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We investigated a method for the angular multiplexing and de-multiplexing of digital holograms recorded in microscope off-axis configuration. The multiplexing has been performed rotating numerically one hologram at different angles and adding all the rotated holograms to obtain a single synthetic digital hologram. Then the digital holograms were de...
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... hologram is padded with zeros [15] up to 1400 X 1400 square pixels to allow the whole five rotated holograms to be contained in the multiplexed hologram. Obviously the dimension of the padding window depends on the chosen angle of rotation. Then we add the five holograms in order to multiplexed them in a single synthetic hologram shown in Fig. 1. Moreover, a reference hologram is acquired in a region of the sample far from the MEMS in order to calculate the phase retardation caused only by the MEMS subtracting the phase shift due to the interferometer. The reference hologram is multiplexed in the same way of the MEMS hologram. The multiplexing of the reference hologram is ...
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... be employed to multiplex digital holograms during the recording process by rotating the CCD array in five different angular positions. The acquired holograms are then multiplexed in single synthetic hologram. We show here the results obtained by means of this multiplexing approach versus the pure NM technique proposed in the previous sections. Fig. 10 shows the multiplexed holograms (a,b) and their amplitude reconstruction in the image plane (c,d) and in the BFP (e,f) obtained by rotating the CCD (left column) and by the NM (right column) technique, respectively. The specimen, used in this case, is a lithium niobate crystal with a reversed domain of hexagonal shape having an optical ...
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... main difference between the two set of images is the shape of the five multiplexed holograms and of their respective reconstructions. On the contrary, the fringe orientation and then the position of the five images in BFP is the same in both cases (see Fig.10 (e) and 10(f)). ...
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... the contrary, the fringe orientation and then the position of the five images in BFP is the same in both cases (see Fig.10 (e) and 10(f)). Therefore, the holograms multiplexed by rotating the CCD can be de-multiplexed by the same procedure explained in the section 3. The obtained amplitude and phase reconstructions are shown in Fig.11. Looking at the phase profiles, across the wall of the hexagonal domain, it results that the phase step value doesn't change in the two cases. ...
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... discuss briefly the impact of the hologram on the phase reconstruction precision. In Fig. 12 we present a graph of the phase standard deviation (std) on an identical area of the phase reconstructions vs. the number of multiplexed holograms. It results that the std increases slightly with the number of multiplexed holograms. We note that the phase std in the case of two multiplexed holograms is significantly increased compared ...
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... Holographic multiplexing enables the simultaneous acquisition of more than a single complex wavefront in a single camera exposure [34][35][36] . A standard off-axis hologram possesses parallel linear interference fringes, which act as a carrier frequency for the complex wavefront data of the sample, represented by the corresponding crosscorrelation (CC) terms in the spatial frequency domain, which prevents overlap with the central autocorrelation (DC) term and enables reconstruction of the sample complex wavefront from a single image 37 , as shown in Fig. 1a. ...
Dynamic holographic profiling of thick samples is limited due to the reduced field of view (FOV) of off-axis holography. We present an improved six-pack holography system for the simultaneous acquisition of six complex wavefronts in a single camera exposure from two fields of view (FOVs) and three wavelengths, for quantitative phase unwrapping of thick and extended transparent objects. By dynamically generating three synthetic wavelength quantitative phase maps for each of the two FOVs, with the longest wavelength being 6207 nm, hierarchical phase unwrapping can be used to reduce noise while maintaining the improvements in the 2π phase ambiguity due to the longer synthetic wavelength. The system was tested on a 7 μm tall PDMS microchannel and is shown to produce quantitative phase maps with 96% accuracy, while the hierarchical unwrapping reduces noise by 93%. A monolayer of live onion epidermal tissue was also successfully scanned, demonstrating the potential of the system to dynamically decrease scanning time of optically thick and extended samples.
... www.nature.com/scientificreports/ and the use of special optical components [19][20][21][22][23] , to record different areas of the object in a single-shot, have been developed and proved to be more efficient ways to extend the FOV of the imaging system. In this work, we present a new method of optically multiplexing two FOVs into a single off-axis interferogram, by using a special optical component: the Fresnel bi-prism, in the object beam, to double the FOV in DH. ...
We propose a new configuration of single-shot off-axis digital holographic system to realize double the camera field-of-view (FOV) of the existing off-axis Mech-Zehnder type holographic setup. The double FOV is obtained by double spatial frequency multiplexing of two different areas of an object beam by inserting a Fresnel bi-prism in it, which divides the object beam into two, both carrying different object information. The image sensor is placed at the plane where these two different FOVs overlap so as to record simultaneously two parts of the wavefront of the object in a single-shot. The multiplexed hologram is carrying two interferometric images corresponding to two different FOVs of the object which are modulated with two different spatial carrier frequencies. The feasibility of the proposed digital holographic system is experimentally demonstrated by imaging two different areas of a resolution test target. The limitation of the proposed system and a method to overcome it, are also discussed. The proposed system is useful in a wide range of applications including microscopy and optical metrology.
... Holographic multiplexing offers a method of recording multichannel wavefronts into one hologram. [14,[41][42][43][44][45][46][47][48] The multiplexed holograms contained different wavefronts of the sample with the same number of pixels. The encoded complex wavefront can be completely reconstructed from a single exposure. ...
Modern quantitative optical imaging is developing toward high throughput and powerful data processing capabilities. Holography is a powerful technique to characterize quantitative phase delays introduced by light–matter interactions. The spatial bandwidth utilization of imaging sensors in digital holography can be expanded via an off-axis multiplexing technique, which is a powerful tool for high-throughput quantitative optical imaging. However, the highest bandwidth utilization of sensor is limited at 58.9% to keep the signal spectra away from the zeroth spectra. Kramers–Kronig relation is introduced into the off-axis multiplexing technology to allow for the overlapping between the signal spectra and unwanted spectra. The bandwidth utilization of sensor in a diffraction-limited optical system can reach 78.5% in one hologram. It opens a new route to multiplexing quantitative optical imaging and helps to improve the performance of iterative-free and constraint-free modern optical microscopes in various spectral regimes.
... Here we present a method of multiplexing off-axis FF-OCT signals by splitting the sample beam into two beams and delivering them at the detector plane with different angles of incidence, similar to what has been done in digital holography [9][10][11]. The two angles generate carrier fringes with orthogonal orientations. ...
Full-field swept-source optical coherence tomography (FF-SS-OCT) is an emerging technology with potential applications in ophthalmic imaging, microscopy, metrology, and other domains. Here we demonstrate a novel method of multiplexing FF-SS-OCT signals using carrier modulation (CM). The principle of CM could be used to inspect various properties of the scattered light, e.g. its spectrum, polarization, Doppler shift, or distribution in the pupil. The last of these will be explored in this work, where CM was used to acquire images passing through two different optical pupils. The two pupils contained semicircular optical windows with perpendicular orientations, with each window permitting measurement of scattering anisotropy in one dimension by inducing an optical delay between the images formed by the two halves of the pupil. Together, the two forms of multiplexing permit measurement of differential scattering anisotropy in the x and y dimensions simultaneously. To demonstrate the feasibility of this technique our carrier multiplexed directional FF-OCT (CM-D-FF-OCT) system was used to acquire images of a microlens array, human hair, onion skin and in vivo human retina. The results of these studies are presented and briefly discussed in the context of future development and application of this technique.
... Here, we follow the concept of frequency multiplexing, where the frequency domain is divided to store a set of optical signals. Hologram frequency multiplexing has been successfully applied for hologram compression [29,30], optimizing spatial bandwidth capacity [31], increasing Field of View [32,33], improve measurement time in digital holographic tomography [34], color imaging [35], or multiplexing different imaging modalities [36]. Single exposure hologram multiplexing might be physically realized by dividing beams with beam splitters [32,33], or diffractive gratings [34,36]. ...
This work develops a single-shot holographic profilometer that enables shape characterization of discontinuous deep surfaces. This is achieved by combining hologram frequency multiplexing and an illumination technique of complex amplitude in multi-incidence angle profilometer. Object illumination is carried out from seven directions simultaneously, where the radial angular coordinates of illumination plane waves obey the geometric series. It is shown that: (i) the illumination pattern provides the required frequency separation of all object wavefronts in transverse frequency space, which is necessary for hologram demultiplexing, and (ii) numerical generation of longitudinal scanning function (LSF) is possible, which has large measurement range, high axial resolution, and small side lobes. Low side lobes of LSF and the developed multiplexed field dependent aberration compensation method are essential to minimize the negative influence of speckle noise of single-shot capture on the measurement result. The utility of the proposed method is demonstrated with experimental measurement of heights of two step-like objects.
... The holographic method of recording wave fields makes it possible to record the storage of the entire volume of information about the object of study, namely, the information we need about the size and location of the aerosol particle in space [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. This method provides an opportunity to see the investigated object in separate layers. ...
The article describes a device based on the holographic method for measuring the parameters of dispersed aerosols. In the proposed device, the measured particle is irradiated with two beams perpendicular to the main radiation axis, while the resulting holographic image in each of the projections gives an increased amount of information (in contrast to existing solutions) about the parameters of the particles. The information obtained is processed layer by layer using digital holography methods to form a volumetric representation of the aerosol under study, which significantly increases the information content of measurements in comparison with existing devices. Methods and algorithms for layer-by-layer processing of the obtained holographic images are described, which make it possible to reconstruct the parameters of aerosols of complex shapes. The design of the device and an algorithm for layer-by-layer reconstruction of aerosol images are proposed.
... Finally, the efforts in hologram multiplexing, which is introducing multiple measurements in a single hologram, should be noted. Multiplexing can be achieved either by hardware [26][27][28][29] or software [30]. Although the solutions were often grounded on band limitation of the signal which is also being utilized in this work, they did not investigate them from the compression point of view. ...
Image plane off-axis holograms (IP-OAH) are the most common data captured in digital holographic microscopy and tomography. Due to increasing storage and data transmission requirements, lossy compression of such holograms has been subject of earlier investigations. However, hologram compression can not be allowed to hinder the metrological capabilities of the measurement technique itself. In this work, we present lossy and lossless IP-OAH compression approaches that are based on conventional compression codecs, but optimized with regard to bandwidth of the signal. Both approaches outperform respective conventional codecs, while the lossy approach is shown to uphold the accuracy of holographic phase measurements.
... In this particular implementation, we show that the random and sparse nature of the impulse response function in coherent COACH can be used to spatially multiplex more than one hologram into a single 2D recorded matrix. Hologram multiplexing can be very useful for applications that aim for holographic data compression [4][5][6][7], imaging in fast dynamics [8][9][10], and fast hologram reconstruction [11], to mention a few. Herein, we employ the multiplexing scheme to enhance the acquisition frame rate of a system that is limited by the sensor, up to the frame rate of the coded phase mask (CPM) display device. ...
Optical, spatial, or temporal multiplexing is a well-known approach to optimize the performance of imaging systems. Following the recent discovery about the capability to record a coherent hologram in an interferenceless working mode, we propose a motionless method to spatially multiplex more than one hologram in a single camera exposure. Using the rather simple multiplexing framework based on coded aperture correlation holography, we effectively increase the acquisition rate of dynamic scenes and the holographic data compression by two-fold. Quantitative or qualitative phase microscopy and acquisition of a bipolar hologram from a single camera shot, experimentally confirm the applicability of the suggested technique.
... This is because the large data volumes involved means that a service provider's network would have to achieve data rates of the order of terabytes per second to transmit dynamic holographic content [42]. One technique used for efficient data handling is multiplexing [43][44][45][46][47][48][49][50][51][52][53], where several channels of information are combined into a single data package. This allows the management of holographic dynamic scenes. ...
In this paper we present an optodigital protocol for the compression of 3D dynamic scenes recorded with an off-axis Fresnel holographic system. The compression protocol involves optical scaling, sampling with binary masks, and multiplexing of the optical field data obtained after a filtering process applied to Fresnel holograms. Volume reduction of up to 93.71% and a 16-fold decrease in the transfer time are achieved. Virtual-optical reconstruction is performed for different values of the parameters involved in the compression protocol. The correlation coefficient is used as a metric to measure the loss caused by the volume reduction process. Furthermore, we show that a high level of lossy compression can be achieved with this protocol, with better reconstruction quality than the MPEG-4 video compression technique. Finally, we perform the experimental reconstruction using a holographic projection system based on a phase-only spatial light modulator, thus highlighting the potential of our proposal.
... Many authors utilized this redundancy in order to capture multiplexed holograms, that is holograms that contain more than one measurement. There have been both hardware [18][19][20][21] and software 22 approaches to improve the bandwidth utilization, however they have not been investigated from the compression perspective. The redundancy is analytically discussed in sec. ...
