Optical systems have been increasingly adapted as key parts in various industrial and commercial applications such as projection systems, 3D imaging, medical diagnostics, etc. For many such applications, a uniform spatial illumination of the surface of interest with a specific beam shape is a prerequisite. Depending on the chosen light source there could be several constraints in achieving the required beam shape and intensity distribution. For example, a laser source has an inhomogeneous intensity distribution and has divergence related restrictions of the beam size on an incident surface. Such limitations in incident light uniformity and intensity can be solved by using an optical beam diffuser.
An optical light diffuser causes the incident light source to uniformly spread/scatter across the surface of interest with a desired illumination profile . It eliminates any bright/dark spots across the surface and ensures homogenous intensity distribution.
Refractive Diffusers
One common family of diffusers are refractive optical elements such as micro-lens arrays. Such diffusers are called refractive optical diffusers as they work based on the principle of optical refraction. Refractive diffusers are insensitive to the wavelength of the incident light and respond similarly to all wavelengths with high efficiencies. This property makes it attractive to shape and profile incident light for many applications where polychromatic broadband response is desired. However, refractive diffusers are limited by their angle accuracy and choice of beam shapes. This makes refractive diffusers inadequate for applications that require highly accurate intensity distributions and profiles.
Diffractive Diffusers
Alternatively, diffractive diffusers that contain diffractive micro-optical elements can be used to produce nearly any arbitrary shapes and intensity distributions. They can generate complex intensity distributions, beam shapes and profile as desired with high accuracy and efficiencies. However, diffractive diffusers are highly sensitive to the wavelength of the incident light and need to be tailored to a specific application with specific incident wavelength of the light.
Broadband Hybrid Diffusers
By combining the advantages of refractive diffusers and of diffractive diffusers novel hybrid diffusers can be fabricated. They contain two types of structures in them, a larger scale micro-lens array acting as the refractive diffuser and a smaller scale diffractive pattern acting as the diffractive diffuser. They have a polychromatic response yet allow high accuracy beam shaping. Hybrid diffusers can thus be used to shape an incident beam into any arbitrary shape precisely as desired with excellent homogeneity across the broadband of incident light (from UV to NIR). Hybrid diffusers have excellent tolerance to input conditions and can be readily used by simply mounting them in front of a laser source. Such broadband hybrid diffusers are highly desired in applications such as LIDAR, cinema projection, medical diagnostics, advanced spectroscopy, and laser shows.