Showing papers in "Journal of Modern Optics in 2022"
TL;DR: In this paper , an elliptical silicon array for broadband absorption inside ultra-thin silicon solar cells is proposed, where the arrangement of the nanowires (NWs) modifies the absorption intensities.
Abstract: The present study proposes an elliptical silicon array for broadband absorption inside ultra-thin silicon solar cells (SCs). The simulation results suggest that breaking the arrangement of the nanowires (NWs) modifies the absorption intensities. The efficient design of irregular NWs can contribute to improved absorption of such structures in comparison with ordinary structures. Single elliptical NWs exert significant optical antenna effects, which enable higher absorption of particular frequencies. However, in the case of NW arrays enhanced absorption is the outcome of trade off between an optical antenna and diffraction effects. In this study, a structure composed of a semi-periodic NW is suggested which can achieve improved performance in ultra-thin silicon SCs.
12 citations
TL;DR: In this paper , a double-sideband-suppressed carrier (DSB-SC)-based 60 GHz mm-wave system with a dual-drive Mach-Zehnder modulator (DD-MZM) operating in the null point region was investigated.
Abstract: Free space optic (FSO) communication offers a supplement to optical fibre for satisfying the demand of next-generation wireless networks. This paper signifies photonic generation of a double sideband-suppressed carrier (DSB-SC)-based 60 GHz mm-wave by operating a dual-drive Mach–Zehnder modulator (DD-MZM) in the null point region. The radiofrequency (RF) carrying signal is investigated for dual-hop FSO/RF links of 500 m/50 m by taking optical links in the turbulent atmosphere.At the data rates of 1.25, 2.5, and 5 Gb/s, overall operation is evaluated in terms of bit error rate (BER) as a function of the received optical power. In our analysis, system performance under the Gamma-Gamma (ΓΓ) matches with the Lognormal (LN) model in moderate fluctuation using aperture averaging effect. The results are obtained with a maximum difference in the receiver sensitivity of ∼1 dB at BER = 10−6 between ΓΓ and LN models.
6 citations
TL;DR: In this paper , the authors proposed a method to characterize the spectral-temporal distribution of single photons by taking advantage of spectral filtering, frequency entanglement between two single photons and a reference, followed by the generalized Hong, Ou and Mandel interferometer.
Abstract: New methods are proposed to characterize the spectral-temporal distribution of single photons. The presented protocols take advantage of spectral filtering, frequency entanglement between two single photons the one of interest and a reference, followed by the generalized Hong, Ou and Mandel interferometer. The measurement of the coincidence probability in these different schemes reveals the chronocyclic Wigner, the pseudo-Wigner distribution and the spectrogram at the single-photon level.
6 citations
TL;DR: In this article , a switchable bifunctional metasurface for broadband absorber and linear-to-circular polarization converter (LTCPC) in terahertz regime was proposed.
Abstract: We proposed a switchable bifunctional metasurface for broadband absorber and linear-to-circular polarization converter (LTCPC) in terahertz regime. When vanadium dioxide (VO2) is in the metallic state, the designed metasurface acts as a broadband terahertz absorber. The results demonstrate that the absorptance is above 90% and the bandwidth ratio is 68.6% from 0.981 to 2.011 THz. When VO2 is in the insulated state, the proposed structure behaves as an LTCPC with ellipticities 1 and −1 in frequency bands of 0.391∼0.517 and 0.673∼2.363 THz, respectively. The axis ratio is lower than 3 dB. The designed metasurface provides a new method for designing multifunctional terahertz devices.
6 citations
TL;DR: In this paper , the average intensity of partially coherent twisted Laguerre-Gaussian beam (PCTLGB) propagating through anisotropic atmospheric turbulence is derived based on the extended Huygens-Fresnel principle.
Abstract: Analytical formulas for average intensity of partially coherent twisted Laguerre-Gaussian beam (PCTLGB) propagating through anisotropic atmospheric turbulence are derived based on the extended Huygens–Fresnel principle. Our results indicate that PCTLGB gradually evolves from dark hollow distribution to flat-topped distribution and finally degenerates to Gaussian distribution both in free space and atmospheric turbulence. We also find that the effect of atmospheric turbulence on propagation characteristics for PCTLGB can be effectively reduced by adjusting twisted factor, topological charge and beam order. An important result is that PCTLGB has stronger anti-turbulence ability when vortex phase and twisted phase have the same chirality, and it can resist atmospheric turbulence more effectively than the beam without twisted phase under the same conditions. Our results will be useful in free space optical communication, lidar detection and imaging.
5 citations
TL;DR: A new colour image encryption scheme that combines real-valued discrete Gabor transform, 3D chaotic system with bit scrambling, and large key space is proposed that is feasible and secure.
Abstract: A new colour image encryption scheme that combines real-valued discrete Gabor transform (RDGT), 3D chaotic system with bit scrambling is proposed. First, the plaintext image is performed by the real-valued discrete Gabor transform. Subsequently, the transformed image undergoes Arnold transform to disorder bit values, and the coefficients of Arnold transform are selected from the chaotic sequence. Finally, the processed image matrix is XORed and scrambled with the 3D chaotic sequence after cyclic shift operation. The proposed algorithm possesses a large key space, and the keys are related to the plaintext image. Since the correlation of the ciphertext image is significantly smaller than that of the original image, the performance of the proposed algorithm is acceptable. Simulation results and performance analyses illustrate that the proposed colour image encryption scheme is feasible and secure.
4 citations
TL;DR: In this article , the authors investigated the focusing properties and focal shift of a partially coherent vortex cosine-hyperbolic-Gaussian beam (PCvChGB) passing through a lens system.
Abstract: In this paper, we investigate the focusing properties and focal shift of a partially coherent vortex cosine-hyperbolic-Gaussian beam (PCvChGB) passing through a lens system. Based on the extended Collins formula, the analytical expression for a PCvChGB propagating through a thin lens is derived in detail. By using the obtained formula, the influences of the spatial coherence length, the Fresnel number, and the initial beam parameters on the focusing properties and the focal shift of a PCvChGB are discussed numerically. It is shown that the average intensity distribution in the focal region and the focal shift of the focused PCvChGB are strongly affected by the above factors. The obtained results could be beneficial for applications of vortex cosine-hyperbolic-Gaussian beam (vChGB) beams in beam shaping and atom optics.
4 citations
TL;DR: In this article , a deep convolutional neural network (CNN)-based three-dimensional (3D) objects classification using an augmented holographic phase image dataset is proposed, where off-axis Fresnel digital holography is used for retrieving 3D object information as phase images.
Abstract: A Deep Convolutional Neural Network (CNN)-based three-dimensional (3D) objects classification using an augmented holographic phase image dataset is proposed. Off-axis Fresnel digital holography is used for retrieving 3D object information as phase images. The phase image dataset of the five different 3D objects considered in this study is prepared under various recording distances and rotational angles. The CNN based architecture classifies the 3D objects into two sets comprising of TRUE and FALSE classes with higher accuracy and minimal loss on the training set for the phase image dataset. The CNN has achieved higher precision, lower recall, and higher F1-score for the TRUE class on the test set. The experimental results demonstrate that the proposed CNN is capable of classifying 3D objects with an overall accuracy of 86% and AUC of 96% for the phase image dataset. The feasibility and classification performance are deduced from a proof of the concept experiment.
4 citations
TL;DR: In this article , a staircase concatenation method was introduced to investigate the effect of the taper angle and diameter on the sensor's sensitivity, and it was revealed that the sensitivity changes versus taper diameter and angle could be justified considering the coupled power to different modes of the tapered fiber as well as the ratio of the power outside the fibre taper to the total power for different modes.
Abstract: In this study, extensive research has been carried out to determine the optimum geometry resulting in the highest sensitivity for the tapered fibre-optic sensors in a broad geometrical range. A staircase concatenation method was introduced to investigate the effect of the taper angle and diameter on the sensor’s sensitivity. The results show that the sensor’s sensitivity increases by reducing the taper diameter. Moreover, the effect of the tapering angle on the sensitivity has an optimum point. As a result, there is an optimum taper curvature for exponential-linear profiles, which results in the highest sensitivity. Indeed, it was revealed that the sensitivity changes versus taper diameter and angle could be justified considering the coupled power to different modes of the tapered fibre as well as the ratio of the power outside the fibre taper to the total power for different modes.
3 citations
TL;DR: Wang et al. as discussed by the authors utilized a scattering medium with ideal optical properties as the physical key, and the plaintext is transformed into four noise-like holograms with the help of the four-step phase shifting digital holography.
Abstract: Scattering-medium-based optical image encryption provides an intrinsically tamper-resistant physical key. In this paper, we utilize a scattering medium with ideal optical properties as the physical key. The plaintext is transformed into four noise-like holograms with the help of the four-step phase-shifting digital holography. Low-frequency components of the four holograms are extracted and combined into a new image by the lifting wavelet transform (LWT). Then the combined image is scrambled by the nonlinear 3D chaos-based cyclic shift. In decryption, the digital optical phase conjugation (DOPC) technique is utilized to extract plaintext. Numerical simulations prove the feasibility of the proposed method, and the security analysis shows that our method can resist different attacks.
3 citations
TL;DR: In this article , the optical response of a hybrid electro-optomechanical system interacting with a qubit was investigated, and a tunable switch between OMIT and OMIA of the probe field was provided.
Abstract: We investigate the optical response of a hybrid electro-optomechanical system interacting with a qubit. In our experimentally feasible system, tunable all-optical-switching, double-optomechanically induced transparency (OMIT) and optomechanically induced absorption (OMIA) can be realized. The proposed system is also shown to generate anomalous dispersion. Based on our theoretical results, we provide a tunable switch between OMIT and OMIA of the probe field by manipulating the relevant system parameters. Also, the normal-mode-splitting (NMS) effect induced by the interactions between the subsystems are discussed in detail and the effects of varying the interactions on the NMS are clarified. These rich optical properties of the probe field may provide a promising platform for controllable all-optical-switch and various other quantum photonic devices.
TL;DR: In this article , a cross-coupled resonator induced shifted absorption (CRISA) is proposed to bring new optical analogues of quantum coherence phenomena, which produces a new very narrow reflection dip positioned at single-pass phase shift θ = − π/2 which they refer to as crosscouple resonator inducing shifted absorption.
Abstract: We report, for the first time to the best of our knowledge, a technique that employs ′cross-coupling structure’ in the cascaded microring resonators (MRRs) to bring new optical analogues of quantum coherence phenomena. The new configuration resembles a standard double resonator (SDR) but uses cross-coupled–based directional couplers (DCs) instead of the typical direct-coupled–based DCs. One of its unique features is that it does not exhibit the typical SDR’s signature quantum coherence analogue effects like coupled-resonator induced transparency (CRIT) or coupled-resonator induced absorption (CRIA). On the contrary, it produces a new very narrow reflection dip positioned at single-pass phase shift θ = − π/2 which we refer to as cross-coupled resonator induced shifted absorption (CRISA). We compare extensively CRISA’s characteristics with the CRIT, CRIA, and Autler-Townes splitting (ATS) found in SDR. The technique opens up new configurations with richer optical behaviours that could find potentially still unexplored applications.
TL;DR: In this article , the propagation properties of a circular cosh-Gaussian beam (CiChGB) in a fractional Fourier transform (FRFT) optical system are investigated theoretically.
Abstract: The propagation properties of a circular cosh-Gaussian beam (CiChGB) in a fractional Fourier transform (FRFT) optical system are investigated theoretically. The analytical expressions for a CiChGB propagating through apertured and unapertured FRFT systems are derived based on the Collins formula and the expansion of the hard-aperture function into a finite sum of Gaussian functions. From the obtained expressions, the evolution of the intensity distribution at the output plane is analysed with illustrative numerical examples. It is shown that the intensity distribution of the CiChGB propagating in FRFT is closely dependent on the decentred beam parameter and the aperture size besides the fractional order of the FRFT system. The results obtained may be beneficial to applications in laser beam shaping, optical trapping, and micro-particle manipulation.
TL;DR: In this article, dual quasi-bound states in the continuum (quasi-BICs) in all-dielectric metamaterial consisting of a silicon stair-like resonator were investigated.
Abstract: In this work, we design and numerically investigate dual quasi-bound states in the continuum (quasi-BICs) in all-dielectric metamaterial consisting of a silicon stair-like resonator by breaking the symmetry in the direction perpendicular to the metamaterials. By introducing this unique degree of freedom beyond the in-plane symmetry, one can observe the evolution from BICs to quasi-BICs and efficiently control the Q-factors and frequencies of quasi-BICs. The charge density distribution, far-field radiations and near-field distributions demonstrate the dominant electric quadrupole responses in such two quasi-BICs. Further, we examine actively tunable response of such two quasi-BICs with respect to a change in the Fermi energy of graphene layer, indicating the potential applications in designing quasi-BIC-based modulators, filters and sensors.
TL;DR: In this paper, the skew information-based coherence and the norm of coherence for two-qubit Bell-diagonal states under the influence of correlated Pauli channels, such as correlated dephase, depolarizing and classical noisy channels, were analyzed.
Abstract: In this paper, we study analytically the skew information-based coherence, and compare its dynamics with that of the norm of coherence for two-qubit Bell-diagonal states under the influence of correlated Pauli channels, such as correlated dephase, depolarizing and classical noisy channels, respectively. The similar as well as different features between the skew information-based coherence and norm of coherence are discussed. In addition, the physical mechanism of preserving quantum coherence based on memory coefficient of correlated channels and non-Markovian memory effect is also expounded.
TL;DR: The method does not require the physical model of the underwater scene because of the use of deep learning and the enhancement of objects with different materials and textures is obvious, which illustrates that the proposed method is effective and robust.
Abstract: In the paper, a method of underwater image enhancement based on the neural network of Mueller matrix images is presented. The novelty of our study lies in the employment of the neural network based on Mueller matrix imaging, which can provide complete information of the target, to conduct underwater image enhancement. To establish the dataset, we obtain the Mueller matrix images of different objects under different water turbidity. We utilize an improved neural network based on U-net and a loss function using the high-level feature extractor to enhance the underwater images. The method does not require the physical model of the underwater scene because of the use of deep learning. The enhancement of objects with different materials and textures is obvious, which illustrates that the proposed method is effective and robust. Our method is superior compared with the state-of-the-art methods in terms of quantitative measures and visual quality.
TL;DR: In this article, a theoretical approach has been adopted to study GaAs-based InAlAs/InGaAs/GaAsSb type-II heterostructures, which can be employed in a semiconductor laser diode operating in the NIR range as per the observed results.
Abstract: ABSTRACT In this research work, a theoretical approach has been adopted to study GaAs-based InAlAs/InGaAs/GaAsSb type-II heterostructures. The 6 × 6 k·p Hamiltonian matrix with self-consistent calculations has been carried out to calculate the wavefunctions, localization of the charge carriers (probability density of charge carriers) and their dispersed energy states (Discrete energy level) under variable quantum well width and external strain of the double quantum well heterostructure. Bulk band structures of InAlAs/GaA for different aluminium compositions have been reported. The quantum well size and external strain effect on optical gain have also been explored. Computational analysis showed the generated light has a 1.93 μm NIR lasing wavelength. At 12 GPa, optical gain reaches 7450 cm−1 and wavelength 1.93 μm. Peak gain is 5931 cm−1 for 2 nm well width. The developed type-II structure can be employed in a semiconductor laser diode operating in the NIR range as per the observed results.
TL;DR: In this article , an ultra-compact micro-optical element was designed to generate high-quality micro-sized high-order Bessel beam (HoBB) for complex-environment optical manipulation and long-distance optical communication.
Abstract: Compared with traditional vortex beams, high-order Bessel beams (HoBBs) have the unique characteristics of non-diffraction and self-healing, which makes them more competitive in fields of complex-environment optical manipulation and long-distance optical communication. With the progress of machining technology, the realization of micro-nano-sized optical components becomes possible, and integrated optics becomes the trend of future development. However, up to now, the traditional devices for generating HoBBs have a large volume and high weight, which makes it difficult to achieve optical integration. Here, we have designed an ultra-compact micro-optical element to generate high-quality micro-sized HoBBs. Good morphology of the element prepared via laser direct writing (LDW), and beam characteristics of non-diffraction and self-healing were demonstrated experimentally.
TL;DR: In this paper , the performance of all-optical exclusive-OR (XOR) logic gate is investigated at high operating temperatures (TOP) using different SOAs technologies such as conventional SOAs, carrier reservoir (CR)-SOAs, reflective SOAs (RSOAs), and photonic crystal (PC)-SOA, for the first time to our knowledge.
Abstract: A critical area of research is studying the performance of semiconductor optical amplifiers (SOAs) at high temperatures. In this paper, the performance of all-optical exclusive-OR (XOR) logic gate is investigated at high operating temperatures (TOP) using different SOAs technologies such as conventional SOAs, carrier reservoir (CR)-SOAs, reflective SOAs (RSOAs), and photonic crystal (PC)-SOAs, for the first time to our knowledge. The time-dependent differential equations of SOAs, CR-SOA, RSOAs, and PC-SOAs at different operating data rates have been solved. The performance of the XOR logic gate is evaluated by calculating the quality factors and plotting the eye diagrams for each amplifier. Besides, the dependence of the key operating parameters on the TOP is examined and assessed for each scheme. The results showed that the RSOAs perform better at high temperatures than other proposed SOA technologies.
TL;DR: A deep-learning-based method single-shot 3D reconstruction method (SSR) for colour textured objects is proposed, and it can reconstruct colourTextured objects with high precision and the experimental results show that the proposed method provides good guidance for the practical application and scientific research of fringe projection profilometry based on colour textures.
Abstract: Three-dimensional (3D) shape reconstruction based on structured light technique is one of the most crucial techniques in the field of optical measurement due to the nature of non-contact and high-precision. In recent years, researchers found that the deep-learning method can significantly improve the quality and efficiency of 3D reconstruction. So far, the research object of structured light 3D reconstruction technology related to deep-learning methods usually adopts plaster models. However, the surface of the reconstructed objects always contains rich colour texture information in a real-world scenario, which affects the accuracy of the reconstruction, especially for some single-shot applications. To solve the above problem, we propose a deep-learning-based method single-shot 3D reconstruction method (SSR) for colour textured objects, and it can reconstruct colour textured objects with high precision. The experimental results show that the proposed method provides good guidance for the practical application and scientific research of fringe projection profilometry based on colour textured objects.
TL;DR: In this article , the authors discussed the evolution characteristics of optical vortices with the cross phase in free space and found that both splitting and rotating can occur for vortice with circular symmetry due to cross phase.
Abstract: We discussed evolution characteristics of optical vortices with the cross phase in free space and found that both splitting and rotating can occur for vortices with circular symmetry due to cross phase. The rotation is bidirectional and the rotational direction will reverse at some certain distance. The physical mechanism behind the splitting and rotating of vortices is considered to be the effective anisotropic diffraction, which results from the cross phase. We also investigated the dynamics of superimposed pattern with two astigmatic vortices of opposite cross phase. The rotating of vortices always happens, however, the splitting only occurs for nonzero net cross phase coefficient. The results in the paper provide us with a theoretical method to control the dynamics of vortices by adjusting the cross phase, then may find potential applications in the field of optical tweezers.
TL;DR: In this paper , a new method for realizing the response broadening of organic photodetectors (OPDs) using non-fullerene acceptor IEICO-4F doping has been proposed.
Abstract: A new method for realizing the response broadening of organic photodetectors (OPDs) using non-fullerene acceptor IEICO-4F doping has been proposed in this paper. It was found that when the mass ratio of P3HT:IEICO-4F:PC61BM in the active layer was 10:2:8, the spectral response range of OPDs was extended to 400–900 nm. The responsivity (R) and external quantum efficiency (EQE) of ternary OPDs reached 230, 263, 199 mA·W–1 and 46%, 62%, 54% under 630, 530, 460 nm illumination and –1.5 V bias, respectively. The detectivity (D*) reached 1012 Jones. The results showed that the addition of IEICO-4F increased the exciton dissociation interface and improved the dissociation rate of the active layer, thus improving the photocurrent of the device. In addition, the addition of IEICO-4F promoted the crystallization of the film, reduced charge recombination, and thereby reduced the dark current of the device.
TL;DR: In this article , the authors examined the applicability and relevance of the Nyquist sampling theorem in phase-stepping digital shearography, which has become a useful tool in the generation of displacement gradient maps of extended objects, and in non-destructive testing.
Abstract: The Nyquist criterion, or Nyquist sampling theorem, has been used as a gold standard in signal processing and in digital imaging. In this work, we examine its applicability and relevance in phase-stepping digital shearography, which has become a useful tool in the generation of displacement gradient maps of extended objects, and in non-destructive testing (NDT). We show, with experimental data and quantitative measurements from our digital shearography experiments, that it is not necessary to comply strictly with the Nyquist criterion in digital shearography. Operation of the digital imaging device in the sub-Nyquist domain is perfectly feasible, and even desirable, in many cases. This will suggest, to the experimentalist in shearography, the best possible ways to perform image sampling in the case of digital shearography.
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TL;DR: In this article, a rotary binocular vision measurement system (RBVMS) consisting of two cameras and two theodolites, with the latter employed as a two-dimensional rotation platform, was introduced.
Abstract: This paper introduced a rotary binocular vision measurement system (RBVMS) consisting of two cameras and two theodolites, with the latter employed as a two-dimensional rotation platform. The camera was driven by mounting it on the theodolite to cover different areas, effectively increasing the measuring range. In the camera calibration stage, virtual 3D points were generated by accurately moving the planar calibration board. A two-order radial and two-order tangential distortion model was considered. The experimental results showed that the intrinsic parameters of the camera had high stability, and the mean reprojection error was about 0.035 pixels. A unit quaternion method was applied to calibrate the transformation matrix between the camera and the theodolite. By solving the transformation matrix between the two theodolites, the measurement data of each position was unified under a fixed coordinate system. At 500 mm in front of the camera, the camera's field of view was about 200 mm. Two targets of different sizes were measured to verify the effectiveness and accuracy of the method. The measurement accuracy of 300 mm and 600 mm targets was about 0.014 mm and 0.027 mm, respectively.
TL;DR: In this article , a kind of optical design method based on double-layer random microlens array is proposed for better white lighting, which can eliminate the incomplete overlap of rays and colour shadow effectively, and the proposed optical system design method can solve the problems of white point shift, colour difference, uniformity in mixed white light illumination.
Abstract: The high quality mixed white light is widely used in some fields of illumination of machine vision and optical projection. Optical design can improve white light production using RGB LEDs mixture method. In this paper, a kind of optical design method based on double-layer random microlens array is proposed for better white lighting. The design effect is verified by some comparisons with the double-layer non-random microlens array system. Experimental results show that the normalized standard deviation of white point shift is decreased from 0.05 to 0.01, the average colour difference is decreased from 44 to 2.5, and the illumination uniformity is increased from 0.66 to 0.82. The proposed design method can eliminate the incomplete overlap of rays and colour shadow effectively, and the proposed optical system design method can solve the problems of white point shift, colour difference, uniformity in mixed white light illumination.
TL;DR: In this article, an Optimized Convolutional Neural Network-based Multi-gas Optical Sensor (OCNN-MOS) developed using photonic crystals was used for the detection of different gases, namely, N2, CH4 and CO.
Abstract: This study relates to an Optimized Convolutional Neural Network-based Multi-gas Optical Sensor (OCNN-MOS) developed using photonic crystals. A square-shaped dielectric rod with cubic lattice index was used for the detection of different gases, namely, N2, CH4 and CO. Three nanocavities were present in the proposed OCNN-MOS, with one nanocavity located at the centre (refractive index 2.6) and the other two were the sub-nanocavities located along the path of the output and input respectively. A grey wolf optimization technique was used for optimizing its hyperparameters and for the improvement of its performance. The proposed OCNN-MOS was connected with a clean air generator for diluting the flow of hydrocarbon, a flow controller, and three standard sample gas cylinders for the conduction of the experiment. A concentrated gas mixture of 60–200 ppm was used in the experiment. The proposed optimization achieved an improvement of 7.06% in the performance of CNN.
TL;DR: In this paper , a sensitivity refractive index (RI) sensor based on surface plasmon resonance (SPR) effect in D-shaped high birefringence photonic crystal fiber (PCF) is presented and studied by the finite element method.
Abstract: A sensitivity refractive index (RI) sensor based on surface plasmon resonance (SPR) effect in D-shaped high birefringence photonic crystal fibre (PCF) is presented and studied by the finite element method (FEM). Through the designing of air holes arrangement in PCF, the birefringence of optical fibre is improved and the SPR effect of y-polarized core mode is directionally excited. The designed D-shaped PCF with gold film in the damaged air holes enhances the interaction of the evanescent field with the external medium. Simulation results indicate that the sensor has a sensing range from 1.30 to 1.37, and the average spectral sensitivity is 10348.3 nm/RIU. The maximum spectral sensitivity of 19,288 nm/RIU and a high resolution of 5.18 × 10−6 RIU can be obtained at 1.37. This high sensitivity sensor has broad application prospects in life science and other research fields.
TL;DR: In this paper , a theoretical formulation followed by numerical analysis is carried out to study the hot carrier effects (HCEs) on Brillouin amplification in AIIIBV and AIIBVI semiconductors.
Abstract: A theoretical formulation followed by numerical analysis is carried out to study the hot carrier effects (HCEs) on Brillouin amplification in AIIIBV and AIIBVI semiconductors. The threshold condition for the onset of Brillouin amplification and the parameters characterizing Brillouin amplification of the Brillouin cell are estimated. Numerical analysis is made for three different Brillouin cells at illuminated by a pulsed CO2 laser. HCEs of intense pump beam modifies the momentum transfer collision frequency of carriers and consequently the nonlinearity of the Brillouin medium, which in turn (i) lowers the threshold intensity, (ii) enhances the parameters characterizing Brillouin amplification, (iii) shifts the enhanced Brillouin gain spectrum towards smaller values of magnetic field, and (iv) widens the range of magnetic field at which peak of Brillouin gain spectrum (around resonance) occurs. The incorporation of HCEs in the analysis validate the selection of appropriate Brillouin medium for the fabrication of efficient Brillouin amplifiers.
TL;DR: In this article , a human visual perception-based underwater imaging model is first built to generate images with high contrast and rich colours, then a level adjustment algorithm is developed to improve the brightness of the image.
Abstract: Due to the light absorption and scattering by water, the underwater image quality is often severely degraded. To solve this problem, we propose an underwater image restoration method that uses level adjustment and colour equalization algorithms to obtain high-quality underwater images. A human visual perception-based underwater imaging model is first built to generate images with high contrast and rich colours. Then, a level adjustment algorithm is developed to improve the brightness of the image. Finally, a colour equalization algorithm is designed to filter the local characteristics and achieve image brightness, colour, and contrast adjustment with nonlinear and filtered local characteristics. Extensive numerical and experimental results show that the proposed method can improve the underwater images and is superior to the recently reported methods.
TL;DR: In this article , the authors proposed a multiple-input multiple-output (MIMO) terrestrial-satellite laser communication uplink system based on optical spatial modulation with medium-based modulation (OSM-MBM) joint modulation.
Abstract: This paper proposes a multiple-input multiple-output (MIMO) terrestrial-satellite laser communication uplink system based on optical spatial modulation with medium-based modulation (OSM-MBM) joint modulation. The Málaga(M) distribution is used to describe the combined effects of near-ground turbulent light intensity scintillation, beam wander and angle of arrival fluctuation. The closed expression of the bit error rate (BER) of the OSM-MBM joint modulation MIMO terrestrial-satellite laser communication uplink is derived. The simulation analyzes the influence of transmitting radius, receiving aperture, beam divergence, zenith angle and signal-to-noise ratio on the system error performance, and compares it with traditional modulation, media-based modulation and optical space modulation. Finally, the experiment is verified by Monte Carlo. This research provides a theoretical reference for the engineering realization of the modulation technology for the MIMO terrestrial-satellite laser communication uplink system.