Holographic Imaging System Research Articles

Progress in volume holographic imaging system

Volume holographic imaging system (VHIS) incorporates a volume hologram grating (VHG) as the critical optical field processing component in a new imaging system.High spectral resolution and high sensitivity in obtaining 3D information at multi-depths are achieved without time consuming scanning mechanism and complex reconstruction algorithms by utilizing the Bragg diffraction selectivity and degeneracy properties.We briefly introduced the system structures and principles,then we presented intensively on how these VHGs were devised and VHIS were configured into the qualified spectral VHIS (S-VHIS) and multiplexed VHG imaging systems.The superiorities over conventional imaging systems and the features to be improved of VHIS were summarized and discussed. Key words: Volume holographic imaging system; Volume hologram grating; Spectral imaging; 3D multi-depth imaging

A Holographic In-Line Imaging System for Meteorological Applications

A digital holographic in-line imaging instrument aimed for meteorological measurements is presented. The system is designed to capture detailed information of macroscopic hydrometeors in a large imaging volume. We suggest the use of holographic imaging to overcome the depth of field limitations of conventional macroimaging systems in meteorological imaging applications. The first low magnification holographic imaging prototype built for measuring free falling hydrometeors in the size range of a few tens of micrometers to several millimeters is described. The design of the imaging setup is discussed in detail, calibration and characterization measurements of magnification, position accuracy, and resolving power are presented. Field measurements during snow falls and rain were made and reconstructed images of snowflakes and raindrops are shown and analyzed. The results of laboratory tests and the field tests show high quality and resolution of reconstructed holograms to enable detailed image analyses on snowflakes, raindrops, and other types of hydrometeors.

Simultaneous multiplane imaging of human ovarian cancer by volume holographic imaging

Ovarian cancer is the most deadly gynecologic cancer, a fact which is attributable to poor early detection and survival once the disease has reached advanced stages. Intraoperative laparoscopic volume holographic imaging has the potential to provide simultaneous visualization of surface and subsurface structures in ovarian tissues for improved assessment of developing ovarian cancer. In this ex vivo ovarian tissue study, we assembled a benchtop volume holographic imaging system (VHIS) to characterize the microarchitecture of 78 normal and 40 abnormal tissue specimens derived from ovarian, fallopian tube, uterine, and peritoneal tissues, collected from 26 patients aged 22 to 73 undergoing bilateral salpingo-oophorectomy, hysterectomy with bilateral salpingo-oophorectomy, or abdominal cytoreductive surgery. All tissues were successfully imaged with the VHIS in both reflectance- and fluorescence-modes revealing morphological features which can be used to distinguish between normal, benign abnormalities, and cancerous tissues. We present the development and successful application of VHIS for imaging human ovarian tissue. Comparison of VHIS images with corresponding histopathology allowed for qualitatively distinguishing microstructural features unique to the studied tissue type and disease state. These results motivate the development of a laparoscopic VHIS for evaluating the surface and subsurface morphological alterations in ovarian cancer pathogenesis.

Volume Holographic Reflection Endoscope for In-Vivo Ovarian Cancer Clinical Studies.

We present the design for an endoscopic system capable of imaging tissues of the ovary at two selected imaging depths simultaneously. The method utilizes a multiplexed volume hologram to select wavefronts from different depths within the tissue. It is the first demonstration of an endoscopic volume holographic imaging system. The endoscope uses both gradient index (GRIN) optical components and off the shelf singlet lenses to relay an image from the distal tip to the proximal end. The endoscope has a minimum diameter of 3.75 mm. The system length is 30 cm which is connected to a handle that includes the holographic components and optics that relay the image to a camera. Preliminary evaluation of the endoscope was performed with tissue phantoms and calibrated targets, which shows lateral resolution ≈ 4 μm at an operating wavelength of 660 nm. The hologram is recorded in phenanthraquinone doped poly methacrylate and is designed to produce images from two tissue depths. One image is obtained at the tissue surface and the second 70 μm below the surface. This method requires no mechanical scanning and acquires an image at the camera frame rate. The preliminary ex-vivo results show good correlation with histology sections of the same tissue sections.

Millimetre‐wave end‐fired antenna array for active 3D holographic imaging system

A compact Ka-band (26.5–40 GHz) dielectric rod end-fired antenna array for the three-dimensional (3D) active holographic imaging system is presented. Without horn shape feeding, the new antenna array is specially designed with characteristics such as small size, high gain, good radiation pattern, easy realisation, low insertion loss and low mutual coupling. In the imaging system, the spacing of sending and receiving antenna units is 1.5 wavelengths with mutual coupling <−30 dB and a gain of 12–16 dB. The results and analysis provide guidelines for the design of millimetre-wave end-fired antenna arrays.

Research on speckle denoising by lensless Fourier transform holographic imaging with angular diversity

The signal-to-noise ratio and resolution of the reconstructed image is seriously influenced by speckle noise in digital holography, so it is essential to reduce the speckle noise and improve the image quality. Intensity correlation between two speckle patterns with the rectangle speckle spot is analyzed and deduced, and the minimal angular difference of illumination beams is given quantitatively under a special situation. A lensless Fourier transform holographic imaging system with angular diversity is designed based on the lens property, in which the direction of the wave can be changed by shifting the fiber instead of conventionally rotating the mirror, and the formor can change the direction of illumination with a fixed illumination size and location. Eighty one holograms with uncorrelated speckle patterns are recorded at different illumination angles by shifting the fiber. Then a digital reconstruction is achieved only by a fast Fourier transform, and the multiple reconstructed images are averaged. Experimental results show that the speckle contrast of the averaged reconstructed image can be reduced to 14.6% that from a single reconstructed image, and the signal-to-noise ratio is improved 6.9 times. This proposed digital holographic imaging method can suppress the speckle noise greatly, has a simple setup, and is easy to operate.

Improving the Atmosphere Turbulence Tolerance in Holographic Ghost Imaging System by Channel Coding

Atmospheric turbulence (AT) severely cuts down the image resolutions of holographic ghost imaging (HGI) since orbital angular momentum (OAM) entangled states are associated with the spatial distribution of wave-functions. In this paper, we investigate the method to improve AT tolerance in HGI system. Since Reed-Solomon (RS) codes are important non-binary error correction codes which have strong correcting ability against noise, we use RS codes to develop a RS-coded HGI scheme. In order to verify the improvement quantitatively, we compute and compare the Peak Signal-to-Noise ratio (PSNR) of the reconstructed image in HGI without and with RS codes. The numerical results show that PSNRs go down quickly with the increase of the strength of turbulence, and they are improved greatly by using RS codes. For different grayscale objects, the results show that the improvement by RS codes is enhanced with the increasing correction ability, but it does not work for the same object by enlarging its grayscale to suit for more errors.

Generation and evolution of the terahertz vortex beam

Based on the complementary V-shaped antenna structure, ultrathin vortex phase plates are designed to achieve the terahertz (THz) optical vortices with different topological charges. Utilizing a THz holographic imaging system, the two dimensional complex field information of the generated THz vortex beam with the topological number l=1 is directly obtained. Its far field propagation properties are analyzed in detail, including the rotation, the twist direction, and the Gouy phase shift of the vortex phase. An analytic Laguerre-Gaussian mode is used to simulate and explain the measured phenomena. The experimental and simulation results overlap each other very well.

An approach for sensing marine plankton using digital holographic imaging

The goal of this paper is to use digital holographic imaging for sensing marine plankton in recording sampling volume. The process stage of this approach includes: wavefront recording using in-line holographic recording set up and numerical reconstruction using Fresnel approximation and convolution algorithm. So, by capturing hologram of marine plankton and reconstructing hologram, the recorded optical field of marine plankton is retrieved. Digital holographic imaging is an extremely powerful technique for the study of marine plankton fields as it allows instantaneous, noninvasive, high-resolution recording of substantial volumes. Finally, this paper presents that it is possible for digital holographic imaging system to sense marine plankton according to laboratory results.

Biological controls on resuspension and the relationship between particle size and the Kolmogorov length scale in a shallow coastal sea

Abstract Measurements of suspended particle matter (SPM) and turbulence have been obtained over five tidal surveys during spring and summer 2010 at station L4 (50.25° N 04.22° W, depth 50 m), in the Western English Channel. The relationship between turbulence intensity and bed stress is explored, with an in-line holographic imaging system evaluating the extent to which material is resuspended. Image analysis allows for the identification of SPM above a size threshold of 200 μm, capturing particle variability across tidal cycles and the two seasons. Dissipation of turbulent kinetic energy, which exceeds 10− 5 W kg− 1, yields maximum values of bed stress of between 0.17 and 0.20 N m− 2, frequently resulting in the resuspension of material from the bed. Resuspension is shown to promote aggregation of SPM into flocs, where the size of such particles is theoretically determined by the Kolmogorov microscale, lk. During the spring surveys, flocs of a size larger than lk were observed, though this was not repeated during summer. It is proposed that the presence of gelatinous, biological material in spring allows flocculated particles to exceed lk. This suggests that under specific circumstances, the limiting factor on the growth of flocculated SPM is not only turbulence, as previously thought, but the presence or absence of certain types of biological particle.

A theoretical investigation into the 3D point spreading situation of a scanning holographic imaging system based on random phase encoding

In this paper, by analyzing variance and noise probability distribution of the reconstructed image, a point spreading situation of adjacent section under the conventional optical scanning holography (OSH) method and a new one based on random-phase encoding (RPE) are studied. Simulation results show that, compared to the conventional OSH at the same de-focus distance, the RPE-OSH can lead the distribution of reconstructed adjacent sections to be more homogeneous and manifested as a speckle-like pattern on the in-focus image. Further study shows that the complex amplitude probability distribution of adjacent section meets the shape of Gaussian curve, and noise can be filtered out by some corresponding filters. So aliasing and interference on the in-focus image can be removed.

The Fourier Spectrometer as a Holographic Micro-Object Imaging System in Low-Coherence Light

A new method of obtaining images of microobjects by processing digital interferograms, recorded using a modified Fourier spectrometer, is proposed. The process by which interferograms, which image the spatial characteristics of a microobject, are formed, is described. The requirements imposed on the width of the source radiation spectrum in order to transmit the spatial structure of the object are discussed. Results of an experiment to record the image of a microobject in white light are presented.

Complete presentation of the Gouy phase shift with the THz digital holography

Three dimensional information of the Gouy phase shift in a converging spherical terahertz (THz) beam is directly observed by using a THz balanced electro-optic holographic imaging system. The major properties of the Gouy phase shift are presented, including the longitudinal and transverse distributions, relationships with the frequency and the f-number, influence on the THz polarization. The imaging technique supplies an accurate and comprehensive measurement method for observing and understanding the Gouy phase shift.

Generalized linear reconstructing algorithm based on homomorphic signal processed in digital holographic microscopy

In order to improve the accuracy and the speed of reconstructing an image, the digital holographic generalized linear reconstructing algorithm based on homomorphic signal processing is proposed. By using the pre-magnification digital holographic imaging system and the principle of homomorphic signal processing, the proposed algorithm is analyzed theoretically. The achieving condition for and reconstructing process of the proposed algorithm is presented. Then the theoretical results are demonstrated by simulations and experimental data. Results show that the zero-order term of digital hologram frequency spectrum can be eliminated effectively by the proposed algorithm so as to realize the high-precision reconstruction of the digital hologram. Because a whole quadrant is chosen as the filtered area, the manual frequency filtering operation needed in common linear reconstructing algorithm is avoided and then the reconstructing speed is improved greatly. Meanwhile, the high-frequency component of the reconstructed original image can be reserved up to the hilt so that the high resolution image can be achieved.

球面参考光预放大数字全息成像系统分辨力

球面参考光预放大数字全息成像系统分辨力

Optimized digital micro-holographic imaging system

Based on the analysis of the recording and reconstructing of hologram and the point spread function of pre-magnification digital micro-holographic system (PMDMHS), the performances of the six common PMDMHSs are compared in imaging resolution, imaging quality and conveniences, for the first time to our knowledge. The results show that the digital image-plane holography (DIPH) has the highest imaging resolution and the best imaging quality; the resolution of DIPH is independent of the photosensitive surface size of the recording device; this system can completely record the information about the object transmitted through the micro-objective (MO); it is not needed to consider the size of illuminated region of object. Moreover, the reconstruction process of DIPH is very simple. DIPH is an optimized digital holographic imaging system. The DIPH with equal curvature of reference wavefront and object wavefront is very conducive to phase unwrapping and phase aberration compensation; therefore DIPH is more suitable for phase microscopy. The experimental results demonstrate the validation of the theoretical analysis.

High-resolution digital holographic microscopy realized by small size CCD camera

In order to achieve high-resolution imaging by reducing the cost of digital holographic microscopy system, the recording and reconstruction process of image-plane digital holographic system (IPDHS) and its point spread function are analyzed. Then, the determination factor of lateral resolution of IPDHS is investigated. It is concluded that the dependence of lateral resolution of IPDHS on the photosensitive surface size of the recording device is very weak, which is completely different from the common knowledge that the lateral resolution of digital holographic imaging system can be improved by using large size recording device. Then the imaging characteristics of an IPDHS are analyzed. The results show that the information about the tested object can be completely recorded and reconstructed by image-plane digital holography, and that the lateral resolution of IPDHS is higher than that of pre-magnification digital holography. Two IPDHS with plane and spherical reference wave are built. The experimental results are in accordance with the theoretical analysis.

Fourier transform digital holographic adaptive optics imaging system

A Fourier transform digital holographic adaptive optics imaging system and its basic principles are proposed. The CCD is put at the exact Fourier transform plane of the pupil of the eye lens. The spherical curvature introduced by the optics except the eye lens itself is eliminated. The CCD is also at image plane of the target. The point-spread function of the system is directly recorded, making it easier to determine the correct guide-star hologram. Also, the light signal will be stronger at the CCD, especially for phase-aberration sensing. Numerical propagation is avoided. The sensor aperture has nothing to do with the resolution and the possibility of using low coherence or incoherent illumination is opened. The system becomes more efficient and flexible. Although it is intended for ophthalmic use, it also shows potential application in microscopy. The robustness and feasibility of this compact system are demonstrated by simulations and experiments using scattering objects.

Dynamic holographic images using poly(N-vinylcarbazole)-based photorefractive composites

We present the optimization of poly(N-vinylcarbazole) (PVCz)-based photorefractive composite films for use in a dynamic holographic imaging system. The compositions of the composite films used in this study included PVCz/4-azacycloheptylbenzylidenemalononitrile (7-DCST)/carbazoylethylpropionate (CzEPA), N-ethylcarbazole (ECz), benzyl n-butyl phthalate (BBP)/[6,6]-phenyl-C61-butyric acid methyl ester (PCBM), or 2,4,7-trinitro-9-fluorenone (TNF) (44/35/20/1 wt%). PVCz with molecular weights of 23 000, 100 000, 290 000, 370 000, and 810 000 gmol−1 were used. The PPC film (PVCz with Mw: 370000/7-DCST/CzEPA/TNF, 44/35/20/1 wt%) was observed to be the most well-balanced for photorefractive performance. To demonstrate the practical application of these films, dynamic holographic images were reflected from a spatial light modulator (SLM). The optimized PPC film was used in the dynamic holographic imaging system, and well-balanced dynamic holographic images were obtained.

Experimental research on terahertz Gabor inline digital holography of concealed objects

Terahertz (THz) radiation has the characteristics of penetrating nonmetallic and nonpolar materials that are opaque to visible light, which makes THz digital holography have an application potential of imaging concealed objects with certain barriers. A CO(2) pumped continuous THz Gabor inline digital holographic imaging system was utilized to conduct experimental researches on imaging concealed objects. Paper, Teflon, a plastic express envelope, and silicon wafers were used as barriers. High-quality reconstructed images were obtained. Compared with the reconstruction results without any barriers, the results verify the feasibility of THz Gabor inline digital holography in imaging concealed objects.