Active Photonic Materials Research Articles

Bi Cluster Engineering for Tunable Broadband NIR Optical Response

AbstractNear‐infrared (NIR) broadband active photonic materials play a crucial role in various domains such as optical communication, phototherapy, and medical imaging. However, the construction of NIR photonic materials with tunable optical response still remains a great challenge. This manuscript proposes a topological structure engineering strategy in Bi‐activated glass for the realization of the controllable NIR emission. By manipulating the topological structure of glass, the Bi cluster configuration can be precisely control, with the cluster size from 2.78 to 1.64 nm. Correspondingly, various optical properties including broadband emission, excited state absorption (ESA), and even unsaturable loss (UL) can be rationally switched. Based on the above findings, Bi cluster‐activated bulk glasses, optical fibers, and the derived NIR active devices with notably improved performance can be successfully fabricated. Their application potentials in optical communication and NIR imaging are also demonstrated. The study highlights the promise of Bi cluster‐activated materials in advancing NIR photonic materials and devices. Furthermore, the topological‐mediated cluster regulation strategy may also provide new insights into the fundamental science and cutting technology of other cluster‐activated materials.

Annealing effect on the morphology, linear and non-linear optical properties of squaraine derivative thin films for optoelectronics applications

Squaraine is a class of organic compounds that possess unique optical properties, including strong absorption of light, high fluorescence quantum yields, etc. Here, we explore the structural and spectroscopic investigations of 2,4-Bis[4-(N,N-dibenzylamino)-2,6 dihydroxyphenyl] squaraine dye (SQ) under different conditions of thermal effects. The molar absorptivity (εmolar) spectra were used to describe the electric dipole strength (q2) and the oscillator strengths (f) of SQ dye. The Surface morphology of SQ dye was investigated by AFM and the average roughness shows dependence on the annealing effect. A slight change in the optical energy gap (⁓ 0.3 eV) after annealing up to 473 K reflects the optical stability of our investigated thin films. The optical band transitions and photoluminescence (PL) emission spectra were described before and after annealing at 423 & 473 K. As the temperature annealing film increased to 473 K, the nonlinear parameters such as χ(3) and n2 decreased by about 44% and 36%, respectively. The good thermal stability, suitable optical band gap, and refractive index offer potential applications as active photonic materials in photonic/optoelectronic applications.

Dual-color light emission and optical waveguide behavior in core-shell heterostructures based on surface doping of cocrystal with rare earth ions

Organic core-shell structures/heterostructures are burgeoning as active photonic materials, i.e., optical waveguides, controllable multi-emissions, input-output optical logic gates. Here, a new conception that rare-earth (RE) ions as the surface dopants for the construction of organic cocrystal@RE complexes core-shell heterostructures was first proposed. Organic cocrystal Tpy-1,4-DITFB (Tpy = 2,2’:6′,2″-terpyridine; 1,4-DITFB = 1,4-diiodotetrafluorobenzenes) as inner-core has been designed. The RE ions of Eu(Ⅲ) and Tb(Ⅲ) are dopped on the surfaces of Tpy-1,4-DITFB cocrystal via epitaxial growth method. The effect of the compositions and morphologies of core-shell heterostructures on the optical behaviors were investagted via fluorescence spectroscopy. Spatially adjacent dual-color emission in the di-block core-shell heterostructures brings about tunable regulation of optical waveguide modes, offering potential applications for input/output optical logic gate and biomedical.

Intense luminescence in nanostructured germanate glass

The phosphors free of active dopants have been attracted much attention due to their interesting optical properties and potentials for construction of rare-earth free functional materials. In this letter, we report the construction of phosphor free of active dopants via nanocrystallization of glass. In a typical example, a single-phase Zn2GeO4 phosphor is fabricated via controllable crystallization of the germinate glass. Intense green luminescence with the central wavelength at 523 nm can be realized in nanostructured glass and it is estimated to be ∼150 times higher than that of the as-made glass. The physical mechanism is associated with the formation of Zn related interstitial defects during the disorder-order phase transformation in glass. The progress in this work indicates that the avenue of glass crystallization provides an effective strategy for the development of novel active photonic materials free of active dopants.

Bio-Organic Chiral Nematic Materials with Adaptive Light Emission and On-Demand Handedness.

Real-time active control of the handedness of circularly polarized light emission requires sophisticated manufacturing and structural reconfigurations of inorganic optical components that can rarely be achieved in traditional passive optical structures. Here, robust and flexible emissive optically-doped biophotonic materials that facilitate the dynamic optical activity are reported. These optically active bio-enabled materials with a chiral nematic-like organization of cellulose nanocrystals with intercalated organic dye generated strong circularly polarized photoluminescence with a high asymmetric factor. Reversible phase-shifting of the photochromic molecules intercalated into chiral nematic organization enables alternating circularly polarized light emission with on-demand handedness. Real-time alternating handedness can be triggered by either remote light illumination or changes in the acidic environment. This unique dynamic chiro-optical behavior presents an efficient way to design emissive bio-derived materials for dynamic programmable active photonic materials for optical communication, optical coding, visual protection, and visual adaptation.

Cellulose nanocrystals with different morphologies and chiral properties

The study reports the morphology and optical properties of a variety of cellulose nanocrystals (CNC) obtained from different natural sources with different dimensions and composition. A library of CNCs components with different dimensions, sulfate contents, and crystallite sizes was prepared under identical hydrolysis conditions from five distinct sources representing traditional choices ranging from soft and hard wood pulps to microcrystalline cellulose. High-resolution atomic force microscopy, scanning electron microscopy, scanning transmission electron microscopy, and X-ray diffraction confirmed that all CNCs have a well-defined needle-like morphology with different aspect ratios and axi-asymmetric cross-sections. Varying the cellulose sources resulted in wide variability of the CNC dimensions, including length (120–210 nm), aspect ratio (30–70), height (2.9–3.6 nm), and width (6–11 nm). Specifically, the CNCs from microcrystalline sources have large cross-sectional dimensions and produce straight CNC bundles, but CNCs from wood pulps have small cross-sections and form twisted bundles of a few individual nanocrystals. Chemical composition and surface potentials were found to be less critical to the resulting chiral characteristics and structural colors while the CNCs with high aspect ratios form chiral films with large pitch values and thus longer wavelengths of selective reflection. Such flexible chiral CNC materials with controlled optical signature can be further considered for development of advanced materials for colorimetric sensors, tunable and active photonic materials, optical coatings, chiral inks and 3D printed photonic structures.

Doping silica beyond limits with laser plasma for active photonic materials

The limited solubility of rare-earths in silica hampers the development of loss-compensated photonic integrated circuits. We report a novel method using femtosecond laser plasma assisted hybrid material integration of rare-earth-doped tellurite with silica, achieving high doping concentration of Er3+ and Yb3+-ions, 1.63 × 1021 atoms.cm−3,without segregation validated by Er3+:4I13/2 lifetime of 9.1 ms. The sequential ablation of two individual rare-earth (Er3+/Yb3+) doped-tellurite glass targets produces an exceptional intermixing of Er3+ and Yb3+-ions extending to the pristine silica with sharp interface. Formation of such homogeneous glass structure with Er3+-Yb3+-ions in a matrix of silica is not possible to realise by conventional methods.

III–Vs on Si for photonic applications—A monolithic approach

As the age of Moore’s law is drawing to a close, continuing increase in computing performance is becoming increasingly hard‐earned, while demand for bandwidth is insatiable. One way of dealing with this challenge is the integration of active photonic material with Si, allowing high‐speed optical inter‐ and intra‐chip connects on one hand, and the economies of scale of the CMOS industry in optical communications on the other. One of the most essential active photonic materials is InP, stemming from its capability in combination with its related materials to produce lasers, emitting at wavelengths of 1300 and 1550 nm, the two most important wavelengths in data‐ and telecom.However, integrating InP with Si remains a challenging subject. Defects arise due to differences in lattice constants, differences in thermal expansion coefficients, polarity and island‐like growth behavior. Approaches to counter these problems include epitaxial lateral overgrowth (ELOG), which involves growing InP laterally from openings in a mask deposited on a defective InP/Si substrate. This approach solves some of these problems by filtering out the previously mentioned defects. However, filtering may not be complete and the ELOG and mask themselves may introduce new sources for formation of defects such as dislocations and stacking faults.In this work, the various kinds of defects present in InP ELOG layers grown by hydride vapor phase epitaxy on Si, and the reason for their presence, as well as strategies for counteracting them, are investigated. The findings reveal that whereas dislocations appear in coalesced ELOG layers both on InP and InP/Si, albeit to varying extents, uncoalesced ELOG layers on both substrate types are completely free of threading dislocations. Thus, coalescence is a critical aspect in the formation of dislocations. It is shown that a rough surface of the InP/Si substrate is detrimental to defect‐free coalescence. Chemical‐mechanical polishing of this surface improves the coalescence in subsequent ELOG leading to fewer defects.Furthermore, ELOG on InP substrate is consistently free of stacking faults. This is not the case for ELOG on InP/Si, where stacking faults are to some extent propagating from the defective substrate, and are possibly also forming during ELOG. A model describing the conditions for their propagation is devised; it shows that under certain conditions, a mask height to opening width aspect ratio of 3.9 should result in their complete blocking. As to the potential formation of new stacking faults, the formation mechanism is not entirely clear, but neither coalescence nor random deposition errors on low energy facets are the main reasons for their formation. It is hypothesized that the stacking faults can be removed by thermal annealing of the seed and ELOG layers.Furthermore, concepts for integrating an active photonic device with passive Si components are elucidated by combining Si/SiO2 waveguides used as the mask in ELOG and multi‐quantum well (MQW) lasers grown on ELOG InP. Such a device is found to have favorable thermal dissipation, which is an added advantage in an integrated photonic CMOS device.

Complete band gaps in three-dimensional quantum dot photonic crystals

Because of the generation of polaritons, which are quasiparticles possessing the characteristics of both photonics and electronics, active photonic materials offer a possible solution to transfer electromagnetic energy below the diffraction limit and further increase the density of photonic integrated circuits. A theoretical investigation of these exciting materials is, therefore, very important for practical applications. Four different kinds of polaritons have been studied in this thesis, (1) surface polaritons of negative-index-material cylindric rods, (2) exciton polaritons of semiconductor quantum dots, (3) localized plasmon polaritons of metallic nanoshells, and (4) surface plasmon polaritons of subwavelength hole arrays in thin metal films. All these types of polaritons were found to strongly affect the optical properties of the studied active photonic materials. More specifically, (1) for two-dimensional photonic crystals composed of negative-index-material cylindric rods, the coupling among surface polaritons localized in the rods results in dispersionless anti-crossing bands; (2) for three-dimensional diamond-lattice quantum-dot photonic crystals, the exciton polariton resonances lead to the formation of complete band gaps in the dispersion relationships; (3) for metallic nanoshells, the thickness of the metal shell strongly modifies the localized plasmon polaritons, and therefore influences the degree of localization of the electromagnetic field inside the metallic nanoshells; (4) for subwavelength hole arrays in thin metal films, high-order surface-polariton Bloch waves contribute significantly to the efficient transmission. To numerically simulate these active photonic materials, we introduced three approaches, (1) an extended plane-wave-based transfer-matrix approach for negative- index-material media, (2) a plane-wave method for semiconductor quantum-dot photonic crystals, and (3) an auxiliary-differential-equation finite-difference time- domain approach for semiconductor quantum-dot arrays. A brief perspective is also given at the end of this thesis.

Heat and temperature distribution in a cladding-pumped, Er: Yb co-doped phosphate fiber

High-gain-per-unit-length, Er: Yb co-doped, phosphate glass fibers are a new class of active photonic materials. Due to their high concentration of active ions (typically 2–6×1020 cm−3), the generation of heat in these materials is rather severe. To facilitate the design of cladding-pumped, high-power lasers and amplifiers using these materials, we introduce two diagnostic techniques for measuring the total heat and the profile of temperature distribution along the length of an active fiber. Thermal experiments on a 6.0-cm-long piece of cladding-pumped phosphate fiber with Er: Yb doping (3:16 wt %) are conducted, and the results are compared with indirect estimates of total heat by scattered light measurements using a power-balance argument. The difference between the two methods is about 8.0%. Even at low pump powers, the temperature of the core (without heat-sinking) is found to be a large fraction of the glass transition temperature. The temperature distribution along the length of the fiber is found to be relatively flat compared with the absorption profile. Our thermal diagnostic tools yield valuable information that can be used to optimize the design of fiber lasers and amplifiers.

Nanostructured silicon as a photonic material

Photonics applications of silicon are presented. In particular it is demonstrated that silicon when rendered low dimensional, e.g. in form of nanocrystals or quantum wires, can be turned into an active photonic materials which shows light amplification characteristics, non-linear optical effects, photon confinement in both one and two dimensions, photon trapping with evidences of light localization, and gas sensing properties.