Dichroic filter

Summary

A dichroic filter, thin-film filter, or interference filter is a color filter used to selectively pass light of a small range of colors while reflecting other colors. By comparison, dichroic mirrors and dichroic reflectors tend to be characterized by the colors of light that they reflect, rather than the colors they pass. Dichroic filters can filter light from a white light source to produce light that is perceived by humans to be highly saturated in color. Such filters are popular in architectural and theatrical applications. Dichroic reflectors known as cold mirrors are commonly used behind a light source to reflect visible light forward while allowing the invisible infrared light to pass out of the rear of the fixture. Such an arrangement allows intense illumination with less heating of the illuminated object. Many quartz-halogen lamps have an integrated dichroic reflector for this purpose, being originally designed for use in slide projectors to avoid melting the slides, but n

Official source

https://en.wikipedia.org/wiki/Dichroic_filter

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Reactively sputtered coatings on architectural glazing for coloured active solar thermal façades

Virginie Hody-Le Caër, Martin Joly, Stefan Mertin, Jean-Louis Scartezzini, Andreas Schueler

Covering a standard solar thermal collector with a coloured glazing, which is opaque to the human eye but highly transparent to solar energy, permits a perfect architectural integration of solar panels into glazed building façades. The colours are based on interference in the thin-film coating on the reverse side of the glass. Coloured thin-film filters with optimised energetic performance and angular stability in their coloured reflection were deposited by reactive magnetron sputtering. For substrates up to 100 mm in diameter the geometric configuration of the deposition chamber and the process parameters were optimised. The optical properties of the coatings were determined by spectroscopic ellipsometry and spectrophotometry. Furthermore, by means of a window test bench, the CIELAB colour coordinates of real-size glasses were determined as a function of the viewing angle. It was also demonstrated that the colour of solar collector glazing can be matched to colours of commercial windows. In comparison to uncoated glass panels, the presented coloured samples for solar thermal panels have an energy loss of only 2.8–4.5% at normal solar incidence. This difference reduces for higher angles of incidence. Thus, taking into account the angular distribution of solar radiation, the energetic losses are even lower.

Elsevier2014

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The integration of color filters with microfluidics has attracted substantial attention in recent years, for on-chip absorption, fluorescence, or Raman analysis. We describe such tunable filters based on the micro-flow of liquid crystals. The filter operation is based on the wavelength-dependent liquid crystal birefringence that can be tuned by modifying the flow velocity field in the microchannel. The latter is possible both temporally and spatially by varying the inlet pressure and the channel geometry, respectively. We explored the use of these optofluidic filters for on-chip absorption spectroscopy in poly(dimethylsiloxane) microfluidic systems; by integrating the distance-dependent color filter with a dye-filled micro-channel, the absorption spectrum of a dye could be measured. Liquid crystal microflows substantially simplify the optofluidic integration, actuation and tuning of color filters for lab-on-a-chip spectroscopic applications.

Royal Society of Chemistry2013

Light spectral filtering based on spatial adiabatic passage

Victor Javier Cadarso Busto

We present the first experimental realization of a light spectral filter based on the spatial adiabatic passage technique. We demonstrate that a fully integrable CMOS-compatible system of three coupled identical total internal reflection silicon oxide waveguides with variable separation along their propagation direction can be used simultaneously as a low-and high-pass spectral filter within the visible range of wavelengths. Light is injected into the right waveguide, and after propagating along the system, long wavelengths are transferred into the left output, whereas short wavelengths propagate to the right and central outputs. The stopband reaches values up to -11 dB for the left output and approximately -20 dB for the right plus central outputs. The passband values are close to 0 dB for both cases. We also demonstrate that the filtering characteristics of the device can be controlled by modifying the parameter values, which define the geometry of the triple-waveguide system. However, the general filtering behavior of the system does not critically depend on technological variations. Thus, the spatial adiabatic passage filtering approach constitutes an alternative to other integrated filtering devices, such as interference or absorbance-based filters.

Nature Publishing Group2013