Designing of diffractive optical elements (DOEs) requires knowledge about possible methods of calculating and simulating their performance, possible materials and characteristics of the particular range of radiation. The demand for compact and lightweight setups intuitively leads to the application of diffractive elements, which are characterised by both these features, having though one significant drawback – large chromatic aberration. As DOEs are meant to introduce specific phase shift, they are related to one particular design wavelength (DWL). However, thanks to different design approaches (e.g. kinoforms of higher order), elements functioning also for broader spectral ranges can be created. They are thicker, thus usage of appropriate material, having small attenuation coefficient or adjusting structure height during design process is required. Here, a simple method of designing diffractive lenses working in on- and off-axis regimes is presented. Using 3D printing for manufacturing is possible because different materials, polyamide, wax or chocolate, are relatively transparent below 0.5 THz. Each material has its own limitations like hardness, thermal resistance or ability for mechanical processing that have to be considered. Thus, using such simple methods of manufacturing for DOEs working for frequencies larger than 0.5 THz can be achieved using different design approach and ordinary devices with easily accessible materials (e.g. paraffin). It seems very important to create a method of producing diffractive elements that will be available in many laboratories to show the advantage of using such optical structures.
Novel thermovision imaging systems having high efficiency require very sophisticated optical components. This paper describes the diffractive optical elements which are designed for the wavelengths between 8 and 14 μm for the application in the FLIR cameras. In the current paper the authors present phase only diffractive elements manufactured in the etched gallium arsenide. Due to the simplicity of the manufacturing process only binary phase elements were designed and manufactured. Such solution exhibits huge chromatic aberration. Moreover, the performance of such elements is rather poor, which is caused by two factors. The first one is the limited diffraction efficiency (c.a. 40%) of binary phase structures. The second problem lies in the Fresnel losses coming from the reflection from the two surfaces (around 50%). Performance of this structures is limited and the imaging contrast is poor. However, such structures can be used for relatively cheap practical testing of the new ideas. For example this solution is sufficient for point spread function (PSF) measurements. Different diffractive elements were compared. The first one was the equivalent of the lens designed on the basis of the paraxial approximation. For the second designing process, the non-paraxial approach was used. It was due to the fact that f/# was equal to 1. For the non-paraxial designing the focal spot is smaller and better focused. Moreover, binary phase structures suffer from huge chromatic aberrations. Finally, it is presented that non-paraxially designed optical element imaging with extended depth of focus (light-sword) can suppress chromatic aberration and therefore it creates the image not only in the image plane.
This work is dedicated to the evaluation of the chromatic properties of high order kinoforms. Typical kinoform (of the first order) is a phase only structure having the phase retardation varying in the range 0-2π. Such structures are very commonly used in many practical applications for different ranges of electromagnetic radiation like ultraviolet, visible, infrared, terahertz and millimeter waves. Besides those benefits such structures have one crucial disadvantage - they suffer from big chromatic aberration. This limits their practical application only to the narrowband work, where main wavelength must be well defined (Δλ/λ<<1). This paper presents other type of diffractive structures called high order kinoforms (HOK). They exhibit phase retardation of n2π, where n is an integer number much bigger than 1. Due to this fact they are relatively thin and therefore can be manufactured using laser lithography in thick photoresist (deeply etched). On the other hand they are thick enough to suppress chromatic aberrations. In comparison to the well-known Fresnel lens, the high order kinoform structure has precisely controlled phase retardation between different zones. In the case of the Fresnel lens (known from XVIII/XIX century), phase retardations between different zones are random (designing process is based on the geometrical optics). In the case of the high order kinoform working as the spherical lens - taking into account the real size of the detector - it can be shown that the most of the energy being focused in the focal spot will be registered by the detector for different wavelengths. The paper presents simple theoretical considerations, numerical modeling and their experimental evaluation.
A study of imaging in an isoplanatic optical setup with a spatially incoherent illumination is presented. In such optical
setups a light intensity distribution in an image plane can be calculated by a convolution of an input field with a Point
Spread Function (PSF). Additionally a numerical simulation of incoherent monochromatic illumination is done by an
integration of intensity images obtained with different random initial phase distributions (equivalent to a long exposure
with a rotating diffuser in an optical setup). When an optical system is non space-invariant the point source image
changes in various regions of the image plane and imaging simulation becomes complicated. Method with a simple
convolution with PSF distribution cannot be applied because there is no one well defined PSF for the whole optical
setup. This second method needs a bigger computational effort but can provide imaging modelling for both isoplanatic
and non space invariant situations. In this contribution we compare the two mentioned methods in terms of imaging
quality and its agreement with theoretical expectations. We give some statistical analysis of a contrast and noise level of
the obtained pictures. We discuss the advantages and limitations of both modelling techniques for typical greyscale test
The experimental demonstration of a blind deconvolution method on an imaging system with a Light Sword optical
element (LSOE) used instead of a lens. Try-and-error deconvolution of known Point Spread Functions (PSF) from an
input image captured on a single CCD camera is done. By establishing the optimal PSF providing the optimal contrast of
optotypes seen in a frame, one can know the defocus parameter and hence the object distance. Therefore with a single
exposure on a standard CCD camera we gain information on the depth of a 3-D scene. Exemplary results for a simple
scene containing three optotypes at three distances from the imaging element are presented.
There is a continuous demand for the computer generated holograms to give an almost perfect reconstruction with a
reasonable cost of manufacturing. One method of improving the image quality is to illuminate a Fourier hologram with a
quasi-random, but well known, light field phase distribution. It can be achieved with a lithographically produced phase
mask. Up to date, the implementation of the lithographic technique is relatively complex and time and money
consuming, which is why we have decided to use two Spatial Light Modulators (SLM). For the correctly adjusted light
polarization a SLM acts as a pure phase modulator with 256 adjustable phase levels between 0 and 2π. The two
modulators give us an opportunity to use the whole surface of the device and to reduce the size of the experimental
system. The optical system with one SLM can also be used but it requires dividing the active surface into halves (one for
the Fourier hologram and the second for the quasi-random diffuser), which implies a more complicated optical setup. A
larger surface allows to display three Fourier holograms, each for one primary colour: red, green and blue. This allows to
reconstruct almost noiseless colourful dynamic images. In this work we present the results of numerical simulations of
image reconstructions with the use of two SLM displays.
A method of a digital holography based on the use of a self-imaging of the phase element is presented and assessed in
terms of image quality and resolution. The experimental results of digital hologram acquisition and reconstructions are
given for a standard USAF test pattern. The self imaging effect is used in the reference beam of the Mach-Zehnder
interferometer in order to project a structured phase modulated beam directly onto the photosensitive matrix of a digital
camera. The main advantage of this method is a simple optical setup and the possibility of performing phase-shifting
with a single camera exposure. The numerical reconstruction takes advantage of the Talbot effect and does not involve
any approximation or interpolation techniques. In order to evaluate the applicative potential of the method, in this work
the image quality is checked for various parameters of the optical setup, especially the period of the self-imaging
structure and imaging distances.
A method of color projection of 2D images utilizing red, green and blue laser sources and Fourier holograms addressed
on a single phase modulator has been reported. High quality rich-colored images were achieved, although the main
difficulty in reaching the TV-quality is the presence of a 0th diffractive order. It is inevitably created due to a limited fill
factor and phase modulation nonlinearity of the used Spatial Light Modulator (SLM) device. However, in certain
conFigureurations the light energy contributing to the spurious diffractive order can be focused in a single point in space
and absorbed with an amplitude filter. In this work we present the experimental results of a color projection with the
non-diffracted peak shifted outside the viewing range in both transverse directions and along the optical axis.
This work presents the observation, measurement and utilization of phase modulation in-time flickering, on a high-end
Liquid Crystal on Silicon (LCoS) Spatial Light Modulator (SLM). The flicker due to binary driving electronics is a
negative effect. However, this drawback can be minimized by appropriate adjustment of phase modulation depth, which
results in a time-synchronization of peak efficiencies for selected wavelengths. In this paper optimal parameters for three
wavelengths of primary RGB colors are investigated. The result is optimal performance of the SLM for full-color
A diffractive optical element with self-imaging capabilities is used to make a phase-shifting digital holography optical system simpler and cheaper. Sequential phase-shifting requires multiple exposures, and parallel phase-shifting demands a more complicated optical system. As opposed to typical phase-shifting methods, using the self-imaging diffractive optical element requires only one exposure on a low-cost CMOS matrix, and due to the small number of needed elements, the optical system is very compact. Instead of the approximation and interpolation methods, the properties of the self-imaging effect are utilized in the recording process and in the numerical reconstruction process.