[Editors Pick] Current Optics and Photonics Vol. 5 no. 4 (2021 August)
Full-color Non-hogel-based Computer-generated Hologram from Light Field without Color Aberration
Dabin Min, Kyosik Min, and Jae-Hyeung Park *
Department of Electrical and Computer Engineering, Inha University, Incheon 22212, Korea
We propose a method to synthesize a color non-hogel-based computer-generated-hologram (CGH) from light field data of a three-dimensional scene with a hologram pixel pitch shared for all color channels. The non-hogel-based CGH technique generates a continuous wavefront with arbitrary carrier wave from given light field data by interpreting the ray angle in the light field to the spatial frequency of the plane wavefront. The relation between ray angle and spatial frequency is, however, dependent on the wavelength, which leads to different spatial frequency sampling grid in the light field data, resulting in color aberrations in the hologram reconstruction. The proposed method sets a hologram pixel pitch common to all color channels such that the smallest blue diffraction angle covers the field of view of the light field. Then a spatial frequency sampling grid common to all color channels is established by interpolating the light field with the spatial frequency range of the blue wavelength and the sampling interval of the red wavelength. The common hologram pixel pitch and light field spatial frequency sampling grid ensure the synthesis of a color hologram without any color aberrations in the hologram reconstructions, or any loss of information contained in the light field. The proposed method is successfully verified using color light field data of various test or natural 3D scenes.
[Editors Pick] Current Optics and Photonics Vol. 5 no. 2 (2021 April)
Optical Encryption Scheme for Cipher Feedback Block Mode Using Two-step Phase-shifting Interferometry
Seok Hee Jeon 1 and Sang Keun Gil 2 *
1 Department of Electronic Engineering, Incheon National University, Incheon 22012, Korea
2 Department of Electronic Engineering, The University of Suwon, Hwaseong, Suwon 18323, Korea
Current Optics and Photonics Vol. 5 no. 2, pp. 155-163
We propose a novel optical encryption scheme for cipher-feedback-block (CFB) mode, capable of encrypting two-dimensional (2D) page data with the use of two-step phase-shifting digital interferometry utilizing orthogonal polarization, in which the CFB algorithm is modified into an optical method to enhance security. The encryption is performed in the Fourier domain to record interferograms on charge-coupled devices (CCD)s with 256 quantized gray levels. A page of plaintext is encrypted into digital interferograms of ciphertexts, which are transmitted over a digital information network and then can be decrypted by digital computation according to the given CFB algorithm. The encryption key used in the decryption procedure and the plaintext are reconstructed by dual phase-shifting interferometry, providing high security in the cryptosystem. Also, each plaintext is sequentially encrypted using different encryption keys. The random-phase mask attached to the plaintext provides resistance against possible attacks. The feasibility and reliability of the proposed CFB method are verified and analyzed with numerical simulations.
[하이라이트 논문] 한국광학회지 Vol. 32 No.1 (2021 February)_2
목표물 신호 모니터링 및 SPGD 알고리즘 기반 3 채널 타일형 결맞음 빔결합 시스템 연구
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.