Broadband Hybrid Diffuser
June 6, 2022
Broadband hybrid diffusers are a special family of diffusers that are used as beam shapers. To begin with, conventional diffusers alter the radiance of an input light beam by making use of scattering and random diffraction effects. The net effect is a complete scrambling of the light beam’s original radiance, with a round spot having a Gaussian-like intensity profile. Broadband hybrid diffusers, on the other hand, are somewhat more sophisticated in that they can be regarded as beam shapers that tune the input beam’s light radiance into a more convenient output radiance for a specific application, including shape and intensity profile.
First, a broadband diffuser is similar to a micro lens array but with the added capability of being able to have a different radius of curvature for every lenslet composing the microlens array. With this extra design parameter, a broadband diffuser can be used to create considerably more complex output radiances than would be possible with a conventional diffuser or micro lens array. Furthermore, the shape of the final beam varies very little with wavelength and hence the name broadband. This property stems from the fact that the main operating principle is geometrical optics which has fewer issues with chromaticity compared to diffractive optics.
Now, to have tighter control over the final beam radiance, a fine structure can be superimposed onto the lenselet structure of the broadband diffuser. This extra structure is like a diffractive element on its own and its purpose is to exert greater control over the final beam. The lenslets’ function is to obtain the overall beam shape and the diffractive structure controls the fine details of the beam’s distribution. Since this new beam shaper operates using both geometrical and diffractive features, the element is referred to as the broadband hybrid diffuser. Another attribute of broadband hybrid diffusers is that they can be used with light sources that are not coherent or that are multimode.
Broadband hybrid diffusers can be used in those applications in which a complex, or simply difficult to obtain, beam radiance is needed and across a wide spectral range. This can be the case for microscope systems, for instance. Another application is digital cinema projection systems. In this case, an image, that can be a liquid crystal panel or a MEMs device, has to be illuminated with light sources from the three principal colors. A broadband hybrid diffuser will reduce the component count substantially since a single broadband hybrid diffuser can be used for all light sources needed.