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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
> Journal Vol & Issue
Korean Journal of Optics and Photonics
Journal Basic Information
Journal DOI :
Optical Society of Korea
Editor in Chief :
Volume & Issues
Volume 19, Issue 6 - Dec 2008
Volume 19, Issue 5 - Oct 2008
Volume 19, Issue 4 - Aug 2008
Volume 19, Issue 3 - Jun 2008
Volume 19, Issue 2 - Apr 2008
Volume 19, Issue 1 - Feb 2008
Selecting the target year
A New X-Ray Image Sensor Utilizing a Liquid Crystal Panel
Rho, Bong-Gyu ;
Korean Journal of Optics and Photonics, volume 19, issue 4, 2008, Pages 249~254
DOI : 10.3807/HKH.2008.19.4.249
We developed a new x-ray image sensor utilizing a reflection-mode liquid crystal panel as its sensitive element, and tested its functionality by using it to obtain an x-ray image of a printed circuit board. In the liquid crystal x-ray image sensors hitherto reported, the liquid crystal layer is in direct contact with the photoconductive film which is deposited on a glass substrate. In the fabrication of the new x-ray image sensor, a liquid crystal panel is fabricated in the first step by using a pair of glass plates of a few centimeters thicknrss. Then one of the glass substrates is ground until its thickness is reduced to about
. After polishing the glass plate, dielectric films for high reflectance at 630 nm, a film of amorphous selenium for photoconduction, and a transparent conductive film for electrode are deposited in sequence. The new x-ray image sensor has several merits: primarily, fabrication of a large area sensor is more easily compared with the old fashioned x-ray image sensors. Since the reflection type liquid crystal panel has a very steep response curve, the new x-ray sensor has much more sensitivity to x-rays compared with the conventional x-ray area sensor, and the radiation dosage can be reduced down to less then 20%. By combining the new x-ray sensor with CCD camera technology, real-time x-ray images can be easily captured. We report the structure, fabrication process and characteristics of the new x-ray image sensor.
Propagation Characteristics and Tolerance Analysis of Optical Wires in Flexible Optical PCB by Ray Tracing
Yeom, Jun-Cheol ; Park, Dae-Seo ; Kim, Young-Seok ; Kim, Dae-Chan ; Park, Se-Geun ; O, Beom-Hoan ; Lee, El-Hang ; Lee, Seung-Gol ; Jeon, Keum-Soo ;
Korean Journal of Optics and Photonics, volume 19, issue 4, 2008, Pages 255~261
DOI : 10.3807/HKH.2008.19.4.255
In this study, the propagation characteristics and the fabrication tolerance of an optical wire in a flexible optical PCB were analyzed by using a ray-tracing method. It is found from the analysis that the sidewall angle of a core should be controlled within
in order to maintain the propagation loss to less than -1 dB/mm, and that the bending radius of the optical wire should be larger than 5 mm in order to suppress the bending loss below -1 dB. In addition, it is confirmed that the lateral misalignment of
, and the angular tilting of VCSEL of
are allowable for the coupling loss of -1 dB.
Image Watermark Method Using Multiple Decoding Keys
Lee, Hyung-Seok ; Seo, Dong-Hoan ; Cho, Kyu-Bo ;
Korean Journal of Optics and Photonics, volume 19, issue 4, 2008, Pages 262~269
DOI : 10.3807/HKH.2008.19.4.262
In this paper, we propose an image watermark method using multiple decoding keys. The advantages of this method are that the multiple original images are reconstructed by using multiple decoding keys in the same watermark image, and that the quality of reconstructed images is clearly enhanced based on the idea of Walsh code without any side lobe components in the decoding process. The zero-padded original images, multiplied with random-phase pattern to each other, are Fourier transformed. Encoded images are then obtained by taking the real-valued data from these Fourier transformed images. The embedding images are obtained by the product of independent Walsh codes, and these spreaded phase-encoded images which are multiplied with new random-phase images. Also we obtain the decoding keys by multiplying these random-phase images with the same Walsh code images used in the embedding images. A watermark image is then made from the linear superposition of the weighted embedding images and a cover image, which is multiplied with a new independent Walsh code. The original image is simply reconstructed by the inverse-Fourier transform of the despreaded image of the multiplication between the watermark image and the decoding key. Computer simulations demonstrate the efficiency of the proposed watermark method with multiple decoding keys and a good robustness to the external attacks such as cropping and compression.
Occluded Object Reconstruction and Recognition with Computational Integral Imaging
Lee, Dong-Su ; Yeom, Seok-Won ; Kim, Shin-Hwan ; Son, Jung-Young ;
Korean Journal of Optics and Photonics, volume 19, issue 4, 2008, Pages 270~275
DOI : 10.3807/HKH.2008.19.4.270
This paper addresses occluded object reconstruction and recognition with computational integral imaging (II). Integral imaging acquires and reconstructs target information in the three-dimensional (3D) space. The reconstruction is performed by averaging the intensities of the corresponding pixels. The distance to the object is estimated by minimizing the sum of the standard deviation of the pixels. We adopt principal component analysis (PCA) to classify occluded objects in the reconstruction space. The Euclidean distance is employed as a metric for decision making. Experimental and simulation results show that occluded targets are successfully classified by the proposed method.
Key-factors in the Modified Parallel Type to Convert Toed-in Type Stereoscopy
Lee, Kwang-Hoon ; Kim, Dong-Wook ; Kim, Sung-Kyu ;
Korean Journal of Optics and Photonics, volume 19, issue 4, 2008, Pages 276~286
DOI : 10.3807/HKH.2008.19.4.276
The representative alignments for taking a stereo image by using a stereoscopic camera are the toed-in and the parallel alignment. In this paper, we tried to find important factors in the process that captures the stereo image by modifying parallel type 3D camera alignment to take the same object information as, for instance, when toed-in type was used. The modified parallel type 3D camera has merits in both types. As a result, three important factors are found by simulation to be inter-camera distance, field of view and convergence angle for both types. And the change of the convergence angle is known to be the most important factor at the stereo fusible area in processing. The effective ranges of these factors to simulate perfectly toed-in type by modified parallel type are strongly dependent on a user's circumstances such as mobile, official, theater and so on. Additionally, the error of the simulation is reduced when the focal length of the stereo camera is short and the convergence angle becomes smaller.
Fabrication and Evaluation of Diameter 1 m Off-axis Parabolic mirror
Yang, Ho-Soon ; Lee, Jae-Hyeob ; Jeon, Byung-Hyug ; Lee, Yun-Woo ; Lee, Kyoung-Muk ; Choi, Se-Chol ; Kim, Jong-Min ;
Korean Journal of Optics and Photonics, volume 19, issue 4, 2008, Pages 287~293
DOI : 10.3807/HKH.2008.19.4.287
The collimator which makes a collimated beam, is an essential instrument for assembly and evaluation of telescopes. Recently, the Cassegrain type collimator has been widely used for its compact size as the focal length of high resolution cameras becomes longer. However, this kind of collimator has a disadvantage in that the secondary mirror is a heat source which can degrade the evaluation accuracy for an IR camera system. In this paper, we present the fabrication and measurement process for an off-axis parabolic mirror with the physical diameter pf 1 m, effective diameter 930 mm, and the focal length 6 m. After four months of works we obtained the final surface wave-front error of 30.4 nm rms (
), which is capable of evaluation of an IR camera as well as a visible camera.
Simulation of Cholesteric Liquid Crystal Color Filter by Using User-defined Coating Property of an Illumination Design Software
Beom, Tae-Won ; Cui, Hao ; Lee, Hak-Suk ; Yang, Jeong-Mun ; Park, Jong-Rak ; Yoon, Ki-Cheol ; Jang, Won-Gun ;
Korean Journal of Optics and Photonics, volume 19, issue 4, 2008, Pages 294~301
DOI : 10.3807/HKH.2008.19.4.294
We have performed modeling and simulations of optical characteristics for a cholesteric liquid crystal (CLC) color filter. Berreman's
matrix method was used for the calculation of reflectance spectra of the CLC color filter with respect to the incident angle. The results were employed as input parameters for a user-defined coating property of an illumination design software based on the ray-tracing method, LightTools. Color shift characteristics of a planar transmission-type CLC color filter were simulated using LightTools. The results were compared with the results obtained with Berreman's
matrix method. It was found that color shift characteristics of the CLC color filter could be simulated to a reasonable accuracy when the reflectance spectra with less than 5 degrees of incremental incidence-angle were used as the input data for the user-defined coating property of LightTools. We have simulated color shift characteristics of a reflection-type CLC color filter having hemi-spherical patterns. The simulation method reported in this paper has been found to be also used for a non-planar CLC color filter structure.
Visual Measurement of Rotational Displacements by Using Two Different Moire Fringes Simultaneously Generated by Repeated Sinusoidal Gratings
Jeong, Youn-Hong ; Oh, Jeong-Hyo ; Jo, Jae-Heung ;
Korean Journal of Optics and Photonics, volume 19, issue 4, 2008, Pages 302~309
DOI : 10.3807/HKH.2008.19.4.302
We present the precise visual measurement method of rotational displacements using two different moire fringes simultaneously generated by repeated sinusoidal gratings. We investigate the variation of moire fringes depending on rotational displacements through computer simulation and experiment using a rotator in detail. The moire fringes are composed of the wide linear fringe part with a long period and the narrow linear fringe part with a short period. These parts are superior to the angle detection of more than 12 degrees and less than 12 degree, respectively. Additionally, the method can be visually used in the determination of the rotational direction by observing the moire fringe's direction.
Inspection System for Tracing Defects of Optical Film Using Contact Image Sensor
Rhee, Hyug-Gyo ; Jeon, Byeong-Hyug ; Lee, Hoi-Yun ; Lee, Yun-Woo ;
Korean Journal of Optics and Photonics, volume 19, issue 4, 2008, Pages 310~314
DOI : 10.3807/HKH.2008.19.4.310
The light from the exterior considerably deteriorates the performance of displays including PDP (plasma display panel). Thus semi-conductor industries have developed a special optical film that can block or absorb the exterior light. In this paper, we propose a new inspection system for tracing the defects of the film. Our system is able to inspect a
area for 10 sec with
Influence of the Parameters of a Heater Array Inducing a Thermo-optic Long-period Grating on its Power Consumption
Kwon, Min-Suk ;
Korean Journal of Optics and Photonics, volume 19, issue 4, 2008, Pages 315~319
DOI : 10.3807/HKH.2008.19.4.315
We investigate theoretically the power consumption of a notch filter using a thermo-optic long-period grating, which is induced by a heater array consisting of periodic heaters and pads made of metal thin-film. Since the power consumed by the heater array is converted to joule heat that generates the thermo-optic long-period grating, the characteristics of the notch filter are dynamically controlled by adjusting it. The power necessary for appropriate coupling efficiency depends on the parameters of the heater array, which are the width and length of a heater, pad width, and the thickness of the thin-film. We explain an approximate method of analyzing the influence of the parameters on the consumed power. Using the analysis method, we simulate the change of the power depending on the parameters. From the simulation, we suggest a few guidelines on the parameters required to reduce the power.
Optimization of Q-switched Operation at a Laser-Diode Pumped Nd:YAG Ceramic Laser
Shin, Dong-Joon ; Kim, Byung-Tai ; Kim, Duck-Lae ;
Korean Journal of Optics and Photonics, volume 19, issue 4, 2008, Pages 320~326
DOI : 10.3807/HKH.2008.19.4.320
The output characteristics of a laser-diode pumped electrooptic Q-switched Nd:YAG ceramic laser were investigated. The output energy of a Q-switched Nd:YAG ceramic laser was optimized under an output coupler reflectivity of 77%, a laser-diode pulse width of
, and a delay time of
. The output energy of the Q-switched pulse was measured to be 0.35 mJ with a pulse width of 4 ns under a pump energy of 17.9 mJ. The output efficiency and the peak power were 1.9% and 87.5 kW, respectively.
Image Enhancement for 3D Shape Measurement Using Large Aperture Projection System
Yoon, Doo-Hyun ; Kim, Hak-Il ;
Korean Journal of Optics and Photonics, volume 19, issue 4, 2008, Pages 327~333
DOI : 10.3807/HKH.2008.19.4.327
In general, a lens with large NA makes image quality better. There are many kinds of cheap concave mirrors with large aperture and NA. This paper presents a method that uses a large aperture projection imaging system to enhance the image used for 3D shape measurement. This method makes it possible to enhance reflection uniformity on the object surface and increases SNR (Signal to Noise Ratio). Using a large aperture lens, it is possible to obtain a brighter image, reducing the shading nature in the image boundary, and enhancing the reflection uniformity even on woven surfaces. Because of the exorbitant cost of a large aperture projection lens larger than 150 mm in diameter, a refractive lens was exchanged with a concave mirror resulting in the same optical effect. In experiment, changing NA
, image contrast was enhanced from 46 to 1.33. Incidentally, the effect of the concave mirror was tested successfully through the experiment.
Atomic Coherence Spectroscopy in the Paraffin Coated Rb Atom Vapor Cell
Lee, Hyun-Joon ; Yu, Ye-Jin ; Bae, In-Ho ; Moon, Han-Seb ;
Korean Journal of Optics and Photonics, volume 19, issue 4, 2008, Pages 334~340
DOI : 10.3807/HKH.2008.19.4.334
We investigated the electromagnetically induced transparency (EIT) and the Hanle spectrum in a paraffin coated Rb vapor cell. The EIT spectrum was observed in the
transition of the
-line by using two independent external cavity diode lasers, and the Hanle spectrum was observed by using one external cavity diode laser in the
-type scheme between the Zeeman sublevels of the
transition of the
-line. In the Hanle spectrum, we could observe the dual-structured spectrum in the paraffin coated vapor cell. We investigated the dual-structured lineshape by applying an external magnetic field, and varying the direction of the magnetic field. The narrow linewidth of dual-structured EIT was measured to be approximately 200 Hz.