepackets are hence termed Vortex Light Bullets. They exhibit a striking level of internal dynamics and interact in a complex manner with asymmetries present in their surroundings and pave the way for a better understanding of spatiotemporal dynamics of nonlinear waves.

Published in Phys. Rev. X 3, 041031 (2013) >>> more
Featured as a highlight in Nature Photon. 8, 169 (2014) >>> more


Cavity Optical Pulse Extraction - Building Lasers with Hawking Radiation

The interaction of ultrashort, high-power pulses with slow light stored in resonant structures leads to the study of non-stationary optics. Researchers from Jena, in collaboration with researchers from Australia, have shown that non-stationary optics has the potential to lead to the development of sources of pulsed radiation without the need for pulsed laser sources. Structurally non-stationary optics is related to wave mechanics in warped space-time and therefore opens a path towards laboratory cosmology and gravito-quantum-electrodynamics.

Published in Sci. Rep. 3, 2607 (2013) >>> more


Metamaterials for spatial and spectral light shaping

Plasmonic metamaterials open up new possibilities for the design of diffractive elements and holograms. These materials strongly interact with light and already an ultra-thin layer allows for comprehensive modulation of light amplitude and phase. Variations in the geometry of the metamaterial are used to adjust the local transmission and dispersion properties in order to shape light spatially and spectrally. Based on the fishnet metamaterial we constructed a computer-generated hologram which projects different images at two distinct wavelengths in the near infrared.

Published in Adv. Mater. 24, 6300 (2012) >>> more
Featured on the front cover of Adv. Mater. >>> more
Featured as a highlight of Advances in Engineering >>> more
Featured as a highlight of Renewable Energy Global Innovations >>> more


Nanowires shine bright

Optically excited nanostructures usually elude the observability of their characteristic light distribution patterns unless involved and time-consuming near-field microscopy is applied. In our recent work we present a novel method which permits sensing the infrared near-field in GaAs nanowires in the far-field. Collecting their second harmonic generated signal, guided wave patterns along the nanowires are precisely mapped. Our approach opens promising paths for the characterization and advancement of nanoscale optical devices, like e.g. nanolasers.

Published in Nano Lett. 12, 5412 (2012) >>> more


Giant optical activity of loop-wire metamaterials

A metamaterial with a three dimensional chiral unit cell shows an optical activity in the VIS/NIR spectral range which exceeds by far any natural material. Based on a combined spectroscopic and interferometric characterization, the entire complex transmission response in terms of a Jones matrix is disclosed. The polarization output state of light after propagation through the nanostructures can be decoded for any excitation configuration. The rotation of the polarization azimuth of linearly polarized light exceeds 50° at wavelengths around 1.08 μm.

Published in Nano Lett. 11, 4400 (2011) >>> more
Read German reprint article in: Photonik 2, 40 (2012) >>> more
or Photonik International 1, 21 (2012) >>> more


Observation of non-diffracting Airy plasmons

Even though diffraction is a ubiquitous process in nature, non-diffracting 2D beams, i.e. Airy plasmons, have been generated at nanostructured gold surfaces. These self accelerating Airy plasmons are excited by an engineered nanoscale phase grating. The Airy plasmon demonstrates significant beam bending and was observed by scanning nearfield optical microscopy. Their self-healing properties, suggest novel applications in plasmonic circuitry and surface optical manipulation.

Published in Phys. Rev. Lett. 107, 116802 (2011) >>> more
Read viewpoint by Salandrino and Christodoulides >>> more


At last! The observation of the light bullet

The long quest for the light bullet finds its end by their unambiguous experimental observation in microstructured fibers. Light Bullets are wave packets that are localized in all three dimensions (3D) as they propagate in space or evolve in time. Stringent evidence of the excitation of light bullets is based on time-gated images and spectra which perfectly match numerical simulations. A novel adiabatic evolution mechanism is revealed which eventually is also responsible for their decay.

Published in Phys. Rev. Lett. 105, 263901 (2010) >>> more
Read viewpoint by Frank Wise >>> more