Gratings are the core element of the spectrometer. For imaging spectrometers beside the polarization sensitivity and efficiency the imaging quality of the diffraction grating is essential. Lenses and mirrors can be produced with lowest wavefront aberrations. Low aberration imaging quality of the grating is required not to limit the overall imaging quality of the instrument. Different types of spectrometers will lead to different requirements on the wavefront aberrations for their specific diffraction gratings. The wavefront aberration of an optical grating is a combination of the substrate wavefront and the grating wavefront. During the manufacturing process of the grating substrate different processes can be applied in order to minimize the wavefront aberrations. The imaging performance of the grating is also optimized due to the recording setup of the holography. <p> </p>This technology of holographically manufactured gratings is used for transmission and reflection gratings on different types of substrates like prisms, convex and concave spherical and aspherical surface shapes, free-form elements. All the manufactured gratings are monolithic and can be coated with high reflection and anti-reflection coatings. Prism substrates were used to manufacture monolithic GRISM elements for the UV to IR spectral range preferably working in transmission. Besides of transmission gratings, numerous spectrometer setups (e.g. Offner, Rowland circle, Czerny-Turner system layout) working on the optical design principles of reflection gratings. The present approach can be applied to manufacture high quality reflection gratings for the EUV to the IR. <p> </p>In this paper we report our latest results on manufacturing lowest wavefront aberration gratings based on holographic processes in order to enable at least diffraction limited complex spectrometric setups over certain wavelength ranges. Beside the results of low aberration gratings the latest achievements on improving efficiency together with less polarization sensitivity of diffractive gratings will be shown for different grating profiles.
We present a new method for the fabrication of diffractive and refractive micro-optical components. The method is suitable for high-quality rapid prototyping of optical components and allows the fast experimental test of designs for computer-generated holograms or refractive microstructures. Our method is based on employing a digital-multimirror device (DMD) as a switchable projection mask. The DMD is imaged into a photoresist layer using a Carl Zeiss lithography objective with a demagnification of 10:1 and a numerical aperture of 0.32 on the image side. The resulting pixel size is 1.368×1.368 µm. In comparison with laser direct writing with a single spot, our method is a parallel processing of nearly 800,000 pixels (1024×768 pixels). This fabrication method can be applied to all MOEMS components. The method adds a new dimension in MOEMS processing, reducing the fabrication complexity, and improves the flexibility of process simulation and design.
We present a new method for the fabrication of diffractive and refractive microoptical components. The method is suitable for low-volume production, process development, high quality rapid prototyping of optical components and allows the fast experimental test of designs for a wide variety of different microoptical components e.g. computer generated holograms, blazed diffraction gratings or refrative microstructures. Our method is based on employing a computer-controlled digital-multi-micromirror device (DMD) as a switchable projection mask. The DMD is imaged into a photoresist layer using a Carl Zeiss lithography objective with a demagnification of 10:1 and a numerical aperture of 0.32 on the image side. The resulting pixel-size is 1.36 μm x 1.36μm. In comparison with laser direct writing with a single spot our method is a parallel processing of nearly 800000 pixels (1024 x 768).
The image quality of an inspection microscope depends strongly on the performance of the illumination system. Especially in the case of laser-based illumination it is necessary to transform the original beam profile into a homogeneous light spot with a flat top field distribution. Simultaneously, speckles caused by the coherence of the laser have to be reduced. Here we discuss different ways to homogenize the multi mode beam profile of a pulsed compact 157 nm excimer laser. A variety of setups, combining dynamic acting diffusers, microlens arrays and primary lenses were realized and characterized in several geometrical arrangements. The homogenizers were evaluated and characterized especially with respect to the statistical behavior on the integrated pulse number.
We suggest an optical system for beam homogenization and speckle reduction of spatially highly coherent Laser beams. The new method is applicable to laser beams with moderate temporal coherence. Based on the finite temporal coherence the spatial coherence is reduced prior to the homogenizer component. The new design was experimentally tested for ArF - Excimer laser at 193nm. For this Deep UV application we used silicon micromirrors in combination with fused silica microlenses with a pitch of 150 μm . In contrast to former fly's eye homogenizers for laser beams the new method employs a large number of sub-apertures even for lasers with high spatial coherence. This results in a speckle free and uniform intensity distribution in the target plane. Furthermore the pupil filling can be increased drastically. Experimental results for a DUV microscopy application are presented and discussed.
We suggest a new 3D-camera system for integral photography (IP). Our method enables high resolution three-dimensional imaging by employing a low-definition electronic camera. In contrast to conventional IP a moving microlens array (MLA) is used. The intensity distribution in the MLA image-plane is sampled sequentially by using a pinhole array. The inversion problem from pseudoscopic to orthoscopic images is dealt with by electronic means. The new method is suitable for real-time three-dimensional imaging. We verified the new method experimentally. Integral photographs with a resolution of 3760 pixel x 2560 pixel (188 x 128 element images) are presented.
In this work, we present a new deep etching sequence for the fabrication of circular cavities in straight silicon sidewalls. This approach allows alternating anisotropic/isotropic etches without affecting the profile generated in prior etching steps. This process sequence is crucial for realizing silicon structures that enable a variety of new applications, such as turbulence promoted liquid injector to disperse liquid effectively at the minimum injection pressure for electronic cooling, micro-evaporator or micro-combustors, surface enhancement (increase boiling nucleate sites) for micro-channel heat transfer, fluid mixing enhancer, isolation of electronic microstructures and release of mechanical microstructures.
A solution is described for replication of polymer microoptical elements on arbitrary substrates. The replication is done on wafer scale level and includes the adjustment step between the optical elements and the substrate. Demonstrators are various microlens arrays, structures for the efficient coupling between monomode waveguides or multimode fibers and photodiodes, and between multimode waveguides and LED's. Out of the many different replication techniques, UV-reaction molding is chosen for this application. This technique has advantages against hot embossing and injection molding. Network polymers which are stable against temperature changes can be used. The replication is made in thin layers on a solid substrate resulting in high mechanical stability and very good flatness of the samples. The process introduces mechanical stress nor thermal load on the substrate which can be a fully processed semiconductor wafer containing elements like diodes or LEDs.
A replication technique allowing for the wafer scale integration of microoptical elements is presented and illustrated by various examples. The technique is based on polymer UV reaction moulding using a modified contact mask aligned where mask and wafer are replaced by the replication tool and an arbitrary substrate, respectively. The technology takes advantage of the high precision and adjustment accuracy of photolithography equipment. The replication masters are nickel shims, etched Silicon wafers or uv-transparent fused silica tools. The latter ones allow for replication on opaque substrates. Additionally, polymer elements with unique properties can be obtained by the combination of replication and resist technology using partially transparent replication tools. Wafer scale hybrid integration of microoptical subsystems is accomplished by replication of polymer elements like lenses, lens arrays, micro prisms etc. onto semiconductor wafers containing detectors or VCSELs, or by combining microoptical elements on both sides of a glass wafer. The use of thin layers of uv cured polymers on inorganic substrates results in good thermal and mechanical stability compare to all-polymer devices.
After demonstration of a large variety of microoptic and optoelectronic components in many institutions world-wide, the main interest is focused on their hybrid integration into miniaturized systems. This concerns modules comprising lightsources, detectors, conventional and microoptical elements, like lenses, prisms, filters, and, for some applications, miniaturized actuators. A solution is described for replication of polymer microoptical elements on arbitrary substrates (semiconductor, glass). The replication is done on wafer scale level and includes the adjustment step between the optical elements and the substrate. Demonstrators are 90 degree(s) deflection prisms for the efficient coupling between monomode waveguides and photodiodes and various microlens-arrays. From the many different replication techniques, UV-reaction molding is chosen for this application. This technique has advantages against hot embossing and injection molding. Network polymers which are stable against temperature changes can be used. The replication is made in thin layers on a solid substrate resulting in high mechanical stability and very good flatness of the samples. There is neither mechanical stress nor thermal load on the substrate which can be a fully processed semiconductor wafer containing elements like diodes or VCSELs.
A microoptical receiver module for very high bitrates was designed and realized. We employed well established silicon technologies for integrating the optical components of the microoptical system. For reducing the optical spot size on the photo diode due to the beam divergence of the transmission fiber a monolithically integrated silicon microlens was used. The microlenses were fabricated by melting of photoresist and transferring the preforms into the silicon substrate. We characterized the lenses by lateral shearing interferometry in transmission. The beam diameter on the photodetector (l/e<SUP>2</SUP>) could be reduced by about one order of magnitude to less than 10 micrometers . The sensitivity of the modules was about 0.5 A/W at 1310 nm and 0.6 A/W at 1550 nm.
Polymer multilayer waveguide technology was used to fabricate a polarization-independent phasemodulator. Refractive indices and electro-optic coefficient r<SUB>33</SUB> of the materials used (Co. SANDOZ) were determined by waveguide methods.
Electro-optic waveguide elements are fabricated in the polymer-on-silicon technology. Measured field distributions of the inverted rib waveguides show excellent agreement with vectorial FEM calculations. This method is also used for electro-optic phasemodulator design. The dynamics of electrode poling is studied by reflectrometry. An integrated waveguide interferometer with lateral electrodes allows the determination of the r<SUB>33</SUB>/r<SUB>31</SUB> equals 3.5.