[편집위원회 선정 논문] 한국광학회지 Vol. 32 No.1 (2021 February)_2
목표물 신호 모니터링 및 SPGD 알고리즘 기반 3 채널 타일형 결맞음 빔결합 시스템 연구
3-channel Tiled-aperture Coherent-beam-combining System Based on Target-in-the-loop Monitoring and SPGD Algorithm
Youngchan Kim1, Youngsun Yun1, Hansol Kim2, Hanbyul Chang2, Jaedeok Park4, Yunjin Choe4, Jeongkyun Na2, Joohan Yi2, Hyungu Kang2, Minsu Yeo2, Kyuhong Choi1, Young-Chul Noh1, Yoonchan Jeong2,3, Hyuk-Jae Lee2,3, Bong-Ahn Yu1, Dong-Il Yeom4,5, Changsu Jun1
Korean Journal of Optics and Photonics Vol. 32 No. 1, February 2021, pp. 1-8
We have studied a tiled-aperture coherent-beam-combining system based on constructive interference, as a way to overcome the power limitation of a single laser. A 1-watt-level, 3-channel coherent fiber laser and a 3-channel fiber array of triangular tiling with tip-tilt function were developed. A monitoring system, phase controller, and 3-channel phase modulator formed a closed-loop control system, and the SPGD algorithm was applied. Eventually, phase-locking with a rate of 5–67 kHz and peak-intensity efficiency comparable to the ideal case of 53.3% was successfully realized. We were able to develop the essential elements for a tiled-aperture coherent-beam-combining system that had the potential for highest output power without any beam-combining components, and a multichannel coherent-beam-combining system with higher output power and high speed is anticipated in the future.
[Editors Pick] Current Optics and Photonics Vol. 5 no. 1 (2021 February)
Shannon Entropy as an Indicator of the Spatial Resolutions of the Morphologies of the Mode Patterns in an Optical Resonator
Kyu-Won Park1*, Jinuk Kim1, and Songky Moon2
1Department of Physics and Astronomy & Institute of Applied Physics, Seoul National University, Seoul 08826, Korea
2Faculty of Liberal Education, Seoul National University, Seoul 08826, Korea
Current Optics and Photonics Vol. 5, No. 1, February 2021, pp. 16-22
Faculty of Liberal Education, Seoul National University, Seoul 08826, Korea(Received August 26, 2020 : revised November 17, 2020 : accepted November 28, 2020)We present the Shannon entropy as an indicator of the spatial resolutions of the morphologies of the resonance mode patterns in an optical resonator. We obtain each optimized number of mesh points, one of minimum size and the other of maximum one. The optimized mesh-point number of minimum size is determined by the identifiable quantum number through a chi-squared test, whereas the saturation of the difference between Shannon entropies corresponds to the other mesh-point number of maximum size. We also show that the optimized minimum mesh-point increases as the (real) wave number increases and approximates the proportionality constant between them.
[Editors Pick] Current Optics and Photonics Vol. 4 no. 6 (2020 December)
Comparative Measurement of Transverse Nuclear Magnetization of Polarized 129Xe and 131Xe by Spin-exchange Optical Pumping
Ye Jin Yu, Seong Ho Min, and Han Seb Moon*
Department of Physics, Pusan National University, Busan 46241, Korea
Current Optics and Photonics Vol. 4, No. 6, December 2020, pp. 466-471
We analyze the transverse nuclear magnetizations of 129Xe and 131Xe in a vapor cell containing natural Xe, 87Rb, and buffer gases. The Xe atoms are polarized through spin-exchange optical pumping (SEOP) with Rb atoms under low-magnetic-field conditions. From the free-induction-decay (FID) signal, we measure the nuclear magnetization of the Xe atoms in the Xe-Rb vapor cell. Furthermore, we measure the dependence of the gyromagnetic ratio on the magnetization of 129Xe and 131Xe by examining the amplitude of the FID signal of each isotope, and we evaluate the relationship between the magnetic field gradient and transverse relaxation rate for both of the 129Xe and 131Xe isotopes.
[Editors Pick] Current Optics and Photonics Vol. 4 no. 4 (2020 August)
Terahertz Generation by a Resonant Photoconductive Antenna
Kanghee Lee1,2, Seong Cheol Lee1, Won Tae Kim1, Jagang Park2, Bumki Min2, and Fabian Rotermund1*
1Department of Physics, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Korea
2Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Korea
Current Optics and Photonics Vol. 4, No. 4, August 2020, pp. 373-379
In this study, we investigate terahertz (THz) generation by a photoconductive antenna with electrodes in the shape of split-ring resonators. According to our theoretical investigation based on a lumped-circuit model, the inductance of this electrode structure leads to resonant behavior of the photo-induced current. Hence, near the resonance frequency the spectral components generated by a resonant photoconductive antenna can be greater than those produced by a non-resonant one. For experimental verification, a resonant photoconductive antenna, which possesses a resonance mode at 0.6 THz, and a non-resonant photoconductive antenna with stripe-shaped electrodes were fabricated on a semi-insulating GaAs substrate. The THz generation by both of the photoconductive antennas demonstrated a good agreement with the theoretically expected results. The observed relationship between the resonant electrodes of the photoconductive antenna and the generated THz spectrum can be further employed to design a narrow-band THz source with an on-demand frequency.
[Editors Pick] Current Optics and Photonics Vol. 4 no. 3 (2020 June)
Recent Progress in High-Luminance Quantum Dot Light-Emitting Diodes
Seunghyun Rhee1, Kyunghwan Kim1, Jeongkyun Roh2*, and Jeonghun Kwak1**
1Department of Electrical and Computer Engineering, Inter-university Semiconductor Research Center (ISRC), Seoul National University, Seoul 08826, Korea
2Department of Electrical Engineering, Pusan National University, Busan 46241, Korea
Current Optics and Photonics Vol. 4, No. 3, June 2020, pp. 161-173
Colloidal quantum dots (QDs) have gained tremendous attention as a key material for highly advanced display technologies. The performance of QD light-emitting diodes (QLEDs) has improved significantly over the past two decades, owing to notable progress in both material development and device engineering. The brightness of QLEDs has improved by more than three orders of magnitude from that of early-stage devices, and has attained a value in the range of traditional inorganic LEDs. The emergence of high-luminance (HL) QLEDs has induced fresh demands to incorporate the unique features of QDs into a wide range of display applications, beyond indoor and mobile displays. Therefore it is necessary to assess the present status and prospects of HL-QLEDs, to expand the application domain of QD-based light sources. As part of this study, we review recent advances in HL-QLEDs. In particular, based on reports of brightness exceeding 105 cd/m2, we have summarized the major approaches toward achieving high brightness in QLEDs, in terms of material development and device engineering. Furthermore, we briefly introduce the recent progress achieved toward QD laser diodes, being the next step in the development of HL-QLEDs. This review provides general guidelines for achieving HL-QLEDs, and reveals the high potential of QDs as a universal material solution that can enable realization of a wide range of display applications.
[Editors Pick] Current Optics and Photonics Vol. 4 no. 2 (2020 April)
Analysis of the Design Parameters for a Lightfield Near-eye Display Based on a Pinhole Array
Hyeontaek Lee1, Ungyeon Yang2, and Hee-Jin Choi1*
Department of Physics and Astronomy, Sejong University, Seoul 05006, Korea
Current Optics and Photonics Vol. 4, No. 2, April 2020, pp. 121-126
With the increasing demand for head-mounted display applications, the image quality provided by a near-eye display device is a key factor in satisfying the consumer. Among various techniques to realize a near-eye display that has a thinner volume than the working distance of a human eye, a lightfield image-generation method based on a pinhole array is attracting much attention, with its simple and thin structure. In this paper, we propose a numerical analysis of the visual parameters and verifications with computational reconstruction.
[Editors Pick] Current Optics and Photonics Vol. 4 no. 1 (2020 February)
Simultaneous Generation of Orthogonally Polarized Signals in an Optical Parametric Oscillator Based on Periodically Poled Lithium Niobate
CH. S. S. Pavan Kumar, Byoung Joo Kim, Deok Woo Kim, and Myoungsik Cha*
Department of Physics, Pusan National University, Busan 46241, Korea
Current Optics and Photonics Vol. 4, No. 1, February 2020, pp. 63-68
We built an optical parametric oscillator (OPO) generating orthogonally polarized signals at different wavelengths simultaneously, based on a periodically poled lithium niobate (PPLN) crystal. The OPO was pumped by ns-pulses at 1.064 µm from a diode-pumped solid-state laser, where we found the type-0 and the type-1 quasi-phase matching conditions were satisfied simultaneously in the PPLN crystal. This enabled us to create a coherent light source which can emit dual signals which could be accessed easily by rotating a polarizer.
[Editors Pick] Current Optics and Photonics Vol. 3 no. 6 (2019 December)
Frequency Response Estimation of 1.3 µm Waveguide Integrated Vertical PIN Type Ge-on-Si Photodetector Based on the Analysis of Fringing Field in Intrinsic Region
Dongjun Seo1, Won-Bae Kwon2, Sung Chang Kim2, and Chang-Soo Park1*
chool of Electrical Engineering and Computer Science, Gwangju Institute of Science and Technology (GIST), Gwangju 61005, Korea
2Honam Research Center, Electronics and Telecommunications Research Institute (ETRI), Gwangju 61012, Korea
Current Optics and Photonics Vol. 3, No. 6, December 2019, pp. 510-515
In this paper, we introduce a 1.3-µm 25-GHz waveguide-integrated vertical PIN type Ge-on-Si photo-detector fabricated using a multi-project wafers service based on fringing field analysis in the depletion region. In general, 1.3-µm photodetectors fabricated using a commercial foundry service can achieve limited bandwidths because a significant amount of photo-generated carriers are located within a few microns from the input along the device length, and they are influenced by the fringing field, leading to a longer transit time. To estimate the response time, we calculate the fringing field in that region and the transit time using the drift velocity caused by the field. Finally, we compare the estimated value with the measured one. The photodetector fabricated has a bandwidth of 20.75 GHz at -1 V with an estimation error of<3 GHZ and dark current and responsivity of 110 nA and 0,704 A/W, respectively.