• The Journal of Korean Institute of Communications and Information Sciences
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• v.18 no.9
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• pp.1248-1256
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• 1993

The propagation and delay properties in opical fiber are particularly attractive because digital signal processing and conventional analog signal processing techniques such as those using surface acoustic wave devices are limited In their usefulness for signal bandwidth exceeding one or two GHz, although they are very effective at lower frequencies. Since an accurate, low loss and short time delay elements can be obtained by using such an optical fiber, optical signal precessing has attracted much attention for high speed and broad-band signal precessing in particular channel separation filtering for optical FDM signals. In this paper, we consider a coherent optical lattice filter, which uses coherent light sources and consists of directional couplers and optical fiber delay elemnts. The optical fiber fitters are more restricted than the usual digital filters. The reasons are as follows. 1) the coupling coefficients of directional couplers are restricted to the number between 0 and 1. 2) optical signal E(complex amplitude) is divided into J If-$\boxUl$ and J L/7$\div$$\boxUl$ at the directional coupler. Considering these restrictions and in this case all the coupling coefficients of summing and branching elements are set to be equal, we have given design formulae for optical lattice filter, which make the best use of optical signal energy.

• Journal of the Optical Society of Korea
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• v.20 no.4
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• pp.464-469
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• 2016

All-optical non-return-to-zero (NRZ) -to- return-to-zero (RZ) data-format conversion has been successfully demonstrated using a semiconductor optical amplifier in a fiber-loop mirror (so-called SOA-loop mirror) with a continuous-wave (CW) holding beam. The converted RZ signal after pulse compression has been used to create a 40 Gb/s OTDM (Optical Time Division Multiplexing) signal. Here is proposed an NRZ-to-RZ conversion method without any additional optical clocks, unlike conventional methods based on optical AND logic. In addition, it has the merit of operating at various bit-rate speeds without any controlling device. Moreover, it has a simple structure, and it can be used for all-optical bit-rate-flexible clock recovery.

• Korean Journal of Optics and Photonics
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• v.34 no.6
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• pp.235-240
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• 2023

The optical signal injected into an end-fire optical phased array propagates along the waveguides inside the device and is emitted from the edge of the antenna. In general, reflection and scattering occur at the boundary, thereby reducing the emission efficiency of the optical signal. In this article, we propose a silicon nitride (Si₃N₄) tapered waveguide antenna structure whose width is tapered toward the emitting edge, achieving high emission efficiency operating at the 1,550 nm wavelength. The Si₃N₄ tapered waveguide antenna was numerically designed using the 3D finite-difference time-domain method. The optical signal emission efficiency increased from 78% to 96.3%, while reflectance decreased from 22% to 3.7% compared with the untapered waveguide antenna counterpart. This result will not only boost the optical signal intensity but also mitigate optical noise resulting from back reflection along the waveguide in the end-fire optical phased array device.

• ETRI Journal
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• v.27 no.3
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• pp.267-272
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• 2005

The transmission performance of optical labeling based on a combined frequency shift keying/amplitude shift keying (FSK/ASK) format is studied by numerical simulation. The simulation demonstrates that the bit-error ratio (BER) characteristic of an ASK signal is limited by the extinction ratio, received optical power, and dispersion, simultaneously. However, an FSK signal is mainly limited by the extinction ratio (ER) and received optical power when the peak spectrum, which is used to detect the FSK signal, is relatively narrow.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2011.05a
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• pp.536-538
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• 2011

Net residual dispersion (NRD) available to transmit 160 Gbps OPDM signal is induced in optical transmission links with dispersion management (DM) and optical phase conjugator (OPC) for compensating of chromatic dispersion and self phase modulation (SPM). It is confirmed that the perfect cancellation of accumulated dispersion is necessary to transmit 160 Gbps OTDM signal.

• Proceedings of the KIEE Conference
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• 1995.07c
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• pp.1281-1283
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• 1995

In this paper, we develop a prototype of the Optical SCM transmission module. This module is possible to application to electric facilities for control and measurements. Transmission channel number is two channels, namely, image and digital signal. In the image transmission, modulation method is AM, baseband signal is NTSC video signal and demodulation use PLL. Modulation of digital signal is QPSK, 1.544Mbps and demodulation use PLL. First, we calculate theoretical analysis about RF and Optical link in the transmission. This calculation is well correspond with practical system and transmission experiment is excellent, but this is only two channel model. And now, we plan to multichannel transmission to measure intermodulation, frequency assignments and optimal channel numbers et al.

• Journal of Magnetics
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• v.13 no.2
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• pp.70-75
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• 2008

In this study, a MOKE (Magneto-optical Kerr effect) measurement method for magnetic nanostructures is proposed. Theoretically, the MOKE signal enhancement can be predicted and confirmed when an anti-reflection coated substrate is used. Since MOKE is a ratio of reflectivity and the difference between the reflectivities for two magnetic states, when the reflectivity of the substrate part is reduced by employing an anti-reflection coated substrate, MOKE signal enhancement can be achieved. The enhancement is confirmed by simple numerical MOKE calculations. When the reflectivity of an anti-reflection coated substrate is 0.7%, the calculated MOKE signal is about 79% of its bulk values for the 100-nm wide Fe nanowire with a 1500-nm radius laser beam. It was found that, for various numerical calculations, a larger MOKE signal is obtained relative to a smaller substrate reflectivity.

• Journal of Korea Society of Digital Industry and Information Management
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• v.7 no.2
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• pp.59-65
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• 2011

All-optical signal processing is expected to offer advantages in speed and power consumption against over electronics signal processing. It has a potential to solve the bottleneck issues of ultra-high speed communication network nodes. All-optical serial-to-parallel and parallel-to-serial data converters would make it possible to easily process the serial data information of a high-speed optical packet without optical-to-electronic-to-optical data conversion. In this paper, we explain the principle of simple and easily expandable all-optical serial-to-parallel and parallel-to-serial data converters based on Mach-Zehnder interferometers. We experimentally demonstrate these data converters at 10Gbit/s serial data rate. They are useful all-optical devices for the all-optical implementations of label decoding, self-routing, control of variable packets, bit-wise logical operation, and data format conversion.

• Current Optics and Photonics
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• v.2 no.5
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• pp.395-399
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• 2018

This article investigates the mechanism of electronic signal phase noise degradation induced by laser phase noise in optical links comprising optical resonators. Through theoretical derivation, we find that the phase noise of the output electronic signal has the same spectral shape of optical intensity noise as the output of the optical resonator. We propose that the optical resonator transfers laser phase noise to light intensity fluctuation and then the intensity fluctuation is converted to electric phase noise through AM-PM conversion mechanism in the photodiode. An optical link comprising a Fabry-Perot resonator was constructed to verify the proposed mechanism. The experimental results agree with our theoretical prediction verifying that the supposition is correct.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.7 s.98
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• pp.746-752
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• 2005

In this paper, optical noise effect is reduced by using the loss characteristics of plastic fibers in an optical wireless system. The attenuation coefficient of a plastic fiber for the signal is different from that f3r the noise light, and the length difference between two fibers to the 2PD's behaves like a discriminative element. It is possible to eliminate the optical noise effect and detect only the signal without optical filters. The signal to noise ratio in a differential detector using fibers was 9.7 dB higher than in a single photodiode without optical fiber.