Hybrid-index-based array configuration optimization for Michelson interferometric imaging.

Array configuration design is a critical issue for a high quality of the snapshot point spread function (PSF) and restored image in Michelson imaging interferometer. In classic design, the optimized configurations usually address the few specifications and single objective, which is unable to balance the requirements of both non-redundancy and sampling distribution. In this paper, we formalize mathematically the composite metric to trade-off the multiple demands of observation, and propose the hybrid-index-based array layout optimization strategy. The simulation results demonstrate that, in comparison with the typical distribution, the optimized array using the proposed optimization framework enables the acquisition of more comprehensive spectrum information while utilizing an equal number of apertures, providing superior imaging quality in different observation situations. Furthermore, the designed optimized array masks and the compared conventional array masks were fabricated and used for our experimental validation, further verifying the feasibility of this strategy. This array configuration optimization framework may not only find applications to Michelson interferometric imaging, but also provide a positive impact on all u-v sampling-based imaging modes, including radio interferometry, magnetic resonance imaging, and photonic integrated interferometric imaging.

Analytical target-agnostic piston sensing for segmented telescopes using sparse redundant baseline pairs.

Piston correction is the key to achieving high resolution of segmented telescopes. Phasing with extended objects is still challenging. In this Letter, we propose an analytical target-agnostic phasing approach using redundant baseline pairs. It is derived that the mixed phase distribution caused by redundant sampling can be decoupled via phase modulation. Then the pistons can be resolved by performing phase cross-correlation to remove the object phase. We validate this theory through simulations and experiments. It does not require additional optical paths and is relatively robust against noise, thus providing a simple, fast, and low-system-complexity solution for piston monitoring of the segmented telescope over the period of imaging complex scenes.

Weak non-line-of-sight target echoes extraction without accumulation.

Non-line-of-sight (NLOS) technology has been rapidly developed in recent years, allowing us to visualize or localize hidden objects by analyzing the returned photons, which is expected to be applied to autonomous driving, field rescue, etc. Due to the laser attenuation and multiple reflections, it is inevitable for future applications to separate the returned extremely weak signal from noise. However, current methods find signals by direct accumulation, causing noise to be accumulated simultaneously and inability of extracting weak targets. Herein, we explore two denoising methods without accumulation to detect the weak target echoes, relying on the temporal correlation feature. In one aspect, we propose a dual-detector method based on software operations to improve the detection ability for weak signals. In the other aspect, we introduce the pipeline method for NLOS target tracking in sequential histograms. Ultimately, we experimentally demonstrated these two methods and extracted the motion trajectory of the hidden object. The results may be useful for practical applications in the future.

Color-Tunable Dual-Mode Organic Afterglow for White-Light Emission and Information Encryption Based on Carbazole Doping.

Dual-mode emission materials, combining phosphorescence and delayed fluorescence, offer promising opportunities for white-light afterglow. However, the delayed fluorescence lifetime is usually significantly shorter than that of phosphorescence, limiting the duration of white-light emission. In this study, a carbazole-based host-guest system that can be activated by both ultraviolet (UV) and visible light is reported to achieve balanced phosphorescence and delayed fluorescence, resulting in a long-lived white-light afterglow. Our study demonstrated the critical role of a charge transfer state in the afterglow mechanism, where the charge separation and recombination process directly determined the lifetime of afterglow. Simultaneously, an efficient reversed intersystem crossing process was obtained between the singlet and triplet charge transfer states, which facilitating the delayed fluorescence properties of host-guest system. As a result, delayed fluorescence lifetime was successfully prolonged to approach that of phosphorescence. This work presents a delayed fluorescence lifetime improvement strategy via doping method to realize durable white-light afterglow.

Hypertelescope with multiplexed fields of view.

Hypertelescope interferometers having many highly diluted sub-apertures are capable of directly imaging, within a narrow field of view, celestial objects at a high resolution thanks to pupil densification. This Letter verifies with OpticStudio modeling the possibility of simultaneously imaging multiple such fields. A strategy of multi-field sampling uses a microlens array to generate multiplexed field channels, where independent active corrections of the tip-tilt and piston are applied for compensating for the off-axis aberrations. Adopting this strategy, we have designed a model of a multi-field hypertelescope with OpticStudio. The reported design expands the observing performance of hypertelescopes for directly imaging multiple sources with very high angular resolution.

Wide-band high-resolution synthetic imaging of a segmented large-scaled lightweight diffractive telescope.

In this Letter, we report a segmented large-scaled lightweight diffractive telescope testbed newly built in our laboratory. The telescope, consisting of one 710-mm-diameter element in the center surrounded by eight 352-mm-diameter elements and a smaller eyepiece of achromatic lenses, can realize wide-band high-resolution imaging of 0.55-0.65 µm. The stitching errors are coarsely corrected by adjusting the motion stage mounted on each element. In particular, an optical synthesis system inserted behind the eyepiece is designed to compensate the residual tip-tilt-piston errors. We present the experimental imaging result of two stitched elements, which is the first successful experimental verification obtained by a practical segmented diffractive telescope to enhance the resolution. Moreover, spatial modulation diversity technology is used to restore the synthetic image so as to improve its quality and contrast.

Piston error correction of sparse aperture systems using the metaheuristic stochastic parallel gradient descent algorithm.

The next generation of optical telescopes will provide high-resolution imaging of celestial objects by using the aperture synthesis technique. To preserve the quality of the image, fast corrections of the pistons among subapertures have to be applied, namely, the co-phasing of the array. The image-based co-phasing method via an optimization procedure has been newly developed. Despite simplicity and strong commonality, when dealing with large piston errors, this correction method is also faced with a problem in which the metric function easily falls into the local convergence, especially in the case of broadband imaging with many subapertures. In this study, an improved stochastic parallel gradient descent (SPGD) algorithm based on heuristic search is proposed for co-phasing, termed the metaheuristic SPGD algorithm. The heuristic research scheme assists the original SPGD algorithm in getting rid of local extrema. By iterations of this algorithm, the synthetic system can be co-phased without any additional instruments and operations. The effectiveness of the proposed algorithm is verified by means of simulation. Given the efficiency and superiority, it is expected that the method proposed in this study may find wide applications in multi-aperture imaging.

Piston sensing of sparse aperture systems with a single broadband image via deep learning.

The pistons of sparse aperture systems need to be controlled within a fraction of a wavelength for the system's optimal imaging performance. In this paper, we demonstrate that deep learning is capable of performing piston sensing with a single wide-band image after appropriate training. Taking the sensing issue as a fitting task, the deep learning-based method utilizes a deep convolutional neural network to learn complex input-output mapping relations between the broadband intensity distributions and corresponding piston values. Given a trained network and one broadband focal intensity image as the input, the piston can be obtained directly and the capture range achieving the coherence length of the broadband light is available. Simulations and experiments demonstrate the validity of the proposed method. Using only in-focused broadband images as the inputs without defocus division and wavelength dispersion, obviously relaxes the optics complexity. In view of the efficiency and superiority, it's expected that the method proposed in this paper may be widely applied in multi-aperture imaging.

An Improved Method of Measuring Wavefront Aberration Based on Image with Machine Learning in Free Space Optical Communication.

In this paper, an improved method of measuring wavefront aberration based on image with machine learning is proposed. This method had better real-time performance and higher estimation accuracy in free space optical communication in cases of strong atmospheric turbulence. We demonstrated that the network we optimized could use the point spread functions (PSFs) at a defocused plane to calculate the corresponding Zernike coefficients accurately. The computation time of the network was about 6-7 ms and the root-mean-square (RMS) wavefront error (WFE) between reconstruction and input was, on average, within 0.1263 waves in the situation of D/r0 = 20 in simulation, where D was the telescope diameter and r0 was the atmospheric coherent length. Adequate simulations and experiments were carried out to indicate the effectiveness and accuracy of the proposed method.

Adaptive piston correction of sparse aperture systems with stochastic parallel gradient descent algorithm.

A phased sparse aperture system provides an economic solution to get high resolution images with less volume and weight. The crucial point of such systems is adaptive correction of piston, that is, a close-loop control aiming at stabilizing the optical path differences within a fraction of the wavelength. In this paper, we present an autonomous phasing approach using stochastic parallel gradient descent algorithm through optimization of image quality. The synthetic system can be phased by iteratively commanding piston actuators without any additional optics. Simulations are first performed to test the validity. Then experimental results based on a binocular telescope testbed are presented, showing that our proposed close-loop control of piston correction doesn't only work with both laser and white-light point sources, but also with an extended object.

Research on high-resolution imaging technology based on light field manipulation for a lenslet-based plenoptic camera.

In this paper, an aberration correction method for an extended target is proposed to solve the problem of the lenslet-based plenoptic camera not imaging clearly under the influence of aberrations. We propose a light field manipulation method to improve performance of the light field imaging system. The principle of this method is that the sub-aperture images extracted from the raw light field image are offset when the light field imaging system is affected by aberrations, and the symmetrical arrangement of the sub-aperture image array is destroyed. By repairing the symmetrical arrangement of the sub-aperture image array, the influence of phase aberrations on the imaging system can be eliminated, and the resolution of the plenoptic camera can be improved. We use an image correlation algorithm to process the sub-aperture images of the plenoptic camera, calculate and compensate each sub-aperture image's displacement caused by aberrations, and restore the symmetrical arrangement of the sub-aperture image array; then, a corrected high-resolution refocused image can be generated. In particular, this method uses only the raw light field information obtained by the plenoptic camera in a single exposure, without adding other hardware devices. Furthermore, it takes the extended target itself as the reference image, so the ideal position need not be calibrated in advance. Also, the parallax information of the sub-aperture images is retained, and the method is simple and easy to use. Numerical simulation and experimental results show that the technology proposed in this paper can work well for high-resolution imaging of a plenoptic camera with phase aberrations. This method can be potentially applied to analyze lens aberration, media-induced image distortion such as water turbulence in underwater imaging, and atmospheric turbulence in remote imaging. It may have important application prospects in the fields of astronomical object detection, remote sensing, etc.

Recent advances in organic thermally activated delayed fluorescence materials.

Organic materials that exhibit thermally activated delayed fluorescence (TADF) are an attractive class of functional materials that have witnessed a booming development in recent years. Since Adachi et al. reported high-performance TADF-OLED devices in 2012, there have been many reports regarding the design and synthesis of new TADF luminogens, which have various molecular structures and are used for different applications. In this review, we summarize and discuss the latest progress concerning this rapidly developing research field, in which the majority of the reported TADF systems are discussed, along with their derived structure-property relationships, TADF mechanisms and applications. We hope that such a review provides a clear outlook of these novel functional materials for a broad range of scientists within different disciplinary areas and attracts more researchers to devote themselves to this interesting research field.

Transient and Persistent Room-Temperature Mechanoluminescence from a White-Light-Emitting AIEgen with Tricolor Emission Switching Triggered by Light.

Persistent luminescence from purely organic materials is basically triggered by light and electricity, which largely confines its practical applications. A purely organic AIEgen exhibits not only persistent photoluminescence, but also transient and persistent room-temperature mechanoluminescence. By simply turning on and off a UV lamp, tricolor emission switching between blue, white, and yellow was achieved. The data from single-crystal structure analysis and theoretical calculation suggest that mechanism of the observed persistent mechanoluminescence (pML) is correlated with the strong spin-orbit coupling of the bromine atom, as well as the formation of H-aggregates and restriction of intramolecular motions in noncentrosymmetric crystal structure. These results outline a fundamental principle for the development of new pML materials, providing an important step forward in expanding the application scope of persistent luminescence.

Alkyl Chain Introduction: In†Situ Solar-Renewable Colorful Organic Mechanoluminescence Materials.

Mechanoluminescence (ML) materials are environmentally friendly and emit light by utilizing mechanical energy. This has been utilized in light sources, displays, bioimaging, and advanced sensors. Organic ML materials are strongly limited to application by in situ unrepeatable ML. Now, in situ solar-renewable organic ML materials can be formed by introducing a soft alkyl chain into an ML unit. For the first time, the ML from these polycrystalline thin films can be iteratively produced by simply recrystallizing the fractured crystal in situ after a contactless exposure to sunlight within a short time (≤60 s). Additionally, their ML color and lifetime can be also easily tuned by doping with organic luminescent dyes. Therefore, large-area sandwich-type organic ML devices can be fabricated, which can be repeatedly used in a colorful piezo-display, visual handwriting monitor, and sensitive optical sensor, showing a lowest pressure threshold for ML of about 5 kPa.

Active sparse aperture imaging using independent transmitter modulation with improved incoherent Fourier ptychographic algorithm.

Optical sparse aperture imaging shows great promise for the next generation of high resolution systems. In this paper, we propose and demonstrate an active sparse aperture imaging approach using independent transmitter modulation to digitally overcome phasing errors, correct aberrations, and further improve resolution. The reported imaging scheme consists of a general sparse aperture system and an active illumination unit, specifically an independent pattern projector. A series of raw images are captured with the projector scanned to illuminate the object. Based on the acquired data set, the improved incoherent Fourier ptychographic algorithm is utilized to reconstruct sparse aperture images with distortions removed and contrast enhanced. Furthermore, thanks to illumination pattern modulation, higher resolution beyond the diffraction limit of the synthetic aperture system is gained as a benefit. Good-quality and higher-resolution sparse aperture imagery obtained by employing our proposed technique in both simulation and experiment demonstrates the effectiveness. The reported approach may provide new insights to address the phasing and image restoration problems of sparse aperture systems in the transmitting path rather than only in the receiving path.

Elucidating the Excited State of Mechanoluminescence in Organic Luminogens with Room-Temperature Phosphorescence.

Two stable, purely organic luminogens exhibit both mechano- (ML) and photoluminescence (PL) with dual fluorescence-phosphorescence emissions at room temperature. Careful analysis of the crystal structures, coupled with theoretical calculations, demonstrate that room-temperature phosphorescence and ML properties are strongly related to molecular packing. In particular, the formation and fracture of molecular dimers with intermolecular charge-transfer properties has a significant effect on intersystem crossing, as well as excited triplet state emissions, in both PL and ML processes.

AIEgen with Fluorescence-Phosphorescence Dual Mechanoluminescence at Room Temperature.

We report the first example of an AIEgen (DPP-BO) with fluorescence-phosphorescence dual emission under mechanical stimulation. By carefully analyzing the crystal structure of DPP-BO, the efficient intermolecular and intramolecular interactions should account for its unique mechanoluminescence (ML) properties, especially the abnormal phosphorescence, as further confirmed by controlled experiments and theoretical calculations for the presence of ISC transitions. These results provide important information for understanding the complex ML process, possibly opening up a new way to study the inherent mechanism of ML by broadening the application of AIEgens.

Synthetic aperture imaging by using spatial modulation diversity technology with stochastic parallel gradient descent algorithm.

In this paper, we propose and demonstrate the synthetic aperture imaging by using spatial modulation diversity technology with stochastic parallel gradient descent (SPGD) algorithm. Instead of creating diversity images by means of focus adjustments, the technology, proposed in this paper, creates diversity images by modulating the transmittance of individual sub-aperture of multi-aperture system, respectively. Specifically, spatial modulation is realized by switching off the transmittance of each sub-aperture with electrical shutters, alternately. Based on these multi diversity images, SPGD algorithm is used for adaptively optimizing the coefficients of Zernike polynomials to reconstruct the real phase distortions of multi-aperture system and to restore the near-diffraction-limited image of object. Numerical simulation and experimental results show that this technology can be used for joint estimation of both pupil aberrations and an high resolution image of the object, successfully. The technology proposed in this paper can have wide applications in segmented and multi-aperture imaging systems.

White-light emission strategy of a single organic compound with aggregation-induced emission and delayed fluorescence properties.

A novel white-light-emitting organic molecule, which consists of carbazolyl- and phenothiazinyl-substituted benzophenone (OPC) and exhibits aggregation-induced emission-delayed fluorescence (AIE-DF) and mechanofluorochromic properties was synthesized. The CIE color coordinates of OPC were directly measured with a non-doped powder, which presented white-emission coordinates (0.33, 0.33) at 244 K to 252 K and (0.35, 0.35) at 298 K. The asymmetric donor-acceptor-donor' (D-A-D') type of OPC exhibits an accurate inherited relationship from dicarbazolyl-substituted benzophenone (O2C, D-A-D) and diphenothiazinyl-substituted benzophenone (O2P, D'-A-D'). By purposefully selecting the two parent molecules, that is, O2C (blue) and O2P (yellow), the white-light emission of OPC can be achieved in a single molecule. This finding provides a feasible molecular strategy to design new AIE-DF white-light-emitting organic molecules.

Isostructural doping for organic persistent mechanoluminescence.

Mechanoluminescence, featuring light emission triggered by mechanical stimuli, holds immense promise for diverse applications. However, most organic Mechanoluminescence materials suffer from short-lived luminescence, limiting their practical applications. Herein, we report isostructural doping as a valuable strategy to address this challenge. By strategically modifying the host matrices with specific functional groups and simultaneously engineering guest molecules with structurally analogous features for isostructural doping, we have successfully achieved diverse multicolor and high-efficiency persistent mechanoluminescence materials with ultralong lifetimes. The underlying persistent mechanoluminescence mechanism and the universality of the isostructural doping strategy are also clearly elucidated and verified. Moreover, stress sensing devices are fabricated to show their promising prospects in high-resolution optical storage, pressure-sensitive displays, and stress monitoring. This work may facilitate the development of highly efficient organic persistent mechanoluminescence materials, expanding the horizons of next-generation smart luminescent technologies.