P. Blattner

Microlens lithography and smart masks

Abstract We report on recent progress in the implementation of microlens lithography . In addition, we will introduce a new lithographic method, smart mask lithography. Microlens lithography is aimed at the fabrication of flat panel displays (FPD), multichip modules (MCM) and micromachining. An array of micro-objectives is used to image a photomask onto a resist layer. Microlens lithography provides a resolution of 3 to 5 μm, a depth of focus of 50 to 100 μm, and a working distance of 1 to 3 mm. Smart mask lithography is aimed at the printing of simple mask patterns, such as a matrix of posts or holes, as required for field emission displays (FEDs), or other patterns consisting of dots, lines, circles, or rectangles, as required for MCMs and printed circuit boards). Smart mask lithography covers the range of 1 to 100 μm feature sizes. We will present experimental results and discuss advantage and problems of both methods.

Rigorous diffraction theory applied to microlenses

Abstract In this paper, we discuss the behaviour of small cylindrical microlenses, arranged in one-dimensional arrays and as single elements. For this purpose, we apply a standard rigorous diffraction theory, commonly used for diffraction gratings. We investigate the coupling effect between the elements. It turns out that single elements behave like periodic elements if the spacing is chosen correctly. Furthermore, we compute the complex transmission function by rigorous diffraction theory and compare them with classical theories (combined ray tracing and the thin-element approach). Finally, we discuss the focal properties of microlenses in the rigorous regime.

Scanning near-field optical microscopy: transfer function and resolution limit

We present scanning near-field optical microscopy as an optical instrument characterized by a transfer function. This approach gives some theoretical guidelines for the design of near-field optical measurement systems. We emphasize that it is important to distinguish between the resolution for the optical field and the resolution for the object. In addition, to solve the general inverse diffraction problem the measurement of phase and amplitude of the electromagnetic field is necessary.

Unconventional treatment of focal shift

We present an unconventional approach for the explanation of focal shift behind a lens. It is based on the fact that, within the approximation of Fresnel diffraction, the intensity distributions in the conjugate planes of a lens are equal to their geometrical images. We show that the focus (position of highest intensity) is always shifted towards the lens. The results for a Gaussian beam and a uniform converging spherical wave are presented.

Phase singularities generated by optical microstructures: Theory and experimental results

In this paper, we present theoretical and experimental results of our investigations on high resolution interference microscopy. We were able to measure phase variations with a spatial resolution in the order of 10 nm. For this purpose, we have modified a classical interference microscope based on a Mach-Zehnder interferometer to obtain ultra-high resolution. The optical fields were generated by periodic optical microstructures. The measured optical phase distribution in the near-field compares very well with the results of rigorous diffraction theory.

Design, fabrication, and testing of micro-optical components for sensors and microsystems

We report on our activities in the design, fabrication, characterization and system integration of planar micro- optical elements. Microlens arrays, gratings, diffusers, beam shapers and beam splitters have been fabricated, tested and integrated in chemical analysis systems ((mu) TAS, fluorescence detection), tracking sensors for satellites, displacement sensors, optical lightpipes, LCD projector illumination photospectrometers, neural networks and multiple channel imaging systems for photolithography. Packaging and alignment strategies for sensors and optical microsystems were investigated.

Diffractive optics for compact space communication terminals

Abstract Free-space laser communication links with data rates between 10 and 500 Mbits s−1 are required to cover the large amount of communication needs between low-orbit satellites, geostationary satellites and ground stations. The objective of this paper is to demonstrate the potential of diffactive optical elements for the design of optical and optoelectronic systems for advanced laser communication terminals. Three different examples have been realized: a ring pattern generator, an athermalized and achromatic hybrid collimator system, and a hybrid beacon system.

Interferometric fabrication of modulated submicrometer gratings in photoresist

Interferometric recording is applied to the fabrication of modulated submicrometer gratings in photoresist.High diffraction efficiency requires optimized recording conditions, which are obtained by the use of an on-axis continuous surface-relief grating for the generation of the object beam. The optimized phase function is copied into the resist layer by means of a self-aligned two-step recording process with an intermediate copy in a volume photopolymer hologram. As a result, we demonstrate high carrier frequency surface-relief off-axis fan-out gratings for illumination in transmission with visible light.

Imaging of (sub-) wavelength sized objects

The objective of this paper is to show different aspects of the interaction of light with wavelength sized optical microstructures, and their imaging. Furthermore, we outline that a microoptical structure can generate a laminar or a turbulent optical field.

Direct sampling for diffractive microlens encoding from a rigorous point of view

Rigorous diffraction theory is applied to analyse the direct-sampling (DS) encoding method, which is based on scalar diffraction theory. For given fabrication constraints and constant sampling width of the lens function, the quantized phase profiles obtained with scalar DS are close to the optimum solutions, even for grating period to wavelength ratios as small as about 3. For smaller ratios, the phase profiles obtained by DS can be improved by up to 25%, using a straightforward rigorous steepest-gradient optimization. Applied to cylindrical lenses with NA = 0.5 and 0.63, coding with DS and with rigorously improved DS gives quite similar results for the total diffraction efficiency.