• Transactions of the Society of Information Storage Systems
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• v.1 no.1
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• pp.42-47
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• 2005

We developed an optical pickup system which is used fer Blu-ray Disc. A liquid crystal element was used to make compensation for spherical aberration. Spherical aberration is a difficult problem in the optical pickup system for Blu-ray Disc. To reduce the effects of wavelength variation from the laser source, we designed a diffraction optical element. We took a measurement of all of the parts used to make a pickup system and validated the performance of each part. Then, we made a performance test fur the optical pickup system which we developed for Blu-ray Disc and the results were satisfactory.

• Bulletin of the Korean Chemical Society
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• v.34 no.4
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• pp.1077-1080
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• 2013

Fluorinated polymaleimides with high thermal stability and low optical absorption loss in the optical communication wavelength of $1.55{\mu}m$ were investigated for application in low-loss waveguide materials. The fluorinated polymaleimides were prepared from two monomers phenylmaleimide (H-PMI) and pentafluorophenylmaleimide (F-PMI). All synthesized copolymers had high thermal stability (decomposition temperature $(T_d)=380-430^{\circ}C$). The refractive index of the copolymers could be tuned from 1.4969 to 1.5950 in the TE mode and from 1.4993 to 1.5932 for the TM mode at 632.8 nm by copolymerizing different weight ratios of H-PMI and F-PMI. The refractive index of the copolymers decreased with increasing F-PMI content. In addition, when the amount of F-PMI was increased, optical loss and absorption loss at 632.8 nm and 1550 nm, respectively, decreased.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.1165-1169
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• 2003

This paper presents an approach to optimally design the air-bearing surface (ABS) of the optical flying head for near-field recording technology (NFR). NFR is an optical recording technology using very small beam spot size by overcoming the limit of beam diffraction. One of the most Important problems in NFR is a head disk interface (HDI) issue over the recording band during the operation. A multi-criteria optimization problem is formulated to enhance the flying performances over the entire recording band during the steady state. The optimal solution of the slider, whose target flying height is 50 nm, is automatically obtained. The flying height during the steady state operation becomes closer to the target values than those fur the initial one. The pitch and roll angles are also kept within suitable ranges over the recording band. Especially, all of the air-bearing stiffness are drastically increased by the optimized geometry of the air bearing surface.

• Journal of the Optical Society of Korea
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• v.17 no.6
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• pp.471-480
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• 2013

The beating of two or more lasers that have the same or a finite difference in the central frequencies, is the main source of noise in spectral amplitude coding optical code division multiple access (SAC OCDMA) systems. In this paper we adopt a spatial multiplexing (SM) scheme for SAC OCDMA systems to mitigate this beat noise. The results show that for different code weights and different data rates SM SAC can support a larger number of users than the conventional SAC for all different laser source configurations. However, SM SAC requires a more complex system than the conventional SAC, and almost twice as much optical component.

• Current Optics and Photonics
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• v.5 no.3
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• pp.238-242
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• 2021

In this paper, we present an in line plastic-optical-fiber (POF) temperature sensor based on intensity modulation. The in line POF temperature sensor is composed of a POF, including an in-fiber micro hole filled with reversible thermochromic material, the transmittance of which depends on temperature. The reversible thermochromic material was cobalt chloride/polyvinyl butyral gel. A cobalt chloride solution of concentration 30.8 mM was formulated using 10% water/90% ethanol (v/v) solution, and gelled by dissolving polyvinyl butyral in this solution. Four types of in line POF sensors, with in line micro holes of four different diameters, were fabricated to measure temperature in the range of 25 to 75 ℃. The output optical power of all of these in line POF temperature sensors was inversely proportional to the temperature; the relation between output power and temperature was approximately linear, and the sensitivity was proportional to the diameter of the in-fiber micro hole. The experimental results indicate that an in line POF sensor can be used effectively for measuring moderate temperatures.

• Current Optics and Photonics
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• v.6 no.1
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• pp.39-43
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• 2022

Underwater optical wireless communication (UOWC) is a good candidate for high-speed underwater wireless communication. In this work, we compare the performance of several modulation techniques for a UOWC system consisting of a light-emitting diode (LED) with an operating wavelength of 405 nm and a Si avalanche photodiode (APD). In this work, we consider six modulation schemes: 4-quadrature amplitude modulation (QAM), 8-QAM, quadrature phase shift keying (QPSK), binary phase shift keying (BPSK), on-off keying (OOK), and 4-pulse amplitude modulation (PAM). We also consider the cases of pure water and seawater for the working conditions. Our results show that 4-QAM and 8-QAM perform the best, in terms of communication distance and transmission power efficiency, for all water types considered.

• Korean Journal of Optics and Photonics
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• v.20 no.3
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• pp.148-155
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• 2009

In this paper, we analysed what effect the design variables, such as refractive index, central thickness and radius of curvature, had on the first order properties and image quality of optical systems when temperature changed. The optical parameters were varied at each temperature, then the coupling and ruler methods were used to design an athermalized lens for a phone camera. This concept was first used to design the lens for a 1/3.2" 5M phone camera. The designed lens satisfies all the specifications for a phone camera, and the variations of the back focal length(${\Delta}BFL$) are reduced to $10{\mu}m$ for a temperature range of $-10^{\circ}C$ to $+60^{\circ}C$. Also, the TTL of 5.5 mm results in a compact system. All design concepts and results discussed in this paper are expected to be useful in development for the phone and CCTV camera.

• Journal of Internet Computing and Services
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• v.8 no.4
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• pp.41-49
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• 2007

Ethernet passive optical network(EPON) is the next-generation technology for supporting services of high-quality at low-cost. In the EPON, all optical network units(ONUs) have to share a limited uplink channel for upstream data. In order to satisfy bandwidth demands of users on high-capacity local access networks(LANs), the optical line terminal(OLT) efficiently divides and allocates time slots of uplink channel to all ONUs. We discuss previous schemes for dynamic bandwidth allocation(DBA), such as interleaved polling with adaptive cycle time(IPACT) and sliding cycle time(SLICT). In this paper, dynamic right sizing of maximum-windows(DRSM), as a novel bandwidth allocation service, is proposed for more effective and efficient time slot allocation of the uplink channel. DRSM which is based on past information of bandwidth allocated by OLT calculates maximum available bandwidth and dynamically alters the maximum window size for the next ONU. This scheme does not only exert every effort to meet bandwidth demands of ONUs with the possible scope, it also seeks fairness of bandwidth allocation among ONUs.

• Journal of the Korean Society of Radiology
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• v.15 no.4
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• pp.525-531
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• 2021

The detector of the positron emission tomography (PET) is composed using a plurality of scintillation pixels and photo sensors. The use of multiple photo sensors increases cost and complicates signal processing. In this study, a detector with reduced cost and simple signal processing was designed using a small number of photo sensors. A scintillation pixel and a small number of photo sensors were used, and a optical guide was used to deliver light to all the photo sensors. A reflector is applied to the scintillation pixel and the optical guide to transmit the maximum amount of light to the photo sensor. A diffuse reflector and a specular reflector were used for the reflector, and a flood image was obtained by applying different thicknesses of the optical guide. An optimal combination was selected through comparative analysis of the acquired flood images. As a result, when specular reflectors were used for both the scintillation pixel and the optical guide, excellent flood images were obtained from optical guides of all thicknesses. For the optical guide, the optimal image was obtained when using a 3 mm thickness in consideration of the size of the image and the analysis of the point where the image of the scintillation pixel was formed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.4A
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• pp.579-585
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• 2000

This paper analyzes and compares the blocking performance of all-optical wavelength-routed networks providing circuit switching among users. A connection between two nodes along a particular path must use a single wavelength on all hops, or links, within the path. We then calculate the blocking probability along a lightpath with wavelength conversion in a network with an arbitrary topology and show the network performance improvement offered by node with limited translation technology. We also propose a new schematic method for the performance analysis of different types of network architecture which is composed of nodes with or without wavelength conversion(NC, FC or LC).