Browsing by Author "Poon, Ting-Chung"

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    Acousto-Optics: introduction to the feature issue
    Poon, Ting-Chung; Tsai, C. S.; Voloshinov, V. B.; Chatterjee, M. R. (Optical Society of America, 2009-03-01)
    This Acousto-Optics feature celebrates the scientific careers of two remarkable scientists, Antoni Sliwinski and Adrian Korpel. The feature includes original papers based on a representative selection of topics that were presented at the Tenth Spring School on Acousto-Optics held in Poland in May 2008. (C) 2009 Optical Society of America
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    Adaptive Optical Scanning Holography
    Tsang, P. W. M.; Poon, Ting-Chung; Liu, J. Ping (Springer Nature, 2016-02-26)
    Optical Scanning Holography (OSH) is a powerful technique that employs a single-pixel sensor and a row-by-row scanning mechanism to capture the hologram of a wide-view, three-dimensional object. However, the time required to acquire a hologram with OSH is rather lengthy. In this paper, we propose an enhanced framework, which is referred to as Adaptive OSH (AOSH), to shorten the holographic recording process. We have demonstrated that the AOSH method is capable of decreasing the acquisition time by up to an order of magnitude, while preserving the content of the hologram favorably.
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    All-fiber Spectral Filters based on LP01 - LP11 Mode Coupling and Applications in Wavelength Division Multiplexing and Dispersion Compensation
    Jyothikumar, Jagannathan (Virginia Tech, 1996-06-27)
    All-fiber spectral filters have the advantages of providing low coupling loss and being readily integrated into fiber-optic networks. Spectral filters made of single-mode identical or dissimilar core parallel fibers provide 3-dB spectral widths on the order of 1 to 10 nm. A spectral filter made of single-mode and dual-mode fibers and operating based on coupling of power between LP01 and LP11 modes is proposed for applications as narrowband demultiplexers and as broadband mode converters with spectral widths of fraction of 1 nm to few 10 nm, respectively. With appropriate choice of parameters, filters can be designed such that the LP01 mode of the single-mode fiber is phase matched with the LP11 mode of the dual-mode fiber at a desired wavelength. Thus, significant exchange of power between these two modes can occur. The coupled-mode theory of parallel dielectric waveguides is used to analyze the proposed filter. Transmission expressions are derived from the governing coupled-mode equations and evaluated numerically for example cases. Two cases corresponding to maximum power coupling at 1.33 mm and 1.55 mm wavelengths are examined. Design data and transmission characteristics versus wavelength for these two cases are presented. The influence of the distance between fiber cores on peak transmission wavelength, spectral width, and coupling length is investigated. The application of the proposed filter as mode converter, which is required in the implementation of dispersion compensation using LP11 mode, is elucidated.
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    Analysis and Applications of Microstructure and Holey Optical Fibers
    Kim, Jeong I. (Virginia Tech, 2003-09-10)
    Microstructure and photonic crystal fibers with periodic as well as random refractive-index distributions are investigated. Two cases corresponding to fibers with one-dimensional (1D) radial index distributions and two-dimensional (2D) transverse index distributions are considered. For 1D geometries with an arbitrary number of cladding layers, exact analytical solutions of guided modes are obtained using a matrix approach. In this part, for random index distributions, the average transmission properties are calculated and the influence of glass/air ratio on these properties is assessed. Important transmission properties of the fundamental mode, including normalized propagation constant, chromatic dispersion, field distributions, and effective area, are evaluated. For 2D geometries, the numerical techniques, FDTD (Finite-Difference Time-Domain) method and FDM (Finite Difference Method), are utilized. First, structures with periodic index distributions are examined. The investigation is then extended to microstructure optical fibers with random index distributions. Design of 2D microstructure fibers with random air-hole distributions is undertaken with the aim of achieving single-mode guiding property and small effective area. The former is a unique feature of the holey fiber with periodic air-hole arrangement and the latter is a suitable property for nonlinear fiber devices. Measurements of holey fibers with random air-hole distributions constitute an important experimental task of this research. Using a section of a holey fiber fabricated in the draw tower facility at Virginia Tech, measurements of transmission spectra and fiber attenuation are performed. Also, test results for far-field pattern measurements are presented. Another objective of this dissertation is to explore new applications for holey fibers with random or periodic hole distributions. In the course of measuring the holey fibers, it was noticed that robust temperature-insensitive pressure sensors can be made with these fibers. This offers an opportunity for new low-cost and reliable pressure fiber-optic sensors. Incorporating gratings into holey fibers in conjunction with the possibility of dynamic tuning offers desirable characteristics with potential applications in communications and sensing. Injecting gases or liquids in holey fibers with gratings changes their transmission characteristics. These changes may be exploited in designing tunable optical filters for communication applications or making gas/liquid sensor devices.
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    Analysis of three-dimensional field distributions for focussed unapodized/apodized annular beams
    Bhabu, Shaleen J. (Virginia Tech, 1990-08-14)
    The study of focal shift in focused beams using unapodized apertures has been well documented. However, not much work has been done on apodized apertures. In this thesis we use a Fourier-Optic approach to analyze the field distribution of a focused beam around the region of geometrical focus. The analytical formulation developed is general in nature as it is valid for any arbitrary aperture functions. This is then applied to some specific cases. Two cases of interest that are considered are the unapodized and the Gaussian apodized annular apertures. In order to study the intensity distributions around the geometrical focus, simulation results are presented using closed form analytical expressions and approximate integral forms. Specific emphasis is placed on the focal shift in the two apertures and on the effect of changing various parameters. A prognosis for future work using a-Modulation on Gaussian apodized annular apertures is also presented.
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    Asymmetric cryptosystem based on optical scanning cryptography and elliptic curve algorithm
    Chang, Xiangyu; Li, Wei; Yan, Aimin; Tsang, Peter Wai Ming; Poon, Ting-Chung (Nature Portfolio, 2022-05-11)
    We propose an asymmetric cryptosystem based on optical scanning cryptography (OSC) and elliptic curve cryptography (ECC) algorithm. In the encryption stage of OSC, an object is encrypted to cosine and sine holograms by two pupil functions calculated via ECC algorithm from sender's biometric image, which is sender's private key. With the ECC algorithm, these holograms are encrypted to ciphertext, which is sent to the receiver. In the stage of decryption, the encrypted holograms can be decrypted by receiver's biometric private key which is different from the sender's private key. The approach is an asymmetric cryptosystem which solves the problem of the management and dispatch of keys in OSC and has more security strength than the conventional OSC. The feasibility of the proposed method has been convincingly verified by numerical and experiment results.
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    Asymmetric Optical Scanning Holography Encryption with Elgamal Algorithm
    Wu, Chunying; Ding, Yinggang; Yan, Aimin; Poon, Ting-Chung; Tsang, Peter Wai Ming (MDPI, 2024-09-19)
    This paper proposes an asymmetric scanning holography cryptosystem based on the Elgamal algorithm. The method encodes images with sine and cosine holograms. Subsequently, each hologram is divided into a signed bit matrix and an unsigned hologram matrix, both encrypted using the sender’s private key and the receiver’s public key. The resulting ciphertext matrices are then transmitted to the receiver. Upon receipt, the receiver decrypts the ciphertext matrices using their private key and the sender’s public key. We employ an asymmetric single-image encryption method for key management and dispatch for securing imaging and transmission. Furthermore, we conducted a sensitivity analysis of the encryption system. The image encryption metrics, including histograms of holograms, adjacent pixel correlation, image correlation, the peak signal-to-noise ratio, and the structural similarity index, were also examined. The results demonstrate the security and stability of the proposed method.
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    Autofocusing in optical scanning holography
    Kim, Taegeun; Poon, Ting-Chung (Optical Society of America, 2009-12-01)
    We present autofocusing in optical scanning holography (OSH) with experimental results. We first record the complex hologram of an object using OSH and then create the Fresnel zone plate (FZP) that codes the object constant within the depth range of the object using Gaussian low-pass filtering. We subsequently synthesize a real-only spectrum hologram in which its phase term contains information about a distance parameter. Finally, we extract the distance parameter from the real-only spectrum hologram using fringe-adjusted filtering and the Wigner distribution. Using the extracted distance parameter, we reconstruct a three-dimensional image of the object from the complex hologram using digital convolution, which bypasses the conventional blind convolution to reconstruct a hologram. To the best of our knowledge, this is the first report with experimental results that autofocusing in OSH is possible without any searching algorithm or tracking process. (C) 2009 Optical Society of America
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    Basic Image-Processing Operations By Use Of Acousto-Optics
    Banerjee, P. P.; Cao, D. Q.; Poon, Ting-Chung (Optical Society of America, 1997)
    We describe some basic optical image-processing operations with acousto-optic (AO) Bragg diffraction. Instead of using frequency-plane filters, we place an AO cell behind the abject. We then realize experimentally one-dimensional edge enhancement, which utilizes a high-pass filtering effect in the undiffracted order from the AO cell. A numerical simulation compares well with the experimental results. With two AO cells oriented orthogonally to each other, a second-order mixed derivative operation, evident from the four-corner enhancement of a square, is also demonstrated. (C) 1997 Optical Society of America.
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    Binary Mask Programmable Hologram
    Tsang, Peter Wai Ming; Poon, Ting-Chung; Zhou, C. H.; Cheung, K. W. K. (Optical Society of America, 2012-11-01)
    We report, for the first time, the concept and generation of a novel Fresnel hologram called the digital binary mask programmable hologram (BMPH). A BMPH is comprised of a static, high resolution binary grating that is overlaid with a lower resolution binary mask. The reconstructed image of the BMPH can be programmed to approximate a target image (including both intensity and depth information) by configuring the pattern of the binary mask with a simple genetic algorithm (SGA). As the low resolution binary mask can be realized with less stringent display technology, our method enables the development of simple and economical holographic video display. (C) 2012 Optical Society of America
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    Biodiversity and dynamics of direction finding accuracy in bat biosonar
    Uzair Gilani, Syed (Virginia Tech, 2016-04-04)
    In the biosonar systems of bats, emitted acoustic energy and receiver sensitivity are distributed over direction and frequency through beampattern functions that have diverse and often complicated geometries. This complexity could be used by the animals to determine the direction of incoming sounds based on spectral signatures. The present study in its first part has investigated how well bat biosonar beampatterns are suited for direction finding using a measure of the smallest estimator variance that is possible for a given direction (Cram{'e}r-Rao lower bound, CRLB). CRLB values were estimated for numerical beampattern estimates derived from 330 individual shape samples, 157 noseleaves (used for emission) and 173 outer ears (pinnae). At an assumed unit[60]{dB} signal-to-noise ratio, the average value of the CRLB was 3.9textdegree, which is similar to previous behavioral findings. Distribution for the CRLBs in individual beampatterns were found to have a positive skew indicating the existence of regions where a given beampattern does not support a high accuracy. The highest supported accuracies were for direction finding in elevation (with the exception of phyllostomid emission patterns). Beampatterns in the dataset were also characterized based upon the differences in the type of acoustic signal they are associated with, the functionality of the baffle shape producing them and their phylogeny. In the second part of the study, functionality of various local shape features was investigated under static and dynamic conditions. Each local shape feature was found to have an impact on the estimation performance of the baffle shape. Interaction of the local shape features among themselves as well as their dynamic motion produced a plethora of results, not achievable through either single features or through their static states only.
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    Comparison of two-, three-, and four-exposure quadrature phase-shifting holography
    Liu, J. Ping; Poon, Ting-Chung; Jhou, G. S.; Chen, P. J. (Optical Society of America, 2011-06-01)
    In standard (four-exposure) quadrature phase-shifting holography (QPSH), two holograms and two intensity maps are acquired for zero-order-free and twin-image-free reconstruction. The measurement of the intensity map of the object light can be omitted in three-exposure QPSH. Furthermore, the measurements of the two intensity maps can be omitted in two-exposure QPSH, and the acquisition time of the overall holographic recording process is reduced. In this paper we examine the quality of the reconstructed images in two-, three-, and four-exposure QPSH, in simulations as well as in optical experiments. Various intensity ratios of the object light and the reference light are taken into account. Simulations show that two-and three-exposure QPSH can provide reconstructed images with quality comparable to that of four-exposure QPSH at a low intensity ratio. In practice the intensity ratio is limited by visibility, and thus four-exposure QPSH exhibits the best quality of the reconstructed image. The uniformity and the phase error of the reference light are also discussed. We found in most cases there is no significant difference between the reconstructed images in two- and three-exposure QPSH, and the quality of the reconstructed images is acceptable for visual applications such as the acquisition of three-dimensional scene for display or particle tracking. (C) 2011 Optical Society of America
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    Complex Fresnel hologram display using a single SLM
    Liu, J. Ping; Hsieh, W. Y.; Poon, Ting-Chung; Tsang, Peter (Optical Society of America, 2011-12-01)
    We propose a novel optical method to display a complex Fresnel hologram using a single spatial light modulator (SLM). The method consists of a standard coherent image processing system with a sinusoidal grating at the Fourier plane. Two or three position-shifted amplitude holograms displayed at the input plane of the processing system can be coupled via the grating and will be precisely overlapped at the system's output plane. As a result, we can synthesize a complex hologram that is free of the twin image and the zero-order light using a single SLM. Because the twin image is not removed via filtering, the full bandwidth of the SLM can be utilized for displaying on-axis holograms. In addition, the degree of freedom of the synthesized complex hologram display can be extended by involving more than three amplitude holograms. (C) 2011 Optical Society of America
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    Computer generation of binary Fresnel holography
    Tsang, Peter; Poon, Ting-Chung; Cheung, W. K.; Liu, J. Ping (Optical Society of America, 2011-03-01)
    Binarization of Fresnel holograms by direct thresholding based on the polarity of the fringe pattern is studied. It is found that if the hologram is binarized (i.e., for black and white hologram pixels) in this manner, only the edges of the object are preserved in the reconstructed image. To alleviate the errors caused by binarization, the use of error diffusion has been routinely employed. However, the reconstructed image using such standard technique is heavily contaminated with random noise. In this paper, we propose a novel noniterative method for generating Fresnel holograms that are suitable for binarization. Our method is capable of preserving good visual quality on the reconstructed images. (C) 2011 Optical Society of America
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    Coupled-waveguide Fabry-Perot resonator
    Chang, Cheng-Chun (Virginia Tech, 1992-12-04)
    Narrowband spectral filters find important applications in optical fiber communication systems, particularly in wavelength demultiplexers and single-frequency semiconductor lasers. Conventional Fabry-Perot resonators provide a narrow spectral width but lack the capability of mode discrimination. A new coupled-waveguide Fabry-Perot resonator made of two parallel waveguides with reflecting mirrors at the ends is proposed for application as narrowband tuned spectral filter in single-mode diode lasers and wavelength demultiplexers. The interference of counter propagating waves from reflection by end mirrors and the coupling of waves between the two parallel guides contribute to the operation of this resonator structure. Thus, the device exhibits the attributes of both Fabry-Perot resonator and directional coupler. The coupled-mode theory of parallel waveguides is employed to analyze the proposed structure. Spectral characteristics are derived from the governing coupled-mode equations and related boundary conditions. Two geometries consisting of identical waveguides, as well as nonidentical waveguides, are examined. The spectral characteristics of the proposed resonator demonstrate that significant improvement in mode discrimination capability and longitudinal mode spacing over the conventional Fabry-Perot resonator is achieved. Numerical results for several example cases are presented and the influence of various parameters on spectral properties are investigated.
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    Depth resolution enhancement in double-detection optical scanning holography
    Ou, H. Y.; Poon, Ting-Chung; Wong, K. K. Y.; Lam, Edmund Y. (Optical Society of America, 2013-05-01)
    We propose an optical scanning holography system with enhanced axial resolution using two detections at different depths. By scanning the object twice, we can obtain two different sets of Fresnel zone plates to sample the same object, which in turn provides more information for the sectional image reconstruction process. We develop the computation algorithm that makes use of such information, solving a constrained optimization problem using the conjugate gradient method. Simulation results show that this method can achieve a depth resolution up to 1 mu m. (C) 2013 Optical Society of America
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    Depth resolution enhancement in optical scanning holography with a dual-wavelength laser source
    Ke, J.; Poon, Ting-Chung; Lam, Edmund Y. (Optical Society of America, 2011-12-01)
    In this paper, we use two point sources to analyze the depth resolution of an optical scanning holography (OSH) system with a single-wavelength source. A dual-wavelength source is then employed to improve it, where this dual-wavelength OSH (DW-OSH) system is modeled with a linear system of equations. Object sectioning in DW-OSH is obtained with the Fourier domain conjugate gradient method. Simulation results show that, with the two source wavelengths at 543 nm and 633 nm, a depth resolution at 2.5 mu m can be achieved. Furthermore, an OSH system emulator is provided to demonstrate the performance of DW-OSH compared with a conventional OSH system. (C) 2011 Optical Society of America
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    Development of experiments for the digital signal processing teaching laboratory
    Jen, Kwang-Suz (Virginia Tech, 1988-07-05)
    Digital Signal Processing (DSP) is a technology-driven field which develops as early as mid-1960 when computers and other digital circuitry became fast enough to process large amounts of data efficiently. Since then techniques and applications of DSP have been expanding at a tremendous rate. With the development of large-scale integration, the cost and size of digital components are reducing, and speed of digital components is increasing. Thus the range of applications of DSP techniques is growing. Almost all current discussions of speech bandwidth compression systems are directed toward digital implementation, because these are now the most practical. The importance of DSP appears to be increasing with no visible signs of saturation. This thesis provides the description and results of designing laboratory experiments for the illustration of basic theory in the field of DSP. All experiments are written for the Texas Instruments TMS320I0 digital signal processing microcomputer and based on softwares provided by Atlanta Signal Process, Inc. (ASPI). The use of the 320/pc Algorithm Development Package (ADP) and Digital Filter Design Package (DFDP) developed by ASPI is introduced. The basic concepts, such as linear convolution, Finite Impulse Response (FIR) and Infinite Impulse Response (IIR) filter design, Fast Fourier Transform (FF1), are demonstrated. The IBM PC AT is interfaced with the TMS32010 processor. The experiments and their introductions in the thesis also serve as a manual for the DSP Laboratory; to complement the introductory signal processing course.
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    Development of Tunable Optical Filters for Interrogation of White-Light Interferometric Sensors
    Yu, Bing (Virginia Tech, 2005-04-28)
    Interferometric fiber optic sensors have been extensively used to measure a large variety of physical, chemical and biomedical parameters due to their superior performance. At the Center for Photonics Technology of Virginia Tech, a variety of interferometric fiber optic sensors have been developed in recent years, for efficient oil recovery, partial discharge detection in high voltage transformers, pressure sensing in gas turbine engines, and temperature measurements in gasifiers and boilers. However, interrogating an interferometric sensor involves accurate recovery of a measurand from the phase-modulated lightwaves, and has been a challenge for high performance, high speed, and low-cost, to current white-light interferometry (WLI) techniques, such as the widely used scanning WLI (S-WLI) and spectral-domain WLI (SD-WLI). The performance of a white-light interferometric sensing system depends not only on the design of the probes, but also, to a great extent, on the interrogation strategy to be used. In this Ph.D. research, a tunable optical filter based WLI (TOF-WLI) is proposed and validated as a low cost, yet high performance, solution to the interrogation of various types of interferometric sensors. In addition to the capability of linear/quadrature demodulation, TOF-WLI retains all the features of WLI, is compatible with the SD-WLI, and can be tailored for both static and wideband signals. It also has great potential in surface metrology and biomedical imaging as well as optical spectroscopy. The key, to the success of this new approach in competition with the other available WLI techniques, is that the tunable optical filter (TOF) must be specially designed for sensing and extremely low cost. Therefore, two novel TOFs, a diffraction grating tunable filter (DG-TOF) and an extrinsic Fabry-Perot tunable filter (EFP-TF), are proposed and demonstrated. Laboratory and field test results on using the DG-TOF WLI for partial discharge and thermal fault detection in high voltage power transformers, and the EFP-TF WLI in temperature sensor systems and a turbine engine monitoring system will also be presented to demonstrate the feasibility for efficient sensor interrogation.
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    Deviation Influences on Sectional Image Reconstruction in Optical Scanning Holography Using A Random-Phase Pupil
    Wu, X. L.; Zhou, X.; Wang, Q. H.; Jiang, Y. F.; Xiao, C. J.; Dobson, K.; Poon, Ting-Chung (Optical Society of America, 2013-10-01)
    In this paper, we analyze the influence of two kinds of deviation errors on sectional image reconstruction for an optical scanning holography system using a random-phase pupil. The first deviation occurs in the lateral pixel position while the second occurs in the pixel value of the decoding function. Theoretical analysis and numerical simulation show that these two deviations may lead to noise in the reconstructed image. Additional discussions include the signal-to-noise ratio of the reconstructed image. (c) 2012 Optical Society of America