Advances in design, materials and production technology for micro-optical components have led to strong growth in their use in today's consumer products. In particular, micro-optical components produced by replication technologies such as UV embossing can now withstand the severe processing and environmental requirements of the consumer
electronics industry, including lead-free IR reflow and thermal shock. With their small size and low weight, as well as the possibility of optical function not achievable by conventional optics, micro-optical components and systems are finding applications in a wide variety of products. In the field of multimedia, novel designs and new production techniques are enabling applications in key areas such as illumination and display. The extreme compactness of micro-optical components, with typical thickness under 1 mm and footprints of only some millimeters square, makes them a natural candidate for consumer products such as mobile
phones, pocket projectors and displays. Advances in UV embossing technology, enabling micro-optics to be mounted over various light sources in a variety of different ways, also allow extremely compact opto-electronic modules to be realized at highly competitive prices. In this paper we summarize recent technology developments and describe a number of multimedia applications utilizing state-of-the-art micro-optics.
UV-NanoImprint Lithography (NIL) is a fast and low cost method, which becomes an increasingly important instrument for fabrication of μ-TAS and telecommunication devices. The key elements of UV-NIL are transparent molds and low viscosity resists. Two different transparent mold materials, allowing UV curing through the stamp, were developed: rigid quartz or flexible PDMS. Typical resist viscosities are in a range of <100mPas, ensuring fast and successful filling of the stamp cavities. UV-curing is carried out at a wavelength of 350-450 nm.
Micro- and nano-optical structures offer the possibility to control light on a wavelength scale. This allows further miniaturization of integrated optical circuits. Planar photonic crystal waveguides and microcavities are considered basic building blocks for applications such as microlasers, filters, multiplexers and optical switches. The possibility to tune or switch photonic crystal devices by various ways such as temperature, refractive index change using liquid crystals, free charge carrier density or non linear material effects increases their functionality to form multifunctional, intelligent devices. High-Q cavities in planar photonic crystals exhibit highly localised fields and narrow transmission bands. Due to their strong light confinement even a small perturbation of the localized field can change their transmission properties of the cavity. We present different ways of perturbing the optical environment near a photonic crystal cavity enabling tuning and modulation of the in-plane transmission. Optical switching and wavelength tuning is obtained by means of induced thermo and plasma dispersion effects when focusing a laser onto the cavity structure. The feasibility of high-speed optical integrated circuits based on silicon photonic crystal structures is shown. On the other hand, an AFM tip is used for mechanically tuning and damping the inplane transmission. A future challenge is the integration of more than one silicon tip to combine filter and tuning functionalities and to create a chip-based device.
Recent results of our studies into optical effects where sub-micron length scales play a pivotal role are presented. We start with a discussion of fine optical features produced by relatively large objects, and then move on to consider the big effects that can be produced by sub-micron structures. Topics covered include fine structure in the optical field of microlenses and gratings, and then further down in length scale from microstructured surfaces to resonant filters, photonic crystal waveguides and metallic nanoparticles. For each step we demonstrate potential applications in which such a length scale can present important advantages, as well as discussing some of the disadvantages and challenges in the design and fabrication of such elements. We particularly highlight the sensitivity of many of the structures to small variations in optical situation (e.g. geometry, orientation, material, polarization) leading significant optical effects for small-scale changes. Methods for the characterization of optical fields produced by objects at these smaller dimensions are also presented.
We present recent applications of one-dimensional (1D) and two-dimensional (2D) periodic structures. The structures were designed using rigorous diffraction theory and produced by modern micromachining techniques (electron beam writing, optical lithography). In addition, interferometric recording of periodic structures was investigated in order to fabricate periodic structures with arbitrary profile shapes.
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.
An electromagnetic field is characterized by an amplitude, a phase and a polarization state. In this paper, we intend to gain an understanding of the interaction of light with microstructures in order to determine their optical properties. Measurements of the amplitude and phase close to gratings are presented using a heterodyne scanning probe microscope. We discuss some basic properties of phase distributions. Indeed, coherent light diffracted by microstructures can give birth to phase dislocations, also called phase singularities. Phase singularities are isolated points where the amplitude of the field is zero. The position of these special points can lead us to information about the structure (shape, surface defects, etc), by comparing with rigorous diffraction calculation using e.g. the Fourier Modal Method (FMM). We present high-resolution measurements of such phase singularities and compare them with theoretical results. Polarization effects have been studied in order to understand the field conversion by the fiber tip.
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