52 research outputs found
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
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