Aug 5, 2021

Fly’s eye arrays for uniform illumination in digital projector optics

Category: Product News

The fly’s eye array is a useful optical element in illuminations systems. It is a two-dimensional array of individual optical elements assembled or formed into a single optical element and used to spatially transform light from a non-uniform distribution to a uniform irradiance distribution at an illumination plane. This blog post discusses the use of a fly's eye spatial light integrator in a digital projector and how such an element can be modelled in OpticStudio.

In digital projector design, we want to ensure that the digital source matches the projected image when it comes to the irradiance profile. This constraint, therefore, requires a projector design to encompass a uniformly illuminated spatial light modulator - usually in the form of an LCD panel. In theory, this sounds easy, but the source beams on such a panel are typically Gaussian (i.e., not uniform). Thus, a device is required to "de-Gauss", or spatially transform the non-uniform beam profile into a uniform one. One such device with this capability is a pair of fly's eyes light integrator arrays.

What is a fly’s eye array?

A fly’s eye array is a two-dimensional array of individual optical elements assembled into a single optical element. It is used to spatially transform light from a nonuniform distribution to a uniform irradiance distribution at the image plane. Digital projection systems that use fly’s eye arrays are often used in conjunction with lamp assemblies which have a parabolic reflector providing semi-collimated incident light. At present, they are mostly used in LCD digital projector light engines to deliver homogenous illumination to the spatial light modulator illumination plane. 

Fly's Eye Array

 A fly’s eye array can be seen in the above figure. (This photograph is provided courtesy of In Vision, Each of the individual optical elements in the array can be square or rectangular in shape. The surface shape of individual optical elements can be spherical or anamorphic (different optical power in the vertical and horizontal meridians). The optical power is typically only on one surface of the array with the second surface usually being planar. 

One of the easiest ways to model this setup in OpticStudio is by using an array object. For the provided example, a Lenslet Array 1 object was chosen which consists of an array of rectangular volumes, each with a flat front face and a user-definable number of repeating curved back faces. The back surface may be planar, spheric, conic, polynomial aspheric, or toroidal. This allows great flexibility in defining - and optimizing - the precise surface shape of the lens elements in the array. The graphic below shows a single Lenslet Array 1 object, which comprises a 7 x 5 array of rectangular lenses, each of which is a rectangular section of a spherical lens.

Single Lenslet Array 1 object, which comprises a 7 x 5 array of rectangular lenses, each of which is a rectangular section of a spherical lens.

Other objects which may be useful for this application include the Lenslet Array 2 object and the Hexagonal Lenslet Array object. You can read more about these arrays and their specifications in the help documentation: The Setup Tab...Editors Group (Setup Tab)...Non-Sequential Component Editor...Non-Sequential Geometry Objects. 

Lens arrays are also supported in sequential optical design, via the User-Defined Surface capability.

To learn more on how fly’s eye arrays work, what design trade-offs are, and read about a real fly’s eye illumination system for a digital projector, you can access the entirety of this Knowledgebase article here. To try out Zemax capabilities please download a free trial here.

Blog Author:
Kerry Herbert
Field Marketing Manager

Knowledgebase Article Author:
Michael Pate