Michael Abraham

Grid polarizer for the visible spectral region

We report on the fabrication of a grid polarizer for the visible spectral region, based on metallic grids with periods below 100 nm. Theoretical calculations of the degree of polarization predict useful values for the visible region, if the period is in the range of 100 nm. The properties of the polarizer are shown to be strongly dependent on the optical constants of the metal and the substrate. For the fabrication of the grids, direct e-beam writing in combination with a dry etching process has been used. Metallic grids with 50 nm lines and a period of 100 nm were fabricated on a glass substrate. Measurements of the degree polarization were made at a wavelength of 670 nm. The results are compared to theoretical calculations made in the framework of a rigorous diffraction theory.

Micromachined aperture probe tip for multifunctional scanning probe microscopy

Abstract The paper presents a new concept of a micromachined integrated sensor for combined atomic force/near-field optical microscopy. The sensor consists of a microfabricated cantilever with an integrated waveguide and a transparent near-field aperture tip. The advantage compared to the fiber-based near-field tips is the high reproducibility of the aperture and the control of the tip–sample distance by the AFM-channel. The aperture tip is fabricated in a reliable batch process which has the potential for implementation in micromachining processes of scanning probe microscopy sensors and therefore leads to new types of multifunctional probes. For evaluation purposes, the tip was attached to an optical fiber by a microassembly setup and subsequently installed in a near-field scanning optical microscope. First measurements of topographical and optical near-field patterns demonstrate the proper performance of the hybrid probe.

Photoetchable glass for microsystems: tips for atomic force microscopy

The authors present the use of photoetchable glasses in the field of microsystem technology. Its properties make it an ideal material for a wide variety of microsystems. A method to fabricate tips for atomic force microscopy out of this material is proposed. The main advantage of these tips with respect to conventional silicon-based tips is their large aspect ratio. Silicon nitride is used as a material for the cantilevers, which are on top of a glass carrier. Experimental results are presented.

Ultra-long glass tips for atomic force microscopy

A new variety of ultra-long tips for atomic force microscopy has been fabricated using photoetchable glass. Photoetchable glass is structured by UV exposure through a quartz mask followed by a heat treatment and etch process in hydrofluoric acid. The process is based on different etching rates with a ratio of about 1:20 between unexposed and exposed parts of the glass. Tips longer than with a tip radius down to 20 nm are possible. The cantilevers are made from silicon carbide. The mechanical properties of such long tips are compared, in theory and in practice, with conventional cantilevers from silicon and silicon nitride. Their strong sensitivity to friction forces for contrast formation in atomic force microscopy is discussed.

Achieving mass fabrication of microoptical systems by combining deep-x-ray lithography, electroforming, micromolding, and embossing

The paper reviews the application of deep X-ray lithography in conjunction with electroforming, plastic molding, and stamping (LIGA) for a mass production of micro- and submicron-structured photonic devices. LIGA technology offers almost total design freedom in lateral structuring and a high aspect ratio of 100. Vertical walls with heights up to 1 mm and optical grade surfaces enable their use as functional optical surfaces. It is possible to process a variety of materials such as metals and different polymers, including those with nonlinear optical properties. Therefore, Y-branches, couplers, and structures for the positioning and fixing of fibers, detectors, and light emitters can be integrated on one chip to build up hybrid optoelectronic devices.

Microfabrication of new sensors for scanning probe microscopy

The paper presents a new concept of a micromachined integrated sensor for combined atomic force/near-field optical microscopy. The sensor consists of a microfabricated cantilever with an integrated waveguide and a transparent near-field aperture tip. The fabrication process involves a novel method for the micromachining of optical near-field tips with an aperture diameter of 100 to 200 nm. A simple concept is introduced for the effective light coupling from the cantilever into the tip.

Very low-loss passive fiber-to-chip coupling with tapered fibers

A novel passive fiber-to-chip coupling based on the use of fiber tapers embedded in a guiding structure is proposed. By beam-propagation calculations it is verified that this new coupling method exhibits a very low insertion loss. Major advantages of the proposed method compared with butt coupling are demonstrated by simulation results: first, tolerance requirements for the fibers, e.g., diameter variations and core eccentricity, and for fabrication of the alignment structure are reduced by at least 1 order of magnitude. Second, coupling to waveguides of nearly arbitrary dimensions and refractive indices seems to be possible. Experimental results on thermal drawing of fiber tapers are presented and used as input data for the simulations. A concept for fabrication of the new coupling method with the Lithographic Galvanik Abformung (LIGA) technique is presented.

Selectively erasable liquid crystal for high-resolution display and optical storage applications

Devices and applications of a new bistable liquid crystal are presented. This material consists of a small fraction of inorganic particles of a nanometer size dispersed in a nematic liquid crystal with positive dielectric anisotropy. Using an AC-electric field of transparent homeotropic state is obtained. It can be addressed by local optical writing using a low power diode laser, which transforms the transparent state into a strongly scattering multidomain one. The written information is stable in space and time. Local erasing is achieved by the application of a moderate voltage and a simultaneous laser pulse directed at the pixel to be erased. Based on this material a projection display system was developed. New high contrast and high viewing angle reflection and transmission displays are presented. These types of reflection displays may also be used as high resolution optically addressed, spatial light modulators for optical information processing.