In this study, we report spatial resolution enhancement and image quality improvement of a digital holographic microscopy using speckle patterns generated from a moving diffuser. In this method, speckle patterns are produced by moving a diffuser in the in-plane directions and incident on an object. In comparison with other methods for generating speckle illuminations, it realizes a simple and low-cost optical setup in digital holographic microscopy.
KEYWORDS: Digital holography, 3D image reconstruction, Speckle, Holograms, Image sensors, Image quality, Digital recording, Image processing, Digital imaging, Denoising
In this study, we demonstrate reduction of speckle noises of digital holography using speckle correlation properties in the longitudinal direction. In this method, it is assumed that digital holograms of diffuse objects are recorded on an image sensor. Using multiple holograms recorded by moving the image sensor to the longitudinal direction, the speckle noise of a reconstructed image is reduced and therefore the image quality is improved by the proposed method.
The reflection and transmission of coherent light from a biological system can yield information about its condition. In the case of blood exposed to the air, there is a change in the properties of the speckle patterns observed in the coagulation process. This can be studied by means of the rate of temporal variation, the contrast, and also the fractality of patterns. The fractality of the speckle pattern can be investigated by a fractal dimension, which can quantify a level of the complexity of platelet aggregation structure and a fibrin network formed in the process of blood coagulation. In addition, dynamic characteristics of a movement in blood also contain information on the progress of the coagulation process. Fractality and dynamic characteristics are investigated simultaneously for speckle patterns observed in the coagulation process of stored horse blood. Experimental results show the feasibility of the proposed method for detecting hemolysis and formation of platelet aggregation structure and the fibrin network during the coagulation process.
Digital holographic microscopy (DHM) is actively investigated in the field of bio-imaging as a quantitative phase microscopy. In recent years, digital holographic technique for enhancing the spatial resolution using speckle patterns has been reported by several research groups, and we reported the enhancement of the spatial resolution in DHM using speckle illuminations generated from a ring-slit aperture. In this study, by applying the two-wavelength method to DHM using speckle illuminations, we realize the enhancement of spatial resolution and the extension of measurement range of shape measurement in DHM.
It has been known that speckle images observed for living bodies illuminated by laser light sometimes show fractal appearances. This has been utilized, for example, for tomographic imaging of the porcine arterial tissue. Fractality can also be seen in speckle images generated by the blood in the process of coagulation. A fractal dimension (FD) of the speckle image is, thus, expected to be a global marker of haemostasis, arteriosclerosis, and so on. In the present study, we experimentally investigate fractality of biospeckle pattern observed in coagulation process of horse blood.
In this study, we propose digital holographic microscopy using speckle illuminations and two-wavelength method. In this method, the spatial resolution is enhanced by speckle illuminations, and the measurement range in depth direction is extended by two-wavelength method. We demonstrate the proposed method experimentally.
In this study, we propose a method to enhance the spatial resolution of digital holographic microscopy with
speckle illuminations. In this method, speckle patterns are generated from coherence light passing through ringslit
apertures instead of the most typical circular apertures, to obtain higher numerical aperture. The results
show that a reconstructed image with the higher resolution is obtained using ring-slit apertures.
In this study, we propose a method to enhance the spatial resolution of digital holographic microscopy with speckle-illumination. In this method, speckle patterns are generated from coherence light passing through ring-slit apertures instead of the most typical circular apertures, to obtain higher numerical aperture. The results show that a reconstructed image with the higher resolution is obtained using ring-slit apertures.
Since the optical inter-satellite communication has attractive advantages such as high-speed transmission with high
confidence, almost no electronic magnetic interference, and low power consumption, it has been activity investigated.
However, directivity control of the laser beams requires a bulky and complicated system in satellite mobile
communications. A more flexible and high accurate system with small and simple mechanism has been desired. In this
study, we propose a new method of optical inter-satellite communication with a dynamically reconfigurable optical
directional device in which diffraction gratings are automatically rewritten and reorganized in response of incident
conditions by moving satellites. For realizing such a device, we have developed Sn2P2S6 crystals which have a high
sensitive photorefractivity and dynamic reconfigurable property. Furthermore, this crystal has hundreds times faster
response than conventional photorefractive materials such as BaTiO3. These features are extremely advantageous to
construct a high-speed and flexible communication system with a large tolerance to displacement of moving satellites.
To investigate the possibility of the dynamically reconfigurable optical inter-satellite communication system, we
experimentally evaluate the temporal and spatial characteristics of Sn2P2S6 crystals for the variation of the beam incident
angle. Moreover, the diffraction beam from the crystal has phase conjugate wavefronts of the beam entering from the
counter direction. We try to utilize this behavior to suppress the beam spread and to reduce the background light such as
sunlight with a spatial filtering technique that has sensitivity in wavefront differences of the signal and background light.
A new method for improving detection performance of modified amplitude-modulated joint transform correlators by using a smoothed amplitude-modulated filter (AMF) is proposed. Smoothing of the filter is done to reduce dependence of the detection performance on a threshold value. Simulation results show that recognitions of intratarget scenes can be optimized by using a single smoothed AMF generated at low threshold.
Effects of the threshold value on the multiple-target detection performance of a modified amplitude-modulated joint transform correlator are studied on the basis of computer simulations, using human fingerprint and face images. Correlation outputs are quantitatively measured by means of a primary-to-secondary peak ratio and a peak-to-correlation-deviation ratio. The simulation results reveal that the detection of high-contrast targets can be optimized by using a low-threshold. In the case of low-contrast targets, the optimization depends on spatial-frequency contents and noise.
Second-order statistics of phase are investigated by computer simulations for speckles produced by illuminating a diffuser by coherent light with a negative power-law intensity distribution. Under such an illumination condition, the generated speckles are known to show fractal properties in their intensity distributions, thus being called fractal speckles. The present study shows that the phase of fractal speckles, as well as of ordinary speckles, exhibits a self-affine property of the type of fractional Brownian motions.
Speckle patterns produced by scattering in random media are sometimes employed as tools for optical measurements and information processing. In those applications of speckles, spatial and temporal correlation properties play sometimes fundamental roles. Therefore, design and control of correlation properties in the scattered fields are an attractive and important subject. From this viewpoint, two types of speckle patterns having extraordinary spatial correlations are reviewed and discussed in this article. The first type of scattered fields is nondiffracting, or propagation-invariant speckles. This type of waves has Bessel-type long tails in transverse intensity correlations and extremely long correlation in the propagation direction. Two schemes for generating nondiffracting speckles by means of an annular aperture and an axicon lens are described. Relations to general nondiffracting beams are also discussed briefly. The second type of waves having long-range correlations is fractal speckles, which have negative power- law intensity correlations in lateral and longitudinal directions. Results of computer simulations are shown for fractal speckles with wide range of a parameter D governing the spatial extent of correlations.
KEYWORDS: Fractal analysis, Diffusers, Correlation function, Speckle pattern, Speckle, Near field diffraction, Far-field diffraction, Scattering, Monte Carlo methods, Spatial filters
Some recent development on the properties of speckle intensity distributions that have fractal properties are presented. First, computer simulations are discussed for speckles produced by power-law illuminated diffusers with a wide range of the exponent 0 < D < 3 for the power function. By the simulation, the previous theoretical prediction for 1 < D < 3 is confirmed, and new results are found for D <EQ 1. Next, axial correlation property in the Fresnel diffraction region of the power-law illuminated diffuser is discussed on the theoretical and experimental basis. It is theoretically shown that the axial correlation function obeys the power function with the exponent of D - 2, which is subsequently confirmed by experiment. Finally, a method for producing fractal speckles in the image plane of a scattering object is proposed. Such speckles are actually generated and their power-law correlation behavior is demonstrated experimentally.
Some topics on the light scattering phenomena in random mass fractals are reviewed. First, the basic property of the single forward scattering is introduced. Then, as an example of multiple scattering effects from fractal media, fractal dependence of coherent peaks in the enhanced backscattering is discussed. These two types of scattering phenomena in mass fractals are interesting from a diagnostic or analyzing viewpoint of fractal optics. On the other hand, the third one treats with the generation of fractal speckles, aiming at optical synthesis of desired fractality. Simple methods for producing random intensity distributions with mass fractal properties in diffraction and image regions are described.
Intensity distributions and their correlation properties are investigated theoretically and experimentally for speckle fields produced by a double scattering process by means of a random fractal object and an ordinary phase screen. Speckle patterns generated in the Fraunhofer diffraction plane (a focal plane of a Fourier-transforming lens) of the second diffuser have clustered and self-similar appearances, and hence are regarded to be fractal. Their intensity correlation functions are shown to obey a power law. The similar intensity distributions and correlation properties are also observed in lateral planes at different distances from the lens. The correlation function in the longitudinal direction is also examined and found to have a power-law behavior, indicating the existence of 3D fractality of the field. Finally, fractality of speckle patterns produced in the Fresnel diffraction region of the ordinary diffuser is demonstrated.
We sometimes want to know some information hidden in highly dense media in which the light suffers a strongly multiple scattering, such as the existence of a tumor in a biological tissue and a state of a material behind a layer of paint. In such situations, optical measurement techniques which have the advantage of a non-contact and non-invasive method have been remarked and studied actively by many scientists.1 In the present paper, we pay attention to speckle-like intensity fluctuations generated by multiply scattered light and to their angular correlation properties, and investigate an effect of objects buried in highly dense media on an angular correlation function of the scattered intensity. The angular correlation function is derived theoretically and numerical simulation results are shown.
Speckle patterns having fractal properties are produced in the image plane as well as in the diffraction regions of a planar diffuser. Such a pattern has no definite speckle size and exhibits a statistical self-similar feature within a limited extent. The intensity correlation function is shown to obey a power-law, which is a typical property of fractal distributions.
Enhanced backscattering from random fractal media is investigated by means of Monte Carlo simulations based on a randomized Menger sponge model of the media. Dependence of the coherent peak on the fractal dimension D is obtained for 1.5 less than or equal to D less than or equal to 2.79, and it is found that the slope of the peak shoulder in a log-log plot increases with D until D equals 2.5 and then decreases for a further increase in D. This behavior is elucidated on the basis of probabilities of the scattering free path, the number of scattering in a multiple scattering path, and the separation of two end particles in a scattering path.
Effect of objects buried in highly dense media on the properties of angular intensity correlation of the scattered light is investigated by means of a theoretical approach and numerical simulations. In the case of an object located just behind the scattering medium, a Fourier transform relation between the angular correlation function and the intensity distribution in the illumination plane where the object exists is derived theoretically for transmitted light. When the object is buried in the medium, such a boundary condition is not satisfied, and it was found from the simulation results that the effect of the object on the angular correlations can be observed more strongly for the object being somewhat deep rather than near the output surface. For reflected light, on the other hand, the influence of the object on the angular correlation function becomes small because of a scattering component not reaching the object.
It is shown that reproduction of sounds from old wax cylinders using various optical methods gives quite excellent materials in optics education. The laser-beam reflection method is explained by the geometrical optics, and is further discussed on the basis of the diffraction theory. Various techniques for improving the quality of reproduced sounds are introduced. Fiber optics is used for reproduction of sounds in a low pressure stylus contacting method. Applications of the laser- beam reflection method to other analogue recordings are introduced.
A new compact optical processor is proposed for implementing the synaptic interconnections of artificial neural networks. As a consequence of exploiting coordinate transformations, the synaptic elements are compact and applicable to any information. Hence, for use in conjunction with spatial light modulators, the proposed system leads to a programmable neural network. The synaptic interconnections between neurons are performed by means of diffractive optical elements. The required local phase variations of the diffractive optical elements are determined by using the Wigner distribution function. Preliminary experimental verification is presented for the 1-D and the 2-D synapses of neural networks
A new method is proposed for evaluating the local displacement of objects in speckle photography by using a Wigner distribution function (WDF). It is applied to evaluate the displacement of 1D specklegrams as well as specklegrams of the ground glass and rubber plate which are slightly shifted and stretched, respectively. As a preliminary study, the local spectra W(x,(omega) ) are qualitatively and quantitatively verified in comparison with the theoretical results and the conventional Young''s interference fringes. The results show the feasibility of evaluating the displacement of objects using the WDF.
Since the introduction of the concept of fractal by Mandelbrot1, diffraction phenomena
by fractal objects have attracted several researchers26. Some of them have treated
the diffraction from random phase screens with fractal properties24. Others have discussed
the diffraction by simple regular fractals. In a recent paper7, we reported the
Fraunhofer diffraction by Koch curves which are more complicated fractals in the sense
that they may contain a rotational operation in their generation. In this paper, we discuss
the dimensionality of regular Koch curves and their diffraction patterns, and extend
the discussion to the randomized Koch curves and their diffraction patterns.
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