Local Light Field Research Articles

Local Light Field Control Enables Efficient Quantum Dot Color Conversion Films for Mini‐LED Backlit Displays

AbstractQuantum dot (QD) color conversion films (QD‐CCFs) are used in ultrahigh definition (UHD) Mini‐LED backlit displays due to their narrow band emission and high color purity. However, their poor light conversion efficiency (LCE) leads to greater film thickness and thus high cost. Herein, this study proposes a local light field control strategy to enhance the LCE of QD‐CCFs using high‐refractive BN nanosheets. The LCEs of the green and red QD‐CCFs can increase from 29.9% and 34.8% to 67.4% and 91.0% after adding BN nanosheets, respectively. Combining the experimental data with the finite‐difference time domain (FDTD) simulations, the enhanced LCEs can be attributed to observably increased blue light absorption and improved light extraction efficiency of the light emitted from QDs. The white Mini‐LEDs, prepared by integrating the optimized QD‐CCFs containing BN nanosheets with blue Mini‐LED chips, show a high luminous efficiency of 70.2 lm W−1, a high external quantum efficiency of 36.2%, and a wide color gamut of 96.3% Rec. 2020 standards. This work provides an interesting idea for designing high‐efficiency QD‐CCFs toward low‐cost UHD Mini‐LED backlit displays.

Femtosecond Drift Photocurrents Generated by an Inversely Designed Plasmonic Antenna.

Photocurrents play a crucial role in various applications, including light detection, photovoltaics, and THz radiation generation. Despite the abundance of methods and materials for converting light into electrical signals, the use of metals in this context has been relatively limited. Nanostructures supporting surface plasmons in metals offer precise light manipulation and induce light-driven electron motion. Through the inverse design optimization of a gold nanostructure, we demonstrate enhanced volumetric, unidirectional, intense, and ultrafast photocurrents via a magneto-optical process derived from the inverse Faraday effect. This is achieved through fine-tuning the amplitude, polarization, and gradients in the local light field. The virtually instantaneous process allows dynamic photocurrent modulation by varying optical pulse duration, potentially yielding nanosources of intense, ultrafast, planar magnetic fields and frequency-tunable THz emission. These findings open avenues for ultrafast magnetic material manipulation and hold promise for nanoscale THz spectroscopy.

Generalized Transition Moment and Oscillator Strength for Optimal Control of Excited States Using Near-Field Light.

The near field is a highly localized light field that is present in the vicinity of materials. It holds considerable potential for manipulating molecular excitation through the design of nanostructures. To that end, a simple yet applicable computational method is required. This letter presents an optimization strategy to achieve targeted electronic excitation in molecules using near-field light. The generalized transition moment and oscillator strength based on the multipolar Hamiltonian can incorporate key parameters affecting the near field, including shape, size, and material composition. This calculation helps optimize electronic transitions through manipulation of the aforementioned parameters. The feasibility of the proposed scheme was demonstrated using a scanning tunneling microscopic setup with light, wherein the near field is controlled by varying the tip position in two dimensions. This approach paves the way for further innovations, which may ultimately enable precise control of molecular behavior by using tailored near-field interactions.

Directly printed plasmonic substrates of gold micro-flake array for plasmonically-enhanced infrared absorption-spectroscopic biodetection

Infrared absorption-spectroscopy (IRAS) is an essential tool for identifying molecular species with specific spectral fingerprints and widely used to characterize and identify known or unknown chemical substances in scientific research and industry. Recently, plasmonic substrates that can dramatically enhance local light field have greatly boosted the performance of IRAS technology, which is generally called plasmonically-enhanced infrared absorption-spectroscopy (PEIRAS), for high-sensitivity biochemical detection. However, the fabrication of micro/nano-structures of noble metals, such as gold and silver, is still challenging and costly, which thus hinders the broad use and further development of PEIRAS technologies. Here, we present a precision photoreduction and replacement reaction combined technology to directly print plasmonic substrates of periodic gold micro-flake array for PEIRAS biodetection. Such a periodic gold micro-flake array exhibits a strong plasmonic surface-lattice resonance whose reflection spectra can be precisely tailored to desired wavelength for PEIRAS biodetection. It has been experimentally demonstrated that the directly printed plasmonic substrate of PEIRAS can be utilized to detect bovine serum albumin via IRAS at the limit of concentration level at 10 nM. The additive printing nature of its fabrication technology makes such a plasmonic substrate promising for widespread IRAS biodetection applications.

Tunable reflection coating to reduce exposure power threshold for interference-assisted two-photon polymerization lithography

We proposed a strategy to significantly reduce the exposure power threshold for two-photon lithography on tunable reflection coating substrates. The focused light spot at the photoresist-reflective interface is modulated into a multi-layered distribution, which has an enhanced optical field compared to the incident light. The interference of incident and reflected light at the interface enhances the local light field by 1.6–3.4 times, equivalent to reducing the incident exposure power. The tailored multilayer nanowires fabricated by a single scan and the exposure power modulation mechanism proposed in this study would be of profound importance in the fields of semiconductor electronic devices.

The role of host pigments in coral photobiology

Corals have the ability to synthesize various pigments, responsible for their characteristic vivid coloration. Most coral host pigments are green fluorescent protein (GFP)-like pigments exhibiting diverse spectral properties covering almost the entire visible spectrum, with pigments fluorescing from cyan to red. The type of pigment a coral can synthesize varies inter- and intraspecifically. However, the precise role of host pigments in coral biology has not been fully elucidated. Host pigments have the ability to modify local light fields and could thus contribute to optimizing the light exposure of the photosymbionts. Such fine-tuning of the light microenvironment could enable the holobiont to adapt to broader environmental conditions. Putative mechanisms include energy transfer between host pigments, as well as modulation of their scattering properties via tissue plasticity and granule formation that affect the distribution and organization of host pigments in coral tissue. These mechanisms can enable either photoprotection or photoenhancement depending on the coral’s environment. In this review, we summarize and discuss current knowledge about the link between host pigments and symbiont photosynthesis in reef-building corals, and discuss limitations and challenges of experimental investigation of this connection.

Robust Local Light Field Synthesis via Occlusion-aware Sampling and Deep Visual Feature Fusion

Novel view synthesis has attracted tremendous research attention recently for its applications in virtual reality and immersive telepresence. Rendering a locally immersive light field (LF) based on arbitrary large baseline RGB references is a challenging problem that lacks efficient solutions with existing novel view synthesis techniques. In this work, we aim at truthfully rendering local immersive novel views/LF images based on large baseline LF captures and a single RGB image in the target view. To fully explore the precious information from source LF captures, we propose a novel occlusion-aware source sampler (OSS) module which efficiently transfers the pixels of source views to the target view’s frustum in an occlusion-aware manner. An attention-based deep visual fusion module is proposed to fuse the revealed occluded background content with a preliminary LF into a final refined LF. The proposed source sampling and fusion mechanism not only helps to provide information for occluded regions from varying observation angles, but also proves to be able to effectively enhance the visual rendering quality. Experimental results show that our proposed method is able to render high-quality LF images/novel views with sparse RGB references and outperforms state-of-the-art LF rendering and novel view synthesis methods.

Laser defined and driven bio-inspired soft robots toward complex motion control.

The design and actuation of soft robots are targeted at extreme motion control as well as high functionalization. In spite of robot construction optimized by bio-concepts, its motion system is still hindered by multiple actuator assembly and reprogrammable control for complex motions. Herein, our recent work is summarized and an all-light solution is proposed and demonstrated using graphene-oxide-based soft robots. It will be shown that, with a highly localized light field, lasers can define actuators precisely to form "joints" and facilitate efficient energy storage and release to realize genuine complex motions.

Twisted lattice nanocavity with theoretical quality factor exceeding 200 billion

Simultaneous localization of light to extreme spatial and spectral scales is of high importance for testing fundamental physics and various applications. However, there is a longstanding trade-off between localizing a light field in space and in frequency. Here we discover a new class of twisted lattice nanocavities based on mode locking in momentum space. The twisted lattice nanocavity hosts a strongly localized light field in a 0.048 λ3 mode volume with a quality factor exceeding 2.9 × 1011 (∼250 μs photon lifetime), which presents a record high figure of merit of light localization among all reported optical cavities. Based on the discovery, we have demonstrated silicon-based twisted lattice nanocavities with quality factor over 1 million. Our result provides a powerful platform to study light-matter interaction in extreme conditions for tests of fundamental physics and applications in nanolasing, ultrasensing, nonlinear optics, optomechanics and quantum-optical devices.

Lightwave nano-converging enhancement by an arrayed optical antenna based on metallic nano-cone-tips for CMOS imaging detection

A kind of gold-coated glass nano-cone-tips (GGNCTs) is developed as an arrayed optical antenna for highly receiving and converging incident lightwaves. A local light field enhancement factor (LFEF) of ~ 2 × 104 and maximum light absorption of ~ 98% can be achieved. The near-field lightwave measurements at the wavelength of 633 nm show that the surface net charges over a single GGNCT make a typical dipole oscillation and the energy transmits along the wave vector orientation, thus leading to a strong local light field enhancement. An effective detection method by near-field coupling an arrayed GGNCT and complementary metal–oxide–semiconductor (CMOS) sensor for highly efficient imaging detection is proposed. The lightwave detection at several wavelengths, including typical 473 nm, 532 nm, 671 nm, and 980 nm, shows a notable characteristic that a better capability of the net charge distribution adjusting and localized aggregating can be obtained at the absorption peak of the GGNCT developed and a stronger signal detection achieved. The research lays a foundation for further developing a light detector with an ideal optoelectronic sensitivity and broad spectral suitability, which is based on integrating GGNCTs as an arrayed optical antenna with common sensors.

Excited States of Metal-Adsorbed Dimethyl Disulfide: A TDDFT Study with Cluster Model.

The optical near field refers to a localized light field near a surface that can induce photochemical phenomena such as dipole-forbidden transitions. Recently, the photodissociation of the S–S bond of dimethyl disulfide (DMDS) was investigated using a scanning tunneling microscope with far- and near-field light. This reaction is thought to be initiated by the lowest-energy highest occupied molecular orbital (HOMO) to lowest unoccupied molecular orbital (LUMO) transition of the DMDS molecule under far-field light. In near-field light, photodissociation proceeds at lower photon energies than in far-field light. To gain insight into the underlying mechanism, we theoretically investigated the excited states of DMDS adsorbed on Cu and Ag surfaces modeled by a tetrahedral 20-atom cluster. The frontier orbitals of the molecule were delocalized by the interaction with the metal, resulting in narrowing of the HOMO–LUMO gap energy. The excited-state distribution was analyzed using the Mulliken population analysis, decomposing molecular orbitals into metal and DMDS fragments. The excited states of the intra-DMDS transitions were found over a wider energy range, but at low energies, their oscillator strengths were negligible, which is consistent with the experimental results. Sparse modeling analysis showed that typical electronic transitions differed between the higher and lower excited states. If these low-lying excited states are efficiently excited by near-field light with different selection rules, the S–S bond dissociation reaction can proceed.

Broadband antireflective subwavelength structures for infrared detection

Enhancing infrared window transmittance of zinc sulfide (ZnS) is an effective way to improve the infrared detection imaging quality. In this study, the antireflective subwavelength structure (ASS) is designed and fabricated on ZnS substrate, aiming to suppress surface Fresnel reflection and achieve high transmittance within the far-infrared band. The structure parameters of ASS such as height, period, and fill factor are initially set based on the effective medium approximation theory, and are optimized via the rigorous coupled-wave analysis (RCWA) method. Moreover, the antireflective ASS mechanism is explored by using the local light field selective enhancements in structures for capturing incident photons. In addition, a femtosecond laser Bessel beam is used to experimentally fabricate the designed ASS on the ZnS substrate for obtaining large array height, resulting in transmittance enhancement in the far-infrared region. Ultimately, the broadband and wide-angle ASS with the anti-laser damage properties and hydrophobicity is achieved on the optical window. Hence, the clarity of the infrared image captured by the infrared detection system is improved.

Optically controlled silicene and germanene transistors driven by spin-bias

The transistor is the core unit of digital integrated circuits, and its performance and integration are the main determinants of chip performance. With the continuous progress of nano-manufacturing technology and process, high power and heat consumption have become a major problem restricting the development of integrated circuits. Using topological insulators instead of traditional semiconductors, and the spin and valley degrees of freedom instead of charge as information carriers, to design and fabricate transistors, and the use of optical interconnections to replace metal interconnections between functional units, are effective solutions of the thermal power consumption problem of nano-integrated circuits. Based on the two-dimensional topological insulators-silicene and germanene, we theoretically propose a kind of optically controlled transistor suitable for spin bias. The effects of off-resonant circularly polarized light on the output currents of silicene and germanene transistors are calculated by using the non-equilibrium Green's function method. It is shown that the topological properties of silicene (germanene) and the output characteristics of drain current are controlled by the chirality and intensity of incident light. Under the coaction of weak left circularly polarized light and spin bias, the silicene transistors output pure spin current and fully polarized spin-up current. Under the action of strong field, the phase transition of the edge state of the silicene forms a band gap, the transistor is cut off, and the output current is almost zero. Different from the silicene transistor, the germanene transistor can obtain stable pure spin current under a weak light field, and output 100% polarized spin-down current under a strong field. By simultaneously applying off-resonant circularly polarized light of different chirality to the central device region, the germanene transistor can be turned off effectively by using the edge state phase transition induced by the polarized light field and the energy band mismatch caused by the local light field. The output poles of spin-dependent currents are almost equal for silicene and germanene transistors in the ON state, however, the breakdown voltage of the germanene transistor is significantly higher than that of the silicene transistor, and optically controlled germanene transistor can maintain effective operation at higher temperatures.

Cooperative Light-Field Image Super-Resolution Based on Multi-Modality Embedding and Fusion With Frequency Attention

Light field (LF) imaging is an advanced visual perception system, which can record the intensity and direction information of light rays and provide multi-viewpoint images from a single capture. However, there is a trade-off between spatial and angular resolutions due to the restricted sensor size, which limits the wide applications of LF cameras. To address this problem, we propose a cooperative network to super-resolve LF sub-aperture images based on the multi-modality fusion. Specifically, in order to fully explore the LF information, we adopt various modalities and extract corresponding features to emphasise diverse LF characteristics. Then, we design a multi-scale fusion module to effectively integrate global and local LF features and apply frequency-aware attention mechanism to adaptively reinforce fused features. Extensive experiments demonstrate the superiority of our method on both qualitative and quantitative evaluations, with competitive execution efficiency.

Directional light scattering by germanium trimer and its metasurface structures under the substrate effects

Considering germanium (Ge) material with one of the highest refractive index and semi-metal properties, the light scattering properties of Ge trimer and its metasurface structures are studied theoretically in this paper. In contrast to other dielectric materials, for which the magnetic-type resonance is commonly dominant, Ge has a strong electric-type resonance due to its semi-metal properties, which can be seen in the visible and near-infrared spectral range. The influence of the unique feature on the Fano line shapes can be reflected in the scattering spectra. Simultaneously, taking into account the substrate effects, we show that the behavior of the light scattering anisotropy exhibits a big difference in the presence of the different substrates, which can be manipulated to some extent. The results can provide a feasible way to control the “hot spots” in the local light field. Our work in this paper shows that Ge trimers as an excellent candidate can be applied to enhanced spectroscopy, directional sources, and other nanometer photonic devices, as well as on metasurface structures.

Stacked Dual-Band Quantum Well Infrared Photodetector Based on Double-Layer Gold Disk Enhanced Local Light Field.

We propose a stacked dual-band quantum well infrared photodetector (QWIP) integrated with a double-layer gold disk. Two 10-period quantum wells (QW) operating at different wavelengths are stacked together, and gold nano-disks are integrated on their respective surfaces. Numerical calculations by finite difference time domain (FDTD) showed that the best enhancement can be achieved at 13.2 and 11.0 µm. By integrating two metal disks, two plasmon microcavity structures can be formed with the substrate to excite localized surface plasmons (LSP) so that the vertically incident infrared light can be converted into electric field components perpendicular to the growth direction of the quantum well (EZ). The EZ electric field component can be enhanced up to 20 times compared to the incident light, and it is four times that of the traditional two-dimensional hole array (2DHA) grating. We calculated the enhancement factor and coupling efficiency of the device in the active region of the quantum well. The enhancement factor of the active region of the quantum well on the top layer remains above 25 at the wavelength of 13.2 μm, and the enhancement factor can reach a maximum of 45. Under this condition, the coupling efficiency of the device reaches 2800%. At the wavelength of 11.0 μm, the enhancement factor of the active region of the quantum well at the bottom is maintained above 6, and the maximum can reach about 16, and the coupling efficiency of the device reaches 800%. We also optimized the structural parameters and explored the influence of structural changes on the coupling efficiency. When the radius (r1, r2) of the two metal disks increases, the maximum coupling efficiency will be red-shifted as the wavelength increases. The double-layer gold disk structure we designed greatly enhances the infrared coupling of the two quantum well layers working at different wavelengths in the dual-band quantum well infrared photodetector. The structure we designed can be used in stacked dual-band quantum well infrared photodetectors, and the active regions of quantum wells working at two wavelengths can enhance the photoelectric coupling, and the enhancement effect is significant. Compared with the traditional optical coupling structure, the structure we proposed is simpler in process and has a more significant enhancement effect, which can meet the requirements of working in complex environments such as firefighting, night vision, and medical treatment.

Fast method for high-resolution holographic 3D display with white light as illumination

In this research, we propose a fast-computational light field image encoding method for a white light high-resolution full-parallax holographic 3D display and full-color rainbow holographic 3D display. With this method, a novel priority-based sequential rendering is used to improve the computation speed. The local visible 3D data is rendered at a higher priority and then used for rendering multiple local element light field images (EIs) at the holographic plane with the corresponding pinhole array behind the holographic plane. The EIs are independently coded as hogels by multiplying the corresponding phase function without using computation-intensive fast Fourier transform. This parallel computation method is implemented for both a full-parallax holographic 3D display and full-color rainbow holographic 3D display. An ultra high-resolution of a full-parallax hologram and a full-color rainbow hologram both at the resolution of 200 000 × 200 000 pixels only cost 14 min and 78 min, respectively. Our experimental results have also shown the effectiveness of the proposed high-resolution 3D display method.

Stable directional emission in active optical waveguides shielding external environmental influences.

The skillful confinement of light brought by the composite waveguide structure has shown great possibilities in the development of photonic devices. It has greatly expanded the application range of an on-chip system in dark-field imaging and confined the laser when containing an active medium. Here we experimentally proved a stable directional emission in an active waveguide composed of metal and photonic crystal, which is almost completely unaffected by the external environment and different from the common local light field that is seriously affected by the structure. When the refractive index of samples on the surface layer changes, it can ensure the constant emission intensity of the internal mode, while still retaining the external environmental sensitivity of the surface mode. It can also be used for imaging and sensing as a functional slide. This research of chip-based directional emission is very promising for various applications including quantitative detection of biological imaging, coupled emission intensity sensing, portable imaging equipment, and tunable micro lasers.

LiNbO3 waveguide with embedded Ag nanowire and 3L MoS2 for strong light confinement and ultra-long propagation length in the visible spectral range.

A vertical slot LiNbO3 waveguide with an Ag nanowire and 3L MoS2 embedded in the low-refractive index slot region is proposed for the purpose of improving light confinement. We find that the proposed waveguide has a novel dielectric based plasmonic mode, where local light field is enhanced by the Ag nanowire. The mode exhibits an extremely large figure of merit (FoM) of 6.5×106, one order of magnitude larger than that the largest FoM of any plasmonic waveguide reported in the literature to date. The waveguide also has an extremely long propagation length of 84 cm in the visible wavelength at 680 nm. Furthermore, the waveguide has a low sub-micro bending loss and can be directly connected to all-dielectric waveguides with an extremely low coupling loss. The proposed vertical slot LiNbO3 waveguide is a promising candidate for the realization of ultrahigh integration density tunable circuits in the visible spectral range.

Ultrafast laser-inscribed nanogratings in sapphire for geometric phase elements.

We systematically studied femtosecond laser-inscribed self-organized nanogratings and geometric phase elements such as a polarization diffraction focusing lens and Q-plate in sapphire crystal. Besides the void structures observed in the focus, nanogratings with periods of 150~300 nm were observed, depending on a nanoslit that took the role of a seeding effect by localized light field enhancement. The non-polarized refractive index change and birefringence were measured with values around 1∼2×10-3 and 6×10-4, respectively. Based on the laser-inscribed form birefringence, a geometric phase lens and Q-plate were successfully demonstrated in sapphire with high imaging and a focusing effect. We expect that our findings may promote the understanding of laser-induced nanogratings in bulk and potential applications in geometric phase elements.