3D Photonic Nanostructures Research Articles

Near‐Infrared Light‐Driven Three‐Dimensional Soft Photonic Crystals Loaded with Upconversion Nanoparticles

AbstractEndowing advanced functional three‐dimensional (3D) nanostructures with remote and dynamic controllability is currently in the spotlight of soft‐matter photonics research. Herein, the near‐infrared (NIR) light‐driven reversible and dynamic photonic bandgap modulation of a soft photonic crystal, i.e., blue phase liquid crystals (BPLCs) with 3D nanostructures, is demonstrated through the integration of judiciously designed core‐shell upconversion nanoparticles (UCNPs) and a novel axially‐chiral azobenzene‐based molecular photoswitch. The UCNPs exhibit high UV/vis emissions upon irradiations with 808 nm NIR light, and the intensity ratio of UV/vis luminescence can be facilely modulated through changing the excitation power. With the UCNPs as NIR‐to‐UV/vis light nanotransducers, the chiral molecular photoswitch shows reversible photoisomerization upon modulating the 808 nm NIR light intensity. Furthermore, NIR light‐driven BPLCs loaded with the photoswitch and UCNPs are demonstrated, in which the photonic reflection can red‐shift toward a longer wavelength under 808 nm light irradiation with high‐power density and the blue‐shift took place at lower power density with the same wavelength of light. This work may provide new insights into the large‐scale fabrication of 3D photonic nanostructures with tailorable functionalities toward emerging applications of soft‐matter photonics and future integrated communication technologies.

Bioinspired Color-Changing Photonic Polymer Coatings Based on Three-Dimensional Blue Phase Liquid Crystal Networks.

Photonic polymer coatings that can adaptively respond to the constant changes of surrounding environments are of profound significance for diverse applications such as optical sensors, information encryption, and adaptive camouflage. Here, we report the fabrication of humidity-driven color-changing photonic polymer coatings on the basis of judiciously designed hydrogen-bonded three-dimensional (3D) blue phase liquid crystal networks. Thanks to the inherent self-assembled 3D photonic nanostructures and tough covalent bonding between the polymers and substrate surfaces, the resulting polymer coatings are found to exhibit vivid structural colors, and humidity-driven reversible color changes across the visible spectrum of light can be achieved upon breaking the hydrogen bonds and subsequent conversion into a hygroscopic polymer coating. As the proof-of-concept applications, we demonstrate the information encryption, inkjet-printable photonic patterns, bioinspired adaptive camouflage, and colorimetric humidity sensor with such promising humidity-driven color-changing photonic polymer coatings. The results disclosed herein are expected to provide new insights into the development of stimuli-responsive advanced functional materials with tailorable 3D photonic nanostructures toward technological applications ranging from sensing, display, anticounterfeiting, and biomimetic camouflage.

Electrically modulated large range tuning of self-assembled photonic bandgaps in polymer-stabilised blue phases

ABSTRACT Developing 3D photonic nanostructures with stimuli-directed controllability has been a burgeoning but challenging area in the field of optical materials as there are numerous opportunities in next-generation communication systems. In this study, polymer-stabilised blue phase I material systems with self-assembled 3D tunable photonic bandgap (PBG) were prepared by using different acrylate monomers. From the comparison of the electric responsive behaviours, the electrical tunability of the material system was noteworthyly improved by using chiral acrylate monomers. And a reversible electrically modulated large range red shifting of the PBG was achieved through the fabrication of the chiral polymer network. Besides, the optical quality and response time can be improved by increasing the polymerisable chiral monomer concentration.

3D Chiral Photonic Nanostructures Based on Blue‐Phase Liquid Crystals

3D photonic nanostructures with intrinsic chirality have recently entered the research limelight due to their fundamental importance and potential technological applications. Blue‐phase liquid crystals (BPLCs) with chiral cubic nanostructures are an inventive example of 3D chiral photonic nanostructures. The inherently self‐organized 3D chiral nanostructures give rise to a complete photonic bandgap, which results in the selective reflection of circularly polarized light in all three dimensions. Herein, a comprehensive review of the state‐of‐the‐art of BPLCs and their potential applications is presented. First, the history and fundamentals of BPLCs are introduced. Then, the recent endeavors in the design, synthesis, and properties of BPLCs such as lattice orientation control with different techniques, photonic bandgap tuning with external fields, and fabrication of free‐standing BPLC polymer films are summarized. Finally, a discussion of the future challenges and potential applications of BPLCs is provided. It is believed that this review would stimulate innovative ideas for the design and engineering of novel chiral nanostructured materials for advanced photonic systems with tailorable functionalities.

3D Chiral Plasmonic Metamaterials Fabricated by Direct Laser Writing: The Twisted Omega Particle

The plasmonic version of a 3D chiral meta‐atom which consists of a loop‐wire structure, namely the so‐called twisted omega particle, is experimentally realized. The structure is fabricated by direct laser writing and subsequent electroless silver plating, a novel technique capable of producing truly 3D photonic nanostructures. In this case, the metallic wire of finite length supports an electric dipole resonance, whereas the loop acts as a split‐ring resonator which exhibits a magnetic dipole resonance, leading to the separation of right‐handed circularly polarized light and the left‐handed one. The arising optical activity is discussed in terms of a single oscillator model system used classically to describe the generation of natural optical activity in chiral media, and it is shown that the twisted omega particle acts as its exact plasmonic analogue.

High Numerical Aperture Hexagonal Stacked Ring-Based Bidirectional Flexible Polymer Microlens Array.

Flexible imprinted photonic nanostructures that are able to diffract/focus narrow-band light have potential applications in optical lenses, filters, tunable lasers, displays, and biosensing. Nanophotonic structures through holography and roll-to-roll printing may reduce fabrication complexities and expenses and enable mass production. Here, 3D photonic nanostructures of a stacked ring array were imprinted on acrylate polymer (AP) over poly(ethylene terephthalate) (PET) substrate through holography and lift-off processes to create a microlens array (MLA). The surface structure of the array consisted of circular nonostepped pyramids, and repeated patterns were in hexagonal arrangements. Stacked-ring-based MLA (SMLA) on a flexible AP-PET substrate showed efficient bidirectional light focusing and maximum numerical aperture (NA = 0.60) with a reasonable filling factor. The nanostructures produced a well-ordered hexagonally focused diffraction pattern in the far field, and power intensities were measured through angle-resolved experiments. The variation of nanostep dimensions (width and height) and the number of steps resulted in different photonic bandgaps, and the arrays produced distance-dependent narrow-band light focusing. The validation of the SMLA was demonstrated through the text, image, and hologram projection experiments. It is anticipated that imprinted bidirectional SMLA over flexible substrates may find applications in optical systems, displays, and portable sensors.

Liquid‐Crystal Nanostructures: Stimuli‐Directing Self‐Organized 3D Liquid‐Crystalline Nanostructures: From Materials Design to Photonic Applications (Adv. Funct. Mater. 1/2016)

Nature is a fabulous gallery of 3D photonic nanostructures, formed through evolution and natural selection over billions of years. Soft nanotechnology—i.e., exploiting self-organized soft materials in nanotechnology—is emerging as a vibrant field of research in the bottom-up nanofabrication of intelligent, stimuli-driven 3D photonic materials and devices. On page 10, L. Wang and Q. Li provide a glimpse of the advancements in design, fabrication, and applications of self-organized 3D liquid crystalline photonic nanostructures.

Stimuli‐Directing Self‐Organized 3D Liquid‐Crystalline Nanostructures: From Materials Design to Photonic Applications

3D photonic nanostructures with desirable functionalities in the visible light region and beyond have been recently given vast and increasing attentions because of the ability to control or confine electromagnetic waves in all three dimensions. Although substantial progress has been made in fabricating 3D nanostructures by means of lithography and nanotechnology, various bottlenecks still need to be overcome, and developing soft 3D stimuli‐directed nanostructures with tailored properties remains a challenging but exciting work. In this context, soft nanotechnology—i.e., exploiting self‐organized soft materials in nanotechnology—is emerging as a vibrant and burgeoning field of research in the bottom‐up nanofabrication of intelligent stimuli‐driven 3D photonic materials and devices. Liquid‐crystalline materials undoubtedly represent such a marvelous dynamic system that combines the liquid‐like fluidity and crystal‐like ordering from molecular to macroscopic material levels. Importantly, being “soft” makes the materials responsive to various stimuli such as temperature, light, mechanical force, and electric and magnetic fields as well as chemical and electrochemical reactions, resulting in a fascinating tunability of dynamic photonic bandgaps in the 3D nanostructure that provides numerous opportunities in all‐optical integrated circuits and next‐generation communication systems. Here, the development of 3D photonic nanostructures is reviewed, culminating with perspectives for the future scope and challenges of these emerging soft 3D photonic nanostructures towards device applications.

Integrated three-dimensional photonic nanostructures for achieving near-unity solar absorption and superhydrophobicity

In this paper, we proposed and realized 3D photonic nanostructures consisting of ultra-thin graded index antireflective coatings (ARCs) and woodpile photonic crystals. The use of the integrated ARC and photonic crystal structure can achieve broadband, broad-angle near unity solar absorption. The amorphous silicon based photonic nanostructure experimentally shows an average absorption of ∼95% for λ = 400–620 nm over a wide angular acceptance of θ = 0°–60°. Theoretical studies show that a Gallium Arsenide (GaAs) based structure can achieve an average absorption of >95% for λ = 400–870 nm. Furthermore, the use of the slanted SiO2 nanorod ARC surface layer by glancing angle deposition exhibits Cassie-Baxter state wetting, and superhydrophobic surface is obtained with highest water contact angle θCB ∼ 153°. These properties are fundamentally important for achieving maximum solar absorption and surface self-cleaning in thin film solar cell applications.

Three-dimensional photonic crystals fabricated by simultaneous multidirectional etching

We discuss three-dimensional (3D) photonic crystals fabricated by simultaneous multidirectional plasma etching. First, we investigate a method for controlling the ion sheath used in reactive ion etching for obtaining multidirectional etching. We then discuss the fabrication tolerance from an analytical perspective. Based on our results, we demonstrate the fabrication of 3D photonic crystals with thicknesses of 1, 1.5, and 2 lattice periods in the surface-normal direction on single-crystalline silicon wafers, which show high reflectance $(\ensuremath{\sim}100%)$ and low transmittance $(\ensuremath{-}17\phantom{\rule{0.28em}{0ex}}\mathrm{dB})$ at optical communication wavelengths, suggesting the formation of a complete photonic band gap. We reveal that the shape of the etched holes limits the performance of 3D photonic crystals and suggest possible ways to improve the band-gap effect. Moreover, we show that 3D photonic crystals with short lattice constants show high reflectance $(\ensuremath{\sim}80%)$ at visible to near-infrared wavelengths. By investigating the influence of absorption on the characteristics of 3D photonic crystals, we reveal that the reflectance remains as high as 94% in the photonic band-gap range even when the absorption of silicon is taken into account. We find that a unique increase of absorption occurs at several discrete wavelengths below the photonic band gap, suggesting the possibility of manipulating light absorption. These results not only simplify the fabrication of 3D photonic crystals, but also provide a basis for realizing 3D photonic nanostructures that include other materials.

Three-dimensional photonic crystals created by single-step multi-directional plasma etching.

We fabricate 3D photonic nanostructures by simultaneous multi-directional plasma etching. This simple and flexible method is enabled by controlling the ion-sheath in reactive-ion-etching equipment. We realize 3D photonic crystals on single-crystalline silicon wafers and show high reflectance (>95%) and low transmittance (<-15dB) at optical communication wavelengths, suggesting the formation of a complete photonic bandgap. Moreover, our method simply demonstrates Si-based 3D photonic crystals that show the photonic bandgap effect in a shorter wavelength range around 0.6 μm, where further fine structures are required.

Structure, function, and self-assembly of single network gyroid ( I 4 1 32) photonic crystals in butterfly wing scales

Complex three-dimensional biophotonic nanostructures produce the vivid structural colors of many butterfly wing scales, but their exact nanoscale organization is uncertain. We used small angle X-ray scattering (SAXS) on single scales to characterize the 3D photonic nanostructures of five butterfly species from two families (Papilionidae, Lycaenidae). We identify these chitin and air nanostructures as single network gyroid (I4(1)32) photonic crystals. We describe their optical function from SAXS data and photonic band-gap modeling. Butterflies apparently grow these gyroid nanostructures by exploiting the self-organizing physical dynamics of biological lipid-bilayer membranes. These butterfly photonic nanostructures initially develop within scale cells as a core-shell double gyroid (Ia3d), as seen in block-copolymer systems, with a pentacontinuous volume comprised of extracellular space, cell plasma membrane, cellular cytoplasm, smooth endoplasmic reticulum (SER) membrane, and intra-SER lumen. This double gyroid nanostructure is subsequently transformed into a single gyroid network through the deposition of chitin in the extracellular space and the degeneration of the rest of the cell. The butterflies develop the thermodynamically favored double gyroid precursors as a route to the optically more efficient single gyroid nanostructures. Current approaches to photonic crystal engineering also aim to produce single gyroid motifs. The biologically derived photonic nanostructures characterized here may offer a convenient template for producing optical devices based on biomimicry or direct dielectric infiltration.