• Journal of the Optical Society of Korea
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• v.13 no.1
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• pp.107-111
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• 2009

The properties of the chirped fiber Bragg grating (CFBG) as a chromatic dispersion compensator in differential phase-shift-keyed (DPSK) transmission are analyzed. Comparisons of a performance of a CFBG in between DPSK and On-Off Key (OOK) are shown by simulations using the commercial numerical modeling software, $OptSim^{TM}$. In the simulation, we compared the performance of the CFBG when they were used in the RZ-OOK 40 Gbps and the RZ-DPSK 40 Gbps transmission. The simulation results show the performance of an overall transmission with a CFBG in DPSK is inferior to the case of OOK, although DPSK generally has a 3 dB higher SNR (signal-to-noise ratio) than OOK.

• Journal of the Optical Society of Korea
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• v.12 no.4
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• pp.244-248
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• 2008

We have evaluated the performance of strain-chirped fiber Bragg grating (FBG) based tunable dispersion compensator in a 40 Gb/s transmission link. In our proposed compensator, the value of dispersion could be changed from -353 ps/nm to -962 ps/nm by adjusting the rotation angle of the metal beam on which the FBG was mounted. In order to evaluate the effect of ripples in reflectivity and variations in passband of the FBG based dispersion compensator, transmission performance has been measured with our tunable dispersion compensator. Error-free transmission of a 40 Gb/s non-return-to-zero (NRZ) signal over conventional single-mode fiber (SMF) was achieved.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.4
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• pp.971-980
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• 2013

System performance improvement through the concentrated residual dispersion per span (RDPS) in special transmission fiber spans in optical transmission links with dispersion management (DM) for wavelength division multiplexed (WDM) transmission is investigated through the comparison with the performance in optical transmission links with uniform RDPS in every fiber spans. It is confirmed that, in optical links with RDPS of 0 ps/nm uniformly distributed in the rest fiber spans, if RDPS of 300 ps/nm and 1,320 ps/nm are concentrated in 5th-13th fiber spans and 6th-13th fiber spans, respectively, then the best performance is obtained. It is also confirmed that optimal net residual dispersion (NRD) controlled by precompensation and postcompensation are 10 ps/nm and -10 ps/nm, respectively, in all two cases, and the effective launching power range below 1 dB eye opening penalty (EOP) in the concentrated RDPS of 300 ps/nm and 1,320 ps/nm are improved by 2 dB and 6 dB than optical transmission links with the uniformly distributed RDPS, respectively.

• ETRI Journal
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• v.30 no.2
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• pp.261-267
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• 2008

In this paper, we propose and demonstrate a cost-effective technique to upgrade the capacity of dense wavelength division multiplexing (DWDM) networks to a 40 Gb/s line rate using the existing 10 Gb/s-based infrastructure. To accommodate 40 Gb/s over the link optimized for 10 Gb/s, we propose applying a combination of super-FEC, carrier-suppressed return-to-zero, and pre-emphasis to the 40 Gb/s transponder. The transmission of 40 Gb/s DWDM channels over existing 10 Gb/s line-rate long-haul DWDM links, including $40{\times}40$ Gb/s transmission over KT's standard single-mode fiber optimized for 10 Gb/s achieves successful results. The proposed upgrading technique allows the Q-value margin for a 40 Gb/s line rate to be compatible with that of 10 Gb/s.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.05b
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• pp.327-330
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• 2000

The scanning Maxwell-stress microscopy (SMM) is a dynamic noncontact electric force microscopy that allows simultaneous access to the electrical properties of molecular system such as surface potential, surface charge, dielectric constant and conductivity along with the topography. The Scanning near-field optical / atomic force microscopy (SNOAM) is a new tool for surface imaging which was introduced as one application of the atomic force microscope (AFM). Operated with non-contact forces between the optical fiber and sample as well as equipped with the piezoscanners, the instrument reports on surface topology without damaging or modifying the surface for measuring of optical characteristic in the films. We report our recent results of its application to nanoscopic study of domain structures and electrical functionality in organic thin films by SMM. Furthermore, we have illustrated the SNOAM image in obtaining the merocyanine dye films as well as the optical image.

• Journal of the Korean Institute of Telematics and Electronics
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• v.24 no.4
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• pp.696-700
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• 1987

Guide modes in a graded index multinmode optical fiber are turned into clad modes when the optical fiber was bended into a perpendicular direction to its optical axes by microbending forces, which causes the loss of the guiding optical power. The theories reported on this microbending power loss can be applied to calculation of the transmission power loss only when the beding period equals to the mode coupling length. In this paper, we obtained the general expression of the optical power transmission loss in a graded index multimode fiber bended periodically. This can be applied to the calculation of the power loss of the periodically microbended fiber with an arbitrary bending shape and period. Also, by using the beam theory in mechanics, we could derive the expression of the displacement of the optical fiber caused by the external force which bends the fiber into a periodic trapezoidal shape. Experiments were carried out to determine the dependence of the power loss on the period of the microbending forces. Experimnetal results were in good agreement (in the same order of the magnitude) with theoritical values derived in our work within the bending period region of 2mm-10mm.

• Korean Journal of Optics and Photonics
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• v.24 no.6
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• pp.297-310
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• 2013

With the explosive growth of internet data traffic due to the FTTH penetration, prevalence of smart devices and cloud network service, the demand for higher bandwidth is ever increasing with the pace of more than 40% annual growth. To accommodate ultra high bandwidth traffic, optical components in each hierarchy have progressed rapidly. WDM has begun to be deployed along with higher bandwidth service in the access network. Next-generation ROADM is under development for efficient network management in the metro network. For long-haul transmission, an advanced modulation scheme based on coherent transmission technology has been adopted to enhance spectral efficiency. In this paper, core components to meet the demands of high speed, high efficiency and low power consumption will be reviewed.

• Journal of Sensor Science and Technology
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• v.10 no.1
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• pp.9-15
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• 2001

The extrinsic Fabry-Perot interferometric (EFPI) optical fiber sensor shows good sensitivity and resolution, and has many advantages over optical fiber sensors of other types. However, this EFPI optical fiber sensor has a disadvantage that the distinction of measuring directions is difficult due to the measurement method by using only fringe counting. In this paper, the transmission-type extrinsic Fabry-Perot interferometric (TEFPI) optical fiber sensor was developed, which has been improved by the additional function and whose measuring system is different from that of the conventional EFPI optical fiber sensor. Then the application result of the TEFPI optical fiber sensor to the strain and temperature measurement was explained in detail.

• Korean Journal of Optics and Photonics
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• v.14 no.6
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• pp.578-582
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• 2003

We propose a novel structure of wavelength selective optical add/drop module comprising two tap couplers and a fiber Bragg grating. The device has unique features including a simpler structure and a lower cost of implementation as compared with existing devices for the same operation. The module performance has been measured and analyzed experimentally. The implemented prototype module shows good performance with no-crosstalk power penalty in a 155 Mbps per channel wavelength-division-multiplexing transmission system but suffers from a relatively high loss of 3.5 ㏈ and 21 ㏈ for transmitted and dropped channels, respectively. While the dropped channel extinction ratio was more than 25 ㏈, the transmitted channel extinction ratio was more than 35 ㏈.

• Electronics and Telecommunications Trends
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• v.34 no.5
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• pp.81-90
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• 2019

The data rate for transmission through fiber-optic cables has increased to 400 Gbps in single-wavelength channels. However, speeds up to 1 Tbps are required now to meet the ever-increasing bandwidth demand driven by the diverse requirements of contemporary applications for high-quality on-demand video streaming, cloud services, various social media, and emerging 5G-enabled applications. Because the data rates of the per-channel optical interfaces depend strongly on the operational speed of the optoelectronic devices used in optical transceivers, ultrahigh-speed photonic devices and components, and eventually, chip-level transmitter and receiver technologies, are essentially required to realize futuristic optical transceivers with data rates of 1 Tbps and beyond. In this paper, we review the recent progress achieved in high-speed optoelectronic devices, such as laser diodes, optical modulators, photodiodes, and the transmitter-receiver optical subassembly for optical transceivers in data centers and in metro/long-haul transmission.