[Editor's Pick] Current Optics and Photonics Vol. 6 no. 4 (2022 August) A New Instrument for Measuring the Optical Properties of Wide-field-of-view Virtual-reality Devices Hee Kyung Ahn1, Hyun Kyoon Lim2, and Pilseong Kang1 * Current Optics and Photonics Vol. 6 No. 4 (2022 August) pp. 392-399 DOI: https://doi.org/10.3807/COPP.2022.6.4.392 Fig. 1 The structure of a typical light-measuring devices (LMD) for virtual-reality/augmented-reality (VR/AR) devices. Keywords: Augmented Reality, Spectroradiometer, Virtual Reality OCIS codes: (120.2040) Displays; (120.5240) Photometry Abstract ght-measuring devices (LMDs) are frequently used to measure luminance and color coordinates of displays. However, it is very difficult to use a conventional LMD for measuring the optical properties of virtual-reality (VR) devices with a wide field of view (FOV), because of their confined spaces where the entrance pupil of a LMD is located. In this paper, a new LMD that can measure the optical properties of wide-FOV VR devices, without physical conflict with the goggles of the VR device, is proposed. The LMD is designed to fully satisfy the requirements of IEC 63145-20-10, and a pivot-point correction method for the LMD is applied to improve its accuracy. To show the feasibility of the developed LMD and the correction method, seven VR devices with wide FOV are measured with it. From the results, all of them are successfully measured without any physical conflict, and a comparison to their nominal values shows that the FOVs have been properly measured. [하이라이트 논문] 한국광학회지 Vol. 33 No.4 (2022 August) 이중 슬릿 회절 실험을 이용한 박막의 두께와 굴절률 측정 Measurement of the Thickness and Refractive Index of a Thin Film Using a Double-slit Experiment 김희성ㆍ박수봉¶ㆍ김덕우¶ㆍ김병주ㆍ차명식† 한국광학회지 Vol. 33 No.4 (2022 August) pp. 159-166 DOI: https://doi.org/10.3807/KJOP.2022.33.4.159 Fig. 1 Schematics of experimental setup. Lens 2 images the focal point of lens 1 (A) to CCD, satisfying (1/S1)+(1/S2)=1/f, where f (= 1 m) is the focal length of lens 2. Keywords: 회절, 이중 슬릿 실험, 굴절률, 두께 측정, 박막 OCIS codes: (120.2650) Fringe analysis; (120.5050) Phase measurement; (310.0310) Thin films 초록 본 연구에서는 이중 슬릿 회절 실험을 이용하여 박막의 두께와 굴절률을 측정하는 실험을 수행하였다. 투명 기판 위에 입혀진 박막이 만드는 투과광의 위상 단층의 크기를 이중 슬릿을 통과하여 나타나는 회절 패턴을 분석하여 측정하였다. 이로부터 두께와 굴절률을 동시에 결정하기 위해 공기와 증류수 속에서 각각 한 번씩 실험을 수행하였다. 이 방법의 유효함을 확인하기 위해 도파로 결합법으로 측정한 두께와 굴절률과 비교하였다. 본 연구에서 제안한 측정법은 기존의 선행 연구들과 더불어 박막의 두께와 굴절률을 동시에 측정할 수 있는 새로운 방법으로 응용될 수 있을 것으로 기대된다. Abstract We measured the thickness and refractive index of a thin film using a double-slit diffraction experiment. The amount of phase step in the transmitted light generated by the thin film on the transparent substrate was measured by analyzing the diffraction pattern from the double slits. Experiments were conducted not only in air but also in distilled water, to determine thickness and refractive index simultaneously. To verify the validity of this method, we compared our values for thickness and refractive index to those measured using the well-established waveguide-coupling method. The suggested method is expected to be applied as a new method to simultaneously measure the thickness and refractive index of thin films, along with existing methods. [Editor's Pick] Current Optics and Photonics Vol. 6 no. 3 (2022 June) Spectral Reconstruction for High Spectral Resolution in a Static Modulated Fourier-transform Spectrometer Ju Yong Cho1, Seunghoon Lee2, Hyoungjin Kim1, and Won Kweon Jang1* Current Optics and Photonics Vol. 6 No. 3 (2022 June) pp. 244-251 DOI: https://doi.org/10.3807/COPP.2022.6.3.244 Fig. 1 The static modulated Fourier-transform spectrometer during the reconstruction process and a magnified optical layout for its optical-path difference. (a) Schematic view of the static modulated Fourier-transform spectrometer consisting of a modified Sagnac interferometer. S, source; SD, source driver; M1, fixed mirror; M2, displaced mirror; BS, beam splitter; FL, focusing lens; D, onedimensional detector; CI, computer interface; SI, sample interferogram; TM, transfer-function matrix of the spectrometer; RS, reconstructed spectrum. (b) Magnified optical layout near the one-dimensional detector array. Keywords: Interferometer, Reconstruction, Spectrometry, Static modulation OCIS codes: (000.4430) Numerical approximation and analysis; (070.4790) Spectrum analysis;(120.3180) Interferometry; (300.6300) Spectroscopy, Fourier transforms Abstract We introduce a spectral reconstruction method to enhance the spectral resolution in a static modulated Fourier-transform spectrometer. The optical-path difference and the interferogram in the focal plane, as well as the relationship of the interferogram and the spectrum, are discussed. Additionally, for better spectral reconstruction, applications of phase-error correction and apodization are considered. As a result, the transfer function of the spectrometer is calculated, and then the spectrum is reconstructed based on the relationship between the transfer function and the interferogram. The spectrometer comprises a modified Sagnac interferometer. The spectral reconstruction is conducted with a source with central wave number of 6,451 cm−1 and spectral width of 337 cm−1. In a conventional Fourier-transform method the best spectral resolution is 27 cm−1, but by means of the spectral reconstruction method the spectral resolution improved to 8.7 cm−1, without changing the interferometric structure. Compared to a conventional Fourier-transform method, the spectral width in the reconstructed spectrum is narrower by 20 cm−1, and closer to the reference spectrum. The proposed method allows high performance for static modulated Fourier-transform spectrometers. [Editor's Pick] Current Optics and Photonics Vol. 6 no. 2 (2022 April) Highly Birefringent Slotted-porous-core Photonic Crystal Fiber with Elliptical-hole Cladding for Terahertz Applications Yong Soo Lee1, Soeun Kim2 *, and Kyunghwan Oh1 ** Current Optics and Photonics Vol. 6 No.2 (2022 April) pp. 129-136 DOI: https://doi.org/10.3807/COPP.2022.6.2.129 Fig. 1 Transverse cross section of the proposed photonic crystal fiber (PCF) design, and the extended view of the slotted porous core. Keywords: High birefringence, Photonic crystal fiber, Terahertz OCIS codes: (060.2280) Fiber design and fabrication; (060.5295) Photonic crystal fibers; (260.1440) Birefringence Abstract We propose a photonic crystal fiber (PCF) with a slotted porous core and elliptical-hole cladding, for high birefringence in the terahertz regime. Asymmetry in the guided mode is obtained mainly by using arrays of elliptical air holes in the TOPAS® polymer cladding. We investigate the tradeoff between several structural parameters and find optimized values that can have a high birefringence while satisfying the single-mode condition. The optical properties in the terahertz regime are thoroughly analyzed in numerical simulations, using a full-vector finite-element method with the perfectly-matched-layer condition. In an optimal design, the proposed photonic crystal fiber shows a high birefringence of 8.80 × 10−2 and an effective material loss of 0.07 cm−1> at a frequency of 1 THz, satisfying the single-mode-guidance condition at the same time. The proposed PCF would be useful for various polarization-management applications in the terahertz range. [Editor's Pick] Current Optics and Photonics Vol. 6 no. 1 (2022 February) Design of an 8× Four-group Zoom System without a Moving Group by Considering the Overall Length Sung Min Park, Jea-Woo Lee, and Sung-Chan Park* Current Optics and Photonics Vol. 6 No.1 (2022 February) pp. 104-113 DOI: https://doi.org/10.3807/COPP.2022.6.1.104 (a) (b) Fig. 1 Paraxial ray traces in an equivalent optical system: (a) Ray tracing in the forward direction, (b) ray tracing in the reverse direction. Keywords: Aberrations, First orders, Tunable polymer lens, Zoom lens, Zoom position OCIS codes: (080.2740) Geometric optical design; (120.4570) Optical design of instruments; (220.3620) Lens system design Abstract We present a method to count the overall length of the zoom system in an initial design stage. In a zoom-lens design using the concept of the group, it has been very hard to precisely estimate the overall length at all zoom positions through the previous paraxial studies. To solve this difficulty, we introduce T eq as a measure of the total track length in an equivalent zoom system, which can be found from the first-order parameters obtained by solving the zoom equations. Among many solutions, the parameters that provide the smallest T eq are selected to construct a compact initial zoom system. Also, to obtain an 8× four-group zoom system without moving groups, tunable polymer lenses (TPLs) have been introduced as a variator and a compensator. The final designed zoom lens has a short overall length of 29.99 mm, even over a wide focal-length range of 4‒31 mm, and an f-number of F/3.5 at wide to F/4.5 at tele position, respectively. [Editor's Pick] Current Optics and Photonics Vol. 5 no. 6 (2021 December) Fourier Modal Method for Optical Dipole Radiation in Photonic Structures Sungjae Park1ㆍJoonku Hahn2ㆍHwi Kim1* Current Optics and Photonics Vol. 5 No.6 (2021 December) pp. 597-605 DOI: https://doi.org/10.3807/COPP.2021.5.6.597 Fig. 1 Photonic multiblock structure with an optical-source-embedding block, and the optical field distributions for (a) a dipole with polarization P = (1, 0, 0) and (b) a dipole with polarization P = (0, 0, 1). The thicknesses of block #1, the cathode, block #2, the active block, block #3, and the anode are 70 nm, 8 nm, 31 nm, 38 nm, 157 nm, and 114 nm respectively, and their refractive indices (n + jk) are 1.88, 0.191 + 3.24j, 1.71, 1.84 + 0.00272j, 1.94, and 0.129 + 3.19j, respectively. Keywords: Fourier modal method, Numerical modeling OCIS codes: (000.3860) Mathematical methods in physics; (050.1755) Computational electromagnetic methods; (050.1960) Diffraction theory Abstract An extended Fourier modal method (FMM) for optical dipole radiation in three-dimensional photonic structures is proposed. The core elements of the proposed FMM are the stable bidirectional scatteringmatrix algorithm for modeling internal optical emission, and a novel optical-dipole-source model that prevents numerical errors induced by the Gibbs phenomenon. Through the proposed scheme, the FMM is extended to model a wide range of source-embedded photonic structures. [Editor's Pick] Current Optics and Photonics Vol. 5 no. 5 (2021 October) Absolute Depth Estimation Based on a Sharpness-assessment Algorithm for a Camera with an Asymmetric Aperture Beomjun Kim, Daerak Heo, Woonchan Moon, and Joonku Hahn * School of Electronic and Electrical Engineering, Kyungpook National University, Daegu 41566, Korea Current Optics and Photonics Vol. 5 No.5 (2021 October) pp. 514-523 DOI: https://doi.org/10.3807/COPP.2021.5.5.514 (a) (b) Fig. 1 Defocus model. (a) Geometry of the camera, and (b) the radius of the CoC when half of the aperture size is 7 mm. Keywords: Coded aperture, Depth estimation, Image reconstruction OCIS codes: (100.2000) Digital image processing; (100.3008) Image recognition, algorithms and filters; (100.3020) Image reconstruction-restoration; (120.3940) Metrology; (170.1630) Coded aperture imaging Abstract Methods for absolute depth estimation have received lots of interest, and most algorithms are concerned about how to minimize the difference between an input defocused image and an estimated defocused image. These approaches may increase the complexity of the algorithms to calculate the defocused image from the estimation of the focused image. In this paper, we present a new method to recover depth of scene based on a sharpness-assessment algorithm. The proposed algorithm estimates the depth of scene by calculating the sharpness of deconvolved images with a specific point-spread function (PSF). While most depth estimation studies evaluate depth of the scene only behind a focal plane, the proposed method evaluates a broad depth range both nearer and farther than the focal plane. This is accomplished using an asymmetric aperture, so the PSF at a position nearer than the focal plane is different from that at a position farther than the focal plane. From the image taken with a focal plane of 160 cm, the depth of object over the broad range from 60 to 350 cm is estimated at 10 cm resolution. With an asymmetric aperture, we demonstrate the feasibility of the sharpness-assessment algorithm to recover absolute depth of scene from a single defocused image. [Editor's 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 Current Optics and Photonics Vol. 5 No.4 (2021 August) pp. 409-420 DOI: https://doi.org/10.3807/COPP.2021.5.4.409 (a) (b) (c) Fig. 1 Proposed method: (a) original color light field data with the same FoV for all color channels, (b) resampling by zeropadding, and (c) interpolation. Vertical axis is represented in ray angle θx. Abstract 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. [Editor's Pick] Current Optics and Photonics Vol. 5 no. 3 (2021 June) Binary-phase Complex Spatial Light Modulators Driven by Mirror Symmetry Minho Choi and Jaewu Choi * Department of Information Display, Kyung Hee University, Seoul 02447, Korea Current Optics and Photonics Vol. 5 No.3 (2021 June) pp. 261-269 DOI: https://doi.org/10.3807/COPP.2021.5.3.261 Fig. 1 Schematics of a BP-C-SLM. (a) A-SLM, (b) binary-phase spatial light modulators (BP-SLM), (c) physical combination of one A-SLM with one BP-SLM to achieve a BP-C-SLM, (d) an intrinsically fused BP-C-SLM, and (e) the information-doubling process, using the two physically combined SLMs or the intrinsically fused BP-C-SLM. Abstract Binary-phase complex spatial light modulators (BP-C-SLMs) are proposed and simulated. This study shows that bottom-top mirror-symmetrical uniaxial systems between two orthogonal polarizers allow one to construct BP-C-SLMs. BP-C-SLMs double the information-handling capacity per pixel, compared to the conventional amplitude-only spatial light modulators (A-SLMs), as well as being simply implemented with a single spatial light modulator (SLM), rather than a combination of an A-SLM and a binary-phase SLMs. Under limited conditions, BP-C-SLMs can control only the amplitude in single-phase space, and act as A-SLMs. [Editor's 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 Jeon1 and Sang Keun Gil2 * 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 (2021 April) pp. 155-163 DOI: https://doi.org/10.3807/COPP.2021.5.2.155 Fig. 1 Block diagrams for encryption. (a) Conventional CFB mode, (b) proposed CFB method. Abstract 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. 12345
[Editor's Pick] Current Optics and Photonics Vol. 6 no. 4 (2022 August) A New Instrument for Measuring the Optical Properties of Wide-field-of-view Virtual-reality Devices Hee Kyung Ahn1, Hyun Kyoon Lim2, and Pilseong Kang1 * Current Optics and Photonics Vol. 6 No. 4 (2022 August) pp. 392-399 DOI: https://doi.org/10.3807/COPP.2022.6.4.392 Fig. 1 The structure of a typical light-measuring devices (LMD) for virtual-reality/augmented-reality (VR/AR) devices. Keywords: Augmented Reality, Spectroradiometer, Virtual Reality OCIS codes: (120.2040) Displays; (120.5240) Photometry Abstract ght-measuring devices (LMDs) are frequently used to measure luminance and color coordinates of displays. However, it is very difficult to use a conventional LMD for measuring the optical properties of virtual-reality (VR) devices with a wide field of view (FOV), because of their confined spaces where the entrance pupil of a LMD is located. In this paper, a new LMD that can measure the optical properties of wide-FOV VR devices, without physical conflict with the goggles of the VR device, is proposed. The LMD is designed to fully satisfy the requirements of IEC 63145-20-10, and a pivot-point correction method for the LMD is applied to improve its accuracy. To show the feasibility of the developed LMD and the correction method, seven VR devices with wide FOV are measured with it. From the results, all of them are successfully measured without any physical conflict, and a comparison to their nominal values shows that the FOVs have been properly measured. [하이라이트 논문] 한국광학회지 Vol. 33 No.4 (2022 August) 이중 슬릿 회절 실험을 이용한 박막의 두께와 굴절률 측정 Measurement of the Thickness and Refractive Index of a Thin Film Using a Double-slit Experiment 김희성ㆍ박수봉¶ㆍ김덕우¶ㆍ김병주ㆍ차명식† 한국광학회지 Vol. 33 No.4 (2022 August) pp. 159-166 DOI: https://doi.org/10.3807/KJOP.2022.33.4.159 Fig. 1 Schematics of experimental setup. Lens 2 images the focal point of lens 1 (A) to CCD, satisfying (1/S1)+(1/S2)=1/f, where f (= 1 m) is the focal length of lens 2. Keywords: 회절, 이중 슬릿 실험, 굴절률, 두께 측정, 박막 OCIS codes: (120.2650) Fringe analysis; (120.5050) Phase measurement; (310.0310) Thin films 초록 본 연구에서는 이중 슬릿 회절 실험을 이용하여 박막의 두께와 굴절률을 측정하는 실험을 수행하였다. 투명 기판 위에 입혀진 박막이 만드는 투과광의 위상 단층의 크기를 이중 슬릿을 통과하여 나타나는 회절 패턴을 분석하여 측정하였다. 이로부터 두께와 굴절률을 동시에 결정하기 위해 공기와 증류수 속에서 각각 한 번씩 실험을 수행하였다. 이 방법의 유효함을 확인하기 위해 도파로 결합법으로 측정한 두께와 굴절률과 비교하였다. 본 연구에서 제안한 측정법은 기존의 선행 연구들과 더불어 박막의 두께와 굴절률을 동시에 측정할 수 있는 새로운 방법으로 응용될 수 있을 것으로 기대된다. Abstract We measured the thickness and refractive index of a thin film using a double-slit diffraction experiment. The amount of phase step in the transmitted light generated by the thin film on the transparent substrate was measured by analyzing the diffraction pattern from the double slits. Experiments were conducted not only in air but also in distilled water, to determine thickness and refractive index simultaneously. To verify the validity of this method, we compared our values for thickness and refractive index to those measured using the well-established waveguide-coupling method. The suggested method is expected to be applied as a new method to simultaneously measure the thickness and refractive index of thin films, along with existing methods. [Editor's Pick] Current Optics and Photonics Vol. 6 no. 3 (2022 June) Spectral Reconstruction for High Spectral Resolution in a Static Modulated Fourier-transform Spectrometer Ju Yong Cho1, Seunghoon Lee2, Hyoungjin Kim1, and Won Kweon Jang1* Current Optics and Photonics Vol. 6 No. 3 (2022 June) pp. 244-251 DOI: https://doi.org/10.3807/COPP.2022.6.3.244 Fig. 1 The static modulated Fourier-transform spectrometer during the reconstruction process and a magnified optical layout for its optical-path difference. (a) Schematic view of the static modulated Fourier-transform spectrometer consisting of a modified Sagnac interferometer. S, source; SD, source driver; M1, fixed mirror; M2, displaced mirror; BS, beam splitter; FL, focusing lens; D, onedimensional detector; CI, computer interface; SI, sample interferogram; TM, transfer-function matrix of the spectrometer; RS, reconstructed spectrum. (b) Magnified optical layout near the one-dimensional detector array. Keywords: Interferometer, Reconstruction, Spectrometry, Static modulation OCIS codes: (000.4430) Numerical approximation and analysis; (070.4790) Spectrum analysis;(120.3180) Interferometry; (300.6300) Spectroscopy, Fourier transforms Abstract We introduce a spectral reconstruction method to enhance the spectral resolution in a static modulated Fourier-transform spectrometer. The optical-path difference and the interferogram in the focal plane, as well as the relationship of the interferogram and the spectrum, are discussed. Additionally, for better spectral reconstruction, applications of phase-error correction and apodization are considered. As a result, the transfer function of the spectrometer is calculated, and then the spectrum is reconstructed based on the relationship between the transfer function and the interferogram. The spectrometer comprises a modified Sagnac interferometer. The spectral reconstruction is conducted with a source with central wave number of 6,451 cm−1 and spectral width of 337 cm−1. In a conventional Fourier-transform method the best spectral resolution is 27 cm−1, but by means of the spectral reconstruction method the spectral resolution improved to 8.7 cm−1, without changing the interferometric structure. Compared to a conventional Fourier-transform method, the spectral width in the reconstructed spectrum is narrower by 20 cm−1, and closer to the reference spectrum. The proposed method allows high performance for static modulated Fourier-transform spectrometers. [Editor's Pick] Current Optics and Photonics Vol. 6 no. 2 (2022 April) Highly Birefringent Slotted-porous-core Photonic Crystal Fiber with Elliptical-hole Cladding for Terahertz Applications Yong Soo Lee1, Soeun Kim2 *, and Kyunghwan Oh1 ** Current Optics and Photonics Vol. 6 No.2 (2022 April) pp. 129-136 DOI: https://doi.org/10.3807/COPP.2022.6.2.129 Fig. 1 Transverse cross section of the proposed photonic crystal fiber (PCF) design, and the extended view of the slotted porous core. Keywords: High birefringence, Photonic crystal fiber, Terahertz OCIS codes: (060.2280) Fiber design and fabrication; (060.5295) Photonic crystal fibers; (260.1440) Birefringence Abstract We propose a photonic crystal fiber (PCF) with a slotted porous core and elliptical-hole cladding, for high birefringence in the terahertz regime. Asymmetry in the guided mode is obtained mainly by using arrays of elliptical air holes in the TOPAS® polymer cladding. We investigate the tradeoff between several structural parameters and find optimized values that can have a high birefringence while satisfying the single-mode condition. The optical properties in the terahertz regime are thoroughly analyzed in numerical simulations, using a full-vector finite-element method with the perfectly-matched-layer condition. In an optimal design, the proposed photonic crystal fiber shows a high birefringence of 8.80 × 10−2 and an effective material loss of 0.07 cm−1> at a frequency of 1 THz, satisfying the single-mode-guidance condition at the same time. The proposed PCF would be useful for various polarization-management applications in the terahertz range. [Editor's Pick] Current Optics and Photonics Vol. 6 no. 1 (2022 February) Design of an 8× Four-group Zoom System without a Moving Group by Considering the Overall Length Sung Min Park, Jea-Woo Lee, and Sung-Chan Park* Current Optics and Photonics Vol. 6 No.1 (2022 February) pp. 104-113 DOI: https://doi.org/10.3807/COPP.2022.6.1.104 (a) (b) Fig. 1 Paraxial ray traces in an equivalent optical system: (a) Ray tracing in the forward direction, (b) ray tracing in the reverse direction. Keywords: Aberrations, First orders, Tunable polymer lens, Zoom lens, Zoom position OCIS codes: (080.2740) Geometric optical design; (120.4570) Optical design of instruments; (220.3620) Lens system design Abstract We present a method to count the overall length of the zoom system in an initial design stage. In a zoom-lens design using the concept of the group, it has been very hard to precisely estimate the overall length at all zoom positions through the previous paraxial studies. To solve this difficulty, we introduce T eq as a measure of the total track length in an equivalent zoom system, which can be found from the first-order parameters obtained by solving the zoom equations. Among many solutions, the parameters that provide the smallest T eq are selected to construct a compact initial zoom system. Also, to obtain an 8× four-group zoom system without moving groups, tunable polymer lenses (TPLs) have been introduced as a variator and a compensator. The final designed zoom lens has a short overall length of 29.99 mm, even over a wide focal-length range of 4‒31 mm, and an f-number of F/3.5 at wide to F/4.5 at tele position, respectively. [Editor's Pick] Current Optics and Photonics Vol. 5 no. 6 (2021 December) Fourier Modal Method for Optical Dipole Radiation in Photonic Structures Sungjae Park1ㆍJoonku Hahn2ㆍHwi Kim1* Current Optics and Photonics Vol. 5 No.6 (2021 December) pp. 597-605 DOI: https://doi.org/10.3807/COPP.2021.5.6.597 Fig. 1 Photonic multiblock structure with an optical-source-embedding block, and the optical field distributions for (a) a dipole with polarization P = (1, 0, 0) and (b) a dipole with polarization P = (0, 0, 1). The thicknesses of block #1, the cathode, block #2, the active block, block #3, and the anode are 70 nm, 8 nm, 31 nm, 38 nm, 157 nm, and 114 nm respectively, and their refractive indices (n + jk) are 1.88, 0.191 + 3.24j, 1.71, 1.84 + 0.00272j, 1.94, and 0.129 + 3.19j, respectively. Keywords: Fourier modal method, Numerical modeling OCIS codes: (000.3860) Mathematical methods in physics; (050.1755) Computational electromagnetic methods; (050.1960) Diffraction theory Abstract An extended Fourier modal method (FMM) for optical dipole radiation in three-dimensional photonic structures is proposed. The core elements of the proposed FMM are the stable bidirectional scatteringmatrix algorithm for modeling internal optical emission, and a novel optical-dipole-source model that prevents numerical errors induced by the Gibbs phenomenon. Through the proposed scheme, the FMM is extended to model a wide range of source-embedded photonic structures. [Editor's Pick] Current Optics and Photonics Vol. 5 no. 5 (2021 October) Absolute Depth Estimation Based on a Sharpness-assessment Algorithm for a Camera with an Asymmetric Aperture Beomjun Kim, Daerak Heo, Woonchan Moon, and Joonku Hahn * School of Electronic and Electrical Engineering, Kyungpook National University, Daegu 41566, Korea Current Optics and Photonics Vol. 5 No.5 (2021 October) pp. 514-523 DOI: https://doi.org/10.3807/COPP.2021.5.5.514 (a) (b) Fig. 1 Defocus model. (a) Geometry of the camera, and (b) the radius of the CoC when half of the aperture size is 7 mm. Keywords: Coded aperture, Depth estimation, Image reconstruction OCIS codes: (100.2000) Digital image processing; (100.3008) Image recognition, algorithms and filters; (100.3020) Image reconstruction-restoration; (120.3940) Metrology; (170.1630) Coded aperture imaging Abstract Methods for absolute depth estimation have received lots of interest, and most algorithms are concerned about how to minimize the difference between an input defocused image and an estimated defocused image. These approaches may increase the complexity of the algorithms to calculate the defocused image from the estimation of the focused image. In this paper, we present a new method to recover depth of scene based on a sharpness-assessment algorithm. The proposed algorithm estimates the depth of scene by calculating the sharpness of deconvolved images with a specific point-spread function (PSF). While most depth estimation studies evaluate depth of the scene only behind a focal plane, the proposed method evaluates a broad depth range both nearer and farther than the focal plane. This is accomplished using an asymmetric aperture, so the PSF at a position nearer than the focal plane is different from that at a position farther than the focal plane. From the image taken with a focal plane of 160 cm, the depth of object over the broad range from 60 to 350 cm is estimated at 10 cm resolution. With an asymmetric aperture, we demonstrate the feasibility of the sharpness-assessment algorithm to recover absolute depth of scene from a single defocused image. [Editor's 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 Current Optics and Photonics Vol. 5 No.4 (2021 August) pp. 409-420 DOI: https://doi.org/10.3807/COPP.2021.5.4.409 (a) (b) (c) Fig. 1 Proposed method: (a) original color light field data with the same FoV for all color channels, (b) resampling by zeropadding, and (c) interpolation. Vertical axis is represented in ray angle θx. Abstract 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. [Editor's Pick] Current Optics and Photonics Vol. 5 no. 3 (2021 June) Binary-phase Complex Spatial Light Modulators Driven by Mirror Symmetry Minho Choi and Jaewu Choi * Department of Information Display, Kyung Hee University, Seoul 02447, Korea Current Optics and Photonics Vol. 5 No.3 (2021 June) pp. 261-269 DOI: https://doi.org/10.3807/COPP.2021.5.3.261 Fig. 1 Schematics of a BP-C-SLM. (a) A-SLM, (b) binary-phase spatial light modulators (BP-SLM), (c) physical combination of one A-SLM with one BP-SLM to achieve a BP-C-SLM, (d) an intrinsically fused BP-C-SLM, and (e) the information-doubling process, using the two physically combined SLMs or the intrinsically fused BP-C-SLM. Abstract Binary-phase complex spatial light modulators (BP-C-SLMs) are proposed and simulated. This study shows that bottom-top mirror-symmetrical uniaxial systems between two orthogonal polarizers allow one to construct BP-C-SLMs. BP-C-SLMs double the information-handling capacity per pixel, compared to the conventional amplitude-only spatial light modulators (A-SLMs), as well as being simply implemented with a single spatial light modulator (SLM), rather than a combination of an A-SLM and a binary-phase SLMs. Under limited conditions, BP-C-SLMs can control only the amplitude in single-phase space, and act as A-SLMs. [Editor's 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 Jeon1 and Sang Keun Gil2 * 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 (2021 April) pp. 155-163 DOI: https://doi.org/10.3807/COPP.2021.5.2.155 Fig. 1 Block diagrams for encryption. (a) Conventional CFB mode, (b) proposed CFB method. Abstract 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.
