Optical Memory Effect Research Articles

Surface Modification of Nickel Oxide (II) Thin Films Obtained by Gas-Phase Deposition

The technology of producing stable electrochromic anode nanocomposite thin film coatings based on nickel oxide (II) has been developed, which are used as active layers for modulating light flux in the manufacture of various technical devices. The method involves introduction of carbon nanoparticles (carbon-containing particles) into outer layers of nickel oxide (II) thin films obtained by gas-phase deposition under conditions of cathodic polarization in potentiostatic mode in aqueous media containing water-soluble hydroxylated fullerene derivatives - fullerenol С60(ОН)24, without change of their optical density in the initial state. The technology of the method realization allows to effectively change electrochromic properties of nickel oxide (II) thin films and to obtain a nanocomposite, which is a matrix of a thin layer of nickel oxide (II), doped with carbon nanoparticles, with increased contrast and having the ability to maintain a colored state after switching off polarization under open chain conditions for a long time without energy consumption in solution and in air, i.e., characterized by an “optical memory effect”.

Multi-target object scattering imaging with intensity correlation of structured illumination.

Imaging through scattering layers based on the optical memory effect (OME) concept has been widely investigated in recent years. Among many scattering scenarios, it is very important to recover hidden targets with proper spatial distribution in the scene where multiple targets out of the OME range exist. In this Letter, we put forward a method for multi-target object scattering imaging. With the help of intensity correlation between the structured illumination patterns and recorded speckle images, the relative position of all hidden targets can be obtained and the movement of the targets within the OME range can be tracked. We experimentally implement scattering imaging with 16 targets and the motion tracking of them. Our results present a significant advance in a large field of view scattering imaging with multiple targets.

Speckle autocorrelation separation for multi-target scattering imaging.

Imaging through scattering media remains a big challenge in optics while the single-shot non-invasive speckle autocorrelation technique (SAT) is well-known as a promising way to handle it. However, it usually cannot recover a large-scale target or multiple isolated small ones due to the limited effective range of the optical memory effect (OME). In this paper, we propose a multi-target scattering imaging scheme by combining the traditional SA algorithm with a Deep Learning (DL) strategy. The basic idea is to extract each autocorrelation component of every target from the autocorrelation result of a mixed speckle using a suitable DL method. Once we get all the expected autocorrelation components, a typical phase retrieval algorithm (PRA) could be applied to reveal the shapes of all those corresponding small targets. In our experimental demonstration, up to five isolated targets are successfully recovered.

Temperature-Dependent Electrochromic Devices for Energy-Saving Dual-Mode Displays.

Electrochromic (EC) devices show promising prospects with the increasing demand for energy-efficient and sustainable technologies. Multifunctionality integration is an inevitable characteristic for EC devices to adapt to changing environments. Herein, a dual-mode temperature-dependent EC device is demonstrated for the first time. Combined with the transparent PVA/EG-ZnCl2 organohydrogel electrolyte, the devices exhibit good EC performances over a wide temperature range (-40 to 40 °C). The evolutions of ion/electron transport kinetics-related indicators with temperature are further explored and simulated to reveal the mechanism of the temperature dependence of EC devices. Significantly, the optimized tungsten oxide-based EC device shows high performances at the extremely low temperature of -40 °C with a large transmittance modulation (80.8% @660 nm) and outstanding optical memory effects (97.3% retention of the initial transmittance modulation after 32 h) without electrical energy consumption. Furthermore, with a perovskite quantum dot photoluminescence film serving as the backlight, the device can switch display modes between emissive and reflective to realize its functionality in bright or dark conditions. This work provides a broad application prospect for EC devices in diverse environments of light (bright/dark) and temperature (hot/cold).

Optical memory effect of excised cataractous human crystalline lenses.

Cataracts increase the amount of scattered light in the crystalline lens producing low-contrast retinal images and causing vision impairment. The Optical Memory Effect is a wave correlation of coherent fields, which can enable imaging through scattering media. In this work, we characterize the scattering properties of excised human crystalline lenses by measuring their optical memory effect and other objective scattering parameters, finding the relationship between them. This work has the potential to help fundus imaging techniques through cataracts as well as the non-invasive correction of vision through cataracts.

Spectra-separated depth-of-field extended fluorescence imaging through scattering media using speckle deconvolution

Over the last decade, many methods have been proposed to achieve optical imaging through scattering media. Among them, speckle deconvolution utilizing the optical memory effect of the medium is widely employed due to its advantages in imaging speed and relatively simpler setup. However, practical applications of speckle deconvolution method are rarely demonstrated as most of the existing systems are based on transmission geometry to ensure direct incoherent illumination and easy detection. Here we propose an imaging system in reflection configuration that is able to retrieve the hidden fluorescent object behind a thin scattering media by speckle deconvolution. The object speckle pattern and speckle pattern from a point source (point spread function of the system, PSF) are spectrally separated to facilitate non-invasive image acquisitions. It is shown that, to reconstruct object faithfully, spectral de-correlation and chromatic aberration induced depth de-correlation between the object speckle pattern and the PSF have to be compensated. Speckle correlation is employed to characterize the depth-of-field (DOF) range in this reflection imaging system. Within the DOF, focus and defocus effects in the reconstructed objects are observed when rescaling the PSF onto different axial planes. Beyond the DOF, hidden objects that originally fail in reconstruction can be retrieved by PSF stacking and PSF rescaling. The proposed approach is potentially to find wide applications in biomedical imaging, ranging from deep tissue fluorescence microscopy to small animal imaging.

Low-Cost Fabrication of High-Performance Fluorinated Polythiophene-Based Vis–NIR Electrochromic Devices toward Deformable Display and Camouflage

Flexible electrochromic devices (FECDs) are extensively used in smart windows, deformable electronic displays, and wearable electronics. However, it remains very challenging to fabricate low-cost yet high-performance visible–near-infrared (vis–NIR) FECDs. In this work, we overcome this hurdle by developing a fluorinated polythiophene derivative with superior overall electrochromic performance and simple electropolymerization patterning. Fluorophenyl-modified polythiophene (band gap: 1.74 eV) can be readily synthesized via a one-step Grignard coupling with a high yield of >90% together with successive low-potential electropolymerization at 1.0 V vs Ag/AgCl. The intermolecular hydrogen bonding from the fluorine substitution of polythiophene backbones allows the facile electrodeposition of free-standing polymer films with a compact morphology and also leads to mechanical strength and electrical conductivity enhancement. Interestingly, such polymer films exhibit intriguing overall electrochromic performances with reversible color changes between deep red and light green upon doping/dedoping, including high optical contrast throughout the NIR region (max. 80% at 1600 nm), fast response time (0.93 s), high coloration efficiency (up to 752 cm2 C–1), outstanding stability against cycling (<3% reduction after 5,000 cycles), and excellent optical memory effect. The fabricated FECDs by electropolymerization patterning of such polymers display robust mechanical stability (<5% decay in optical contrast after 5,000 bending cycles with a bending radius of 1 cm) under a low driving voltage (0.85 V). We further demonstrate the applications of such patterned electrochromic devices toward deformable displays, color-changing electronic on-skin tattoos, and infrared camouflage with stable color-switching and robust mechanical properties.

Displacement-sensible imaging through unknown scattering media via physics-aware learning

Imaging through unstable scattering scenes is a challenging task and the focus of attention. More computational techniques and optimization methods have been introduced in objects recovery hidden behind opaque scattering media. A combination of the optical memory effect (OME) prior and deep learning (DL) has been demonstrated in scalable imaging through unknown diffusers with high fidelity. Here, a displacement-sensible imaging method is proposed to reconstruct the hidden objects with unseen depth-of-field (DOF) positions, and the reconstructed objects with different displacements are aligned with the practical imaging size. Related physics priors to DOF are excavated by utilizing the speckle-correlation magnification and developing a flexible DL framework to recover the objects with variable DOF positions. This flexible physics-aware learning approach gives a heuristic to complex imaging problems with specific application scenes.

Scatter imaging with super-memory effect based on adaptive β-parameter hybrid input-output algorithm-assisted estimation of point spread function

It is of great significance to realize the imaging of the target behind the scattering medium, which is often limited by the optical memory effect range. In this paper, a non-invasive super-memory effect scattering imaging method based on adaptive β-parameter hybrid input-output (APHIO) algorithm-assisted point spread function (PSF) estimation is proposed. An iterative algorithm APHIO is designed to use the speckle autocorrelation region to constrain the iterative region and optimize the value of the parameter β in the traditional HIO algorithm. Besides, the estimated PSF of the imaging system is combined with a new scanning method to better reconstruct the target object with super-memory effect range. The results show that the APHIO algorithm has the characteristics of faster convergence and more stable reconstruction quality than the traditional HIO algorithm. The overall imaging framework has a good performance in the reconstruction efficiency of the target with super-memory effect range.

Optical Memory Effect of excised cataractous human crystalline lenses

Optical Memory Effect of excised cataractous human crystalline lenses

Electrochromic devices constructed with water-in-salt electrolyte enabling energy-saving and prolonged optical memory effect

Electrochromism, a promising energy conversion technology, has shown enormous prospects in various energy-efficient applications. The novel Zn2+ based aqueous electrochromic system exhibits self-coloration and large transmittance modulation, while the performance is stagnated by the limited bleaching voltage causing poor kinetics of the reaction. To clear the obstacles of trapped zinc ions and short lifetime, the emerging water-in-salt (WIS) electrolytes of Zn2+ were introduced into tungsten oxide-based electrochromic devices for the first time. The ZnCl2 WIS electrolyte leads to an expanded electrochemical stability window up to 2.4 V by suppressing the electrolysis of water molecules. The electrochromic device with ZnCl2 WIS electrolyte shows enhanced performance of large transmittance modulation of 64% at 660 nm, a short response time (4.8/3.6 s for coloring/ bleaching), and high cyclic stability when compared with that of 2 M ZnCl2 aqueous electrolyte. The enhanced performance is further revealed by the theoretical analyses and numerical simulation of the ion transportation kinetics in the electrochromic layer. Moreover, a patterned electrochromic display is fabricated by a simple brush-painting method. The display utilizing ZnCl2 WIS electrolyte yields a prolonged optical memory effect compared to that with 2 M ZnCl2, where the content of this display is still visible even after three days without external energy consumption. This work presents good feasibility for electrolyte design strategy and provides an attractive electrolyte candidate for high-performance electrochromic applications.

Large field-of-view non-invasive imaging through scattering layers using fluctuating random illumination

Non-invasive optical imaging techniques are essential diagnostic tools in many fields. Although various recent methods have been proposed to utilize and control light in multiple scattering media, non-invasive optical imaging through and inside scattering layers across a large field of view remains elusive due to the physical limits set by the optical memory effect, especially without wavefront shaping techniques. Here, we demonstrate an approach that enables non-invasive fluorescence imaging behind scattering layers with field-of-views extending well beyond the optical memory effect. The method consists in demixing the speckle patterns emitted by a fluorescent object under variable unknown random illumination, using matrix factorization and a novel fingerprint-based reconstruction. Experimental validation shows the efficiency and robustness of the method with various fluorescent samples, covering a field of view up to three times the optical memory effect range. Our non-invasive imaging technique is simple, neither requires a spatial light modulator nor a guide star, and can be generalized to a wide range of incoherent contrast mechanisms and illumination schemes.

Development of a Photonic Switch via Electro-Capillarity-Induced Water Penetration Across a 10-nm Gap.

With narrow and dense nanoarchitectures increasingly adopted to improve optical functionality, achieving the complete wetting of photonic devices is required when aiming at underwater molecule detection over the water-repellent optical materials. Despite continuous advances in photonic applications, real-time monitoring of nanoscale wetting transitions across nanostructures with 10-nm gaps, the distance at which photonic performance is maximized, remains a chronic hurdle when attempting to quantify the water influx and molecules therein. For this reason, the present study develops a photonic switch that transforms the wetting transition into perceivable color changes using a liquid-permeable Fabry-Perot resonator. Electro-capillary-induced Cassie-to-Wenzel transitions produce an optical memory effect in the photonic switch, as confirmed by surface-energy analysis, simulations, and an experimental demonstration. The results show that controlling the wetting behavior using the proposed photonic switch is a promising strategy for the integration of aqueous media with photonic hotspots in plasmonic nanostructures such as biochemical sensors.

Non-invasive imaging through scattering medium beyond the memory effect via polarization-modulation

The phenomenon of light scattering has brought challenges to many fields. In recent years, a novel method based on speckle-correlation has been proposed to look through scattering medium. However, the field of view (FOV) of this method is limited by the angular range of the optical memory effect (OME). In this paper, a polarization modulation-based method is proposed to look through the scattering medium beyond the OME range. This method can achieve single-shot non-invasive looking through multilayer scattering medium by using a polarization camera. Targets beyond the 4 times OME range is recovered by a single shot and a larger one also can be restored by moving the camera to collect the light signal. Unlike other methods that aim at imaging beyond OME, this method can reconstruct targets without reference points. The proposed method has no restriction on the target distribution, and both a single target or two separate targets can be recovered. The effectiveness of the method is verified through experiments.

Edge memory effect for hidden object tracking

Tracking objects through a scattering medium is highly desirable. As many recent advances have shown, non-invasive imaging and tracking in real-time can be achieved by utilizing optical memory effect for speckle correlations. Limited by the memory effect range, this method however works only for tiny objects, which reduces its popularity in tracking applications where the object is sizable but only its trajectory, not its image, is important. In this work, we show that the difference of speckle images is still correlated even when the moving object’s size is beyond the memory effect range. We have experimentally demonstrated the successful tracking of the hidden moving object, with its sizes exceeded the memory effect range. Our proposed technique requires a standard camera only, with no need to adopt other hardware techniques such as wavefront shaping, laser illuminated detection, or interferometric detection, hence is appealing for hidden object tracking in real-world applications.

Multi-Spectral Scattering Imaging Method Based on Optical Memory Effect

Multi-Spectral Scattering Imaging Method Based on Optical Memory Effect

Electrochromic Devices Constructed with Water-in-Salt Electrolyte Enabling Energy-Saving and Prolonged Optical Memory Effect

Electrochromic Devices Constructed with Water-in-Salt Electrolyte Enabling Energy-Saving and Prolonged Optical Memory Effect

How to Build the “Optical Inverse” of a Multimode Fibre

When light propagates through multimode optical fibres (MMFs), the spatial information it carries is scrambled. Wavefront shaping reverses this scrambling, typically one spatial mode at a time—enabling deployment of MMFs as ultrathin microendoscopes. Here, we go beyond sequential wavefront shaping by showing how to simultaneously unscramble all spatial modes emerging from an MMF in parallel. We introduce a passive multiple-scattering element—crafted through the process of inverse design—that is complementary to an MMF and undoes its optical effects. This “optical inverter” makes possible single-shot widefield imaging and super-resolution imaging through MMFs. Our design consists of a cascade of diffractive elements, and can be understood from the perspective of both multi-plane light conversion, and as a physically inspired diffractive neural network. This physical architecture outperforms state-of-the-art electronic neural networks tasked with unscrambling light, as it preserves the phase and coherence information of optical signals flowing through it. We show, in numerical simulations, how to efficiently sort and tune the relative phase of up to ~ 400 step-index fibre modes, reforming incoherent images of scenes at arbitrary distances from the fibre facet. Our optical inverter can dynamically adapt to see through experimentally realistic flexible fibres—made possible by moulding optical memory effects into its design. The scheme is based on current fabrication technology so could be realised in the near future. Beyond imaging, these concepts open up a range of new avenues for optical multiplexing, communications, and computation in the realms of classical and quantum photonics.

Scalable Inkjet Printing of Electrochromic Smart Windows for Building Energy Modulation

Electrochromic smart windows are promising for green buildings due to energy efficiency, long optical memory effect, and tunable optical transmission. However, their wide application in buildings is impeded by challenges in scalability, cost‐effectiveness, and limited optical contrast. Quantitative field study of energy savings enabled by electrochromic smart windows in buildings is also lacking. Herein, with the established inkjet printing procedures, electrochromic smart windows (900 cm2) are fabricated. With large optical contrast (≈60%), fast switching kinetics (tc = 43 s, tb = 70 s), and long optical memory retention (transmittance &lt;10% for 7 h), when installed onto the outdoor testbed, these electrochromic smart windows can effectively reduce the internal temperature, especially in summer tropical weather. The energy savings brought by electrochromic smart windows are found to be higher in sunny days than in rainy days. Specifically in a sunny day, the heat gain reduction can reach 42.3%, and for a comfortable targeted indoor temperature of 25 °C, the cooling load savings can be 28.9% compared to regular double‐glazing units‐based reference testbed. This study demonstrates the scalability of inkjet printing technique for fabricating large‐area electrochromic devices and the substantial energy savings obtained from testbed results.

Noninvasive imaging of two isolated objects through a thin scattering medium beyond the 3D optical memory effect by speckle-based difference strategy.

The shape of two objects hidden behind a thin scattering medium is retrieved by the presented method. One of the two objects keeps stationary, while the other one is supposed to be gradually moving, and the Euclidean distance between them is always beyond the range of the 3D optical memory effect. We capture two speckle patterns to image the two isolated objects by using a developed speckle-differential-based strategy and the traditional speckle autocorrelation technique. The feasibility of our method is demonstrated by theoretical analysis and a set of experiments.