- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Optimized thermochromic properties of VO2/CoFe2O4 nanocomposite films via band gap engineering
摘要： VO2/CoFe2O4 nanoparticle composites were synthesized by hydrothermal method combined with annealing treatment. The nanocomposites consist of quasi-spherical nanoparticles with an average size of about 70 nm. The thermochromic properties of the nanocomposite films can be modulated by changing film thickness and the content of CoFe2O4 in the nanocomposites. The band gap of the VO2/CoFe2O4 nanocomposites increases with increasing CoFe2O4 additive content. The introduction of CoFe2O4 into VO2 matrix can not only lower the phase transition temperature, but also optimize the luminous transmittance and solar modulation ability of the VO2/CoFe2O4 nanocomposites as well. Our findings demonstrate a promising avenue in constructing VO2-based smart films with excellent thermochromic performance.
关键词： Solar modulation ability,VO2/CoFe2O4 nanocomposite,Luminous transmittance,Phase transition temperature
更新于2025-09-23 15:21:21
-
Tunable Luminescence Contrast in Photochromic Ceramics (1-x)Na0.5Bi0.5TiO3-xNa0.5K0.5NbO3:0.002Er by an Electric Field Poling
摘要： A binary solid solution of Er3+ doped (1-x)Na0.5Bi0.5TiO3-xK0.5Na0.5NbO3 (x=0.02, 0.04, 0.06, 0.08, 0.10, 0.12) ferroelectric ceramics has been developed, and a reversible photochromic (PC) reaction and its associated luminescence modulation are realized via alternating the 405-nm light irradiation and thermal stimulation (200 oC). The basic crystal structure, domain structure, ferroelectricity and dielectric behavior of the ceramics were measured. A moderate luminescence contrast ΔRt over 50% is obtained in the fresh samples. Meanwhile, a greatly enhanced luminescence contrast ΔRt is obtained via an electric poling for compositions x=0.02, 0.04, 0.06. For example, ΔRt is promoted from 53.4% to 85.3% for x=0.02. However, the luminescence contrast ΔRt of compositions x=0.08, 0.10, 0.12 is depressed after poling. The mechanisms of enhanced PC reaction and luminescence contrast ΔRt are discussed and proposed. The present study may open a window for enhancing the PC reaction.
关键词： Luminescence modulation,Poling,Ceramics,ferroelectrics,photochromic
更新于2025-09-23 15:21:21
-
Outage and BER performances of indoor relay-assisted hybrid RF/VLC systems
摘要： In this study, the authors analyse the outage performance of the indoor relay-assisted hybrid radio frequency (RF)/visible light communication (VLC) systems. They derive closed-form expressions for the outage probability of the end-to-end signal-to-noise ratio. Then they obtain the optimal approximation parameter with optimising the outage probability using the differential evolution algorithm. Moreover, they analysed the average bit error rate (BER) performance of the hybrid RF/optical system using pulse position modulation method while assuming the timing error in synchronisation. Finally, they present some numerical results utilising the newly derived exact closed-form expressions.
关键词： pulse position modulation,hybrid RF/VLC,BER,differential evolution algorithm,relay-assisted,outage probability
更新于2025-09-23 15:21:21
-
Flexibly adjustable depth-of-focus photoacoustic microscopy with spatial light modulation
摘要： Through focusing the excitation laser, optical-resolution photoacoustic microscopy (OR-PAM) is capable of measuring optical absorption properties down to micrometer-scale lateral resolution within biological tissues. The focused Gaussian beam routinely employed in the OR-PAM setups is inadequate for acquiring the volumetric images of biological specimens with thickness from tens micrometers to millimeter without scanning in depth because of the inconsistent lateral resolution along the depth direction due to its short depth of focus (DoF). Here, we integrate a spatial light modulator (SLM) into the optical path of an OR-PAM for realizing the flexibly adjustable DoF. By simply switching the phase patterns assigned onto the SLM interface, three representative illumination beams are produced, including conventional short-DoF Gaussian beam (GB), needle-like Bessel beam (BB), and extended depth-of-focus beam (EDFB). These modulations can be well realized based on the extended Nijboer-Zernike theory. The photoacoustic excitations show variable DoFs ranging from hundreds of micrometers (GB and BB) up to 1.38 mm (EDFB) but a consistent lateral resolution of (cid:2)3.5 lm. The proposed method is confirmed by volumetric imaging of multiple tungsten fibers positioned at different depths.
关键词： spatial light modulation,photoacoustic microscopy,depth-of-focus,extended depth-of-focus beam,Bessel beam,optical-resolution
更新于2025-09-23 15:21:21
-
Highly longitudinally polarized coherent anti-Stokes Raman scattering microscopy with improved spatial resolution
摘要： We proposed a method to enhance the longitudinally polarized component and improve the spatial resolution of radially polarized coherent anti-Stokes Raman scattering (CARS) microscopy by phase modulation. A specially designed phase pattern is applied onto the pump beam to suppress the radially polarized ?eld component at the focal region. With this modulation, the calculated intensity ratio between the longitudinally and radially polarized CARS ?eld is increased from 2.57 to 14.7, and the simulation of CARS imaging on a 120 nm polystyrene bead shows more than 3-fold spatial resolution improvement for both forward and backward detection. It is expected that this method could also be applied to other nonlinear optical imaging modalities for enhancing the longitudinally polarized component.
关键词： spatial resolution,microscopy,phase modulation,longitudinally polarized,coherent anti-Stokes Raman scattering
更新于2025-09-23 15:21:21
-
Correlation of Small-Signal Modulation with Digital Modulation Characteristics of High-Speed Semiconductor Lasers
摘要： This paper introduces correlation of the small-signal modulation characteristics with those of digital modulation of high-speed multiple-quantum-well semiconductor laser. The accuracy of applying the common small-signal approximation to calculate the modulation bandwidth is evaluated by comparing the obtained values with those calculated by the reliable technique of time-integration of the rate equations. Also, we present correlation between the maximum bit rate and the small-signal bandwidth at given bias current and modulation index. We show that the bandwidth frequencies predicted by the small-signal approximation are higher than those calculated by the time integration. The difference increases with the increase of the bias current reaching 8 GHz when the current exceeds 3.5 times the threshold current. We predict also the modulation conditions required to achieve modulation speed as high as 40 Gbps. The ratio of the maximum bit rate to the small-signal bandwidth exceeds unity and reaches 1.6 under deep modulation with modulation index equal to 0.5.
关键词： high-speed semiconductor lasers,small-signal modulation,digital modulation,modulation bandwidth,maximum bit rate
更新于2025-09-23 15:21:01
-
Mathematical Operations of Transmissive Near Fields Controlled by Metasurface with Phase and Amplitude Modulations
摘要： Metasurfaces show great potential due to their powerful ability to manipulate electromagnetic waves as desired, which has been widely investigated in the microwave, terahertz, infrared, and visible regimes. Here, it is proposed to control near-field distributions through use of a metasurface with both amplitude and phase modulations. A C-shaped particle is designed to provide stable and continuous amplitude and phase profiles independently of transmitted waves by varying its opening and orientation angles. Benefiting from both amplitude and phase modulations on the metasurface, differentiation and integration on electric-field distributions can be achieved by changing the arrangements of complex coefficients on the metasurface. Besides, the differential operation can be utilized to show the edges of predesigned electric-field distributions. It is believed that the proposed method will accelerate the pace of metasurfaces towards many applications by engineering and operating the near-field distributions.
关键词： metasurfaces,complex amplitudes,amplitude modulation,phase modulation,integral operations,differential operations
更新于2025-09-23 15:21:01
-
Strategically Modulating Carriers and Excitons for Efficient and Stable Ultrapurea??Green Fluorescent OLEDs with a Sterically Hindered BODIPY Dopant
摘要： Ultrapure colors are vital for displays to obtain the highly desired wide color-gamut. Till now, only boron-dipyrromethene derivatives (BODIPYs) have demonstrated ultrapure full-colors but suffer from low excitons utilization efficiency as dopants in organic light-emitting diodes. It is proposed here that with a thermally activated delayed fluorophore to sensitize BODIPYs, all excitons can be recycled, which, still, is challenged by exciton loss through Dexter energy transfer (DET) from sensitizer to dopant and direct charge trapping on BODIPYs. Hence, a sterically hindered BODIPY-type dopant with a bulk substituent on the meso-position is developed to suppress DET, exhibiting a high photo-luminance quantum yield of 98% and a small full width at half maximum of 28 nm. Moreover, the device structure is elaborately designed, successfully modulating carriers and excitons to avoid charge trapping on dopant and also trigger multiple-sensitizing processes to reduce exciton loss. Consequently, a state-of-the-art maximum external quantum efficiency/power efficiency of 19.0%/85.7 lm W?1 are realized together with an ultrapure-green emission of Commission Internationale de l’Eclairage coordinates of (0.26, 0.67) and a long half-lifetime of 2947 h at an initial luminance of 1000 cd m?2.
关键词： carrier modulation,ultrapure green emission,exciton modulation,high-efficiency devices,fluorescent organic light-emitting diodes,long-lifetime devices
更新于2025-09-23 15:21:01
-
Effect of quintic nonlinearity on self-phase modulation and modulation instability in multiple coupled quantum wells under electromagnetically induced transparency
摘要： The self-phase modulation and modulation instability of an optical probe electromagnetic field in multiple quantum well systems under electromagnetically induced transparency has been investigated. The probe field experiences large Kerr and quintic nonlinearities that can be controlled by two controlling laser beams. The probe beam experiences self-phase modulation which is suppressed by the quintic nonlinearity. The probe field is modulationally unstable due to the existence of large nonlinearities. The bandwidth of unstable frequencies and growth of the instability could be controlled by the probe beam power, the Rabi frequency and detunings of two control fields. The presence of the higher order nonlinearity and dispersion significantly reduce the instability growth and bandwidth of unstable frequency.
关键词： Self-phase modulation,Coupled quantum well,Modulation instability,electromagnetically induced transparency
更新于2025-09-23 15:21:01
-
Flexible Multi-Group Single-Carrier Modulation: Subcarrier Mapping and Power Allocation Optimization
摘要： Orthogonal frequency division multiplexing (OFDM) and single-carrier frequency domain equalization (SC-FDE) are two commonly adopted modulation schemes for frequency-selective channels. Compared to SC-FDE, OFDM generally achieves higher data rates, but at the cost of higher transmit signal peak-to-average power ratio (PAPR) that leads to lower power amplifier efficiency. This paper studies a multi-group single-carrier modulation scheme, termed flexible multi-group single-carrier (FMG-SC), which encapsulates both OFDM and SC-FDE as special cases, thus achieving more flexible rate-PAPR trade-offs between them. Specifically, in FMG-SC, the total bandwidth is divided into a set of orthogonal subcarriers, which, based on the channel gains, are flexibly mapped to multiple non-overlapping groups, and SC-FDE is applied over each group independently to send multiple data streams in parallel. We investigate the joint subcarrier grouping and power allocation optimization problem to maximize the achievable rate of our proposed FMG-SC scheme for both the cases with Gaussian signaling and with practical modulation constellation (e.g., quadrature amplitude modulation (QAM)), respectively. For both cases, the optimization problem is non-convex in general, for which we propose a two-step approach for finding a high-quality approximate solution efficiently. First, with any given subcarrier grouping, we show that the optimal power allocation can be obtained via convex optimization techniques. Second, with fixed power allocation, we propose low-complexity algorithms for the subcarrier grouping design catering to the SC-FDE receiver. Numerical results show that our proposed algorithms perform close to the optimal solution obtained via exhaustive search over all subcarrier groupings, yet with substantially reduced complexity. Moreover, the achievable rate of our proposed FMG-SC scheme with Gaussian signaling approaches the OFDM channel capacity and significantly outperforms that of SC-FDE. Furthermore, with practical modulation constellation, numerical results show that our proposed FMG-SC scheme greatly outperforms the existing single-carrier frequency division multiple access (SC-FDMA) in terms of achievable rate, but with moderately increased PAPR.
关键词： frequency-domain equalization,single-carrier modulation,subcarrier grouping,peak-to-average power ratio,Multicarrier modulation,power allocation
更新于2025-09-23 15:21:01