Mads Demenikov

Image artifacts in hybrid imaging systems with a cubic phase mask

We present the first analytical analysis of image artifacts in defocused hybrid imaging systems that employ a cubic phase-modulation function. We show that defocus artifacts have the form of image replications and are caused by a net phase modulation of the optical transfer function. Both numerical simulations and experimental images are presented that exhibit replication artifacts that are compatible with the analytical expressions.

Miniaturization of zoom lenses with a single moving element

We present an analysis of single-moving-element zoom lenses in the thin-lens limit and show how the length of these zoom lenses is determined by the zoom-factor, sensor-dimension and the depth-of-focus. By decreasing the sensor size and extending the depth-of-focus, the lengths of these zoom lenses can be reduced significantly. As an example we present a ray-traced design of a miniaturized single-moving-element zoom lens with a 2.3 x zoom-factor and show how the exploitation of modern miniaturized detector array combined with wavefront coding enables a reduction in length of almost three orders-of-magnitude to 10mm.

Parametric blind-deconvolution algorithm to remove image artifacts in hybrid imaging systems

Hybrid imaging systems employing cubic phase modulation in the pupil-plane enable significantly increased depth of field, but artifacts in the recovered images are a major problem. We present a parametric blind-deconvolution algorithm, based on minimization of the high-frequency content of the restored image that enables recovery of artifact-free images for a wide range of defocus. We show that the algorithm enables robust matching of the image recovery kernel with the optical point-spread function to enable, for the first time, optimally low noise levels in recovered images.

Experimental demonstration of continuously variable optical encoding in a hybrid imaging system

We demonstrate an experimental method to obtain a continuously variable hybrid imaging system that uses two generalized cubic phase masks, to enable real-time optimization of the trade between extended depth-of-field and noise gain. We obtain point-spread functions as a function of the rotation angle and show an example of optimization based on recovered image quality.

Experimental demonstration of hybrid imaging for miniaturization of an optical zoom lens with a single moving element

We experimentally demonstrate a miniaturized zoom lens with a single moving element based on the concepts and analysis described in Opt. Express 17, 6118 (2009). We show that the implementation of either a cubic or a generalized cubic phase-modulation function makes miniaturization possible in addition to providing extended-depth-of-field imaging. We present recovered images for zoom lenses employing both phase-modulation functions and conclude that the generalized-cubic-phase function yields higher image quality without the artifacts present for the pure-cubic-phase function.

A technique to remove image artefacts in optical systems with wavefront coding

Based on an analytical analysis of the optical transfer function in an optical system with wavefront coding, specifically with a cubic phase mask in the aperture stop, we explain that such systems have image artefacts in the restored images and that these are manifested as replication artefacts. To remove image artefacts we propose to store a set of defocused point spread functions such that a single defocused image can be restored to a set of images, wherein one of them is without image artefacts. The image without image artefacts is determined with a new metric which we define in the wavelet domain.

Development of compact optical zoom lenses with extended-depth-of-field

Development of compact optical zoom lenses for integration in mobile phones is the goal of many companies. Optical zoom lenses change their focal length by the movement of lens elements or change in surface curvature or refractive index and this complicates the zoom lens design. Extended depth-of- field (EDOF) techniques provides the mean to simplify and miniaturize zoom lens designs with moving lens elements and a new EDOF optimization technique is presented. Finally, the starting point and an example of a compact optical zoom lens design with EDOF is also described.

Miniaturization and simplification of zoom lenses using wavefront coding

Traditional zoom lens designs employ multiple moving lens elements to provide simultaneous control of focal length and focal plane. We present an approach to a design of a simplified zoom lens by employing a single moving element to control only the focal length. We show that the defocus in miniaturized zoom lenses with a single moving element can be corrected by the use of wavefront coding, although this introduces a modest reduction in signal-noise-ratio. As an example, we present a design of a miniaturized 10 mm long wavefront coded 2.3x optical zoom lens with a single moving lens element.

Digital image processing as an integral component of optical design

The design of modern imaging systems is intricately concerned with the control of optical aberrations in systems that can be manufactured at acceptable cost and with acceptable manufacturing tolerances. Traditionally this involves a multi-parameter optimisation of the lens optics to achieve acceptable image quality at the detector. There is increasing interest in a more generalised approach whereby digital image processing is incorporated into the design process and the performance metric to be optimised is quality of the image at the output of the image processor. This introduces the possibility of manipulating the optical transfer function of the optics such that the overall sensitivity of the imaging system to optical aberrations is reduced. Although these hybrid optical/digital techniques, sometimes referred as wavefront coding, have on occasion been presented as a panacea, it is more realistic to consider them as an additional parameter in the optimisation process. We will discuss the trade-offs involved in the application of wavefront coding to low-cost imaging systems for use in the thermal infrared and visible imaging systems, showing how very useful performance enhancements can be achieved in practical systems.

The principles and roles of hybrid optical/digital codecs in imaging

The design of modern imaging systems is intricately concerned with the control of optical aberrations. Traditionally this involves a multi-parameter optimisation of the lens optics to achieve acceptable image quality at the detector. There is increasing interest in a more generalised approach whereby digital image processing is incorporated into the design process and the performance metric to be optimised is quality of the image at the output of the image processor. We will discuss the trade offs involved in the application of this technique to low-cost imaging systems for use in the thermal infrared and visible imaging systems, showing how very useful performance enhancements can be achieved in practical systems.