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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Journal of the Optical Society of Korea
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Journal DOI :
Optical Society of Korea
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Volume & Issues
Volume 14, Issue 4 - Dec 2010
Volume 14, Issue 3 - Sep 2010
Volume 14, Issue 2 - Jun 2010
Volume 14, Issue 1 - Mar 2010
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Planar Waveguide Devices for Communication and Sensing Applications
Okamoto, Katsunari ;
Journal of the Optical Society of Korea, volume 14, issue 4, 2010, Pages 290~297
DOI : 10.3807/JOSK.2010.14.4.290
The paper reviews progress and future prospects of two kinds of planar waveguide devices; they are (a) silica and silicon photonics multi/demultiplexers for communications and signal processing applications, and (b) a novel waveguide spectrometer based on Fourier transform spectroscopy for sensing applications.
A Theoretical and Experimental Investigation into Pair-induced Quenching in Bismuth Oxide-based Erbium-doped Fiber Amplifiers
Jung, Min-Wan ; Shin, Jae-Hyun ; Jhon, Young-Min ; Lee, Ju-Han ;
Journal of the Optical Society of Korea, volume 14, issue 4, 2010, Pages 298~304
DOI : 10.3807/JOSK.2010.14.4.298
The pair-induced quenching (PIQ) effect in a highly doped bismuth oxide-based erbium-doped fiber amplifier (EDFA) was theoretically and experimentally investigated. In the theoretical investigation, the bismuth oxide-based EDFA was modeled as a 6-level amplifier system that incorporated clustering-induced concentration quenching, cooperative up-conversion, pump excited state absorption (ESA), and signal ESA. The relative number of paired ions in a highly doped bismuth oxide EDF was estimated to be ~6.02%, determined by a comparison between the theoretical and the experimentally measured gain values. The impacts of the PIQ on the gain and the noise figure were also investigated.
Preparation and Holographic Recording of Fluorescent Photopolymer Films Containing Anthracene Polymer for Security
Park, Tea-Hoon ; Kim, Yoon-Jung ; Kim, Jeong-Hun ; Kim, Eun-Kyoung ;
Journal of the Optical Society of Korea, volume 14, issue 4, 2010, Pages 305~309
DOI : 10.3807/JOSK.2010.14.4.305
Photopolymer films containing fluorescent anthracene polymer, polymethyleneanthracene (PMAn), were prepared with different concentrations of PMAn for holographic recording useful for security documents. The fluorescent photopolymer film showed enhanced fluorescent intensity due to the micro-separation which arose from grating formation and diffusion during photopolymerization. Experimental values of diffraction efficiency were well matched to the simulated values for photopolymers having different PMAn concentrations. Holography patterning was carried out using the fluorescent photopolymer under a photo-mask. A grating was confirmed using microscope techniques in the recorded area under the pattern. Importantly the recorded area showed enhanced fluorescence compared to the unrecorded part, allowing fluorescence patterns at micro scale along with the submicron grating pattern. The fluorescence pattern recorded on the photopolymer film provides additional readability of holographic reading and thus is useful for secure recording and reading of information.
Simulation of Moire Effect in 3D Displays
Saveljev, Vladimir ; Kim, Sung-Kyu ;
Journal of the Optical Society of Korea, volume 14, issue 4, 2010, Pages 310~315
DOI : 10.3807/JOSK.2010.14.4.310
Theoretical and experimental investigations of moires in 3D displays were performed. To describe and minimize moires, we propose the polar representation form of moire waves. The experimental and theoretical data are in good agreement except in the neighborhood of the minimization angle. The implicit formulas are found for visible moires of line gratings at finite distances. The computer simulation and the physical experiments confirm the moire appearance for this case.
Counterfeit Detection Using Characterization of Safety Feature on Banknote with Full-field Optical Coherence Tomography
Choi, Woo-June ; Min, Gi-Hyeon ; Lee, Byeong-Ha ; Eom, Jong-Hyun ; Kim, Ju-Wan ;
Journal of the Optical Society of Korea, volume 14, issue 4, 2010, Pages 316~320
DOI : 10.3807/JOSK.2010.14.4.316
We report an application of full-field optical coherence tomography (FF-OCT) for identifying counterfeit bank notes. The depth-resolved imaging capability of FF-OCT was used for tomographic identification of superficially-identical objects. By retrieving the internal structures of the security feature (cash hologram) of an original banknote, we could demonstrate the feasibility of FF-OCT to identify counterfeit money. The FF-OCT images showed that the hologram consisted of micron scale multi-coated layers including an air gap. Therefore, it is expected that FF-OCT has potential as a new non-invasive tool to discern imitation of currency, and it would find applications in a wide field of counterfeit sciences.
Analysis of the Current-voltage Curves of a Cu(In,Ga)Se
Thin-film Solar Cell Measured at Different Irradiation Conditions
Lee, Kyu-Seok ; Chung, Yong-Duck ; Park, Nae-Man ; Cho, Dae-Hyung ; Kim, Kyung-Hyun ; Kim, Je-Ha ; Kim, Seong-Jun ; Kim, Yeong-Ho ; Noh, Sam-Kyu ;
Journal of the Optical Society of Korea, volume 14, issue 4, 2010, Pages 321~325
DOI : 10.3807/JOSK.2010.14.4.321
We analyze the current density - voltage (J - V) curve of a Cu(In,Ga)
(CIGS) thin-film solar cell measured at different irradiation power densities. For the solar-cell sample investigated in this study, the fill factor and power conversion efficiency decreased as the irradiation power density (IPD) increased in the range of 2 to 5 sun. Characteristic parameters of solar cell including the series resistance (
), the shunt resistance (
), the photocurrent density (
), the saturation current density (
) of an ideal diode, and the coefficient (
) of the diode current due to electron-hole recombination via ionized traps at the p-n interface are determined from a theoretical fit to the experimental data of the J - V curve using a two-diode model. As IPD increased, both
Specialty Fiber Coupler: Fabrications and Applications
Lee, Byeong-Ha ; Eom, Joo-Beom ; Park, Kwan-Seob ; Park, Seong-Jun ; Ju, Myeong-Jin ;
Journal of the Optical Society of Korea, volume 14, issue 4, 2010, Pages 326~332
DOI : 10.3807/JOSK.2010.14.4.326
We review the research on specialty fiber couplers with emphasis placed on the characteristics that make them attractive for biomedical imaging, optical communications, and sensing applications. The fabrication of fiber couplers has been carried out with, in addition to conventional single mode fiber, various specialty fibers such as photonic crystal fiber, double clad fiber, and hole-assisted fiber with a Ge-doped core. For the fiber coupler fabrication, the side polishing and the fused biconical tapered methods have been developed. These specialty fiber couplers have been applied to optical coherence tomography, fluorescence spectroscopy, fiber sensors, and optical communication systems. This review aims to provide a detailed statement on the recent progress and novel applications of specialty fiber couplers.
X-ray Diffraction from X-ray Waveguide Arrays for Generation of Coherent X-ray
Park, Yong-Sung ; Choi, Jae-Ho ;
Journal of the Optical Society of Korea, volume 14, issue 4, 2010, Pages 333~336
DOI : 10.3807/JOSK.2010.14.4.333
The generation of coherent x-ray beams by using a multi-slit diffraction phenomenon is presented. The mode-confinement conditions in the x-ray waveguide (XWG) needed to obtain single-mode beams are determined. The XWGs are stacked to form an XWG array. The core of the XWG array is used as a slit in an opaque screen, similar to those used for visible light. Diffraction patterns that interfered constructively in the XWG array are investigated based on multi-slit diffraction theory. The irradiance distributions are studied at on observation screen. The FWHM of diffracted x-ray spectra were between
radians which lead to a spot-size of a few tens of micrometers on the screen at distance of 1 m. The intensities decrease with increase in the period of the XWG array, i.e. a thicker cladding, due to growth of the higher-order diffraction peaks.
High Sensitive Fiber Optic Temperature Sensor Based on a Side-polished Single-mode Fiber Coupled to a Tapered Multimode Overlay Waveguide
Prerana, Prerana ; Varshney, Ravendra Kumar ; Pal, Bishnu Pada ; Nagaraju, Bezwada ;
Journal of the Optical Society of Korea, volume 14, issue 4, 2010, Pages 337~341
DOI : 10.3807/JOSK.2010.14.4.337
A high sensitivity fiber optic temperature sensor based on a side-polished fiber (SPF) coupled to a tapered multimode overlay waveguide (MMOW) is proposed and studied. Both tapered and non-tapered MMOW were considered to study the effect of tapering of MMOW on the characteristics of the device and to investigate the criticality of the uniformity of the multimode overlay waveguide over the SPF. Present study shows that tapering of the MMOW can be used to tune the desired wavelength range without any loss in the sensitivity. Sensitivity up to 9 nm/
within the temperature range of 25 to
can be achieved with the proposed sensor, almost 6 times higher compared even to state-of-the-art high-sensitivity grating-based fiber optic temperature sensors.
Wideband Gain Flattened Hybrid Erbium-doped Fiber Amplifier/Fiber Raman Amplifier
Afkhami, Hossein ; Mowla, Alireza ; Granpayeh, Nosrat ; Hormozi, Azadeh Rastegari ;
Journal of the Optical Society of Korea, volume 14, issue 4, 2010, Pages 342~350
DOI : 10.3807/JOSK.2010.14.4.342
An optimal wideband gain flattened hybrid erbium-doped fiber amplifier/fiber Raman amplifier (EDFA/FRA) has been introduced. A new and effective optimization method called particle swarm optimization (PSO) is employed to find the optimized parameters of the EDFA/FRA. Numerous parameters which are the parameters of the erbium-doped fiber amplifier (EDFA) and the fiber Raman amplifier (FRA) define the gain spectrum of a hybrid EDFA/FRA. Here, we optimize the length,
concentration, and pump power and wavelength of the EDFA and also pump powers and wavelengths of the FRA to obtain the flattest operating gain spectrum. Hybrid EDFA/FRA with 6-pumped- and 10-pumped-FRAs have been studied. Gain spectrum variations are 1.392 and 1.043 dB for the 6-pumped- and 10-pumped-FRAs, respectively, in the 108.5 km hybrid EDFA/FRAs, with 1 mW of input signal powers. Dense wavelength division multiplexing (DWDM) system with 60 signal channels in the wavelength range of 1529.2-1627.1 nm, i.e. the wide bandwidth of 98 nm, is studied. In this work, we have added FRA's pump wavelengths to the optimization parameters to obtain better results in comparison with the results presented in our previous works.
Effect of Fiber Dispersion and Self-phase Modulation in Multi-channel Subcarrier Multiplexed Optical Signal Transmission
Kim, Kyoung-Soo ; Jeong, Ji-Chai ; Lee, Jae-Hoon ;
Journal of the Optical Society of Korea, volume 14, issue 4, 2010, Pages 351~356
DOI : 10.3807/JOSK.2010.14.4.351
We investigated the combined effect of fiber chromatic dispersion and self-phase modulation (SPM) in multi-channel subcarrier multiplexed (SCM) optical transmission systems. We theoretically analyzed the transmission characteristics of the SCM signals with the effect of SPM and chromatic dispersion in a single-mode optical fiber by numerical simulations based on the nonlinear Schrodinger equation. The numerical simulation results revealed that the effect of fiber dispersion and SPM could occur independently between subcarrier channels in two-channel SCM systems for small optical modulation index (OMI) and large channel spacing. However, for large OMI, small channel spacing, and large fiber launching power, we found a performance degradation of the two-channel system compared to that of a single-channel system. These parameters are therefore important for the optimization of multi-channel SCM systems applicable to radio over fiber networks.
Binary Nonlinear Joint Transform Correlator with Sinusoidal Iterative Filter in Spectrum Domain
Jeong, Man-Ho ;
Journal of the Optical Society of Korea, volume 14, issue 4, 2010, Pages 357~362
DOI : 10.3807/JOSK.2010.14.4.357
The joint transform correlator (JTC) has been the best known technique for pattern recognition and identification. This paper proposes a new technique of fringe adjustment by adopting a sinusoidal amplitude-modulated iterative filter convolved with an interference fringe pattern in the joint power spectrum (JPS) domain. The comparison of our new technique and other techniques is presented to show that the newly proposed technique can successfully improve both the correlation peaks and the peak signal-to-noise ratio (PSNR). Simulated results of enhanced interference fringes are also presented.
Two Step on-axis Digital Holography Using Dual-channel Mach-Zehnder Interferometer and Matched Filter Algorithm
Lee, Hyung-Chul ; Kim, Soo-Hyun ; Kim, Dae-Suk ;
Journal of the Optical Society of Korea, volume 14, issue 4, 2010, Pages 363~367
DOI : 10.3807/JOSK.2010.14.4.363
A new two step on-axis digital holography (DH) is proposed without any assumptions, phase shifting, or complicated optical components. A dual-channel Mach-Zehnder interferometer was employed. Using that setup, the object field can be reconstructed requiring only two step measurements. To eliminate position difference between two charge-coupled device (CCD) cameras, a matched filter algorithm was used. Experimental results are compared to those of the traditional phase shifting technique. The proposed approach can also be applied to single-exposure on-axis DH for real time measurement.
Adaptive Thresholding Technique for Binarization of License Plate Images
Kim, Min-Ki ;
Journal of the Optical Society of Korea, volume 14, issue 4, 2010, Pages 368~375
DOI : 10.3807/JOSK.2010.14.4.368
Unlike document images, license plate images are mostly captured under uneven lighting conditions. In particular, a shadowed region has sharp intensity variation and sometimes that region has very high intensity by reflected light. This paper presents a new technique for thresholding license plate images. This approach consists of three parts. In the first part, it performs a rough thresholding and classifies the type of license plate to adjust some parameters optimally. Next, it identifies a shadow type and binarizes license plate images by adjusting the window size and location according to the shadow type. And finally, post-processing based on the cluster analysis is performed. Experimental results show that the proposed method outperformed five well-known methods.
Precise Detection of Car License Plates by Locating Main Characters
Lee, Dae-Ho ; Choi, Jin-Hyuk ;
Journal of the Optical Society of Korea, volume 14, issue 4, 2010, Pages 376~382
DOI : 10.3807/JOSK.2010.14.4.376
We propose a novel method to precisely detect car license plates by locating main characters, which are printed with large font size. The regions of the main characters are directly detected without detecting the plate region boundaries, so that license regions can be detected more precisely than by other existing methods. To generate a binary image, multiple thresholds are applied, and segmented regions are selected from multiple binarized images by a criterion of size and compactness. We do not employ any character matching methods, so that many candidates for main character groups are detected; thus, we use a neural network to reject non-main character groups from the candidates. The relation of the character regions and the intensity statistics are used as the input to the neural network for classification. The detection performance has been investigated on real images captured under various illumination conditions for 1000 vehicles. 980 plates were correctly detected, and almost all non-detected plates were so stained that their characters could not be isolated for character recognition. In addition, the processing time is fast enough for a commercial automatic license plate recognition system. Therefore, the proposed method can be used for recognition systems with high performance and fast processing.
Analysis of the Motion Picture Quality of Stereoscopic Three-dimensional Images
Choi, Hee-Jin ; Jung, Jae-Hyun ; Kim, Hwi ; Lee, Byoung-Ho ;
Journal of the Optical Society of Korea, volume 14, issue 4, 2010, Pages 383~387
DOI : 10.3807/JOSK.2010.14.4.383
The stereoscopic three-dimensional (3D) display provides a 3D image by inducing binocular disparity for the observers who wear special glasses. With the rapid progress in flat panel display technologies, the stereoscopic 3D display is becoming a new benefit-model of the current display industry, and several kinds of commercial stereoscopic 3D products have been released and are attracting people. Nowadays, the motion picture quality of the 3D image becomes as important as resolution or luminance since most of the commercial 3D products are 3D televisions or 3D monitors which are required to display a clear motion 3D image. In this paper, an analysis and simulation of the motion picture quality of stereoscopic 3D image is proposed, and a comparison of the motion picture performance among the current stereoscopic 3D technologies is also provided.
Comparisons of Object Recognition Performance with 3D Photon Counting & Gray Scale Images
Lee, Chung-Ghiu ; Moon, In-Kyu ;
Journal of the Optical Society of Korea, volume 14, issue 4, 2010, Pages 388~394
DOI : 10.3807/JOSK.2010.14.4.388
In this paper the object recognition performance of a photon counting integral imaging system is quantitatively compared with that of a conventional gray scale imaging system. For 3D imaging of objects with a small number of photons, the elemental image set of a 3D scene is obtained using the integral imaging set up. We assume that the elemental image detection follows a Poisson distribution. Computational geometrical ray back propagation algorithm and parametric maximum likelihood estimator are applied to the photon counting elemental image set in order to reconstruct the original 3D scene. To evaluate the photon counting object recognition performance, the normalized correlation peaks between the reconstructed 3D scenes are calculated for the varied and fixed total number of photons in the reconstructed sectional image changing the total number of image channels in the integral imaging system. It is quantitatively illustrated that the recognition performance of the photon counting integral imaging system can be similar to that of a conventional gray scale imaging system as the number of image viewing channels in the photon counting integral imaging (PCII) system is increased up to the threshold point. Also, we present experiments to find the threshold point on the total number of image channels in the PCII system which can guarantee a comparable recognition performance with a gray scale imaging system. To the best of our knowledge, this is the first report on comparisons of object recognition performance with 3D photon counting & gray scale images.
A Compact Tunable VCSEL and a Built-in Wavelength Meter for a Portable Optical Resonant Reflection Biosensor Reader
Ko, Hyun-Sung ; Kim, Bong-Kyu ; Kim, Kyung-Hyun ; Huh, Chul ; Kim, Wan-Joong ; Hong, Jong-Cheol ; Park, Seon-Hee ; Yang, Seong-Seok ; Jang, Ho-Jin ; Sung, Gun-Yong ;
Journal of the Optical Society of Korea, volume 14, issue 4, 2010, Pages 395~402
DOI : 10.3807/JOSK.2010.14.4.395
This study reports a portable and precision photonic biosensor reader that can measure the concentration of a particular antigen using an optical resonant reflection biosensor (ORRB). To create a compact biosensor reader, a compact tunable vertical-cavity surface-emitting laser (VCSEL) and a compact built-in wavelength meter were manufactured. The wavelength stability and accuracy of the compact built-in wavelength meter were measured to be less than 0.02 nm and 0.06 nm, respectively. The tunable VCSEL emission wavelength was measured with the compact built-in wavelength meter, it has a fast sweep time (~ 10 seconds) and a wide tuning range (> 4 nm) that are sufficient for biosensor applications based on ORRB. The reflection spectrum of a plastic based ORRB chip was measured by the fabricated portable photonic biosensor reader using the VCSEL and wavelength meter. Although the reader is the size of a palmtop device, it could make a precise measurement of the peak wavelength on equal terms with a conventional bulky optical spectrometer.
Micro-Brillouin Spectroscopy Applied to the Glass Transition of Anti-inflammatory Egonol
Kim, Tae-Hyun ; Ko, Jae-Hyeon ; Kwon, Eun-Mi ; Jun, Jong-Gab ;
Journal of the Optical Society of Korea, volume 14, issue 4, 2010, Pages 403~408
DOI : 10.3807/JOSK.2010.14.4.403
The acoustic properties of anti-inflammatory egonol were investigated by using micro-Brillouin scattering spectroscopy, by use of a 6-pass tandem Fabry-Perot interferometer and an optical microscope specially modified for spectroscopic purposes. The measured Brillouin spectrum was composed of a central peak centered at zero and a Brillouin doublet arising from the longitudinal acoustic waves, i.e. propagating density fluctuations. For the first time, the glass transition of egonol was identified to be about
at which the Brillouin peak position and the half width showed abrupt changes. The substantial damping of acoustic phonons of egonol near the glass transition temperature indicated that the contribution of internal relaxation processes such as small-amplitude librations of side chains to the damping of acoustic phonons may be substantial depending on the internal structure of molecules.
Surface Form Measurement Using Single Shot Off-axis Fizeau Interferometry
Abdelsalam, Dahi Ghareab ; Baek, Byung-Joon ; Cho, Yong-Jai ; Kim, Dae-Suk ;
Journal of the Optical Society of Korea, volume 14, issue 4, 2010, Pages 409~414
DOI : 10.3807/JOSK.2010.14.4.409
This paper describes the surface form measurement of a spherical smooth surface by using single shot off-axis Fizeau interferometry. The demodulated phase map is obtained and unwrapped to remove the
ambiguity. The unwrapped phase map is converted to height and the 3D surface height of the surface object is reconstructed. The results extracted from the single shot off-axis geometry are compared with the results extracted from four-frame phase shifting in-line interferometry, and the results are in excellent agreement.
High-brightness Phosphor-conversion White Light Source Using InGaN Blue Laser Diode
Ryu, Han-Youl ; Kim, Dae-Hwan ;
Journal of the Optical Society of Korea, volume 14, issue 4, 2010, Pages 415~419
DOI : 10.3807/JOSK.2010.14.4.415
A phosphor-conversion white light source is demonstrated using an InGaN-based blue laser diode (LD) and a yellow-emitting phosphor excited by the blue LD. The photometric and colorimetric properties of this blue-LD-based white light source are characterized. When injection current of the LD is 100 mA, luminous flux and luminous efficiency of the white light are found to be over 5 lm and 10 lm/W, respectively. When injection current is >90 mA, luminance is estimated to be larger than 10 Mcd/
. In addition, color characteristics of the white light such as chromaticity coordinates, a correlated color temperature, and a color rendering index are found to be quite stable as current and temperature of the LD varies. The demonstrated LD-based white light source is expected to be used in high-brightness illumination applications with good color stability.
Fabrication of Thick Periodically-poled Lithium Niobate Crystals by Standard Electric Field Poling and Direct Bonding
Kim, Byoung-Joo ; Kim, Chung-Sik ; Kim, Dong-Jin ; Lim, Hwan-Hong ; Park, Sung-Kyun ; Cha, Myoung-Sik ; Kim, Kyung-Jo ;
Journal of the Optical Society of Korea, volume 14, issue 4, 2010, Pages 420~423
DOI : 10.3807/JOSK.2010.14.4.420
We fabricated 1 mm-thick periodically-poled lithium niobate (PPLN) crystals by using a high-voltage amplifier for standard electric field poling combined with a voltage multiplier. Furthermore, two 1 mm-thick PPLNs were directly bonded to make a 2 mm-thick PPLN. The large aperture allowed broad angular tuning, and a broad spectral range of quasi-phase matched second-harmonic generation can be achieved in a single channel. High-power applications are also expected.
The Optical Design of Miniaturized Microscope Objective for CARS Imaging Catheter with Fiber Bundle
Rim, Cheon-Seog ;
Journal of the Optical Society of Korea, volume 14, issue 4, 2010, Pages 424~430
DOI : 10.3807/JOSK.2010.14.4.424
In coherent anti-Stokes Raman scattering (CARS) microscopy reported until now, conventional microscope objectives are used, so that they are limited for introduction into a living body. Gradient-index (GRIN) rod lenses might be a solution for miniaturized microscope objectives for in-vivo CARS microscopy. However, due to the inherent large amount of chromatic aberration, GRIN rod lenses cannot be utilized for this purpose. CARS imaging catheter, composed of miniaturized microscope objective and fiber bundle, can be introduced into a living body for minimally invasive diagnosis. In order to design the catheter, we have to first investigate design requirements. And then, the optical design is processed with design strategies and intensive computing power to achieve the design requirements. We report the miniaturized objective lens system with diffraction-limited performance and completely corrected chromatic aberrations for an in-vivo CARS imaging catheter.
The Optical Design of Probe-type Microscope Objective for Intravital Laser Scanning CARS Microendoscopy
Rim, Cheon-Seog ;
Journal of the Optical Society of Korea, volume 14, issue 4, 2010, Pages 431~437
DOI : 10.3807/JOSK.2010.14.4.431
A stack of gradient-index (GRIN) rod lenses cannot be used for coherent anti-Stokes Raman scattering (CARS) microendoscopy for insertion to internal organs through a surgical keyhole with minimal invasiveness. That's because GRIN lens has large amount of inherent chromatic aberrations in spite of absolutely requiring a common focus for pump and Stokes beam with each frequency of
. For this endoscopic purpose, we need to develop a long slender probe-type objective, namely probe-type microscope objective (PMO). In this paper, we introduce the structure, the working principle, and the design techniques of PMO which is composed of a probe-type lens module (PLM) and an adaptor lens module (ALM). PLM is first designed for a long slender type and ALM is successively designed by using several design parameters from PLM for eliminating optical discords between scanning unit and PLM. A combined module is optimized again to eliminate some coupling disparities between PLM and ALM for the best PMO. As a result, we can obtain a long slender PMO with perfectly diffraction-limited performance for pump beam of 817 nm and Stokes beam of 1064 nm.
Duality of Photonic Crystal Radiative Structures and Antenna Arrays
Bozorgi, Mahdieh ; Granpayeh, Nosrat ;
Journal of the Optical Society of Korea, volume 14, issue 4, 2010, Pages 438~443
DOI : 10.3807/JOSK.2010.14.4.438
In this paper, behaviors of photonic crystal (PC) radiative structures and antenna arrays have been compared for two types of uniform and binomial excitations. Appropriate duality has been shown between them. These results can be generalized to other types of excitation and arrangement of photonic crystal radiative arrays such as linear, planar and circular arrays of three dimensional (3D) photonic crystal termination resonators. Using these results in designing photonic circuits has some advantages for shaping a particular radiative beam at the photonic crystal exit, for instance reducing the divergence angle of the main lobe in order to enhance the directivity, for better coupling, or for splitting the emitted beam, for dividing the output beam to the next devices in photonic integrated circuits (PIC). For analysis and simulation of the photonic crystal structures, the finite difference time domain (FDTD) method has been employed.
An Algorithm to Determine Aerosol Extinction Below Cirrus Cloud from Mie-LIDAR Signals
Wang, Zhenzhu ; Wu, Decheng ; Liu, Dong ; Zhou, Jun ;
Journal of the Optical Society of Korea, volume 14, issue 4, 2010, Pages 444~450
DOI : 10.3807/JOSK.2010.14.4.444
The traditional approach to inverting aerosol extinction makes use of the assumption of a constant LIDAR ratio in the entire Mie-LIDAR signal profile using the Fernald method. For the large uncertainty in the cloud optical depth caused by the assumed constant LIDAR ratio, an not negligible error of the retrieved aerosol extinction below the cloud will be caused in the backward integration of the Fernald method. A new algorithm to determine aerosol extinction below a cirrus cloud from Mie-LIDAR signals, based on a new cloud boundary detection method and a Mie-LIDAR signal modification method, combined with the backward integration of the Fernald method is developed. The result shows that the cloud boundary detection method is reliable, and the aerosol extinction below the cirrus cloud found by inverting from the modified signal is more efficacious than the one from the measured signal including the cloud-layer. The error due to modification is less than 10% taken in our present example.
3D Vision-based Security Monitoring for Railroad Stations
Park, Young-Tae ; Lee, Dae-Ho ;
Journal of the Optical Society of Korea, volume 14, issue 4, 2010, Pages 451~457
DOI : 10.3807/JOSK.2010.14.4.451
Increasing demands on the safety of public train services have led to the development of various types of security monitoring systems. Most of the surveillance systems are focused on the estimation of crowd level in the platform, thereby yielding too many false alarms. In this paper, we present a novel security monitoring system to detect critically dangerous situations such as when a passenger falls from the station platform, or when a passenger walks on the rail tracks. The method is composed of two stages of detecting dangerous situations. Objects falling over to the dangerous zone are detected by motion tracking. 3D depth information retrieved by the stereo vision is used to confirm fallen events. Experimental results show that virtually no error of either false positive or false negative is found while providing highly reliable detection performance. Since stereo matching is performed on a local image only when potentially dangerous situations are found; real-time operation is feasible without using dedicated hardware.