Broadband hybrid diffusers are optical components that are used for beam homogenisation as well as other beam shaping operations. A broadband hybrid diffuser is similar to a micro-len array in the sense that it also consists of an array of lenslets, but in addition has a diffractive component to the shaping function. Thus, the principle behind their operation is a combination of the refraction of light with diffraction. This diffractive component is often a low amplitude modulation on the microlens profile at some frequency that corresponds to desired shaping functionality.
This is in contrast with diffractive diffusers that utilize only the diffraction effect, as the name implies.
Conventional micro-lens arrays and broadband diffusers differ in one major aspect. In a micro lens array all lenslets have the same curvature profile and hence they can only provide a radiance homogenisation of the output beam. Conversely, in a broadband diffuser each lenslet in the array can have a different curvature profile which provides a powerful extra degree of freedom that in turn allows other complex beam transformations like Top Hat beam shaping or some simple geometries for the focused spot.
The fact that refraction of light is the dominant effect provides the capability of broadband operation and with no zeroth order present in the final beam distribution, even if the wavelength range extends from the visible to the infrared. In the case that the input beam is a multimode laser beam, a broadband diffuser provides optimum homogenization at the output beam envelope.
In general, broadband hybrid diffusers are meant to be used in those applications in which the input light has a wide spectrum or when more than one laser wavelength is required. Scientific or industrial applications in which more than one laser wavelength is used along the same optical train can be the following:
- High end laser microscopy.
- Laser projection systems.
- Tunable or double frequency lasers.
- Aesthetic applications.
The individual curvature on each lenslet is obtained with algorithms based on a statistical approach in which the combined effect of the ensemble is the only important parameter. The manufacturing process of this component requires specialized tooling and techniques that are different from the manufacturing process of a diffractive optical element that is derived from current step-wise lithographic techniques.