Multimode Output Research Articles

Asymmetric structural colors based on monodisperse single-crystal Cu2O spheres.

Structural colors have attracted broad attention owing to their anti-photobleaching capability and brilliant metallic color. In particular, the asymmetric structural colors generated by a simple material will have great practical significance in the fields of biomimetic materials, double-side display and anti-counterfeiting. The asymmetric optical effects were usually achieved by the plasmonic effects of Ag or Au nanocrystals. Here, for the first time, we realized the asymmetric structural colors based on the asymmetric scattering of Cu2O single-crystal spheres. By spray-coating Cu2O spheres on a glass slide, different structural colors were viewed from the Cu2O film side and the glass slide side. The FDTD simulations confirmed that the asymmetric colors were ascribed to the inhomogeneous distribution of the electric field intensity. The film built by 200 nm Cu2O spheres on a glass slide shows green and cyan structural colors from the front and back sides, respectively. The colors on both sides of the Cu2O films were proved to be tuned by changing the diameters of the Cu2O single-crystal spheres. Different substrates were used to examine the influence of substrates on the asymmetric colors. Finally, inspired by different brilliant colors from the front and back of natural creatures, the patterns of butterfly and petals were fabricated by Cu2O spheres. Impressively, similar to nature, the patterns show completely different colors viewed from the front and back sides. The asymmetric structural colors of Cu2O single-crystal spheres will open up new avenues to realize multi-mode color output and pave their applications in display, biomimetic materials and anti-counterfeiting materials.

A Novel Trajectory Generator Based on a Constrained GAN and a Latent Variables Predictor

Forecasting pedestrian trajectory is critical for versatile applications, such as autonomous driving and social robot, when they work in human-centric environments. However, it is challenging to predict pedestrians’ future trajectories due to the inherent human properties and pedestrians’ social interactions. Recent works predict future trajectories by using a generative model, which captures social interactions with pooling- or graph-based strategies and generates multi-modal outputs with latent variables sampled from random Gaussian noise. Nevertheless, they introduce little human knowledge, which is beneficial for improved prediction performance. In this work, we propose to learn informative latent variables from pedestrians’ future trajectories. Moreover, we present a distance-direction pooling module, which captures social interactions in a more intuitive manner. Besides, we introduce an additional constraint on generative adversarial network optimization to generate more realistic results. Two benchmarking datasets, ETH (Pellegrini et al. , 2010) and UCY (Leal-Taixe et al. , 2014), are used to evaluate the proposed method. Comparisons between our method and several state-of-the-art methods demonstrate the superiority of the proposed method in generating more accurate future trajectories.

Multimodal Transformer With Multi-View Visual Representation for Image Captioning

Image captioning aims to automatically generate a natural language description of a given image, and most state-of-the-art models have adopted an encoder-decoder framework. The framework consists of a convolution neural network (CNN)-based image encoder that extracts region-based visual features from the input image, and an recurrent neural network (RNN)-based caption decoder that generates the output caption words based on the visual features with the attention mechanism. Despite the success of existing studies, current methods only model the co-attention that characterizes the inter-modal interactions while neglecting the self-attention that characterizes the intra-modal interactions. Inspired by the success of the Transformer model in machine translation, here we extend it to a Multimodal Transformer (MT) model for image captioning. Compared to existing image captioning approaches, the MT model simultaneously captures intra- and inter-modal interactions in a unified attention block. Due to the in-depth modular composition of such attention blocks, the MT model can perform complex multimodal reasoning and output accurate captions. Moreover, to further improve the image captioning performance, multi-view visual features are seamlessly introduced into the MT model. We quantitatively and qualitatively evaluate our approach using the benchmark MSCOCO image captioning dataset and conduct extensive ablation studies to investigate the reasons behind its effectiveness. The experimental results show that our method significantly outperforms the previous state-of-the-art methods. With an ensemble of seven models, our solution ranks the 1st place on the real-time leaderboard of the MSCOCO image captioning challenge at the time of the writing of this paper.

Modern ICT to support the Operator controlling Complex Systems

Many process control and service operations in productions are carried out in control centers via visual display unit workstations. The operator's tasks often have great relevance for system safety.Modern Information and Communication Technologies (ICT) should support the operator's workflow and their supervisory role. Multimodal output devices with task adequate structures of relevant information, process variables and units intent to improve the situation awareness of the operating staff. Intuitively designed input devices should promote quick responses in time critical situations to prevent loss of control. Mobil Display Screen Equipment can help to improve the communication between operators in control centers and plant operators in the field.In order to support operators optimally, modern ICT should be selected, designed and implemented carefully in the operating concept. Additional it should be adaptable to the operator's needs in a wide variety of situations.Possible risks, requirements and measurements are described using examples of operation errors and better masteries of situations as improvements due to new ICT.Within Risk Assessments of the control system the requirements of ICT are determined to optimize the operators' workplace and workload in order to support the operators' safety behaviour for their own and other employees' occupational safety and health.

Dual-rod pumping approach for tracking error compensation in solar-pumped lasers

We present here a tracking error compensation concept in solar-pumped lasers, by pumping two thin laser rods simultaneously, each rod by half of the solar collector area instead of the mostly used scheme with one thick rod pumped by a full solar collector area. A semicylindrical fused silica lens allows an efficient focusing of the concentrated solar power from the focal spot of the parabolic mirror into the two thin laser rods mounted within two compound parabolic concentrator-semicylindrical pump cavities. The multimode solar laser output power, the threshold pump power, and the slope efficiency of a single-rod scheme, a dual-rod scheme with two laser beams, and a dual-rod scheme with one laser beam are calculated both numerically and analytically, revealing a clear advantage of the dual-rod one laser beam scheme in terms of solar laser output power and threshold pump power. A large improvement in tracking error compensation capacity is numerically attained with this new approach, leading to 2.57 and 3.00 times enhancement in tracking error width at 10% laser power loss in ΔY (altitude) and ΔX (azimuth) errors, respectively, as compared to the most efficient end-side-pumped scheme by the same collection area.

Modality capacity and appropriateness in multimodal display of complex non-semantic information stream

Abstract The design of multimodal output should be based on modality capacity and appropriateness. Previous relevant research had various limitations such as using over-simplified tasks. We proposed a paradigm with virtual reality to explore the capacity and appropriateness of complex non-semantic information stream. In two experiments, fifty-six college students identified location, magnitude, and/or frequency/duration of visual, auditory, and haptic stimuli, and the bi- and tri-modal combinations. We found that (1) for stimuli of 2–4 bits, visual stimuli were identified faster, more accurately, and with lower workload (p values

Observation of flat chaos generation using an optical feedback multi-mode laser with a band-pass filter.

We demonstrate experimentally that flat and broadband chaotic signals can be easily generated by combining a multi-mode laser diode subject to optical feedback with a band-pass filter. Measurements are made of the RF spectra of multi-mode and single-mode outputs from an external cavity Fabry-Perot (FP) semiconductor laser before and after the filtering procedure. In this way it is found that in the chaos regime the low-frequency energy of the single-mode output is enhanced by about 25 dB comparing with that of the multi-mode output. Moreover, the associated 3-dB chaos bandwidth can reach around 6 GHz for the single mode case. Numerical demonstrations show mode competition is the physical origin of the low-frequency enhancement in the single-mode chaotic outputs.

A Tm3+-doped ZrF4-BaF2-YF3-AlF3 glass microsphere laser in the 2.0 μm wavelength region

This work reports a microsphere laser at ∼2.0 μm in a Tm3+-doped ZrF4-BaF2-YF3-AlF3 (ZBYA) fluoride glass. The ZBYA glass microsphere was fabricated by reflowing the tip of a 1.0 mol% Tm3+-doped ZBYA glass fiber with a CO2 laser. By using a fiber taper for input and output coupling in the Tm3+-doped ZBYA microsphere, single and multi-mode laser outputs at around 2.0 μm were observed under 808 nm laser excitation. The radiation lifetime and emission cross-section of Tm3+ ions in ZBYA glass were calculated to be 6.42 ms and 5.86 × 10−21 cm2, respectively. Our results indicate that the Tm3+-doped ZBYA fluoride glass has potential applications for 2.0 μm lasers.

Octave-wide supercontinuum generation of light-carrying orbital angular momentum.

Nonlinear frequency generation of light-carrying orbital angular momentum (OAM), which facilitates realization of on-demand, frequency-diverse optical vortices, would have utility in fields such as super-resolution microscopy, space-division multiplexing and quantum hyper-entanglement. In bulk media, OAM beams primarily differ in spatial phase, so the nonlinear overlap integral for self-phase matched χ(3) processes remains the same across the 4-fold degenerate subspace of beams (formed by different combinations of spin and orbital angular momentum) carrying the same OAM magnitude. This indistinguishable nature of nonlinear coupling implies that supercontinuum generation, which substantially relies on self/cross-phase modulation, and Raman soliton shifting of ultrashort pulses typically results in multimode outputs that do not conserve OAM. Here, using specially designed optical fibers that support OAM modes whose group velocity can be tailored, we demonstrate Raman solitons in OAM modes as well as the first supercontinuum spanning more than an octave (630 nm to 1430 nm), with the entire spectrum in the same polarization as well as OAM state. This is fundamentally possible because spin-orbit interactions in suitably designed fibers lead to large effective index and group velocity splitting of modes, and this helps tailoring nonlinear mode selectivity such that all nonlinearly generated frequencies reside in modes with high spatial mode purity.

Flat chaos generated by optical feedback multi-mode laser with filter

<sec> Optical chaos has a wide range of applications in communications, such as secure communication, high-resolution lidar ranging, optical time domain reflectometer, and high-rate physical random bit generator.</sec><sec> In recent years, external-cavity feedback semiconductor lasers (ECLs) are the most common chaotic laser generation systems due to their characteristics of wide bandwidth, large amplitude, and simple structure, and the dynamic characteristics of chaotic signals have attracted much attention. However, limited by the relaxation oscillation of the laser, the energy of the chaotic signal directly generated by ECL is mainly concentrated at high relaxation oscillation frequency. Thus, the low-frequency component encounters the problem of energy loss.</sec><sec> In practical applications, the signal detection/acquisition device usually responds to a 3-dB low-pass filtering characteristic. Therefore, the available effective bandwidth of the chaotic signal should actually be 3-dB bandwidth. The lack of low-frequency components will limit the energy utilization rate of chaotic signals and restrict the relevant performances of chaotic applications (such as reliability and transmission of chaotic secure communication, randomness and generation rate of physical random bits, measurement accuracy and range of lidar ranging or optical time-domain reflectometer).</sec><sec> In the paper, we propose a broadband chaos generation scheme with simple structure and losing no low-frequency components. Specifically, we experimentally analyze the radio frequency (RF) spectra of the single-mode and the multi-mode output from an optical feedback Fabry-Perot (FP) semiconductor laser after and before filtering. The experimental results show that comparing with the multi-mode chaotic signal, the low-frequency energy of the single-mode chaotic spectrum is enhanced by 25 dB, and the 3-dB bandwidth of the single-mode chaotic signal can reach 6 GHz. Further theoretical analysis demonstrates that the enhancement of low-frequency component in the single-mode chaotic signal is caused by the mode-competing in multi-mode laser. It is concluded that this method can well solve the problem of low-frequency energy loss in conventional optical feedback chaotic systems, and is beneficial to improving the energy utilization rate of chaotic signals, which is of great significance for improving the performance of chaotic secure communication, random bit generation, lidar ranging, optical time domain reflectometer, and other relevant applications. </sec>

Development of Hartigan’s Dip Statistic with Bimodality Coefficient to Assess Multimodality of Distributions

In general, although some random variables such as wind speed, temperature, and load are known to have multimodal distributions, input or output random variables are considered to follow unimodal distributions without assessing the unimodality or multimodality of distributions from samples. In uncertainty analysis, estimating unimodal distribution as multimodal distribution or vice versa can lead to erroneous analysis results. Thus, whether a distribution is unimodal or multimodal must be assessed before the estimation of distributions. In this paper, the bimodality coefficient (BC) and Hartigan’s dip statistic (HDS), which are representative methods for assessing multimodality, are introduced and compared. Then, a combined HDS with BC method is proposed. The proposed method has the advantages of both BC and HDS by using the skewness and kurtosis of samples as well as the dip statistic through a link function between the BC values in BC and significance level in HDS. To verify the performance of the proposed method, statistical simulation tests were conducted to evaluate the multimodality for various unimodal, bimodal, and trimodal models. The implementation of the proposed method to real engineering data is shown through case studies. The results demonstrate that the proposed method is more accurate, robust, and reliable than the BC and original HDS alone.

Homogenization with coherent light illuminated beam shaping diffusers for vision applications: spatial resolution limited by speckle pattern

BackgroundHomogenizing properties of beam shaping diffusers illuminated with coherent laser light was studied with special regard on their use in vision applications.ExperimentalTwo diffusers projecting circular pattern at different scattering angles (Thorlabs Engineered Diffuser™) were illuminated with different spatial intensity distribution (elliptical Gaussian, nearly flat-top and granular multimode fiber output, respectively) collimated beams.ResultsThe intensity distribution measured at high angular resolution with a CMOS sensor revealed the granular (speckle) pattern of the projected light having contrast of nearly 1. The smallest speckle size (highest speckle density) could be obtained at the largest aperture size using nearly flat-top and multimode fiber illumination.ConclusionAs an important measure of the homogeneity for vision applications the apparent local contrast was calculated as the function of the spatial averaging. Although, the homogeneity requirements depend on the actual application, the usability of such diffusers in combination with coherent light sources is in general strongly limited in megapixel resolution imaging applications, unless time-varying speckle averaging methods can be applied.

Experimental observation for multi-mode dynamic output of fiber ring laser based on modulation condition

In order to detect and analyze the complex multi-mode dynamics of fiber ring laser (FRL), in this experiment, based on the heterodyne detection method together with radio-frequency spectrum, the output of FRL intensities on two kinds of modulation condition are synchronously detected and analyzed. From the low dimension to high dimension chaos, the total intensity and multi-mode characters can be synchronously acquired. These experimental results show the relationships between real-time intensity and frequency evolution behaviors about single mode and total mode. Moreover, according to experimental results, the chaotic characteristics and inner relationships of erbium-doped fiber ring laser (EDFRL) output mode dynamic can be analyzed.

Space-time focusing in a highly multimode fiber via optical pulse shaping.

Fields propagating through a highly scattering material will be distorted in both space (intensity speckles) and time (spectral and temporal speckles), inhibiting tasks such as imaging and communication in both the optical and radio frequency regions. In optics, research thus far has demonstrated spatial focusing, image transmission, and short pulse delivery through bulk scattering materials and multimode fibers by taking advantage of spatial wavefront-shaping techniques. Here, we exploit spectral phase shaping for reference-free characterization of spectral and temporal speckle, and space-time focusing of broadband ultrafast pulses distorted by modal dispersion in a multimode fiber. We show that temporal speckle fields at different multimode fiber output locations are uncorrelated and demonstrate the ability to focus a short pulse at a specific output spatial location, while keeping the field at other output locations noise-like, offering opportunities to expand multimode fiber imaging and communication capacity.

An Yb3+-Ho3+ Codoped Glass Microsphere Laser in the $2.0~\mu$ m Wavelength Regions

In this letter, an Yb 3+ -Ho 3+ codoped sol-gel silica microsphere lasing at around 2.0 μm is reported. The gain microsphere is fabricated by overlaying the 1.0 mol% Yb 3+ -0.2 mol% Ho 3+ codoped sol-gel solution on the surface of a pure silica microsphere and is then heated using a CO 2 laser. Using a traditional fiber taper-microsphere coupling method, we observe the single- and multi-mode microsphere laser outputs around 2.0 μm using a 980 nm laser diode as a pump source, with a low threshold pumping power of 14.7 mW. The ability to fabricate sol-gel codoped silica glass microlasers represents a new generation of low-threshold and compact mid-infrared laser sources for use as miniaturized photonic components for a wide range of applications including gas sensing and medical surgery.

Multimode four-wave mixing with a spatially structured pump.

We demonstrate, to the best of our knowledge, a new four-wave mixing geometry based on structured light. By utilizing near-field diffraction through a narrow slit, the pump beam is asymmetrically structured to modify the phase-matching condition, generating multimode output in both the spatial and frequency domains. We show that the frequency parameter enables selection of various spatial-mode outputs, including a twin-beam geometry, which preserves relative intensity squeezing shared between the two beams. The results suggest that the engineering of atomic states via structured light may provide a pathway to a diverse set of quantum resources based on multimode squeezed light.

Radiometric model for coaxial single- and multimode optical emission from double-clad fiber.

Double-clad fibers (DCFs) are versatile waveguides supporting a single-mode core surrounded by a multimode inner cladding. DCFs are increasingly used for multimodal biomedical applications, such as imaging or therapy, for which the core is typically used for coherent illumination and the inner cladding, to support a concurrent modality. Proper optimization is, however, critical to ensure high optical performance and requires accurate modeling of coaxial single- and multimode output beams. In this paper, we present an approach based on geometrical optics and radiometry, which provides a simple and efficient modeling tool for designing and optimizing DCF-based systems. A radiometric definition of single- and multimode output beams in terms of irradiance and radiant intensity allows for the modeling of the energy distribution along the beams' propagation. We confirmed the validity of the model through comparison with experimental measurements and demonstrate the use of the model for optimizing a catheter for concurrent OCT and laser coagulation.

30-GHz Bandwidth With Directly Current-Modulated 980-nm Oxide-Aperture VCSELs

Directly current-modulated 980-nm vertical-cavity surface-emitting lasers (VCSELs) with oxide-aperture-diameters of $1.5~\mu \text{m}$ exhibit a small-signal −3 dB modulation bandwidth of 31 GHz and a single-mode light-output-power of 3 mW with a side-mode-suppression-ratio (SMSR) of 49 dB at 25 °C at a forward bias current of 3 mA. At 85 °C, the maximum bandwidth is about 25 GHz, the peak power is about 2 mW, and the SMSR remains 49 dB. The bandwidth for a 5.5- $\mu \text{m}$ oxide-aperture-diameter VCSEL reaches 26 and 21 GHz at 25 °C and 85 °C, respectively, with corresponding maximum multi-mode optical output power of about 10 and 6 mW.

The 8×10 GHz Receiver Optical Subassembly Based on Silica Hybrid Integration Technology for Data Center Interconnection**Supported by the National High Technology Research and Development Program of China under Grant No 2015AA016902, the National Natural Science Foundation of China under Grant Nos 61435013 and 61405188, and the K. C. Wong Education Foundation.

An 8×10 GHz receiver optical sub-assembly (ROSA) consisting of an 8-channel arrayed waveguide grating (AWG) and an 8-channel PIN photodetector (PD) array is designed and fabricated based on silica hybrid integration technology. Multimode output waveguides in the silica AWG with 2% refractive index difference are used to obtain flat-top spectra. The output waveguide facet is polished to 45° bevel to change the light propagation direction into the mesa-type PIN PD, which simplifies the packaging process. The experimental results show that the single channel 1 dB bandwidth of AWG ranges from 2.12 nm to 3.06 nm, the ROSA responsivity ranges from 0.097 A/W to 0.158 A/W, and the 3 dB bandwidth is up to 11 GHz. It is promising to be applied in the eight-lane WDM transmission system in data center interconnection.

Generation of optical vortices in an integrated optical circuit

In this work, the generation of optical vortices in an optical integrated circuit is numerically demonstrated. The optical vortices with topological charge m = ±1 are obtained by the coherent superposition of the first order modes present in a waveguide with a rectangular cross section, where the phase delay between these two propagating modes is Δφ = ±π/2. The optical integrated circuit consists of an input waveguide continued with a y-splitter. The left and the right arms of the splitter form two coupling regions K1 and K2 with a multimode output waveguide. In each coupling region, the fundamental modes present in the arms of the splitter are selectively coupled into the output waveguide horizontal and vertical first order modes, respectively. We showed by employing the beam propagation method simulations that the fine tuning of the geometrical parameters of the optical circuit makes possible the generation of optical vortices in both transverse electric (TE) and transverse magnetic (TM) modes. Also, we demonstrated that by placing a thermo-optical element on one of the y-splitter arms, it is possible to switch the topological charge of the generated vortex from m = 1 to m = −1.