JournalTOCs

Optical Review
Journal Prestige (SJR): 0.332

Citation Impact (citeScore): 1
Number of Followers: 2

Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1349-9432 - ISSN (Online) 1340-6000
Published by Springer-Verlag

[2467 journals]

On the BER performance of QoS-aware multi-user OWC uplink using mCAP-NOMA
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  Abstract: Abstract In this paper, we propose and investigate a hybrid multi-band carrierless amplitude and phase modulation and non-orthogonal multiple access (mCAP-NOMA) scheme for quality-of-service (QoS)-aware uplink multi-user optical wireless communication (OWC) systems. Considering the users’ distinctive channel conditions and QoS requirements, we further design three user pairing approaches for the mCAP-NOMA-based uplink OWC system, including channel gain-based user pairing, modulation order-based user pairing and adaptive user pairing. More specifically, the adaptive user pairing approach can dynamically select from the individual channel gain-based or modulation order-based user pairing approaches aiming to obtain a lower average bit error rate (BER) of the uplink OWC system. Simulation results verify the feasibility and superiority of the mCAP-NOMA scheme with adaptive user pairing in an uplink four-user OWC system.
  PubDate: 2023-01-24
Nanoscale ultra-high-resolution non-destructive detection by correlated
double femtosecond laser pulses
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  Abstract: Abstract In this report, ultra-high spatial and temporal resolution non-destructive detection has been demonstrated using correlated double femtosecond laser pulses for the time. Owing to the residual thermal relaxation, our modal system ZnO thin film exhibits an interference between the two correlated femtosecond-laser-induced ultrasonic waves, and sound pressure enhancement has been observed. In comparison, only slight or negligible wave interference/pressure improvement for non-correlated double picosecond and nanosecond laser pulses could be identified. We demonstrate the capability of the correlated femtosecond laser to be used in ultra-precise thickness detection, which has a spatial measurement error as low as 1 nm, however, the errors for both the picosecond and nanosecond laser pulse are > 1 μm, three magnitudes worse than that of their femtosecond counterpart. Correlated femtosecond laser-induced waves presented ultra-high temporal resolution of ps level, which shows advantages over that (ns level) of non-correlated picosecond and nanosecond counterpart. Our results open the opportunities to achieve atomic resolution detection through ultrafast laser technology in the future.
  PubDate: 2023-01-23
Improved resolution for aerial imaging by retro-reflection with two
transparent spheres
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  Abstract: Abstract This paper proposes a method to improve the modulation transfer function (MTF) of aerial images by combining an aerial imaging optical system by retro-reflection with conjugated two transparent spheres. In the proposed optical system, the transparent spheres collimate the light incident on the retro-reflector to improve the resolution by making the light shift the same amount. The resolution was greatly improved by introducing conjugate two transparent spheres in the AIRR optical system. The MTF is increased by slightly increasing placement distance of the transparent spheres from the focal length and increasing diameter of the transparent spheres in the AIRR optical system. Changing the diameter of the transparent spheres at the near-axis approximate focal length improved the MTF, but there was no difference in MTF with diameter of the spheres. This indicates that different transparent spheres diameters do not affect the MTF because the parallel process is not modified. However, for distances other than the near-axis approximate focal length, the MTF was most improved when the diameter of the transparent spheres was larger. Thus, the improvement in resolution in the proposed AIRR optical system is confirmed.
  PubDate: 2023-01-17
Sandwich nano-fin to reduce the aspect ratio requirement of metasurface
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  Abstract: Abstract The current high-aspect-ratio Pancharatnam–Berry (PB)-phase metasurfaces in which vertical dimensions are much larger than the lateral dimensions are challenging to fabricate. Therefore, reducing the aspect ratio requirement has become a research priority. We propose a sandwich nano-fin consisting of GaN/amorphous silicon (a-Si)/GaN on a silica substrate to reduce the strict aspect ratio requirement of current PB-phase metasurfaces. The phase modulation ability and polarization conversion efficiency (PCE) of sandwich nano-fins were investigated. Compared with a conventional GaN nano-fin, the aspect ratio of sandwich nano-fin decreased from 6 to 4 under the same geometric dimension. The PCE of the sandwich nano-fin was up to 68.27%, 1.5 times higher than that of a GaN nano-fin under the same aspect ratio of 4. Moreover, after adding the a-Si layer, the overall PCE improved from 32.17 to 40.54% for the sandwich nano-fin. The sandwich structure simultaneously reduces the challenge of manufacturing and improves efficiency compared to current PB-phase metasurfaces.
  PubDate: 2023-01-11
Do observers use their own interpupillary distance in disparity
scaling'
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  Abstract: Abstract This study investigated whether the individual difference in the observer’s interpupillary distance (IPD) could cause the individual difference in perceived depth in binocular stereopsis. The horizontal retinal disparity (HRD) is one of the most potent depth cues, but the visual system could not uniquely estimate the metric depth from HRD alone. This is because the size of HRD is determined as a function not only of the size of external depth but also of the viewing distance and IPD. Thus to perceive depth veridically from HRD, observers need to adjust the scaling gain (i.e. the magnification factor when converting HRD to perceived depth), taking their IPD into account. To investigate whether the visual system performs such gain calibration, we examined the relationship between IPD size and perceived depth when observing stereograms (i.e. the visual stimulus of fixed HRD) at a fixed viewing distance with 54 observers. The results showed a significant correlation between perceived depth and IPD. This is consistent with the prediction based on the geometric relationship between depth, HRD, IPD, and viewing distance, suggesting that the visual system does calibrate the scaling gain based on the observer’s IPD. However, the measured results did not fully agree with the predictions from the geometry. The results were discussed, focusing on the errors in the estimation of scaling distance.
  PubDate: 2023-01-11
Controlling the transmission angle of terahertz waves based on
polarization-sensitive encoded metagrating metamaterials
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  Abstract: Abstract A polarization-sensitive transmissive all-dielectric-encoded metagrating in the terahertz band is proposed. Encoded metagratings are composed of all-dielectric materials and have the advantages of high transmission characteristics and low loss. Based on the electromagnetic dipole resonance of the all-dielectric resonator, the phase mutation of the unit structure can be realized. The far-field scattering characteristics of the designed metagrating are analyzed. The encoding metagratings can adjust the transmission angle of the terahertz beam by changing the different arrangements of the basic units. According to the generalized Snell’s law, the beam scattering angle of the encoded metagrating is determined by the grating period. Therefore, for the traditional gradient-phase metagrating sequence, only the limited scattering angle can be regulated. To obtain the flexible regulation of the scattering angle of terahertz wave, we introduce the Fourier convolution principle in digital signal processing, and combine the signal control theory with the encoded metagrating sequence. The digitally encoded addition and subtraction operations are used to obtain a new encoded metagrating sequence, which enables flexible regulation of the far-field scattering angle of the terahertz beam.
  PubDate: 2023-01-09
Optimization of blur correction of color images formed with aerial imaging
by retro-reflection
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  Abstract: Abstract We propose a pre-processing method of source image to reduce blur of aerial image that is formed with aerial imaging by retro-reflection (AIRR). In the AIRR optical system, anisotropic blurring occurs due to the influence of diffraction on the surface of the optical element. In this experiment, we measured the point spread function with multiple retro-reflection elements and light source wavelengths as parameters, and applied correction processing based on the results to the aerial image. We also quantitatively evaluated the correction results and analyzed the optimization of the correction function according to the wavelength of light source in the aerial image. The results of this experiment show the possibility of image quality improvement methods in image processing systems for aerial images.
  PubDate: 2023-01-06
A quantitative measurement of binocular fusion for achromatic and
chromatic colors
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  Abstract: Abstract The stereo image consisting of an achromatic image and a chromatic image (mixed stereo pair) can be fused as a three-dimensional (3D) color scene by human observers. It is said that the color in the scene is less vivid than in the chromatic image; however, there is little quantitative measurement for the color degradation. In this paper, we carried out a binocular color matching experiment on a stereoscopic display, and the binocular fusion of achromatic and chromatic colors is quantitatively measured. On an equal lightness plane of the CIELAB color space, the achromatic stimulus was presented to one eye, and the chromatic stimuli with different chromas (3 chroma levels) on different color directions (8 hues) were presented to the other eye. Then, the binocular fusion of two colors received by the two eyes was recorded by the matching experiment. Results show that when one eye is given a gray stimulus and the other eye is given a color stimulus, observers can always fuse the two stimuli. For chromatic stimuli with chroma 8, the perceived chromas degenerate to half of the chromatic patch, and for chromatic stimuli with chroma 12 and 16, the perceived chromas have significant difference on different color directions. However, the interaction between chroma and hue variations was not significant in the results of the 2-way ANOVA, it suggests that there is no difference in the variations across the color directions among the chromas.
  PubDate: 2023-01-03
Improving the luminous efficiency of quantum dot-converted LEDs by doping
boron nitride nanoparticles
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  Abstract: Abstract Quantum dot-converted LEDs (QCLEDs) are a new type of LED device. However, the low luminous efficiency of the QCLED cannot meet the requirements for practical applications. In this study, boron nitride nanoparticles (BN NPs) were doped into the quantum dot color convertor (QCC) of QCLEDs to utilize their strong scattering ability. Through many experiments, we found that as the concentration of BN NPs increased, the blue-light radiation flux decreased monotonically. Meanwhile, the luminous flux and efficiency of the BN-doped QCLEDs showed a 28.18% increase compared to the conventional structure when the BN NP concentration was 0.25 wt%. At the same time, with the increase in the BN NPs, the correlated color temperatures (CCTs) decrease to the range of 2000–3000 K warm white light, and the color coordinates of the devices gradually move to the yellow region. To conclude, doping low-concentration BN NPs in the quantum-dot color convertor (QCC) without excessively affecting the radiation flux of the device is an ideal solution. In addition, QDs are still very expensive, and reducing the amount of QDs in QCLEDs by doping BN NPs and improving the luminous flux and efficiency of QCLEDs has strong application prospects.
  PubDate: 2022-12-29
Correction to: Correction by the skin-to-chest wall distance in
near-infrared spectroscopy and assessment of breast cancer responses to
neoadjuvant chemotherapy
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  PubDate: 2022-12-14
Polarization imaging by use of optical scanning holography
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  Abstract: Abstract Polarization information is useful for various applications such as remote sensing and biomedical imaging. In general, polarization information is obtained using a polarization camera; however, the measured data are two-dimensional (2D) images, which limits its application. In this paper, three-dimensional (3D) polarization imaging by use of optical scanning holography (OSH) is proposed. Polarization-dependent digital holograms are recorded by changing directly the transmission axis of a polarizer in front of a photo detector. In the proof-of-principle experiment, partially Stokes parameters are calculated from the obtained holograms and are compared with the results obtained by a polarization camera. Experimental results show that the proposed method can measure a polarization object although there is the object behind a scattering medium, which opens the door of alternative imaging fields.
  PubDate: 2022-11-29
Ultrafast all-optical switching in a silicon-polymer compound slotted
photonic crystal nanobeam cavity
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  Abstract: Abstract On-chip ultrafast all-optical switching is highly desirable and important for all-optical information processing and photonic integrated circuits (PIC). Although numerous theoretical and experimental all-optical switching has been demonstrated, feasible switching scheme with compact size, ultrafast response, ultralow switching energy and ease to fabricate is still challenging. In this paper, we theoretically and numerically study the all-optical switching based on the Fano resonance in a silicon-polymer compound photonic crystal nanobeam side-coupled with a slotted nanobeam cavity. On one hand, owing to the cavity mode confined in the slotted region filled with polymer materials, the overwhelmingly large Kerr coefficient and ultrafast response can be fully utilized. Fano resonances with sharp asymmetric lineshape is in favor of improving switching operation on the other hand. Even under the excitation of 100 fs pump pulse, obvious all-optical switching can be achieved. Sub-picojoule switching energy, 462 fs switching time and switching contrast as high as 55.6% are realized simultaneously. Our proposed structure is compatible with the complementary-metal–oxide–semiconductor (CMOS) technology, which shows great potential in realizing high-performance and practical integratable all-optical switching.
  PubDate: 2022-11-29
Single-shot phase retrieval system using a deep UV LED source with visible
light converter fluorescent glass
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  Abstract: Abstract We present a single-shot imaging system for reconstructing a complex-valued object illuminated by a deep ultraviolet (DUV) LED source of central wavelength 265 nm based on an analytic (noniterative) phase retrieval method with an aperture-array filter. The diffraction intensity pattern from the object through the array filter is converted into a visible-light intensity one by a fluorescent glass and then imaged by a macro-lens on a low-cost CCD detector for visible light. The phase in the diffraction plane is analytically retrieved from the measured intensity pattern compensated for the spatial coherence of the illuminating light, and then the object can be reconstructed by the inverse Fourier transform of the retrieved complex function in the diffraction plane. The effectiveness of this system is experimentally demonstrated in the reconstructions of portions of a USAF 1951 target and onion cells.
  PubDate: 2022-10-18
  DOI: 10.1007/s10043-022-00770-z
A Mach–Zehnder interferometer based on peanut structure for temperature
and refractive index measurement
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  Abstract: Abstract A fiber Mach–Zehnder (M-Z) interferometer based on the peanut structure is proposed to measure the temperature and the refractive index (RI). This design includes the peanut-like structure parts and a sensing part. The peanut structures are fused with single-mode fiber (SMF) and few-mode fiber (FMF). The middle sensing part is formed by cascading FMF and thin core fiber (TCF). We show that the light intensity ratio between the core and the cladding can be increased using additional FMF in the peanut structure and the middle sensing part. Moreover, the sensitivity of RI can be increased using the TCF in the sensing part. Experimental results show that the maximum RI sensitivity of the sensor is around 210 nm/RIU and the maximum temperature sensitivity reaches 310 pm/℃.
  PubDate: 2022-10-17
  DOI: 10.1007/s10043-022-00765-w
Coherent diffraction imaging through shift-invariant scattering
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  Abstract: Abstract In this paper, we present a method for single-shot phase imaging with a wide field of view based on coherent diffraction imaging. Coherent diffraction imaging can be implemented by compact optical hardware without any interferometric measurement, but one issue is a severely limited field of view. Although this limited field of view is extendable by introducing random optical processes, this solution increases the costs of optical hardware and computations. To solve this issue, we utilize a shift-invariant scattering process in coherent diffraction imaging. This optical process is implemented by inserting a scattering plate on the pupil plane in an imaging system. In the proposed method, a complex amplitude object is illuminated with coherent light, and a single diffraction intensity image from the object is captured through the convolution of the scattering point spread function, which is probed in advance. The object field is reconstructed from the captured intensity image based on the ptychographical iterative engine, taking into account the randomized convolution process. The proposed method is numerically analyzed and experimentally demonstrated.
  PubDate: 2022-10-06
  DOI: 10.1007/s10043-022-00769-6
Relationship between intraocular lens refractive index and illuminance
distribution on retina in off-axis incident light: simulation study of
illumination optics
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  Abstract: Purpose We investigated the relationship between the refractive index of intraocular lenses and optical phenomena such as leading dysphotopsia. Methods A modified Liou–Brennan model including an intraocular lens (IOL) was used to analyze the illumination from off-axis incident light; the IOL was a biconvex single-focus spherical IOL at 20 D with three refractive indices set as 1.413 (low refractive index), 1.458 (medium refractive index), and 1.550 (high refractive index). Pupil diameters were analyzed for three different diameters, 3.0 mm, 5.0 mm, and 7.0 mm. Illumination optic simulations were performed using the optical illumination simulation program for LightTools ver. 9.1.1 (Synopsis Inc. California, USA). Results For off-axis incident light at 80–90°, a bimodal peak was observed. Higher refractive index IOLs resulted in higher peak values for both peaks and larger peak-to-valley. This was more pronounced at larger pupil diameters and peak values closer to the fovea. Conclusion Off-axis incident light consists of light passing between the iris and IOL, through the IOL to the sides of the IOL, and through the anterior and posterior surfaces of the IOL. These results suggest that the occurrence of optical phenomena can be reduced using IOLs with a low refractive index.
  PubDate: 2022-10-05
  DOI: 10.1007/s10043-022-00768-7
Compositionally graded quaternary electron blocking layer for efficient
deep ultraviolet AlGaN-based light-emitting diodes
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  Abstract: Abstract We present the enhancement of ultraviolet (UV) light-emitting diodes (LEDs) using numerical analysis. We have employed a compositionally graded quaternary (AlInGaN) electron blocking layer (EBL) instead of ternary/conventional (AlGaN) EBL. Comparison between our proposed device and reference device reveal that our proposed device shows improved radiative recombination rate and, hence, high emission spectrum. Consequently, the proposed device structure exhibits considerable reduction in efficiency droop at high current density.
  PubDate: 2022-10-03
  DOI: 10.1007/s10043-022-00766-9
Proposal of an infrared electro-optic switch based on
grapheme–silicone–graphene metamaterial with electrically dynamic
tunability
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  Abstract: Abstract The electrically dynamic tunability of a proposed metamaterial switch based on graphene–silicene–graphene heterogeneous structure is theoretically investigated in the terahertz range using the finite difference time domain (FDTD) method. The resonant frequency of the proposed switch can be controlled by the chemical potential of graphene and silicene sheets, independently. As a result, we can easily control the operating frequency of the fixed proposed structure in a desired wide range from 4 to 18 μm, as an electro-optic switch. The proposed switch surface area, insertion losses (IL), extinction ratio (ER) and quality factor (Q) are equal to 0.3 × 5 µm2, 0.15 dB, 30 dB and 40, respectively.
  PubDate: 2022-10-02
  DOI: 10.1007/s10043-022-00764-x
Outage probability analysis of FSO system with Airy beam as carrier
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  Abstract: Abstract Based on the scintillation index of Airy beam and exponentiated Weibull channel model, analytical expressions of outage probability for free-space optical (FSO) communication links with Airy beam as a signal carrier under weak atmospheric turbulence and on–off keying modulation scheme are derived. The outage probability at various propagation distances, transverse scale factors and exponential decay factors has been evaluated. And we compared the outage probability of FSO links with Airy beam and Gaussian beam as a signal carrier. The results show that the outage probability of FSO links with Airy beam as carrier decreases with the increase of threshold parameter and increases with the increase of propagation distance. When the transverse scale factor of Airy beam is about 2 cm, a lower outage probability can be obtained. And the smaller the exponential decay factor of the Airy beam, the lower the outage probability. Under the same source power or source width, the outage probability of FSO links with Airy beam as a carrier is significantly lower than that of FSO links with Gaussian beam as a carrier. The results of this research have some reference significance for the application of Airy beam in FSO communication system.
  PubDate: 2022-09-28
  DOI: 10.1007/s10043-022-00763-y
Multi-scale underwater image enhancement with optimized homomorphic filter
and RGB color correction
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  Abstract: Abstract We propose a multi-scale underwater image enhancement method with an optimized homomorphic filter and a RGB color correction algorithm. The proposed method includes three steps. First, an optimized homomorphic filter was developed to reduce the interference of underwater impurities on the image. The interference of impurity particles on the image is reduced, and a preliminarily optimized image can be obtained. Then, a multi-scale image enhancement algorithm is designed to enhance the color of underwater images. Finally, considering the color bias of the image, an RGB correction algorithm is proposed to correct the color of the image and further improve the image quality. Using public and simulated datasets, extensive qualitative and quantitative experiments are implemented to demonstrate the enhanced results of underwater images under different turbidity and the competitive performance of the proposed method.
  PubDate: 2022-09-20
  DOI: 10.1007/s10043-022-00762-z