Silicon photonics will provide low-cost, high-bandwidth and compact optical components for a wide range of applications in optical communications and interconnects. One of the cited key advantages is ...the capability of wavelength-division multiplexing (WDM). However, the nature of high-index contrast of silicon photonic devices leads to significant challenges when implementing on-chip WDM filters, which is one of the key components in WDM circuits. In this paper, we review several demonstrated silicon photonic WDM circuits based on monolithically integrated silicon nitride (SiN) arrayed-waveguide gratings (AWGs) and thermally tunable silicon microring filters. The use of SiN waveguides with lower index contrast than silicon waveguides enables the realization of high-performance AWGs. Meanwhile, they can evanescently couple to silicon waveguides with high efficiency. The thermally tunable silicon microrings can be used as modulators and wavelength (de)multiplexing filters to implement versatile WDM circuits. Reconfigurability of channel spacing and central wavelengths is achieved by individual tuning of the rings. In this paper, we review silicon photonic circuits for multiple-channel modulators, polarization-insensitive WDM receiver, and variable optical attenuators with multiplexer.
Artificial self‐assembly systems typically exhibit limited capability in creating nature‐inspired complex materials with advanced functionalities. Here, an effective co‐assembly strategy is ...demonstrated for the facile creation of complex photonic structures with intriguing light reflections. Two different lipophilic and amphiphilic bottlebrush block copolymers (BCPs) are placed within shrinking droplets to enable a cooperative working mechanism of microphase segregation and organized spontaneous emulsification, respectively. Layer assemblies of the lipophilic BCP and uniform water nanodroplets stabilized by the bottlebrush surfactant are both generated, and co‐assembled into a bridged lamellar structure with the alternating arrangement of layers and closely packed nanodroplet arrays. Janus microspheres with diverse dual optical characteristics are successfully fabricated, and reflected wavelengths of light are highly tunable simply by changing the formulation or molecular weight of BCP.
A new complex photonic structure, bridged lamellae, with intriguing color reflections is successfully fabricated through well‐controlled co‐assembly of lipophilic and amphiphilic bottlebrush block copolymers within shrinking droplets. Self‐assembled Janus microspheres with precisely tunable dual light reflections are facilely obtained through the manipulation of the co‐assembly at a molecular level.
Photonic materials with angular‐independent structural color are highly desirable because they offer the broad viewing angles required for application as colorants in paints, cosmetics, textiles, or ...displays. However, they are challenging to fabricate as they require isotropic nanoscale architectures with only short‐range correlation. Here, porous microparticles with such a structure are produced in a single, scalable step from an amphiphilic bottlebrush block copolymer. This is achieved by exploiting a novel “controlled micellization” self‐assembly mechanism within an emulsified toluene‐in‐water droplet. By restricting water permeation through the droplet interface, the size of the pores can be precisely addressed, resulting in structurally colored pigments. Furthermore, the reflected color can be tuned to reflect across the full visible spectrum using only a single polymer (Mn = 290 kDa) by altering the initial emulsification conditions. Such “photonic pigments” have several key advantages over their crystalline analogues, as they provide isotropic structural coloration that suppresses iridescence and improves color purity without the need for either refractive index matching or the inclusion of a broadband absorber.
Photonic microparticles are produced in a single, scalable step from an amphiphilic, low‐molecular‐weight bottlebrush block copolymer. By controlling the formation, swelling, and subsequent self‐assembly of giant reverse micelles within an emulsified toluene‐in‐water droplet, a highly porous structure with short‐range correlation is produced. This isotropic inverse photonic architecture allows for a full spectrum of angular‐independent, structurally colored pigments.
Photonic balls can be facilely obtained through interfacial self‐assembly of amphiphilic bottlebrush block polymers (BBCPs) within a water‐in‐oil‐in‐water (w/o/w) multiple emulsion system, and ...polystyrene (PS) has been employed as the skeleton of the balls showing no responsive properties. Here, the design and synthesis of core‐shell BBCPs are demonstrated with a poly(tert‐butyl acrylate)‐block‐polystyrene (PtBA‐b‐PS) block copolymer as the hydrophobic side chains and poly(ethylene glycol) as the hydrophilic block. Interfacial self‐assembly of the core‐shell BBCPs within shrinking droplets produces porous microspheres with full‐spectrum structural colors through an organized spontaneous emulsification process. The PtBA core wrapped by PS in the skeleton of the balls can be converted into polyacrylic acid (PAA) forming an ionic channel responsive to pH variations. Consequently, the hydrolyzed photonic balls show different colors under different pH conditions dependent on varying degrees of ionization and hydration of the PAA channel. Reflected colors can be verified using an optical spectrometer, providing an effective strategy for precise pH indication.
Photonic porous balls with ionic channels are obtained simply through the interfacial self‐assembly of core‐shell bottlebrush block copolymers within an ordered water‐in‐oil‐in‐water multiple emulsion system. These photonic balls show different color reflections when placed in aqueous environments with varied pH, providing photonic indicators for pH dectection.
Investigations of host‐guest interactions at water‐oil (w/o) interfaces are limited in single emulsion systems producing simple self‐assembled objects with limited uses. Here, within hierarchically ...ordered water‐in‐oil‐in‐water (w/o/w) multiple emulsion droplets, interfacial self‐assembly of (polynorbornene‐graft‐polystyrene)‐block‐(polynorbornene‐graft‐polyethylene glycol) (PNPS‐b‐PNPEG) bottlebrush block copolymers can be precisely controlled through host‐guest interactions. α‐Cyclodextrin (α‐CD) in the aqueous phase can thread onto PEG side chains of the bottlebrush surfactants adsorbed at the w/o interface, leading to dehydration and collapsed chain conformation of the PEG block. Consequently, spherical curvature of the w/o internal droplets increases with the increased asymmetry of the bottlebrush molecules, producing photonic supraballs with precisely tailored structural parameters as well as photonic bandgaps. This work provides a simple but highly effective strategy for precise manipulation of complex emulsion systems applicable in a variety of applications, such as photonic pigments, cosmetic products, pesticides, artificial cells, etc.
Precisely tunable photonic supraballs are achieved through the host‐guest interaction between α‐cyclodextrin and bottlebrush block copolymer at oil‐water interfaces during organized spontaneous emulsification (OSE) process. The increased asymmetry of BBCP molecules, resulting from the complexation of α‐CD and PEG within BBCPs, induces increased spherical curvature of internal droplets, leading to a distinct blueshift of structural color.
Self‐assembly is important for creating photonic structures and structural color is typically tunable by varying the size of building blocks, which are themselves obtained after time‐consuming ...chemical syntheses. The molecular conformation of bottlebrush block copolymers (BBCPs) in solution can be manipulated to create libraries of photonic structures. Amphiphilic BBCPs bearing oxidation‐responsive ferrocene groups on the hydrophilic block are used to fabricate porous particles via evaporation‐induced self‐assembly of water‐in‐oil‐in‐water (W/O/W) double emulsions stabilized by the BBCP surfactant. In situ oxidation of the ferrocene groups by hydrogen peroxide at the W/O interface leads to enhanced hydrophilicity, more hydration, and chain extension of the hydrophilic block. Consequently, larger internal water droplets are spontaneously formed, yielding larger pores within the microparticles. The pore diameter is readily tunable from 144 to 301 nm with a single BBCP, thereby generating full‐spectrum structural colors. This work provides a straightforward method for fabrication of libraries of photonic pigments in an easy and scalable manner.
Molecular conformation of amphiphilic bottlebrush block copolymers (PS‐b‐PEOFeCp) is successfully manipulated to create libraries of inverse photonic structures that exhibit full‐spectrum structural colors. In situ oxidation of ferrocene groups grafted on the poly(ethylene oxide) (PEO) block leads to polymer chain elongation in water‐in‐oil‐in‐water double emulsions, resulting in larger internal droplets and thus larger porous structures.
Microspheres bearing large pores are useful in the capture and separation of biomolecules. However, pore size is typically poorly controlled, leading to disordered porous structures with limited ...performances. Herein, ordered porous spheres with a layer of cations on the internal surface of the nanopores are facilely fabricated in a single step for effective loading of DNA bearing negative charges. Triblock bottlebrush copolymers (BBCPs), (polynorbornene‐g‐polystyrene)‐b‐(polynorbornene‐g‐polyethylene oxide)‐b‐(polynorbornene‐g‐bromoethane) (PNPS‐b‐PNPEO‐b‐PNBr), are designed and synthesized for fabrication of the positively charged porous spheres through self‐assembly and in situ quaternization during an organized spontaneous emulsification (OSE) process. Pore diameter as well as charge density increase with the increase of PNBr content, resulting in a significant increase of loading density from 4.79 to 22.5 ng µg−1 within the spheres. This work provides a general strategy for efficient loading and encapsulation of DNA, which may be extended to a variety of different areas for different real applications.
Porous spheres with quaternary ammonium cations are obtained through self‐assembly of and in situ quaternization of triblock bottlebrush block copolymers within an ordered water‐in‐oil‐in‐water multiple emulsion system. The obtained spheres show high performances in loading and encapsulation of DNA macromolecules for many potential applications such as information storage.
Severe COVID-19 disease caused by SARS-CoV-2 is frequently accompanied by dysfunction of the lungs and extrapulmonary organs. However, the organotropism of SARS-CoV-2 and the port of virus entry for ...systemic dissemination remain largely unknown. We profiled 26 COVID-19 autopsy cases from four cohorts in Wuhan, China, and determined the systemic distribution of SARS-CoV-2. SARS-CoV-2 was detected in the lungs and multiple extrapulmonary organs of critically ill COVID-19 patients up to 67 days after symptom onset. Based on organotropism and pathological features of the patients, COVID-19 was divided into viral intrapulmonary and systemic subtypes. In patients with systemic viral distribution, SARS-CoV-2 was detected in monocytes, macrophages, and vascular endothelia at blood-air barrier, blood-testis barrier, and filtration barrier. Critically ill patients with long disease duration showed decreased pulmonary cell proliferation, reduced viral RNA, and marked fibrosis in the lungs. Permanent SARS-CoV-2 presence and tissue injuries in the lungs and extrapulmonary organs suggest direct viral invasion as a mechanism of pathogenicity in critically ill patients. SARS-CoV-2 may hijack monocytes, macrophages, and vascular endothelia at physiological barriers as the ports of entry for systemic dissemination. Our study thus delineates systemic pathological features of SARS-CoV-2 infection, which sheds light on the development of novel COVID-19 treatment.
Photonic pigment particles prepared via self-assembly have been suffering from their poor mechanical performances; i.e., they can easily be damaged and lose structural color under a compression ...force. This greatly limits their uses as mechanochromic pigments. Here, a nanoscale concentric lamellar structure of alternating glassy-rubbery microdomains is successfully created within photonic microparticles through a confined self-assembly and photo-cross-linking strategy. The glassy domain is composed of polystyrene, and cross-linked bottlebrush polydimethylsiloxane served as the supersoft elastic domain. The obtained photonic structure not only shows large deformation and visible color changes under a loaded compression force but also rapidly recovers to its original state in less than 1 s (∼0.16 s) upon unloading. Continuously loading-unloading micro compression test indicates that no obvious damage can be identified after 250 cycles, indicating the high durability of the pigments against deformation. These pigments with different reflected colors are simply obtained using bottlebrush block copolymer formulations with tunable weight percentages of polymer additives. The mechanical robust photonic pigments may be useful in many important applications.
Biodegradable photonic microspheres with structural colors are promising substitutes to polluting microbeads and toxic dyes. Here, amphiphilic polyester‐block‐poly(ethylene glycol) bottlebrush block ...copolymers (BBCPs) with polylactic acid or poly(ϵ‐caprolactone) as the hydrophobic block are synthesized and used to fabricate eco‐friendly photonic pigments. Molecular parameters of BBCPs, including rigidity and symmetry, are precisely tailored by variation of side chain lengths, which enables effective manipulation of interfacial tension (γ). Organized spontaneous emulsion mechanism is enabled only when γ falls in a suitable range (10.6–14.3 mN m−1), producing ordered water‐in‐oil‐in‐water multiple emulsions and ordered porous structures. Consequently, highly saturated and tunable structural colors are observed due to coherent light scattering from the porous structures. Such photonic materials are nontoxic as confirmed by careful safety tests using aquatic model organisms.
Polyester‐block‐poly(ethylene glycol) bottlebrush block copolymers with varied side chain lengths are utilized for the fabrication of biodegradable photonic microspheres. The eco‐friendly photonic pigments with highly saturated structural colors can be the ideal substitutes to nondegradable microbeads and toxic pigments, providing a new strategy to reduce the micro‐polluting items and toxic chemicals in our ecosystem.
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