Cancellation of lateral displacement noise of 3-port gratings for coupling light to cavities

Reflection gratings enable light coupling to optical cavities without transmission through substrates. Gratings that have three ports and are mounted in second-order Littrow configuration even allow the coupling to high-finesse cavities using low diffraction efficiencies. In contrast to conventional transmissive cavity couplers, however, the phase of the diffracted light depends on the lateral position of the grating, which introduces an additional noise coupling. Here we experimentally demonstrate that this kind of noise cancels out once both diffracted output ports of the grating are combined. We achieve the same signal-to-shot-noise ratio as for a conventional coupler. From this perspective, 3-port grating couplers in second-order Littrow configuration remain a valuable approach to reducing optical absorption of cavity coupler substrates in future gravitational wave detectors

Realization of a monolithic high-reflectivity cavity mirror from a single silicon crystal

We report on the first experimental realization of a high-reflectivity cavity mirror that solely consists of a single silicon crystal. Since no material was added to the crystal, the urgent problem of 'coating thermal noise' that currently limits classical as well as quantum measurements is avoided. Our mirror is based on a surface nanostructure that creates a resonant surface waveguide. In full agreement with a rigorous model we realized a reflectivity of (99.79+/-0.01)% at a wavelength of 1.55 {\mu}m, and achieved a cavity finesse of 2784. We anticipate that our achievement will open the avenue to next generation high-precision experiments targeting fundamental questions of physics.Comment: Phys. Rev. Lett., accepte

High precision electron-beam-lithography for optical high performance applications

Due to its high resolution end flexibility, electron beam lithography (EBL) became an essential fabrication technique for micro-optical elements that are used in high performance applications. Nevertheless, the sequential writing strategy used in EBL enforces a stitching approach in order to fabricate large area micro-optical elements. Inherently, the stitching of special subareas leads to inaccuracies in the optical function of the fabricated micro-optics, which usually appears as stray light. In this paper we report about a method to calibrate the stitching process and to reduce the stray light artefacts, respectively. The optimization method is based on the evaluation of angle resolved stray light measurements of special test gratings. In particular, the optimization concerns about spurious stray light peaks, also known as “Rowland ghosts”. In a first step, the qualitative and quantitative characteristics of the observed Rowland ghosts are investigated in a theoretical model in order to deduce the modality of the stitching inaccuracy and the strength of the alignment error. In a second step, the calibration of the subarea-stitching is demonstrated on the example of a contemporary spectrometer grating. It is shown that the Rowland ghosts can be reduced significantly and the stitching process can be controlled in the nm-range

Nano-optical quarter-wave plates for applications in the visible wavelength regime: fabrication, tolerances and in-situ process control

The controlling of the polarization state of light is required for various photonic applications, e.g. for biomedical imaging, lithography, microscopy or ellipsometry. Major advantages ofmicro- and nanostructures for polarization control are realization of elements for spectralbands, where no alternatives exist (e.g. polarizers in the UV wavelength range) and betterintegration with optical elements or sensors. Nano-optical polarizers and wave plates can beused to fully manipulate and convert the state of polarization. The fabrication of sub-wavelength grating quarter-wave plates for applications in the visible and near infraredwavelength regime is challenging. In this work major grating structure deviations, namelygrating ridge tilt, chamfers on top of the ridges, grating displacement and their influence onphase retardation are investigated. Basing on this we present theoretical investigations andexperimental results for an in-situ process control. Thereby, the impact of structure deviationscan be compensated and a fine tuning of the phase retardation becomes feasible. Wedemonstrate this approach by fabrication of a wave plate for 532nm wavelength. This work isthe foundation for future development of such an in-situ process control

Merging Top‐Down and Bottom‐Up Approaches to Fabricate Artificial Photonic Nanomaterials with a Deterministic Electric and Magnetic Response

Artificial photonic nanomaterials made from densely packed scatterers are frequently realized either by top-down or bottom-up techniques. While top-down techniques offer unprecedented control over achievable geometries for the scatterers, by trend they suffer from being limited to planar and periodic structures. In contrast, materials fabricated with bottom-up techniques do not suffer from such disadvantages but, unfortunately, they offer only little control on achievable geometries for the scatterers. To overcome these limitations, a nanofabrication strategy is introduced that merges both approaches. A large number of scatterers are fabricated with a tailored optical response by fast character projection electron-beam lithography and are embedded into a membrane. By peeling-off this membrane from the substrate, scrambling, and densifying it, a bulk material comprising densely packed and randomly arranged scatterers is obtained. The fabrication of an isotropic material from these scatterers with a strong electric and magnetic response is demonstrated. The approach of this study unlocks novel opportunities to fabricate nanomaterials with a complex optical response in the bulk but also on top of arbitrarily shaped surfaces

Materials Pushing the Application Limits of Wire Grid Polarizers further into the Deep Ultraviolet Spectral Range

Wire grid polarizers (WGPs), periodic nano-optical meta-surfaces, are convenient polarizing elements for many optical applications. However, they are still inadequate in the deep ultraviolet spectral range. We show that to achieve high performance ultraviolet WGPs a material with large absolute value of the complex permittivity and extinction coefficient at the wavelength of interest has to be utilized. This requirement is compared to refractive index models considering intraband and interband absorption processes. We elucidate why the extinction ratio of metallic WGPs intrinsically humble in the deep ultraviolet, whereas wide bandgap semiconductors are superior material candidates in this spectral range. To demonstrate this, we present the design, fabrication and optical characterization of a titanium dioxide WGP. At a wavelength of 193 nm an unprecedented extinction ratio of 384 and a transmittance of 10 % is achieved.Comment: 21 pages, Advanced Optical Materials 201

Plasmonic modes of extreme subwavelength nanocavities

We study the physics of a new type of subwavelength nanocavities. They are based on U-shaped metal-insulator-metal waveguides supporting the excitation of surface plasmon polaritons. The waveguides are simultaneously excited from both sides of the U by incident plane waves. Due to their finite length discrete modes emerge within the nanocavity. We show that the excitation symmetry with respect to the cavity ends permits the observation of even and odd modes. Our investigations include near and far field simulations and predict a strong spectral far field response of the comparable small nanoresonators. The strong near field enhancement observed in the cavity at resonance might be suitable to increase the efficiency of nonlinear optical effects, quantum analogies and might facilitate the development of active optical elements, such as active plasmonic elements

Michelson interferometer with diffractively-coupled arm resonators in second-order Littrow configuration

Michelson-type laser-interferometric gravitational-wave (GW) observatories employ very high light powers as well as transmissively- coupled Fabry-Perot arm resonators in order to realize high measurement sensitivities. Due to the absorption in the transmissive optics, high powers lead to thermal lensing and hence to thermal distortions of the laser beam profile, which sets a limit on the maximal light power employable in GW observatories. Here, we propose and realize a Michelson-type laser interferometer with arm resonators whose coupling components are all-reflective second-order Littrow gratings. In principle such gratings allow high finesse values of the resonators but avoid bulk transmission of the laser light and thus the corresponding thermal beam distortion. The gratings used have three diffraction orders, which leads to the creation of a second signal port. We theoretically analyze the signal response of the proposed topology and show that it is equivalent to a conventional Michelson-type interferometer. In our proof-of-principle experiment we generated phase-modulation signals inside the arm resonators and detected them simultaneously at the two signal ports. The sum signal was shown to be equivalent to a single-output-port Michelson interferometer with transmissively-coupled arm cavities, taking into account optical loss. The proposed and demonstrated topology is a possible approach for future all-reflective GW observatory designs