• Journal of Information Processing Systems
• /
• v.10 no.2
• /
• pp.215-222
• /
• 2014

In this paper, we discuss optical encryption and decryption considering wireless communication channels. In wireless communication systems, the wireless channel causes noise and fading effects of the transmitted information. Optical encryption technique such as double-random-phase encryption (DRPE) is used for encrypting transmitted data. When the encrypted data is transmitted, the information may be lost or distorted because there are a lot of factors such as channel noise, propagation fading, etc. Thus, using digital modulation and maximum likelihood (ML) detection, the noise and fading effects are mitigated, and the encrypted data is estimated well at the receiver. To the best of our knowledge, this is the first report that considers the wireless channel characteristics of the optical encryption technique.

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

• Current Optics and Photonics
• /
• v.5 no.6
• /
• pp.627-640
• /
• 2021

In a free-space coherent optical communication system, wavefront distortion is frequently beyond the correction range of the adaptive-optics system after the laser has propagated through the atmospheric turbulence. A method of residual wavefront correction is proposed, to improve the quality of coherent optical communication in free space. The relationship between the wavefront phase expanded by Zernike polynomials and the mixing efficiency is derived analytically. The influence of Zernike-polynomial distortion on the bit-error rate (BER) of a phase-modulation system is analyzed. From the theoretical analysis, the BER of the system changes periodically, due to the periodic extension of wavefront distortion. Experimental results show that the BER after correction is reduced from 10^-1 to 10^-4; however, when the closed-loop control algorithm with residual correction is used, the experimental results show that the BER is reduced from 10^-1 to 10^-7.

• Journal of the Korea Institute of Military Science and Technology
• /
• v.27 no.3
• /
• pp.329-337
• /
• 2024

Free-space optical communication technology enables the high-speed data transmission and excellent anti-jamming security. We conduct research on satellite-to-ground free-space optical communication links for high-speed transmission of large-capacity surveillance and reconnaissance data. Since the satellite continues to move along its orbit while the optical signal is transmitted between the satellite and the ground, the pointing angle of the beam from the ground terminal needs to be corrected by Point Ahead Angle(PAA) so that the transmitted light reaches the expected location of the satellite. In this paper, we present the algorithm for PAA estimation and control.

• Proceedings of the Optical Society of Korea Conference
• /
• 2005.02a
• /
• pp.308-309
• /
• 2005

• Proceedings of the Korean Magnestics Society Conference
• /
• 2008.12a
• /
• pp.314.1-314.1
• /
• 2008

• Korean Journal of Optics and Photonics
• /
• v.30 no.6
• /
• pp.230-236
• /
• 2019

We propose and demonstrate a searching and autoalignment method for indoor optical wireless communication, using a cost-effective retroreflective sheet and a microelectromechanical system (MEMS) mirror. We use an extremum-seeking method for a single axis and beam steering with a MEMS mirror to maintain a line of sight (LOS) with the optical link. This autoalignment method shows a receiver sensitivity of -31.87 dBm for a bit rate of 2.5 Gb/s over a 7 m communication link.

• Journal of Satellite, Information and Communications
• /
• v.7 no.3
• /
• pp.63-68
• /
• 2012

The VLC (visible light communication) system is communication technology using visible rays (RGB) that come out in LED device. It is energy curtailment effect and possible in ubiquitous network service applications. Also, VLC system has the above advantage about that the communication throughout the whole room is enabled by high power lighting and lighting equipment with white colored LED which are easy to install and have good outward appearance. However, the signal detection performance for the receiver near the network of transmitter boundary is severely degraded and the transmission efficiency decreased due to the influence of the interference signal from the adjacent networks. In this paper, we propose an interference mitigation method with optical relay and optical beamforming scheme in VLC systems, and evaluate the reception performance. For the system BER, the proposed system demonstrates the performance enhancement compared to the not using the optical relay and optical beamforming scheme, and SNR performance gain and higher channel capacity is achieved.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.25 no.11
• /
• pp.123-129
• /
• 2011

In terrestrial wireless optical communication links, atmospheric effects including turbulence, absorption and scattering have significant impact on the system performance. Based on the analysis of transmission in atmospheric channel concerning 830[nm] wavelength diode laser beam, performance of free space optical (FSO) link utilizing Galilean optics as a laser beam transmitting and receving optics, PIN photodiode as a detecting device. In this paper we designed optical link equation for received optical power and we analyze the atmospheric effects on the signal to noise ratio (SNR) and bit error rate (BER) of an terrestrial FSO system. We show that the possible communication distance for BER=$10^{-9}$ in proposed adverse atmospheric conditions.

• Journal of Information Technology Applications and Management
• /
• v.26 no.6
• /
• pp.103-117
• /
• 2019

Demand for high power motors is rapidly increasing as the 4th industry and convergence technology has recently emerged. In order to produce high-strength permanent magnets, the magnets used for magnetization have been increased from DC 300V in the 1970s to DC 2.5kV in the 2010s, Up to DC 10kV in the 2030s, It is expected that higher voltage will be used to magnetize. However, in the case of a magnetizer using an existing electric signal control device, it is necessary to use a control device with a high-voltage insulation function in case a high voltage used for magnetization is leaked to the control device. If a short circuit accident occurs, the controller must be shut down and serious problems such as excessive repair costs arise. In this study, a control system adopting optical communication method instead of electric signal control method is proposed to prevent leakage currents in high-voltage magnetizer. We design a transmitter(Tx) and a receiver(Rx) device for the optical communication control device and implemented a prototype connecting the optical cable. In order to demonstrate the utility of high-voltage magnetizer using the optical communication control device, we analyzed the initial cost and the yearly cost for the years to analyze the net present value. As a result, In the case of the low-voltage magnetizer, the electric signal control method cost less, As the operating voltage of the magnetizer becomes higher. It is confirmed that it takes less cost when the optical communication control device is used.