An OLED device suitable for automobile ceiling lights has been designed, fabricated and evaluated. The OLED structure is fabricated on a thin (120 µm), flexible polymer foil with integrated micro-optics to achieve customized beam shaping in the far field. A pixelated OLED structure matched to a patch-pad microlens matrix was used to convert the OLED Lambertian emission into a Gaussian-shaped illumination beam. Both refractive and diffractive microlenses were investigated. The integrated micro-optics OLED architecture reduces light losses due to waveguiding effects and effectively increases the light extraction by up to 70%.
Replicated micro-optics is playing an increasingly important role in illumination and sensing systems in automobiles. The introduction of new design methods and improvements in materials and production technology has led to components which can offer superior performance, size and weight compared with classical optical elements. Diffractive Optical Elements (DOEs) for applications such as beam shaping can achieve optical performance which is not possible
with conventional optics. Beam forming elements for use with red and white LEDs play a major role in automotive optics. Customised DOEs can offer significantly more design flexibility and functionality over Fresnel lenses for the complex optical system based on a single or multiple LED source with reflector and wavelength converting resin. Thinner modules and improved efficiency are achieved. With CMOS imager sensors, micro-optical lenslet arrays can improve the effective sensitivity by many factors. UV-embossing and injection moulding are used to produce components in high volumes at low production costs. Replicated mounting and alignment features reduce assembly costs. New materials and processes have been developed to enable wafer-scale production by UV-embossing, producing glass-like components with excellent humidity and elevated temperature stability as well as IR-reflow process compatibility.
VCSELs (Vertical-Cavity Surface-Emitting Lasers) emit circularly symmetric beams vertical to the substrate; the small footprint of the active area (around 400 um2) enables the simultaneous fabrication of several thousand devices on a single wafer. Micro-optical components can modify the free-space optical properties of VCSELs for applications such as fiber-coupling in transceiver modules, illumination purposes, or beam profiling in sensing applications. However, the alignment of a laser towards a lens, for example, is expensive when performed separately for each device. Here we demonstrate a wafer-scale replication process to realise microlenses directly on top of the undiced VCSEL wafers. The process combines uv-casting and lithography to achieve material-free bonding pads and dicing lines. Several examples of lenses and gratings are given. An organically modified sol-gel material (ORMOCER) has been used as lens material. The micro-optical components on the wafer show good stability while sawing and bonding, where temperatures up to 220°C may occur. We have compared refractive lenses on top of the VCSELs with lenses on glass substrates. The lenses on the glass wafers were illuminated from the back-side by a planar wave. Spot diameters around 1.2 um and focal lengths of 30 um to 100 um were measured depending on the radii of curvature. On the VCSELs the lenses showed a strong influence on the transversal mode behaviour.
Organic light-emitting diodes (OLED) are rapidly reaching large-scale marketing figures, driven by attractive features like low cost and fast response, being also suitable for application on flexible substrates. All these aspects enable a wide range of applications such as displays, innovative devices in optoelectronics and novel light sources. Furthermore, the benefits expected from OLEDs based devices, if compared to "classical semiconductors" based devices consist of low production costs, lightweight and geometrical flexibility. Novel OLEDs based light sources fulfilling the above-mentioned requirements, call for a considerable effort both in the production processes and in product innovation. Among the variety of possible applicative OLED applications, we focused our research effort on the Automotive sector. Our envisioned approach enabling control of light distribution from an OLED light source include modeling and patterning of the light source, design and fabrication of suitable micro-optics coupled to the flexible transparent Organic Light Emitting Diode (OLED) substrate.
A new wafer-scale replication process for fabricating buried ridge
waveguides for telecom/datacom applications using an uv-curable
sol-gel material is proposed. Spin coating of the core material on
the replication mould is used to form the waveguide cores with a
smooth thin layer. The spin parameters allow an accurate control
of the thickness and homogeneity. The bottom-cladding is uv-cast
between a substrate and the mould, which is covered by the spun
core layer. The ridge waveguide cores are demoulded and buried
under a top cladding. This process allows the stacking of several
layers of waveguides on top of each other to form two-dimensional
waveguide arrays. A specially adapted SUSS mask aligner is used to
control the cladding thickness between individual waveguide layers
and to align them. A waveguide loss comparable to lithographically
fabricated waveguides has been achieved.
We report on an angle-tunable oblique incidence resonant grating filter that can be used to drop individual channels from the C-band for incident TE-polarized light. For tuning purpose, the filter is glued onto a tiltable platform of a MEMS device. Continues scanning of the platform allows to monitor channel presence and power. The reflected wavelength is tuned by changing the angle of incidence of the resonant grating filter, which is composed of two thin films with a grating pattern on top of it. The first layer on a glass substrate acts as a waveguide, and the second layer separates the waveguide from the grating. The grating has been patterned by holographic recording and dry etching. The filter works over a wavelength range of 1520-1580 nm and its response has a Lorentian shape with 0.5 nm FWHM peak width. The MEMS part is based on SOI technology and is processed in only two DRIE steps. The platform measures 2 x 2 mm2 with a through-hole of 1.6 x 1.8 mm2 for light transmission. Two arrays of combs attached to the platform as well as a set of four static combs are used to electrostatically incline the platform by ± 4° with a driving voltage of about 60 V.
Replication technology is playing an increasingly important role in the production of micro-optical elements and systems. Hot embossing, injection moulding and uv-embossing all can produce high quality optical elements in very cost-effective processes. The development of wafer scale replication technology using uv-curable sol-gel and polymer materials enables refractive and diffractive micro-optical elements to be replicated directly onto glass substrates or onto Si or III-V device wafers. New sol-gel materials allow the combination of replication with lithography to leave selected areas material-free for sawing and bonding. The technology is suitable for the production of both planar micro-optical elements and stacked optical microsystems. Replication techniques are inherently of very high resolution, so that optical nanostructures such as subwavelength structures can also be produced by the same technologies. Grating nanostructures with linewidths less than 100 nm have been replicated into polymer and sol-gel materials for the cost-effective fabrication of large area subwavelength structures for applications such as anti-reflection surfaces, polarisers and certain types of resonant filters.
We designed a tunable, oblique incidence resonant grating filter covering the c-band as drop device. Our resonant grating filter consists of a planar waveguide on a glass substrate covered by low index medium that separates the waveguide from the grating on top of it. With these 3 layers we reach a finesse of more than 3000, which would require much more layers in traditional thin film technology. The drop filter can be tuned by tilting the MEMS platform on which the filter will be glued. Tuning over the c-band will require tilt angles of 3° of the MEMS platform in both directions. Measurements indicate a resonance peak shift of 1.2% and a negligible shape change of the resonance peak from 1526nm at 45° angle of incidence to 1573nm at 53° with a full width at half maximum of 0.4nm. In this range the peak wavelength shift is linear with respect to the change of the AOI.
Tandem chirped grating couplers for spectral measurement applications in optical communications are developed. The current devices are designed to monitor data/telecom dense wavelength-division multiplexing (DWDM) channels in the spectral range from 1528 to 1561 nm (C-Band). A replication process provides the diffractive structures, on the gratings a high-index waveguide material is deposited. Design parameters and fabrication tolerances are discussed in detail, and measurement results of the fabricated devices are presented.
We present an approach towards design and fabrication of optical microsystems based on UV-replication techniques using Ormocer materials. An integration of the structures on chip level is demonstrated for Vertical Surface Emitting Lasers (VCSEL). VCSEL's are of increasing interest for various fields such as telecommunications, optical sensing and optical interconnects. In terms of optical system integration, high technological requirements are imposed. UV-replication techniques using Ormocer materials offer a cost-effective way of integrating micro-optical elements directly on the chip with reduced assembly effort. Structures up to several hundred microns thickness and alignment tolerances in the order of few microns can be produced. The method is suitable for the fabrication of single elements, arrays and is extendable to wafer-scale processing. Here, we give an example for the coupling of VCSEL arrays into multimode optical fibers using two different approaches: Focusing of the VCSEL output into the fiber using replicated microlenses and fiber butt-coupling of the VCSEL lasers with help of replicated fiber alignment/guiding structures. Origination of the structure elements is accomplished by direct laser writing into photoresist and resist reflow techniques, respectively. Specific limitations of the corresponding fabrication method are already taken into account during element design and modeling. Results for the replicated lenses show a total fiber launch efficiency better than 70% over the laser operational range with alignment tolerances of approximately +/- 10 micrometers , which can be met by passive fiber alignment. In case of the replicated fiber alignment/guiding structures, fiber launch efficiencies better than 50% over the operation range and peak values better than 80% are reported.
Replication technologies such as embossing, molding and casting in polymer materials are highly attractive for the fabrication of surface-relief diffractive optical elements (DOEs) and are expected to become key technologies for their production in the future. They have very high resolution, typically in the nanometer range, and allow the fabrication of large area, complex microstructure by low-cost, high volume industrial production processes. This paper gives a summary the current main replication technologies for surface microstructure and discusses their extension to a wider range of DOE microstructures, involving developments such as the replication of deeper and higher aspect ration microstructure and the maintenance of an optically precise form for critical surfaces such as imaging DOEs. Examples and recent results for DOE fabrication by replication technology are presented. New possibilities resulting from the combination of replication technology with other processes such as dry etching and thin film coating are discussed.
A novel approach for the fabrication of single-mode channel waveguides combined with focusing grating couplers by replication into polymer substrates is proposed and experimentally demonstrated. The concept is based on fabricating a master structure containing tall ridge patterns (about 3 micrometers high) combined with shallow, focusing grating structures (about 10 nm depth). By a micromolding technique using nickel shims, this pattern is hot embossed into a polymer substrate which is then full-area coated with a high-index dielectric waveguiding film. The focusing grating coupler is directly connected to the channel guide via a width-tapered waveguide section. An incident collimated beam can thus be coupled without the need for additional optics to the stripe waveguide formed by the film deposited on top of the ridge pattern. Results of experiments on stripe waveguides in quartz, focusing grating couplers in polycarbonate and combined channel waveguide and focusing structures in polycarbonate are presented and discussed. The feasibilty of the novel concept has been demonstrated by coupling a collimated free-space laser beam into a ridge waveguide on a replicated sample. The technology should find applications in integrated optical sensors and other low-cost integrated optical devices.
We report on a novel transducer devised for sensitive detection of the binding of molecules in the immediate vicinity of an optical surface. The transducer consists of a chip with a surface coated by an extremely thin waveguide film of amorphous TiO2 structured with a submicron grating relief. This microrelief is composed of two superimposed, uniform diffraction gratings of different periodicities, forming a bidiffractive grating with a frequency spectrum composed of two fundamental spatial harmonics. This bidiffractive grating serves as both an input and an output port for coupling and decoupling light beams to and from the planar waveguide. The bidiffractive coupler has translation-invariant coupling efficiency and allows background-free detection of the light decoupled from the waveguide. We outline the fabrication of the transducer and discuss the material properties of the waveguide film, which are very important for achieving optimum detection sensitivity. We assess the key factors affecting the detection limits of the transducer and comment on the resolution and the dynamic range for the measurement of changes in interfacial mass loading.
Integrated optical transducer platforms for the measurement of small changes in the refractive index or thickness of a sensing layer are of considerable interest for the fabrication of a wide variety of sensors. Progress toward the development of two types of such platform is described. A replicated polymer platform fabricated by the embossing or molding of a surface relief microstructure followed by the evaporation of a dielectric waveguide layer forms the basis of a low-cost disposable device for applications such as medical diagnostics. A fully integrated, monolithic III-V platform with laser, interferometer, modulator, sensor pad, and detector is also being developed for compact, rugged sensors required in applications such as environmental sensing and process control. Both transducer platforms are suitable for many different types of sensors and can be extended to multichannel sensor structures for the simultaneous measurement of a number of analytes.
A laser writing system for the fabrication of continuous-relief micro-optical elements in photoresist is described. The technology enables a wide range of planar micro-optical elements to be fabricated and replicated into polymer film using Ni shims electroformed from the photo-resist originals. The advantages and limitations of laser writing technology for micro-optics fabrication are discussed. Examples of fabricated micro-optical elements include Fresnel microlenses and microlens arrays, kinoforms, and other continuous-relief phase elements.
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.
Fabrication technology and device structures suitable for low- cost production of replicated integrated optical devices are presented and discussed. Shim fabrication and replication techniques such as hot embossing and injection moulding are capable of achieving the submicron resolution, high fidelity requirements of integrated optical structures. Polymeric materials have been shown to be suitable both as replicated substrates and as waveguiding films with losses under 1 dB/cm. High index dielectric waveguiding films are highly suited to sensor applications and have been fabricated with losses under 5 dB/cm. New types of vertically structured integrated optical devices which can be fabricated by replicating a microstructure followed by dielectric coating are presented.
Design considerations and experimental results are presented for the fabrication and characterization of grating couplers in gradient effective index waveguides used for realizing miniature integrated optical sensor modules. Hard dielectric substrates such as glass and fused silica have been structured by photolithographic techniques, while hot embossing has been used for the grating fabrication in plastic substrates. The gradient effective index waveguides were produced by shadow mask evaporation techniques in one single deposition step in a rotating substrate holder arrangement. Optical diffraction measurements, atomic force microscopy, and a newly developed method based on performing spatially resolved grating coupler resonance angle measurements are shown to be valuable tools for the characterization of the waveguides and the grating couplers. The experimental results indicate that the deposition of high-index waveguiding films such as Ta2O5 and TiO2 on previously structured substrates is a viable technique for the cost-effective fabrication of integrated optical sensor chips.
Progress in the fabrication of continuous-relief micro-optical elements by direct laser writing in photoresist followed by replication into epoxy or polymer materials is described. The technology enables a wide range of micro-optical elements to be fabricated and replicated using Ni shims electroformed from the photoresist originals. Examples of fabricated micro- optical elements are described, including microlens arrays, Fresnel microlenses, kinoforms, and other continuous microrelief phase elements.
In the course of ESPRIT II project No. 2103 (MASCOT) a high performance color CCD camera was developed. It is based on a 1K X 1K frame-transfer CCD imager whose pixels are covered with an optimized dielectric filter stripe pattern. A microscanning optical unit is employed to displace the image, with a reproducibility of 1/200th of the pixel period, for programmable color image acquisition with a maximum resolution of 3K X 3K color (RGB, XYZ, etc.) pixels. The CCD's output is immediately digitized to 10 bits using an in- house developed ADC subsystem whose performance of 67 dB S/N at 20 MHz is ideal for this application. The data is stored in one of three fast framestores. The raw data is read out simultaneously from these three framestores at a data rate of 30 MBytes per second and processed, fully digitally, in a special color processor. After non-linear transformations to compensate for detector non-linearities, color matrixing is carried out using one set of 16 matrix parameters which have been optimized for different illumination conditions and color temperatures. They also enable the selection of the type of output data to be generated e.g., RGB for specific phosphors, CIE XYZ tristimulus values, etc. After matrixing, a non-linear table-lookup can be used to introduce gamma correction or other calibration functions. The color processor produces 8-bit color pixels at a rate of 20 MBytes per second, writing these data directly into an 8 MBytes commercial framestore plugged into a PC/AT.
Continuous surface-relief phase gratings for two-dimensional (2-D) array generation have been designed and fabricated by laser-beam writing lithography. Separable and non-separable solutions for the design of 2-D fan-out elements are compared. A 9 X 9 fan-out element has been fabricated in photoresist by laser-beam writing. A diffraction efficiency of 94% and an uniformity better than +/- 8% over the whole array were achieved.
Progress in the fabrication of diffractive optical elements (DOEs) as 2-dimensional continuous-relief microstructures is described. The elements are fabricated by laser-beam writing in photoresist and have typical microreliefs up to 5 micrometers and periods down to 10 micrometers . Examples include fan-out elements and Fresnel microlens arrays. The design and fabrication of a 9 X 9 fan-out DOE with a diffraction efficiency of 94% and an overall uniformity of +/- 8% is described. High quality replicas are produced by low-cost embossing and casting techniques.
A laser beam writing system for the fabrication of micro-optical elements as relief structures in photoresist is described. Using a computer controlled precision xy stage and a modulated, focused laser beam, a wide range of surface relief microstructures has been produced, with typical periods of 10 - 100 micrometers and a maximum relief amplitude of about 5 micrometers . Examples include microlens arrays, kinoforms and other phase structures for applications in optical computing, optical interconnects and micro-optical systems in general.
A CCD camera based optical metrology system has been developed for the accurate measurement of a railway locomotive''s wheel movements with respect to the rails. The system is based on the light-sectioning method implemented with four laser diodes projecting light sheets onto the wheel and rail. A high-resolution CCD camera views the four profiles simultaneously using an appropriately folded and combined beam-path. To minimize the effects of ambient light a special narrow-band dielectric filter was designed manufactured and fitted in front of the camera lens. The desired measurement accuracy requires pixel-synchronous acquisition of the CCD video data. This is realized with a custom-built universal CCD data acquistion system with which profile tracking data compression and storage at 12. 5 Hz (half frame-rate) is made possible. A prototype system was built and tested on railway tracks at up to 140 km/h. In laboratory experiments the system surpassed the required measurement accuracies about fivefold attaining an accuracy of 0. 02 mm in relative position and better than 0. 1 mrad in relative angle. 2.
The application of submicron grating structure for light trapping in thin silicon solar cells has been
investigated theoretically and experimentally. A gain in absorption corresponding to an increase in
thickness of more than a factor of 4 for polarized light and about 3 for unpolarized light has been
demonstrated.
The optical characteristics of diffractive microstructures designed for zero-order read-out are
discussed. Such devices offer new optical behaviour which can be exploited for applications in the
field of visual and machine readable security features. They can be fabricated by low-cost embossing
and evaporation techniques.
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