In display projection applications, micron scale light emitting diode (μLED) array displays present an alternative to conventional lamps as light sources, with the advantage of higher efficiency and smaller form factor (particularly if the array is monolithic). However, μLEDs without inbuilt optics produce an emission pattern similar to a Lambertian distribution. By employing a pair of microlens arrays aligned to the μLED array to collimate the light, and a relay lens to focus the light onto a display panel, we can produce a display that both serves the same function as a traditional illuminator such as one which might be found in an LCOS or a DMD display, and utilises the addressing of the array to generate light over the desired display area only (zoning), rather than having the entire array be illuminated when the display is active. Using raytracing, we find that such system is limited by the performance of small μLEDs needed and the manufacture of the associated micro-optics.
To extend the depth-of-focus of incoherent imaging systems an aspherical pupil plane element is designed to encode the incident wavefront in such a way that the image recorded by the detector can be accurately restored over a large range of defocus. This approach alleviates thermal and chromatic defocus whilst maintaining diffraction-limited resolution for incoherent imaging systems  by using simple and low-cost one- or two-element lenses. However this is bought at the price of a reduction in signal-to-noise ratio of the displayed image as is associated with most inverse filtering problems. This sets a serious limit to future applications, particularly in thermal imaging where the optical systems involve fast optics with a very small depth of field for which signal-to-noise ratio of restored images can be reduced significantly.
This paper gives a review on the design and use of both amplitude filters and phase filters to achieve a large focal depth in incoherent imaging systems. Traditional optical system design enhances the resolution of incoherent imaging systems by optical-only manipulations or some type of post-processing of an image that has been already recorded. A brief introduction to recent techniques to increase the depth of field by use of hybrid optical/digital imaging system is reported and its performance is compared with a conventional optical system. This technique, commonly named wavefront coding, employs an aspherical pupil plane element to encode the incident wavefront in such a way that the image recorded by the detector can be accurately restored over a large range of defocus. As reported in earlier work, this approach alleviates the effects of defocus and its related aberrations whilst maintaining diffraction-limited resolution. We explore the control of third order aberrations (spherical aberration, coma, astigmatism, and Petzval field curvature) through wavefront coding. This method offers the potential to implement diffraction-limited imaging systems using simple and low-cost lenses. Although these performances are associated with reductions in signal-to-noise ratio of the displayed image, the jointly optimized optical/digital hybrid imaging system can meet some specific requirements that are impossible to achieve with a traditional approach.
Conventional optical system design enhances the resolution of incoherent imaging systems by optical-only manipulations or some type of post-processing of an image that has been already formed. This paper gives a brief introduction to a modern method, which employs an aspherical phase filter to alter the transmitted wavefront in such a way that the optical system has a high tolerance to aberrations. As reported in earlier work, this approach alleviates the defocus and its related aberrations whilst maintaining the diffraction-limited resolution for incoherent imaging systems. We propose to explore the control of primary aberration through the use of radially symmetric phase filters and this include spherical aberration, coma, astigmatism, and Petzval field curvature aberration. This method offers the potential to implement diffraction-limited imaging systems using simple and low-cost one- or two-element lenses.
As improving manufacturing techniques drive down the expense of imaging detector arrays, the total costs of future thermal imaging systems will become increasingly dominated by the manufacturing costs of the complex lens systems that are necessary for athermalization and achromatization. The concept of wavefront encoding combined with post-detection digital decoding has previously been shown to produce systems that are insensitive to thermal and chromatic defocus in slow imaging systems. In this paper we describe the application of the wavefront coding technique to thermal imaging systems with particular emphasis on the specific difficulties encountered. These difficulties include the use and effects of fast optics (~f/1), wide fields of view and noise amplification in low-contrast thermal images. Modeling results will be presented using diffraction models. We will describe the optimization of the wavefront encoding technique with a specific aim to reduce weight, size, and cost whilst maintaining acceptable imaging performance.