Image Plane Hologram Research Articles

Fractional Fourier-transform off-axis digital holographic imaging

A fractional Fourier-transform digital holographic imaging method with resolution enhancement features is presented. In an optical configuration, an extended fractional Fourier-transform optical setup is set in the object arm of an off-axis digital holographic recording system to record a fractional Fourier-transform hologram via the optical interference of the fractional Fourier-transform wavefront of an object wave with a reference wave. For reconstruction imaging, the reconstruction approach for fractional Fourier-transform holograms is given. In the experiment, the fractional Fourier-transform digital holograms are recorded under the different recording parameters, and their amplitude images are effectively reconstructed. The imaging results demonstrate that the reconstruction-imaging resolution of fractional-order Fourier-transform holograms is obviously enhanced compared to that of conventional image-plane holograms. The presented fractional Fourier-transform digital holographic imaging with resolution enhancement and optical configuration flexibility provides, to our knowledge, a novel way for off-axis digital holographic imaging.

Dielectric Metasurface Enabled Compact, Single-Shot Digital Holography for Quantitative Phase Imaging.

Quantitative phase imaging (QPI) enables nondestructive, real-time, label-free imaging of transparent specimens and can reveal information about their fundamental properties such as cell size and morphology, mass density, particle dynamics, and cellular fluctuations. Development of high-performance and low-cost quantitative phase imaging systems is thus required in many fields, including on-site biomedical imaging and industrial inspection. Here, we propose an ultracompact, highly stable interferometer based on a single-layer dielectric metasurface for common path off-axis digital holography and experimentally demonstrate quantitative phase imaging. The interferometric imaging system leveraging an ultrathin multifunctional metasurface captures image plane holograms in a single shot and provides quantitative phase information on the test samples for extraction of its physical properties. With the benefits of planar engineering and high integrability, the proposed metasurface-based method establishes a stable miniaturized QPI system for reliable and cost-effective point-of-care devices, live cell imaging, 3D topography, and edge detection for optical computing.

Off-axis image plane hologram compression in holographic tomography – metrological assessment

In this paper, we present a novel study on the impact of lossy data compression on the metrological properties of holographic tomography reconstruction of the refractive index (RI). We use a spatial bandwidth-optimized compression procedure that leverages the properties of image plane off-axis holograms and standardized compression codecs, both widely applied in research and industry. The compression procedure is tested at multiple bitrates, for four different objects and against three reconstruction algorithms. The metrological evaluation is primarily done by comparison to the reconstruction from original data using the root-mean-squared error (RMSE). We show that due to differences between objects and different noise sensitivities of the reconstruction algorithms, the rate-distortion behaviour varies, but in most cases allows for the compression below 1 bit per pixel, while maintaining an RI RMSE less than 10-4.

Comparison of fixed and living biological cells parameters investigated with digital holographic microscope

The statistical analysis and comparison of biophysical parameters of living and fixed, mouse embryonic fibroblasts cells are presented. The parameters are calculated based on phase measurements performed by means of a digital, holographic microscope. The phases are retrieved from off-axis, image plane holograms, followed by custom image segmentation and statistical analysis of cells’ surface, phase volume and dry mass. The results indicated statistically significant differences between fixed and living cell parameters, which is an important message for setting methodology for further diagnosis based on quantitative phase (label-free) analysis.Full Text: PDF

Hyperspectral holographic microscopy of bio-objects based on a modified Linnik interferometer

We present a modified Linnik microinterferometer that can register image-plane hyperspectral holograms in reflection of various microobjects in incoherent light. A voice coil was integrated into the reference arm of the interferometer to enable mirror displacement. A set of interferograms is registered in each pixel of a high-speed CMOS camera. Post processing yields spectrally resolved image-plane holograms of the object. Quantitative phase images of red blood cells are obtained for each spectral component .

Hyperspectral holography: an alternative application of the Fourier transform spectrometer

An alternative application of the Fourier transform spectroscopy (FTS) principles and techniques is proposed. Registration of hyperspectral holograms in incoherent light by using FTS is suggested. This work generalizes and develops our previous results on registration of hyperspectral Fresnel’s and image plane holograms. Theoretical and experimental results are provided and discussed. The proposed method is applied to the problems of digital holographic microscopy, including speckle noise reduction, hyperspectral imaging, and coloring and optical profiling. A major advantage of the proposed method is that it allows simultaneous recovery of the amplitude, the phase, and the spectral frequency σ of the wave field in a single registration process.

Improved polygon-based method for subwavelength pixel pitch computer generated holograms

An improved polygon-based method is proposed for subwavelength pixel pitch computer generated holograms (CGHs). By employing the basic principle of image-plane holograms, and by optimizing the parameters, objects are reconstructed with high quality from the CGHs whose pixel pitch is smaller than wavelength. It is believed that the proposed method is potentially promising for future large viewing angle holographic 3D displays.

Weighted adaptive spatial filtering in digital holographic microscopy

Spatial filtering, a key point to realize real-time measurement, is used commonly in digital off-axis holography to extract desired terms. In this paper, we propose a weighted adaptive spatial filtering method by weighting the adaptive filtering window (obtained from image segmentation) based on signal to noise ratio. The advantages of this method are evaluated by simulations and further verified by recorded digital image plane holograms. The results demonstrate that our method is effective in suppressing noise and retaining the sharp edges in the reconstructed 3D profiles.

Multiplexed synthetic-aperture digital holography

We describe a digital holography imaging system that uses synthetic-aperture techniques for improved spatial resolution. The synthetic aperture is formed by illuminating an object from multiple angles, while a hologram multiplexing scheme is used to collect all of the data within a single camera exposure. We show how the multiplexing can be implemented efficiently with an image-plane hologram recording geometry, present results from a laboratory experiment, and discuss practical trade-offs of the approach.

Nonlinear filtering method of zero-order term suppression for improving the image quality in off-axis holography

In order to alleviate the crosstalk between the reconstructed image and the zero-order image in off-axis digital holography, this paper proposes a novel nonlinear filtering method to suppress the zero-order image. Its feasibility in eliminating the zero-order term is verified by the theoretical analyses, and its robustness is confirmed by applying the appropriately designed nonlinear filter to both a Fresnel hologram and an image plane hologram. Experimental results show that the image reconstructed from the proposed method has the characteristics of enhanced image contrast and improved signal-to-noise ratio. This method also accelerated the speed of processing via a simple calculation procedure.

Virtual-image generation in 360-degree viewable image-plane disk-type multiplex holography

By shifting the rotational axis of the recording film and recording the individual image-plane holograms in reversed sequence with the real-image holographic system [Opt. Express 18, 14012 (2010)], the disk-type multiplex hologram can be made to generate virtual image for walk-around viewing if the recording reference source point is maintained on the symmetry axis of hologram disk. Theoretical formulation and numerical simulation show the characteristics of the reconstructed image. Experimental results are also shown for qualitative comparison.

Coherence requirement in digital holography

In this paper the coherence requirement for different holographic setups (Fresnel hologram, Fourier hologram, and image-plane hologram) is compared. This analysis is based on the investigation of the recorded interference pattern from the superposition of reference wave and object wave in in-line and off-axis mode. The outcome of this investigation can support the choice of light source needed for certain digital holographic setups, as well as the selection of the best applicable setup to take advantage of new short coherence light sources. Moreover, as a byproduct of this investigation, the minimum required recording distance (focal length) to enable Nyquist sampling of the recorded hologram is obtained.

Analysis and interpretation of the Seidel aberration coefficients in digital holography

The most commonly used configurations in digital holography-namely Fourier holograms, Fresnel holograms, and image-plane holograms-are analyzed with respect to Seidel's wave aberration theory. This analysis is performed by taking into account the phase terms involved in the recording and reconstruction processes. The combined phase term from both processes is compared with the Gaussian-reference sphere, from which the wave aberration terms can be obtained. In conjunction with the analysis, for each of the aberration terms, conditions can be set to eliminate them. Wave aberrations are plotted to show how strongly different setups are affected.

Quantitative space-bandwidth product analysis in digital holography

The space-bandwidth product (SBP) is a measure for the information capacity an optical system possesses. The two information processing steps in digital holography, recording, and reconstruction are analyzed with respect to the SBP. The recording setups for a Fresnel hologram, Fourier hologram, and image-plane hologram, which represent the most commonly used setup configurations in digital holography, are investigated. For the recording process, the required SBP to ensure the recording of the entire object information is calculated. This is accomplished by analyzing the recorded interference pattern in the hologram-plane. The paraxial diffraction model is used in order to simulate the light propagation from the object to hologram-plane. The SBP in the reconstruction process is represented by the product of the reconstructed field-of-view and spatial frequency bandwidth. The outcome of this analysis results in the best SBP adapted digital holographic setup.

Very high speed cw digital holographic interferometry

It is reported for the first time the use of a very high speed camera in digital holographic interferometry with an out of plane sensitivity setup. The image plane holograms of a spherical latex balloon illuminated by a cw laser were acquired at a rate of 4000 frames per second, representing a time spacing between holograms of 250 microseconds, for 512 x 512 pixels at 8 bits resolution. Two types of tests were accomplished for a proof of principle of the technique, one with no constrains on the object which meant random movements due to non controlled environmental air currents, and the other with specific controlled conditions on the object. Results presented correspond to a random sample of sequential digital holograms, chosen from a 1 second exposure, individually Fourier processed in order to perform the usual comparison by subtraction between consecutive pairs thus obtaining the phase map of the object out of plane displacement, shown as a movie.

Image-plane disk-type multiplex hologram.

We demonstrate, both theoretically and experimentally, that a disk-type multiplex hologram can be fabricated as an image-plane hologram that is suitable for white-light line-source reconstruction. By adopting the method of direct object-image relationship, we build the theory based on the imaging property of lenses and on coordinate transformation. Numerical simulation shows the characteristics of this type of hologram. Experimental results reveal that the picket-fence effect that is encountered in the traditional multiplex hologram for images viewed at various distances has been eliminated. Using a reconstruction white-light line source of sufficient length, we observed an achromatic three-dimensional image.

Temporal phase unwrapping of digital hologram sequences.

A method for recording and evaluating digital image-plane holograms is presented. Hundreds of holograms of an object that has been subjected to dynamic deformation (e.g., vibrations) are recorded. The phase of the wave front is calculated from the recorded holograms by use of a two-dimensional digital Fourier-transform method. By temporal phase unwrapping it is possible to determine the absolute deformation (included the direction of motion) of the object. Experimental results are presented, and the advantages of temporal phase unwrapping compared with spatial phase unwrapping are discussed.

Image-plane conical multiplex holography by one-step recording

We have demonstrated that it is possible to fabricate the conical multiplex hologram as an image-plane hologram using a simple optical system. Based on ray tracing, the imaging properties of lenses, and coordinate transformation, a theory directly relating the observed image point to the original object point is formulated, which facilitates numerical simulation of the whole observed image. A search over the holographic parameters shows that a condition for the least-distorted image, limited by the particular shape of the hologram, can be obtained. Numerical simulation is given, together with some experimentally reconstructed images of a real object. The result shows that it indeed eliminates the so-called picket-fence effect as encountered in the traditional multiplex holography.

Cross talk in holographic memories with lensless phase-conjugate holograms.

Recently holographic memory with lensless phase-conjugate holograms has attracted much attention because it opens up the possibility of compact holographic memories. We investigate cross-talk noise in compact holographic memories with angular multiplexing. It turns out that the optimum angular separation is the same as that for the Fourier plane hologram in the leading order and that the noise-to-signal ratio is independent of the positions in the output plane, similar to the case of the image plane hologram.

Image-plane cylindrical holographic stereogram

A two-step holographic process is introduced to fabricate a cylindrical multiplex hologram as an image-plane hologram. By adoption of the achromatic angle in the process the hologram is capable of generating an achromatic image. The most important factors, the location as well as the width of the viewing slits, that affect the quality of the observed image are analyzed and discussed. The change of aspect ratio for the observed image as a function of the viewing distance is theoretically and numerically analyzed. This method can not only eliminate the annoying picket-fence effect but can also increase the vertical viewing range for the observer. Computer simulations as well as experimental results are provided.