• Journal of the Korean Society of Combustion
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• v.11 no.3
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• pp.26-35
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• 2006

This work forcus on the development of gas sensor that measure the concentrations of exhaust gas using diode laser, Each diode laser for exhaust gas measurement is set to work at near-IR using both DA and WMS methods. Also use of fiber-coupled optical elements makes such a sensor rugged and easy to align. The results showed that gas concentrations of $O_2$, CO, $CO_2$, NO are accurately measured within ${\pm}2%$ error. The application of WMS method increased the beam intensity 2-3 times higher than DA method. It were experimentally compared WMS (Wavelength Modulation Spectroscopy) with DA (Direct Absorption) for the accuracy.

• Journal of Advanced Navigation Technology
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• v.7 no.2
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• pp.128-134
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• 2003

In this paper, we investigated the degree of compensation for WDM channel signal distortion due to chromatic dispersion, self phase modulation (SPM) and cross phase modulation (XPM) as a function of transmission length using mid-span spectral inversion (MSSI) compensation method. The considered system is $3{\times}40$ Gbps intensity modulation direct detection (IM/DD) WDM transmission system. This system has highly nonlinear dispersion shifted fiber (HNL-DSF) as a nonlinear medium in optical phase conjugator (OPC). We confirmed that the transmission length is more increased by applying MSSI to distorted signal due to chromatic dispersion, SPM and XPM as dispersion coefficient of fiber becomes higher. And the compensation degree of distorted WDM channels due to chromatic dispersion, SPM and XPM becomes better stable as dispersion coefficient of fiber becomes higher.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.35D no.8
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• pp.53-61
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• 1998

Dynamic characteristics of widely tunable SGDBR/SSGDBR laser diodes integrated with an electroabsorption modulator is inestigated using an improved large-signal timef-domain model. First, wide tunning properties of a SGDBR laser diode and a SSGDBR laser diode are analyzed respectively and compared with each other. And, intensity-modulation characteristics of a SGDBR laser diode incorprating an electroabsorption modulator are investigated. It is shown that an external modulation has the lower frequency chirp by 1/20 for almost same extinction ratios than a direct modulation, and a nearly transform-limited pulse train can be generated using the optical gating of an electroabsorption modulator.

• Electrical & Electronic Materials
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• v.11 no.11
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• pp.28-36
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• 1998

Widely tunable diodes integrated with periodically sampled and chirped DBR(distributed Bragg reflector) and an EA(electroabsorption) modulator are analyzed dynamically using the improved largesinal time-domain model. The tuning characteristics of sampled- and chirped-grating DBR laser diodes are demonstrated theoretically. The results of the simulation agree well with those of the experiment. And the intensity-modulation properties of the laser diodes integrated with an EA modulator are calculated. It is shown that the external modulation has the lower frequency chirp by 1/20 for the same extinction ratio than the direct modulation, and also the short pulse train can be generated using the optical gating of an EA modulator.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.5
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• pp.1134-1140
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• 2004

In this paper, we investigated the effect of cross phase modulation(XPM) on compensation for WDM channel distortion due to chromatic dispersion, self phase modulation and XPM as a function of fiber dispersion coefficient and modulation format in 320 Gbps WDM systems. The considered WDM transmission system is based on mid-span spectral inversion(MSSI) compensation method, which has highly nonlinear dispersion shifted fiber(HNL-DSF) as nonlinear medium of optical phase conjugator (OPC) in the mid-way of total transmission line. We confirmed that the maximum channel input power resulting 1 dB eye opening penalty is reduced due to XPM effect on channel distortion, even if MSSI method was applied to WDM system. But, we confirmed that the effect of XPM on channel distortion becomes decrease as fiber dispersion coefficient of WDM system becomes larger. Futhermore, we confirmed that NRZ is better than RZ as a modulation format for similarly compensating overall WDM channels in WDM system with large fiber dispersion coefficient in order to minimize the effect of the XPM on channel distortion.

• 대한방사선방어학회:학술대회논문집
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• 2011.11a
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• pp.346-347
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• 2011

• 한국정보통신설비학회:학술대회논문집
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• 2009.08a
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• pp.314-319
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• 2009

In this paper, the network performance of a turbo coded optical code division multiple access (COMA) system with cross-layer, which is between physical and network layers, concept is analyzed and simulated We consider physical and MAC layers in a cross-layer concept. An intensity-modulated/direct-detection (IM/DD) optical system employing pulse position modulation (PPM) is considered In order to increase the system performance, turbo codes composed of parallel concatenated convolutional codes (PCCCs) is utilized. The network performance is evaluated in terms of bit error probability (BEP). From the simulation results, it is demonstrated that turbo coding offers considerable coding gain with reasonable encoding and decoding complexity. Also, it is confirmed that the performance of such an optical COMA network can be substantially improved by increasing the interleaver length and the number of iterations in the decoding process. The results of this paper can be applied to implement the indoor optical wireless LANs.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.10a
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• pp.856-859
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• 2003

본 논문에서는 이동통신 환경 하에서의 광통신 접목기술을 사용하여 광PCS 시스템의 성능을 컴퓨터 시뮬레이션을 사용하여 수치적으로 분석하였다. 광섬유가 제공할 수 있는 막대한 대역폭을 효율적으로 활용하기 위하여, 광 수신기는 보다 많은 정보를 송신할 수 있도록 충분히 빠른 변조 속도를 요구하며, 광수신기는 수신되는 고속의 광 신호를 전기적 신호로 충분히 검파시킬 수 있는 능력을 가져야한다. 수십 기가 bps 이상의 초고속광통신시스템을 구현하기 위해서는 광섬유의 분산 효과에 의한 펄스촉의 증가를 억제할 수 있는 기술이 요구된다. 따라서 본 논문에서는 광섬유의 chirping 의 영향을 고려하여 시스템의 성능을 직접 변조 방식을 사용하여 수치적 시뮬레이션을 통하여 신호 대잡음 비를 유도하여 시스템의 성능을 비교 분석 하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.3
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• pp.539-546
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• 1997

In this paper, we proposed a new mehtod to analyze the performance degradation by timing jitters in the APD (avalanche photodiode) receivers of intensity modulation/direct detection digital optical communication systems where raised cosine pulse-shaping filters are used to reduce the effect of noise while minimizing intersymbol interferences. The proposed analytical method is an extension of an analytical method we have already developed for pin diode receivers, and incorporates the effects of APD's multiplication factor and resulting shot noise. Using the proposed analytical method, we derive an approximated power penalty due to timing jitters based on an assumption of Gaussian distribution for timing jitters, and compare with that of the conventional analytical method. The results obtained from the proposed analytical method show that conventional analytical methods underestimate the influence of timing jitters on the reciver performance. The results also show that APD's multiplication factor which optimizes receiver sensitivity is smaller than that obtained by the conventional analytical method.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.10
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• pp.41-49
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• 2004

Nonlinear distortion introduced by the optical transmitter using a direct modulation of laser diode(LD) and an indirect modulation of optical modulator can limit considerably the performance of analog optical link system such as subcarrier multiplexing system. In this paper, we have compensated the nonlinear distortion of LD and optical modulator using electrical predistorter. In the case of LD, two-tone experiments using 877.5 MHz and 882.5 MHz have shown reduction of 19 dB in third-order intermodulation product(IMP$_3$). And in the case of optical modulator, we have achieved nearly 21 dB reduction in IMP3 through two-tone experiments using 1.8975 GHz and 1.9025 GHz. The spurious free dynamic ranges of LD and optical modulator are also improved by 5 dB/Hz$^{2}$ 3/ and 7 dB/Hz$^{2}$ 3/, respectively.