Self-Healing Conjugated Microporous Polyanilines for Effective and Continuous Catalytic Detoxification of 4-Nitrophenol to 4-Aminophenol.

Detoxification of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) with high efficiency and dynamic performance is challenging for a polymeric catalyst. Herein, a series of conjugated microporous polyanilines (CMPAs), capable of efficiently catalytically reducing 4-NP, were synthesized based on the Buchwald-Hartwig cross-coupling reaction mechanism. By adjusting the types of linkers and the molar ratios of linker to core, CMPAs with different Brunauer-Emmett-Teller (BET) specific surface areas and reduction degrees were obtained and used as the catalysts in reducing 4-NP. The ultrahigh catalytic reduction efficiency (K = 141.32 s-1 g-1, kapp = 0.00353 s-1) was achieved when using CMPA-3-0.7 as the catalyst (prepared with 4,4'-diaminodiphenylamine as the linker and a 0.7:1 molar ratio of linker to core). The catalytic reduction performance exhibited a strong correlation with the reduction degree and BET specific surface area of CMPAs. Furthermore, they also exhibit excellent cycling stability and dynamic performance. The coexistence of a microporous structure and high BET specific surface area endowed CMPAs with an increased number of catalytic active centers. The reversible redox transformation of CMPAs in the presence of NaBH4 and air enabled self-healing (the oxidation units in CMPAs were reduced to reduction units by NaBH4, and the newly generated reduction unit in CMPAs was subsequently oxidized to its original state by the O2 in the air), leading to the reduction reaction of 4-NP proceeded continuously and stably. The aforementioned factors resulted in the high efficiency of CMPAs for reducing 4-NP to 4-AP, enhancing the practical application prospects of CMPAs in the detoxification of 4-NP wastewater.

Generation of Bloch surface beams with arbitrarily designed phases.

We proposed a new manipulation method for Bloch surface waves that can almost arbitrarily modulate the lateral phase through in-plane wave-vector matching. The Bloch surface beam is generated by a laser beam from a glass substrate incident on a carefully designed nanoarray structure, which can provide the missing momentum between the two beams and set the required initial phase of the Bloch surface beam. An internal mode was used as a channel between the incident and surface beams to improve the excitation efficiency. Using this method, we successfully realized and demonstrated the properties of various Bloch surface beams, including subwavelength-focused, self-accelerating Airy, and diffraction-free collimated beams. This manipulation method, along with the generated Bloch surface beams, will facilitate the development of two-dimensional optical systems and benefit potential applications of lab-on-chip photonic integrations.

Optofluidic microbubble Fabry-Pérot cavity.

An optofluidic microbubble Fabry-Pérot (OMBFP) cavity was investigated. In contrast to plane-plane FP (PPFP) cavities, the optical mode confinement and stability in an OMBFP were significantly enhanced. The optical properties of the OMBFP cavity, including the quality (Q) factor, effective mode area, mode distribution as a function of the core refractive index, microbubble position, and mirror tilt angle, were investigated systematically using the finite element method. In optofluidic lasing experiments, a low lasing threshold of 1.25 µJ/mm2, which was one order magnitude lower than that of the PPFP, was achieved owing to improved modal lateral confinement. Since the microbubble acts as a micro-lens and microfluidic channel in the parallel FP cavity, mode selection and cell-dye laser were easily realized in the OMBFP cavity.

Coupled-mode induced transparency via Ohmic heating in a single polydimethylsiloxane-coated microbubble resonator.

We demonstrate an approach for the realization of coupled-mode induced transparency (CMIT) in a hybrid polydimethylsiloxane (PDMS)-coated silica microbubble resonator, with an Au microwire inserted in the hollow channel. Owing to the large negative thermo-optics coefficient of PDMS, different radial order modes with opposite thermal sensitivities can coexist in this hybrid microcavity. By applying a current through the Au microwire, which acts as a microheater, the generated Ohmic heating could thermally tune the resonance frequencies and the frequency detuning of the coupled mode to achieve controllable CMIT. This platform offers an efficient and convenient way to obtain controllable CMIT for applications, such as label-free biosensing and quantum information processing.

Combining whispering gallery mode optofluidic microbubble resonator sensor with GR-5 DNAzyme for ultra-sensitive lead ion detection.

Lead ions are deleterious pollutants that often reach drinking water, and can cause significant harm to humans (particularly children). An ultra-sensitive lead ion detection method using a whispering gallery mode (WGM) optofluidic microbubble resonator and the classic GR-5 DNAzyme is proposed in this paper. With the auxiliary piranha and Ploy-l-lysine solution, GR-5 DNAzyme was successfully modified on the inner wall of a microbubble. The mode field distribution of the microbubble was analysed, and the optofluidic sensor with thin wall exhibited a maximum bulk refractive index sensitivity of 265.2 nm/RIU. Lead ions at concentrations ranging from 0.1 pM to 100 pM were tested using the proposed WGM optofluidic sensor. The noise was decreased to 2.43 fM using the self-referenced differential method. Thus, a limit of approximately 15 fM was obtained for the detection of lead ions using the WGM optofluidic biosensor. Eight competing metal ions were also used to evaluate the selectivity of the proposed sensor, with results indicating that it has high selectivity for lead ions. Finally, the sensor performance is verified using real samples.

Tunable optofluidic liquid metal core microbubble resonator.

This study introduces design and coupling techniques, which bridge an opaque liquid metal, optical WGM mode, and mechanical mode into an opto-mechano-fluidic microbubble resonator (MBR) consisting of a dielectric silica shell and liquid metal core. Benefiting from the conductivity of the liquid metal, Ohmic heating was carried out for the MBR by applying current to the liquid metal to change the temperature of the MBR by more than 300 °C. The optical mode was thermally tuned (>3 nm) over a full free spectral range because the Ohmic heating changed the refractive index of the silica and dimeter of the MBR. The mechanical mode was thermally tuned with a relative tuning range of 9% because the Ohmic heating changed the velocity and density of the liquid metal.

Ultra-sensitive biomolecular detection by external referencing optofluidic microbubble resonators.

We propose an effective method for biomolecular detection based on an external referencing optofluidic microbubble resonator system (EROMBRS), which possesses good long-term stability and low noise. In this study, EROMBRSs were used for nonspecific detection of bovine serum albumin (BSA) molecules and specific detection of D-biotin molecules. Ultra-low practical detection limits of 1 fg/mL for nonspecific and specific biomolecular detection were achieved.

On-Chip Real-Time Chemical Sensors Based on Water-Immersion-Objective Pumped Whispering-Gallery-Mode Microdisk Laser.

Optical whispering-gallery-mode (WGM) microresonator-based sensors with high sensitivity and low detection limit down to single unlabeled biomolecules show high potential for disease diagnosis and clinical application. However, most WGM microresonator-based sensors, which are packed in a microfluidic cell, are a "closed" sensing configuration that prevents changing and sensing the surrounding liquid refractive index (RI) of the microresonator immediately. Here, we present an "open" sensing configuration in which the WGM microdisk laser is directly covered by a water droplet and pumped by a water-immersion-objective (WIO). This allows monitoring the chemical reaction progress in the water droplet by tracking the laser wavelength. A proof-of-concept demonstration of chemical sensor is performed by observing the process of salt dissolution in water and diffusion of two droplets with different RI. This WIO pumped sensing configuration provides a path towards an on-chip chemical sensor for studying chemical reaction kinetics in real time.

Extreme terahertz electric-field enhancement in high-Q photonic crystal slab cavity with nanoholes.

A one-dimensional photonic-crystal (PC) cavity with nanoholes is proposed for extreme enhancement of terahertz (THz) electric fields using the electromagnetic (EM) boundary conditions. Both slot (for the perpendicular component of the electric displacement field) and anti-slot (for the parallel component of the electric field) effects contribute to the considerable field enhancement. The EM energy density can be enhanced by a factor of (εh/εl)2 in the high-refractive-index material, where εh and εl are the permittivities of the high- and low-refractive-index materials, respectively. Correspondingly, the mode volume can be reduced by a factor of 288, compared with a conventional THz PC cavity, and is three orders of magnitude smaller than the diffraction limitation. Further, the proposed THz cavity design also supports modes with high quality factors (Q) > 104, which induces strong Purcell enhancement by a factor exceeding 106. Our THz cavity design is feasible and attractive for experimental demonstrations, because the semiconductor layer in which the EM is maximized can naturally be filled with quantum-engineered active materials. Thus, the proposed design can possibly be used to develop room-temperature coherent THz radiation sources.

Packaged Droplet Microresonator for Thermal Sensing with High Sensitivity.

Liquid droplet and quasi-droplet whispering gallery mode (WGM) microcavities have been widely studied recently for the enhanced spatial overlap between the liquid and WGM field, especially in sensing applications. However, the fragile cavity structure and the evaporation of liquid limit its practical applications. Here, stable, packaged, quasi-droplet and droplet microcavities are proposed and fabricated for thermal sensing with high sensitivity. The sensitivity and electromagnetic field intensity distribution are analyzed by Mie theory, and a quantified definition of the quasi-droplet is presented for the first time to the best of our knowledge. By doping dye material directly into the liquid, lasing packaged droplet and quasi-droplet microcavity sensors with a high thermal sensitivity of up to 205.3 pm/°C are experimentally demonstrated. The high sensitivity, facile fabrication, and mechanically robust properties of the optofluidic, packaged droplet microresonator make it a promising candidate for future integrated photonic devices.

Controllable and selective single-mode lasing in polymer microbottle resonator.

We report a single-mode dye-doped polymer microbottle resonator (MBR) laser. The selective single-mode lasing from different order whispering gallery modes is achieved by precisely controlling the axial and radial coupling position between a tapered nanofiber and an MBR, respectively. The side-mode suppression ratio is above 20 dB. By doping different fluorescence dyes into the MBR, single-mode lasers at various colors are demonstrated.

Precise measurement of micro bubble resonator thickness by internal aerostatic pressure sensing.

We develop a new, simple and non-destructive method to precisely measure the thickness of thin wall micro bubble resonators (MBRs) by using internal aerostatic pressure sensing. Measurement error of 1% at a bubble wall thickness of 2 µm is achieved. This method is applicable to both thin wall and thick wall MBR with high measurement accuracy.

Stimulated Brillouin laser and frequency comb generation in high-Q microbubble resonators.

We report on the stimulated Brillouin laser (SBL) and over-dense frequency comb generation in high-Q microbubble resonators (MBRs). Both first-order and cascaded SBL are achieved due to the rich high-order axial modes in the MBRs, although the free spectral range (FSR) of azimuthal mode of the MBR is severely mismatched with the Brillouin shift. The SBL is also generated by varying the internal pressure of MBR at fixed initially non-resonant pump light wavelength. In addition, over-dense frequency combs are realized with comb spacings that are one and two FSRs of aixal mode.

Strong coupling of hybrid and plasmonic resonances in liquid core plasmonic micro-bubble cavities.

A thin-wall plasmonic micro-bubble resonator, which is a high-Q optofluidic silica bubble cavity with a thin Ag film on the inside wall of the bubble, is proposed and fabricated to manipulate coupling among various types of resonant modes by changing its wall thickness and refractive index of the liquid in the core. Coupling of high-Q whispering gallery mode/plasmonic resonant mode forms hybrid mode; the hybrid mode can again strongly couple with another interior plasmonic resonant mode in the bubble cavity to achieve tunable high-Q plasmonic resonance that can be feasibly accessed by standard tapered fiber coupling. Therefore, the novel cavity structure provides a unique, yet general, platform to study plasmonic/photonic, hybrid/plasmonic, and plasmonic/plasmonic coupling.

Mode-selective lasing in high-Q polymer micro bottle resonators.

Passive and active polymer micro bottle resonators (MBRs) are fabricated. Equatorial whispering gallery modes and bottle modes are clearly identified, with highest loaded quality (Q) factor above 10(5). Lasing with threshold as low as 1 nJ/pulse is realized in active MBRs. Mode selective lasing is achieved by coupling a tapered fiber to equatorial whispering gallery modes or a group of bottle modes. The bottle mode free spectral range (FSR) is found to be about one fifth of the equatorial modes.

Dielectric bow-tie nanocavity.

We propose a novel dielectric bow-tie (DBT) nanocavity consisting of two opposing tip-to-tip triangle semiconductor nanowires, whose end faces are coated by silver nanofilms. Based on the advantages of the dielectric slot and tip structures, and the high reflectivity of the silver mirror, light can be confined in this nanocavity with low loss. We demonstrate that at 4.5 K (300 K) around the resonance wavelength of 1550 nm, the mode excited in this nanocavity has a deep subwavelength mode volume of 2.8×10(-4) µm³ and a high quality factor of 4.9×10(4) (401.3), corresponding to an ultrahigh Purcell factor of 1.6×10(7) (1.36×10(5)). This DBT nanocavity may find applications for integrated nanophotonic circuits, such as high-efficiency single photon sources, thresholdless nanolasers, and strong coupling in cavity quantum electrodynamics experiments.

Focusing of electromagnetic fields in high-Q hybrid wedge plasmon polariton microresonator.

We theoretically propose a hybrid microresonator consisting of a metallic wedge ring and a silica ring and investigate the existing whispering-gallery-like hybrid wedge plasmon polariton modes. These tightly confined hybrid plasmon modes are found to possess ultrasmall mode volumes while maintaining relatively high quality factors simultaneously at room temperature; that is, high values of Q/V are obtained. For example, a Purcell factor of 70 is achieved at the telecommunication wavelength of 1550 nm. This plasmon microresonator shows great potential in low-threshold plasmonic microlasers and cavity quantum electrodynamics.