Resolution Of Digital Holography Research Articles

Aperture synthesis based solely on phase images in digital holography

Aperture synthesis is an important approach to improve the lateral resolution of digital holography (DH) techniques. The limitation of the accuracy of registration positions between sub-holograms affects the quality of the synthesized image and even causes the failure of aperture synthesis. It is a major issue in aperture synthesis of DH. Currently intensity images are utilized to find the registration positions of sub-holograms in aperture synthesis. To improve the accuracy of registration positions, we proposed a method based on similarity calculations of the phase images between sub-holograms instead of intensity images. Furthermore, a quantitative indicator, degree of image distortion, was applied to evaluate the synthetic results. Experiments are performed and the results verify that the proposed phase-image-based method is better than the state-of-the-art intensity-image-based techniques in the estimation of registration positions and provides a better synthesized final three-dimensional shape image.

Resolution-enhanced digital in-line holography by extension of the computational bandwidth

Higher resolution has always been the goal of imaging. Resolution enhancement in most holographic imaging methods are achieved by collecting more object spectrum. As a computational imaging technology, the resolution of digital holography is determined by the utilized bandwidth in both optical recording and numerical reconstruction. There is little study on whether the collected spectrum is effectively utilized during reconstruction. In this work, we propose a resolution-enhanced digital in-line holography under spherical wave illumination. The collected object spectrum, which cannot be fully used by conventional methods, is effectively utilized by the developed band-extended angular spectrum method with improved computational efficiency. Numerical analysis and optical experiments have been performed to demonstrate that the proposed method can effectively enhance the imaging resolution of digital in-line holography by extension of the computational bandwidth.

3D spatial resolution and spectral resolution of interferometric 3D imaging spectrometry.

Recently developed interferometric 3D imaging spectrometry (J. Opt. Soc. Am A18, 765 [2001]1084-7529JOAOD610.1364/JOSAA.18.000765) enables obtainment of the spectral information and 3D spatial information for incoherently illuminated or self-luminous object simultaneously. Using this method, we can obtain multispectral components of complex holograms, which correspond directly to the phase distribution of the wavefronts propagated from the polychromatic object. This paper focuses on the analysis of spectral resolution and 3D spatial resolution in interferometric 3D imaging spectrometry. Our analysis is based on a novel analytical impulse response function defined over four-dimensional space. We found that the experimental results agree well with the theoretical prediction. This work also suggests a new criterion and estimate method regarding 3D spatial resolution of digital holography.

Resolution enhancement in digital holography by self-extrapolation of holograms

It is generally believed that the resolution in digital holography is limited by the size of the captured holographic record. Here, we present a method to circumvent this limit by self-extrapolating experimental holograms beyond the area that is actually captured. This is done by first padding the surroundings of the hologram and then conducting an iterative reconstruction procedure. The wavefront beyond the experimentally detected area is thus retrieved and the hologram reconstruction shows enhanced resolution. To demonstrate the power of this concept, we apply it to simulated as well as experimental holograms.

Studies on aperture synthesis in digital Fresnel holography

Aperture synthesis can improve image resolution in digital holography by increasing the numerical aperture of the system. In this paper, we show that both the lateral resolution and image field of view can be enhanced at the same time using a more general Fresnel holography setup and hologram stitching. The impact of aperture synthesis on the lateral resolution is investigated both theoretically and experimentally. In the experiment, the synthesis is executed by moving the compact digital holographic system in two directions. Nine holograms are recorded and stitched into one hologram. The reconstruction results show that expanding aperture improves the lateral resolution. The lensless Fresnel holography used in this paper is demonstrated to have the ability to provide a larger numerical aperture and can compress the object spectrum in recording process.

Increment of lateral resolution in digital holography by speckle noise removal

Experimental features such as wavelength, camera specifications and reconstruction distance determine the theoretical limit for lateral resolution in digital holography. However, the actual experimental resolution limit is about 50% below such theoretical limit due to the high-contrast speckle noise presented in the reconstructed holograms. Recently, a technique has been introduced to reduce the contrast of speckle noise that is based on the superposition of uncorrelated hologram reconstructions of the same static object [5] (Garcia-Sucerquia et al., 2006). By this approach of reducing the contrast of the speckle noise, it is experimentally shown that an improvement of the order of 50% can be reached when 100 reconstructed images are superimposed.

Quantitative assessment of lateral resolution improvement in digital holography

Controllable experimental features such as wavelength, camera’s specifications and reconstruction distance, determine the theoretical limit for lateral resolution in digital holography; however, due to the speckle noise associated to any coherent imaging system it is not possible to reach this theoretical limit. In this paper, a quantitative study the lateral resolution for digital holography under the effect the speckle noise is carried out. It is shown that by reducing the contrast of the speckle noise the resolution capabilities of digital holography are improved; the signal-to-noise ratio of the reconstructed holograms is the metric use to quantitatively assess the reached resolution in the holographic experiments.

Resolution enhancement by aperture synthesis in digital holography

The resolution of digital holography as an optical imaging system is described by the point spread function of the system. Here the point spread function of double-aperture digital holography is determined. It promises the possibility of a resolution increase by the use of synthetic apertures, where we combine the digital holograms of two CCD arrays in one large hologram and reconstruct, or we superpose coherently the two reconstructed wave fields after a proper shift. An experimental method for the determination of this shift with subpixel accuracy is given. Furthermore, experimental results on numerically reconstructed wave fields from synthetic holograms stemming from two mutually shifted digital holograms of the same scene are presented.

Incoherent recovering of the spatial resolution in digital holography

We report on a technique to recover the spatial resolution of digitally recorded and reconstructed holograms of large objects. Due to the high-contrast speckle noise diminishes the spatial resolution in coherent imaging systems our proposal is based on the reduction of the contrast of it. This aim is achieved through the superposition on an intensity basis of digitally reconstructed holograms of the same static scene. We show a theoretical justification of the procedure and experimentally-obtained results of applying the technique with digitally reconstructed holograms of an object with very poor optical contrast.