Michal Makowski

Simple holographic projection in color

Extremely simplified image projection technique based on optical fibers and a single Spatial Light Modulator is presented. Images are formed by addressing the modulator with especially iterated Fourier holograms, precisely aligned on the projection screen using phase factors of lenses and gratings. Focusing is done electronically with no moving parts. Color operation is done by spatial side-by-side division of the area of the modulator. Experimental results are given, showing good image quality and excellent resistance to obstructions in the light path. Speckles are suppressed by micro-movements of the screen and by time-averaging of a number of holograms into the final image.

Lensless zoomable holographic projection using scaled Fresnel diffraction.

Projectors require a zoom function. This function is generally realized using a zoom lens module composed of many lenses and mechanical parts; however, using a zoom lens module increases the system size and cost, and requires manual operation of the module. Holographic projection is an attractive technique because it inherently requires no lenses, reconstructs images with high contrast and reconstructs color images with one spatial light modulator. In this paper, we demonstrate a lensless zoomable holographic projection. Without using a zoom lens module, this holographic projection realizes the zoom function using a numerical method, called scaled Fresnel diffraction which can calculate diffraction at different sampling rates on a projected image and hologram.

Minimized speckle noise in lens-less holographic projection by pixel separation.

Images displayed by holographic methods on phase-only light modulators inevitably suffer from speckle noise. It is partly caused by multiple uncontrolled interferences between laser light rays forming adjacent pixels of the image while having a random phase state. In this work the experimental proof of concept of an almost speckle-less projection method is presented, which assumes introducing a spatial separation of the image pixels, thus eliminating the spurious interferences. A single displayed sub-frame consists of separated light spots of very low intensity error. The sub-frames with different sampling offsets are then displayed sequentially to produce a non-fragmented color final image.

Diffractive elements for imaging with extended depth of focus

We present the abilities of diffractive elements for imaging with extended depth of focus. The elements of interest belong to the class of diffractive structures focusing incident light into a segment of the optical axis. We describe the imaging properties of the two following elements of this kind: the annular axicon and the light sword optical element (LSOE). In particular, the point spread functions and the modulation transfer functions of axicons and LSOEs are analyzed experimentally and numerically in detail. The obtained results correspond to different defocusing parameters. The performed experiments confirm the usefulness of axicons and LSOEs for imaging with extended depth of focus.

Three-plane phase-only computer hologram generated with iterative Fresnel algorithm

A novel iterative method of generating three-plane, phase-only computer-generated holograms is presented. It is based on the iterative Fresnel ping-pong two-plane algorithm. A modification is introduced to extend the method for three planes, i.e., two object planes and a hologram itself. The described method enables the design of low-noise and high-efficiency phase-only holograms using a numerical Fresnel propagation algorithm. The source method is described, followed by the modified algorithm. Numerical simulation results and algorithm parameters are discussed, followed by a discussion of the method limitations.

Color image projection based on Fourier holograms

A method of color image projection is experimentally validated. It assumes a simultaneous illumination of a spatial light modulator (SLM) with three laser beams converging in a common point on a projection screen. The beams are masked with amplitude filters so that each one illuminates one third of the area of the SLM. A Fourier hologram of a chosen color component of an input image is calculated, and its phase pattern is addressed on a corresponding part of the SLM area. A full-color flat image is formed on the screen as a result of color mixing. Additional techniques of image optimization are applied: time-integral speckle averaging and an off-axis shift of a zero-order peak. Static and animated experimental results of such a color holographic projection with a good image quality are presented.

Colorful reconstructions from a thin multi-plane phase hologram

A new technique of design and reconstruction of a color hologram is presented. The design is based on an iterative multi-plane optimization algorithm. It allows to encode three different images for a reconstruction at various distances measured from the hologram plane. The distances are calculated in order to obtain a fine color compound image when the hologram is illuminated by three laser beams of RGB colors. A single light phase modulator is used instead of three. The reconstructed red, green and blue component images remain in an exact match in size and position. The 2-D color image is reconstructed at a pre-assumed distance and its color pattern can be easily controlled by the choice of the three input component images.

Experimental evaluation of a full-color compact lensless holographic display

An iterative phase retrieval method for a lensless color holographic display using a single light modulator is experimentally validated. The technique involves iterative calculation of a three-plane synthetic hologram which is displayed on a SLM simultaneously lit with three laser beams providing an RGB illumination. Static and animated two-dimensional flicker-free full color images are reconstructed at a fixed position and captured using a high resolution CMOS sensor. The image finesse, color fidelity, contrast ratio and influence of speckles are evaluated and compared with other techniques of holographic color image encoding. The results indicate the technique superior in a case of full-color real-life pictures which are correctly displayed by this ultra-compact and simple projection setup.

Highly efficient broadband double-sided Fresnel lens for THz range

Modern passive THz setups require effective optical elements with a large numerical aperture. Here we propose a new type of the optical element for THz applications, which is a broadband double-sided Fresnel-like lens with an optimized thickness. The optimization is performed to obtain a very low attenuation, low material cost, and small weight in the element media. It also provides achromatic properties for the assumed wavelength range. The experimental evaluation of the proposed diffractive lens by means of time-domain spectroscopy is presented and discussed.

Efficient image projection by Fourier electroholography.

An improved efficient projection of color images is presented. It uses a phase spatial light modulator with three iteratively optimized Fourier holograms displayed simultaneously--each for one primary color. This spatial division instead of time division provides stable images. A pixelated structure of the modulator and fluctuations of liquid crystal molecules cause a zeroth-order peak, eliminated by additional wavelength-dependent phase factors shifting it before the image plane, where it is blocked with a matched filter. Speckles are suppressed by time integration of variable speckle patterns generated by additional randomizations of an initial phase and minor changes of the signal.