Martin Wegener

EXPERIMENTS ON THE DEPOLARIZATION NEAR-FIELD SCANNING OPTICAL MICROSCOPE

We demonstrate the operation of an apparatus which we call the depolarization near-field scanning optical microscope. It delivers subwavelength resolution with uncoated optical fiber tips without the need for additional modulation techniques. We show that—in the near field—the edges perpendicular to the incident optical polarization are imaged. This dependence on the orientation of the linear polarization as well as the influence of small ellipticities of the polarization state on the imaging process are measured on a well-defined test sample. The transition from near- to far-field imaging as a function of the tip height is demonstrated. The results are in good agreement with recent theoretical predictions.

COMPUTER SIMULATIONS ON NEAR-FIELD SCANNING OPTICAL MICROSCOPY : CAN SUBWAVELENGTH RESOLUTION BE OBTAINED USING UNCOATED OPTICAL FIBER PROBES?

Recent experiments claim that subwavelength resolution can be obtained with an optical scanning microscope using uncoated optical fiber probes. In these experiments, linearly polarized light is sent down the fiber which is reflected and depolarized in the tip-sample region. The internally reflected signal in the orthogonal polarization is detected. Here, numerical solutions of the vector Maxwell equations for a model are discussed. In this model, subwavelength resolution can indeed be obtained in the above mode, while this is not possible without polarization sensitivity. The influence of parameters such as polarization, different scanning modes and tip-sample distance is discussed.

Polarisation dependent coupling in ring resonator filters

We observed a strong polarisation dependence of the coupling between a straight dielectric strip and a ring waveguide. Based on measurements, we explain this behaviour with numerical and analytical vector-field models for a wedge-type inhomogeneity.

Chiral 3D Photonic Crystals as Compact Optical Isolators

We present a novel photonic heterostructure based on chiral 3D photonic crystals allowing for non-reciprocal transmission of light. We fabricate various corresponding structures by means of direct laser writing.

Towards diffraction-unlimited three-dimensional laser lithography

Direct laser writing optical lithography combined with a photo-induced depletion mechanism and tailored depletion-laser foci allows for the fabrication of three-dimensional polymer structures with feature sizes below the diffraction limit. We analyze the scaling of the lateral linewidth with increasing depletion power and compare two photoinitiators suitable for such high-resolution lithography.

Polarizing properties of three-dimensional helical metamaterials

We investigate the polarizing properties of chiral photonic metamaterials composed of three-dimensional metal helices. The calculated spectra reveal pronounced circular dichroism. Our geometry parameters are compatible with fabrication via direct laser writing and electrodeposition.

Three-dimensional photonic band gap structures made by direct laser writing and silicon single-inversion

We realize a variety of silicon photonic crystal structures. Direct laser writing of polymeric templates (square/circular spirals and slanted pore structures) combined with a silicon single-inversion procedure leads to band gaps in the near infrared.

Three-dimensional chiral photonic crystals by direct laser writing

We review our recent work on three-dimensional chiral photonic crystals. High-quality polymeric three-dimensional spiral and layer-by-layer photonic crystals are fabricated via direct laser writing. Polarization stop bands for circularly polarized light are observed, leading up to a suppression of a factor 52 for one circular polarization with respect to the other. The transmittance for the passing polarization is as high as 95 % . These chiral elements are sandwiched between one-dimensional lamellae structures acting as quarterwave plates to form thin-film polarizers, which can be operated under perpendicular incidence.

Three‐dimensional Photonic Quasicrystals: Fabrication and Characterization

Quasicrystals are neither crystalline nor amorphous solids. They are aesthetically highly appealing and posses intriguing physical properties. Recently, three‐dimensional photonic quasicrystals have become available for the near‐infrared spectral region through nanofabrication. This opens the way for photonic transport measurements to understand the influence of symmetry onto transport properties. In this article we describe the fabrication via direct laser writing and silicon single inversion and the optical characterization via Laue‐diffraction experiments.

Silicon double inversion of polymeric templates: a new route towards three-dimensional photonic bandgap materials

We present the successful silicon double inversion of direct laser written polymer templates for three-dimensional (3D) photonic crystals. Combined with plasma pre-treatment it allows for the fabrication of 3D photonic bandgap materials for telecommunication wavelengths.