• Electronics and Telecommunications Trends
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• v.37 no.4
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• pp.81-88
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• 2022

In this study, we investigate the trends and prospects of spatial light modulation (SLM) technology that enables full complex modulation as a next-generation SLM. Current SLM technology, which is used as a key element in holography, augmented reality (AR), XR, and realistic displays, has performance limits that modulate only amplitude or phase. Notably, SLM capable of full complex modulation does not produce diffraction noise, unlike DC and twin image, and thus has a high-efficiency performance. In the future, the application field of next-generation SLM, which can be full-complex modulated, is expected to cover a wide range of holography-AR and-XR devices, optical artificial intelligence, and 6G free space optics communications, which will greatly contribute to the development of a super-realistic metaverse platform and service.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.7
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• pp.47-53
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• 2004

In this paper we introduce a complex escalator (ESC) structure-Equalizer and investigate its performance in complex channels in QPSK undulation systems. The proposed complex equalizer has the complete orthogonalization property and is independent of eigenvalue spread ratio (ESR) of channel. The proposed complex ESC equalizer shows as 7 times faster convergence speed as that of the conventional complex TDL equalizer algorithms in a complex channel model for QPSK systems.

• Korean Journal of Optics and Photonics
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• v.20 no.6
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• pp.328-333
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• 2009

We proposed a three-dimensional holographic display technique without twin image noise by converting a complex hologram to an off-axis hologram. To implement the proposed technique we record the complex hologram of a three dimensional object that is composed of two slides located with different depth locations. We added spatial carrier to the complex hologram and after that, extract the real part of the spatial-carrier-added hologram. This converts the complex hologram to an off-axis hologram. We also reconstruct the off-axis hologram using a spatial light modulator for three dimensional display.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.1A
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• pp.1-7
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• 2012

The conventional Zhu's differential space-time modulation(DSTM) based on quasi-orthogonal design adopted a complex precoder in order to allow an independent joint detection of two complex symbols without any channel informations at a receiver. In this paper, by simply replacing the complex precoder used in Zhu's DSTM with a real precoder, a new DSTM is presented for four transmit antennas. The real precoder enables the receiver to decode two real symbols pair separately, and thus the new DSTM has greatly reduced decoding complexity compared to the Zhu's DSTM. By computer simulation results, the proposed scheme is shown to exhibit almost identical or improved error performance compared to the existing DSTMs.

• Korean Journal of Optics and Photonics
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• v.18 no.1
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• pp.56-65
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• 2007

The effect of gain dispersion on the self-pulsation (SP) characteristics due to the mode beating of two modes emitted in a multisection DFB laser composed of two complex-coupled DFB sections and a phase control section is investigated. When the peak wavelength, ${\lambda}_{p}$, of the gain spectrum of the DFB section is positioned in the center of the lasing wavelengths or the Bragg wavelengths of the two DFB sections, the maximum SP frequencies are higher and the modulation index has better characteristics compared to those cases for ${\lambda}_{p}$ fixed at the lasing wavelength or Bragg wavelength of one DFB section, when the difference between the Bragg wavelengths of the two DFB sections, ${\Dalta}{\lambda}_{B}$, is varied. When ${\lambda}_{p}$ is positioned in the renter of the Bragg wavelengths of the two DFB sections, the maximum SP frequency is higher and of the modulation index has better characteristics compared to those of the case for ${\lambda}_{p}$ positioned in the center of the lasing wavelengths of the two DFB sections.

• Information and Communications Magazine
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• v.31 no.2
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• pp.21-28
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• 2014

본고에서 디지털 홀로그래피를 위한 SLM중 대표적인 몇 가지 기술에 대한 동향을 살펴보았다. 먼저 SLM픽셀 피치에 따른 홀로그램 영상의 특성에 대해 논의하고, 픽셀화된 SLM으로써 현재 상용화 되고 있는 DMD SLM 과 LCoS SLM의 특성에 대해 살펴 보았다. 픽셀화 되지 않은 SLM 인 음향 광학 변조기와 OASLM 에 대해서도 살펴 보았다. 양질의 디지털 홀로그래피를 구현하기 위하여 궁극적으로 필요한 픽셀 피치 1 ${\mu}m$ 이하 SLM 의 개발 현황과 복소 변조 SLM 에 대해서도 알아보았다.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.7
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• pp.80-91
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• 1999

We present various optimal grating structures which give the low threshold gain, good modulation characteristics, small effective linewidth enhancement factor, and large fabrication tolerance in complex-coupled MQW DFB lasers with absorptive gratings. To obtain these, we calculate the complex coupling coefficients using the extended additional layer method and the threshold gain including the modal loss in the absorptive grating region for rectangular and trapezoidal gratings. Based on the comparison of the results for various possible absorptive grating structures, the design guidelines are presented to obtain the low threshold gain or large fabrication tolerance. Among the grating structures studied, the double grating structure consisting of the absorptive grating on the index grating has the largest fabrication tolerance for the threshold gain and the coupling strength. The fabrication tolerance for the coupling ratio is very large for all the grating structures studied.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.502-505
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• 2006

Acoustic holography allows us to predict spatial pressure distribution on any surface of interest from measured hologram. It is noteworthy that the data size is so huge that it takes long time to calculate pressure field. Moreover the reconstructed pressure field is frequently too complicated to get what we want to know. One possible candidate is complex envelope. Complex envelope in time domain is well known and widely used in various engineering field. We have attempted to extend this method to space domain, so that we can have rather simple spatial pressure picture that provides information we need, for example, where sound sources are. First we start with the simplest case. We examine the complex envelope of a plane wave on both space and wave number domain. Then we extend to monopole case. Holographic reconstructed sound field on the monopole is processed according to what we propose. We demonstrate how this method provides better picture for analyzing the sound field.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.37 no.1
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• pp.1-11
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• 2000

We propose a predistorter to compensate for nolinear distortion induced by a high power amplifier employed in multi carrier-code division multiple access (MC-CDMA) systems. The proposed scheme rests upon the fixed point iteration (FPI) associated with the contraction mapping theorem. Unlike the predistorter based on the FPI already presented by the authors in other literatures which operates on complex-valued modulation signals, the proposed predistorter in this paper deals with real-valued FPI on modulation signal amplitudes, resulting in less complexity. Simulation results on a BPSK-modulated, 64-subcarrier synchronous MC-CDMA baseband system with a traveling wave tube amplifier in the transmitter, indicate that the proposed predistorter achieves significant improvement in terms of bit error rate and total degradation over those without the predistorter. Moreover, the proposed predistorter outperforms the complex-valued counterpart, in particular, for small output back-off levels.

• Journal of the Korean Institute of Telematics and Electronics C
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• v.35C no.9
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• pp.11-20
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• 1998

High-speed complex-number arithmetic units are essential to baseband signal processing of modern digital communication systems such as channel equalization, timing recovery, modulation and demodulation. In this paper, a new complex-number multiplication algorithm is proposed, which is based on redundant binary (RB) arithmetic combined with radix-4 Booth recoding scheme. The proposed algorithm reduces the number of partial product by one-half as compared with the conventional direct method using real-number multipliers and adders. It also leads to a highly parallel architecture and simplified circuit, resulting in high-speed operation and low power dissipation. To demonstrate the proposed algorithm, a prototype complex-number multiplier-accumulator (CMAC) core with 10-bit operands has been designed using 0.8-$\mu\textrm{m}$ N-Well CMOS technology. The designed CMAC core contains about 18,000 transistors on the area of about 1.60 ${\times}$ 1.93 $\textrm{mm}^2$. The functional and speed test results show that it can operate with 120-MHz clock at V$\sub$DD/=3.3-V, and its power consumption is given to about 63-mW.