Interference filter | EPFL Graph Search

An interference filter or dichroic filter is an optical filter that reflects one or more spectral bands or lines and transmits others, while maintaining a nearly zero coefficient of absorption for all wavelengths of interest. An interference filter may be high-pass, low-pass, bandpass, or band-rejection. An interference filter consists of multiple thin layers of dielectric material having different refractive indices. There also may be metallic layers. In its broadest meaning, interference filters comprise also etalons that could be implemented as tunable interference filters. Interference filters are wavelength-selective by virtue of the interference effects that take place between the incident and reflected waves at the thin-film boundaries. The important characteristic of the filter is the form of the leaving signal. It is considered that the best form is a rectangle. Additional sources * *M. Bass, Handbook of Optics (2nd ed.) pp. 42.89-42.90 (1995) See also

Polymer multilayer photonic micro- and nanostructures with tailored spectral properties

Amazing and beautiful optical effects are present in Nature. Some examples are the iridescent colors produced by peacocks, butterflies and beetles. While the simulations of some of these structures have already been realized, only a few elements have been fabricated. We are interested to understand and to reproduce some of these amazing optical properties. Applications such as security or decorative elements in different fields like jewelery or horology can be imagined. SEM pictures of the structure of these animals show a frequent combination of periodic or pseudo-periodic elements such as interference filters, multilayer reflectors, microlenses and gratings. The different elements combine angular and spectral effects. This combination enables strong optical effects for a large range of viewing angles and spectra. Different technologies such as standard photolithography, recording of interference patterns, transfer of photoresist structures in glass substrates, replications, hot embossing and spincoating were used to fabricate a variety of optical elements. The fabricated elements were produced with polymer materials because of their ease of use, and the possibility to build multilevel structures with replication methods. A drawback is the small refractive index difference possible between polymers and compared to air. In the first part, different combinations of polymer micro- and nano-optical elements such as corrugated gratings, multilayer Bragg reflectors, microlens arrays, micro-prisms arrays and diffusers were successfully fabricated. Poly (vinyl alcohol) and poly (N-vinycarbazole) with refractive indices of 1.56 and 1.72, respectively, at a wavelength of 500nm were used to fabricate the polymer multilayer reflectors. The micro-optical elements used were: microlenses with diameter between 32 μm and 250 μm and around 20 μm height; prisms with 50 μm period and 25 μm height. The angularly dependent reflectivity of the different fabricated elements was studied. Thanks to the close combination of diffractive, refractive and reflective micro- and nano-optical elements, non-standard artificial visual color effects were produced. The fabricated elements were modeled with different tools according to the dimensions of the different optical elements. Ray tracing analysis was used in the case with micro-optical elements while the Fourier modal method permitted simulation of the interaction of the light with the periodic nano-structures. The specific effects of the variation of the different parameters were highlighted, the basic principles and the limitation of the polymer technology were identified. In the second part, the optical modeling tools and the fabrication technologies developed were used to model and fabricate polymer light emitting diodes in a distributed feedback regime. The optical properties of the different layers were modeled and the physical dimensions of elements with active conductive polymers me-LPPP and F8 were calculated, fabricated and tested. The sensitive dimensions and parameters were underlined. Polymer materials permitted rapid fabrication of complex and innovative optical elements with very simple technologies like spin-coating and replication methods. These technologies allow the combination of nano-optical elements with dimensions of the order of a hundred nanometers with micro-optical elements with dimension of the order of about ten to one hundred microns.

Institut de Microtechnique, Université de Neuchâtel2008

Real-time Java simulations of multiple interference dielectric filters

Olivier Martin

An interactive Java applet for real-time simulation and visualization Of the transmittance properties of multiple interference dielectric filters is presented. The Most commonly used interference filters as well as the state-of-the-art ones are embedded in this platform-independent applet which call serve research and education purposes. The Transmittance applet call be freely downloaded from the site http://cpc.cs.qub.ac.uk.

2008

Microlenses on Bragg Reflectors to Create Iridescent Colors

Hans Peter Herzig, Toralf Scharf

In nature strong colors play an important role in scaring away predators or finding a mate. Often, the strongest and brightest colors arise from coherent scattering and reflection on periodic structures on a length scale of several micro- or nanometers. Until recently, many theoretical combinations of diffractive structure and interference layers have been investigated and nearly nothing has been done on combinations of refractive structures and multilayer interferences. Only a few realizations have been achieved. We constructed and studied optical systems that mimic nature and are fabricated completely from organic materials. In this study we concentrate on combinations of Bragg reflectors and microlenses. Fabrication was carried out by spin-coating of organic interference layers and soft replication of microlenses. We studied reflection properties of such structures and discuss herein their behavior under different illumination conditions. To provide deeper insight, a model based on ray tracing is used that allows simulation of main characteristics. Particular optical configurations exist where the reflected color is insensitive to observation angles, while others have only one preferred direction of response.

2008

Polymer multilayer photonic micro- and nanostructures with tailored spectral properties

Institut de Microtechnique, Université de Neuchâtel2008