• Journal of Advanced Navigation Technology
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• v.12 no.3
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• pp.201-207
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• 2008

Design rule of optical transmission link consisted of dispersion management (DM) controlling accumulated dispersion in total fiber length by precompensation and postcompensation, and optical phase conjugator (OPC) positioned at mid-way are proposed. DM schemes investigated in this paper are 2 types depending on the position of precompensation and postcompensation; bi-end type and concentration type. It is confirmed that effective residual dispersion ranges, as a design parameter of optical link, of transmission section from transmitter to OPC and transmission section from OPC to receiver are independence on the positions of dispersion compensating fiber (DCF) accomplishing precompensation and postcompensation, if both DCF position is symmetry with respect to OPC.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2015.10a
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• pp.964-966
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• 2015

The effect of the deviations of single mode fiber lengths and residual dispersion per span (RDPS) on the compensation for the distorted WDM signals in the dispersion-managed optical links with the specially artificial distributions of the lengths of SMFs and RDPSs. The considered artificial distribution is following; the lengths of SMF and RDPSs between the adjacent fiber span are more descended in the half transmission section from transmitter to optical phase conjugator (OPC), and those are more ascended in the rest half transmission section from OPC to the receiver, as number of fiber spans are more increased.

• Korean Journal of Optics and Photonics
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• v.29 no.2
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• pp.77-84
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• 2018

We analyze the link availability of terrestrial free-space optical (FSO) communication systems in Korea. For this purpose, we utilize several theoretical models to calculate the power losses induced by absorption and scattering in the atmospheric channel, using five-year meteorological data for three major cities in Korea (Seoul, Busan, and Daejeon). Also, we estimate the power variations at the receiver caused by scintillation in the data. Those power losses and variations are used to estimate the availability of FSO links in the three cities. The results show that link availability is estimated to be over 95% in Daejeon for a 3.5-km FSO link, when the transmitter power and receiver diameter are greater than 10 dBm and 7 cm respectively. Slightly worse link availabilities are obtained for Busan and Seoul.

• Korean Journal of Optics and Photonics
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• v.23 no.5
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• pp.217-221
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• 2012

In this paper, we have fabricated by means of the "Micro-Block Stacking (MBS)" method the 8 pin mini DIL integrated Triplexer, which can transmit CATV and voice/data at the same time in a single fiber. Our MBS technique is a novel scheme of compact optical module packaging which secures precision positioning of the components on the optical beam path by prefixed stacks of ceramic blocks. The subassembly in which a laser diode, two receiver photodiodes, two WDM filters, and four micro lenses are integrated is only $5.40mm{\times}2.15mm{\times}1.05mm$ in size. As the Triplexer is aligned to the single mode fiber, the transmitter power of -14.5 dBm and the receiver sensitivities of 0.83 A/W, 0.73 A/W for 1550 nm, 1490 nm, respectively are obtained.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.5
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• pp.560-567
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• 2011

In this paper, we reduced the optical noise interference using polarizers in a visible light communication system. In a transmitter, two light-emitting diodes(LEDs) are modulated synchronously by the original and the reversed signals of the transmitted data, and the two LED lights are radiated through orthogonal polarizers. In a receiver, two optical signals are detected through orthogonal polarizers and differentially amplified to remove the optical noise. In an environment that noise light from a fluorescent lamp is much stronger than the signal, the receiver with orthogonal polarizers removed the 120 Hz noise, and synchronous light transmission of the original and the reversed signals using two LEDs reduced the illumination flickering to about one-eighth that using one LED.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.12 no.6
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• pp.612-620
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• 1987

In this paper, the optical modem for data link realization is designed with the advantages of optical fiber, large bandwidth, high speed and long haul communication. Modem interface, CCITT V.24 and EIA RS-232C is adopted for the compatibility with existing systems, and biphase coding format is used for digital modulation. And also, modem has serveral loopback test facility in order to diagnose system itself. Optical transmitter and receiver are designed to have the receiving sensitivity of -30dBm at $10^-9$BER in the short wavelength region. Developed system is capable of transmitting data rate at 1200bps up to 57.6Kbps in sync., and at any bps within DC to 200Kbps in async transmission.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.6C
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• pp.570-579
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• 2003

The performance of turbo codes is investigated in the direct detection optical PPM channel. We assume that an ideal photon counter is used as an optical detector and that the channel has background noise as well as quantum noise. Resulting channel model is M-ary PPM Poisson channel. We propose the structure of the transmitter and receiver for applying turbo codes to this channel. We also derive turbo decoding algorithm for the proposed coding system, by modifying the calculation of the branch metric inherent in the original turbo decoding algorithm developed for the AWGN channel. Analytical bounds are derived and computer simulation is performed to analyze the performance of the proposed coding scheme, and the results are compared with the performances of Reed-Solomon codes and convolutional codes.

• Current Optics and Photonics
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• v.7 no.4
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• pp.345-353
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• 2023

We propose a turbulence-tolerant Manchester on-off keying (M-OOK) transmission for free-space optical (FSO) communication. At the transmitter end, a M-OOK signal featuring a spectrum with low-frequency components absent is modulated and transmitted into a turbulent channel. At the receiver end, a low-pass filter (LPF) -based adaptive-threshold decision (ATD) with LPF-extracted channel-state information (CSI) and a high-pass filter (HPF)-based fixed-threshold decision (FTD) are employed to compensate for the effects of turbulence, owing to the low-frequency spectral characteristics of the turbulent channel. The performance of LPF-based ATD and HPF-based FTD are evaluated for various cutoff frequencies for the LPF and HPF. Besides, the proposed M-OOK transmission is compared to conventional non-return-to-zero OOK (NRZ-OOK) for different data rates. The proposed technique is verified in simulation. The simulation results show that the proposed M-OOK detection with optimized cutoff frequencies of LPF and HPF has better bit-error-rate (BER) performance compared to NRZ-OOK, and it is close to the theoretical ATD with the knowledge of precise CSI under various degrees of turbulence effects.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.4B
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• pp.323-332
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• 2006

In this paper, we consider a WDM based metro ring connecting broadband access networks by using FT-TR (Fixed Transmitter-Tunable Receiver) type access nodes and a new MAC protocol for fair transmission is proposed. The basic channel access scheme is CSMA/CA(Carrier Sense Multiple Access with Collision Avoidance) and the transferred optical slot is changed to be empty slot by SS(Source-Stripping) which drops a packet from ring-rotated slot. This empty slot can be either used to send head-of-line packet in buffer or transmitted to next access node. In former cases, there is the improvement of network throughput, but latter case leads unfairness problem of transmission. Thus the proposed MAC protocol exploits the advantages form tow cases. It gives downstream access nodes chance to use empty slots and limits the unconditional usage of empty slots at upstream access nodes with probability as called p-Persistent MAC protocol. We use a numerical analysis to evaluate bandwidth efficiency and maximum node throughput and compares simulation results in terms of node throughput, fairness factor, transfer delay depending on probability. Under two different FT-TR type architectures for metro ring network the proposed MAC protocol is evaluated and compared.

• Korean Journal of Optics and Photonics
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• v.12 no.3
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• pp.212-218
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• 2001

We experimentally investigated the dependence of extinction ratio and chirp on bias current which was injected into DFB-LD in a directly modulated 2.5 Obitls transmitter. Through the abnormal dispersion transmission, we found that transmission power penalty is minimized at 8-10 dB extinction ratio (bias current at 1.5-1.8 fold above threshold current). Also, we discussed the relation between extinction ratio and self phase modulation (SPM) through the 240 km abnormal dispersion transmission. When SPM takes effect, we obtained the best receiver sensitivity for specific system configuration at 10.4 dB and 8.4 dB extinction ratio, below and above 200km transmission distance, respectively. ively.