• The Transactions of the Korean Institute of Electrical Engineers D
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• v.50 no.2
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• pp.59-64
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• 2001

In this paper, we propose an alternate method for determining the uniqueness of the reconstruction of a complex sequence from its phase. Uniqueness constraints could be derived in terms of the zeros of a complex polynomial defined by the DFT of the sequence. However, rooting of complex polynomials of high order is a very difficult problem. Instead of finding zeros of a complex polynomial, the proposed uniqueness criteria show that non-singularity of a matrix can guarantee the uniqueness of the reconstruction of a complex sequence from its phase-only data. It has clear advantage over the rooting method in numerical stability and computational time.

• Journal of Power Electronics
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• v.11 no.6
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• pp.837-845
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• 2011

This paper proposes phase current reconstruction techniques for two-phase two-leg and two-phase four-leg inverters using a single current sensor. In the proposed methods, one phase current is sampled simultaneously with a particular branch current by using only one current sensor, and then current reconstruction algorithms are applied to extract the information on two phase currents from the sensor output. The sampled current information is periodically updated at the peak and the valley of the triangular carrier waveform in each switching cycle of pulse-width modulation (PWM). The voltage vector spaces where the phase currents can be reconstructed are evaluated. Compared to the existing method using two individual current sensors in two phases, the proposed schemes can save implementation cost since it is possible to remove one current sensor. In addition, the proposed methods are free from gain discrepancy issues between two current sensors. Simulations and experiments show excellent current reconstruction performance of the proposed methods.

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.935-938
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• 2008

Three-dimensional (3D) display systems based on wavefront reconstruction are presented. To obtain the wavefront of 3D objects, we present holographic recording using temporally or spatially phase-shifting interferometer. In the 3D display systems, phase-only reconstruction using a spatial light modulator and an approach to increase the reconstructed power are presented.

• Journal of Broadcast Engineering
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• v.28 no.1
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• pp.3-20
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• 2023

A computer-generated hologram (CGH) is a digitally calculated and recorded hologram in which the amplitude and phase information of an image is transmitted in free space. The CGH is in the form of a complex hologram, but it is converted into a phase-only hologram to display through a phase-only spatial light modulator (SLM). In this paper, in the process of including the amplitude information of an object in the phase information, when a technique that includes subsampling such as DPAC is used, we showed experimentally that the bandwidth of the phase-only hologram increases, and as a result, aliasing that was not present in the complex hologram can occur. In addition, it was experimentally shown that it is possible to generate a high-quality phase-only hologram by restricting the spatial frequency range even at a distance where the numerical reconstruction performance is degraded by aliasing.

• Current Optics and Photonics
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• v.6 no.6
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• pp.598-607
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• 2022

In this paper, a simple nondestructive technology is used to investigate unstained biological blood cells in three dimensions (3D). The technology employs a reflective phase-only spatial light modulator (SLM) for displaying the phase hologram of the object being tested, and a Fourier lens for its reconstruction. The phase hologram is generated via superposing a digital random phase on the 2D image of the object. The phase hologram is then displayed by the SLM with 256 grayscale levels, and reconstructed by a Fourier lens to present the object in 3D. Since noise is the main problem in this method, the windowed Fourier filtering (WFF) method is applied to suppress the noise of the reconstructed object. The quality of the reconstructed object is refined and the noise level suppressed by approximately 40%. The technique is applied to objects: the National Institute of Standards (NIS) logo, and a film of unstained peripheral blood. Experimental results show that the proposed technique can be used for rapid investigation of unstained biological blood cells in 3D for disease diagnosis. Moreover, it can be used for viewing unstained white blood cells, which is still challenging with an optical microscope, even at large magnification.

• Radiation Oncology Journal
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• v.35 no.3
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• pp.274-280
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• 2017

Purpose: To see the gross tumor volume (GTV) dependency according to the phase selection and reconstruction methods, we measured and analyzed the changes of tumor volume and motion at each phase in 20 cases with lung cancer patients who underwent image-guided radiotherapy. Materials and Methods: We retrospectively analyzed four-dimensional computed tomography (4D-CT) images in 20 cases of 19 patients who underwent image-guided radiotherapy. The 4D-CT images were reconstructed by the maximum intensity projection (MIP) and the minimum intensity projection (Min-IP) method after sorting phase as 40%-60%, 30%-70%, and 0%-90%. We analyzed the relationship between the range of motion and the change of GTV according to the reconstruction method. Results: The motion ranges of GTVs are statistically significant only for the tumor motion in craniocaudal direction. The discrepancies of GTV volume and motion between MIP and Min-IP increased rapidly as the wider ranges of duty cycles are selected. Conclusion: As narrow as possible duty cycle such as 40%-60% and MIP reconstruction was suitable for lung cancer if the respiration was stable. Selecting the reconstruction methods and duty cycle is important for small size and for large motion range tumors.

• Journal of the Optical Society of Korea
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• v.18 no.3
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• pp.230-235
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• 2014

Two-step quadrature phase-shifting digital holography based on the calculated intensity of a reference wave is proposed. In the Mach-Zehnder interferometer (MZI) architecture, the method only records two quadrature-phase holograms, without reference-wave intensity or object-wave intensity measurement, to perform object recoding and reconstruction. When the reference-wave intensity is calculated from the 2D correlation coefficient (CC) method that we presented, the clear reconstruction image can be obtained by some specific algorithm. Its feasibility and validity were verified by a series of experiments with 2D objects and 3D objects. The presented method will be widely used in real-time or dynamic digital holography applications.

• Journal of the Optical Society of Korea
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• v.18 no.3
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• pp.217-224
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• 2014

A major advantage of wavefront reconstruction based on a series of diffracted intensity images using only single-beam illumination is the simplicity of setup. Here we propose a fast-converging algorithm for wavefront calculation using single-beam illumination. The captured intensity images are resampled to a series of intensity images, ranging from highest to lowest resampling; each resampled image has half the number of pixels as the previous one. Phase calculation at a lower resolution is used as the initial solution phase at a higher resolution. This corresponds to separately calculating the phase for the lower- and higher-frequency components. Iterations on the low-frequency components do not need to be performed on the higher-frequency components, thus making the convergence of the phase retrieval faster than with the conventional method. The principle is verified by both simulation and optical experiments.

• Wind and Structures
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• v.18 no.6
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• pp.693-715
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• 2014

Stochastic processes are used to represent phenomena in many diverse fields. Numerical simulation method is widely applied for the solution to stochastic problems of complex structures when alternative analytical methods are not applicable. In some practical applications the stochastic processes show non-Gaussian properties. When the stochastic processes deviate significantly from Gaussian, techniques for their accurate simulation must be available. The various existing simulation methods of non-Gaussian stochastic processes generally can only simulate super-Gaussian stochastic processes with the high-peak characteristics. And these methodologies are usually complicated and time consuming, not sufficiently intuitive. By revealing the inherent coupling effect of the phase and amplitude part of discrete Fourier representation of random time series on the non-Gaussian features (such as skewness and kurtosis) through theoretical analysis and simulation experiments, this paper presents a novel approach for the simulation of non-Gaussian stochastic processes with the prescribed amplitude probability density function (PDF) and power spectral density (PSD) by amplitude modulation and phase reconstruction. As compared to previous spectral representation method using phase modulation to obtain a non-Gaussian amplitude distribution, this non-Gaussian phase reconstruction strategy is more straightforward and efficient, capable of simulating both super-Gaussian and sub-Gaussian stochastic processes. Another attractive feature of the method is that the whole process can be implemented efficiently using the Fast Fourier Transform. Cases studies demonstrate the efficiency and accuracy of the proposed algorithm.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• fall
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• pp.82-83
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• 2021

홀로그램 비디오는 획득 방식에 따라서 다양한 종류의 홀로그램이 존재한다. 이들은 서로 다른 특성을 가지고 있기 때문에, 홀로그램 비디오를 압축하기 위한 방법도 매우 다양하다. 다양한 홀로그램 중에서, 우리는 상용 phase-only-typed SLM에 바로 디스플레이 할 수 있는 phase-only 홀로그램 비디오를 압축하기 위한 코덱을 제안한다. 이때 스케일링 기법을 이용하고, 스케일링 다운과 업으로 인한 화질의 손실을 복원하기 위해 딥러닝 모델을 사용하는 방법을 제안한다.