Tunable random lasers via phase transition for information encryption.

Introducing phase transition materials to random systems provides a promising route to create new optoelectronic functionalities of random lasers. Here, a phase transition random laser with switchable lasing modes is reported, which is designed with a thermoresponsive hydrogel as scattering medium. By manipulating the phase transition in hydrogel, random lasing modes can be switched reversibility between incoherent and coherent random lasing. The phenomenon derives from the changing of light scattering properties in different phase states, thus affecting the optical feedback path of random lasing. Besides, based on its controllable and easily detectable time-domain characteristics, the phase transition random laser is applied in information encoding and transmission. It is the first time that the transition from coherent to incoherent random lasing is observed by varying the sample phase states. This work will inspire the design and application of novel random lasers in photoelectric device.

Switchable whispering gallery mode lasing via phase transition.

Combining phase-transition materials with optical microcavities may advance the applications of whispering-gallery mode (WGM) lasing in performance customization, sensing, and optical switching. In this study, switchable WGM lasing based on phase transition is reported. The device is designed by introducing the phase-transition hydrogel into the capillary microcavity. After approaching the phase-transition point in hydrogel, the number of WGM lasing modes decreases sharply with a significant blueshift in the wavelength. The phenomenon is caused by the increase in light scattering and decrease in effective refractive index of the device. Furthermore, single-mode lasing is obtained by manipulating the phase transition, which exhibits superior reversibility. This study may pave the way for designing and multifunctioning of novel WGM lasing in photonic devices.

Nonpolar Solvent Modulated Inkjet Printing of Nanoparticle Self-Assembly Morphologies.

Patterning of luminescent nanomaterials is critical in the fields of display and information encryption, and inkjet printing technology have shown remarkable significance with the advantage of fast, large-scalable and integrative. However, inkjet printing nanoparticle deposits with high-resolution and well controlled morphology from nonpolar solvent droplets is still challenging. Herein, a facile approach of nonpolar solvent modulated inkjet printing of nanoparticles self-assembly patterns driven by the shrinkage of the droplet and inner solutal convection is proposed. Through regulating the solvent composition and nanoparticle concentration, multicolor light-emissive upconversion nanoparticle self-assembly microarrays with tunable morphologies are achieved, showing the integration of designable microscale morphologies and photoluminescences for multimodal anti-counterfeit. Furthermore, inkjet printing of nanoparticles self-assembled continuous lines with adjustable morphologies by controlling the coalescence and drying of the ink droplets is achieved. The high resolution of inkjet printing microarrays and continuous lines' width < 5 and 10 µm is realized, respectively. This nonpolar solvent-modulated inkjet printing of nanoparticle deposits approach facilitates the patterning and integration of different nanomaterials, and is expected to provide a versatile platform for fabricating advanced devices applied in photonics integration, micro-LED, and near-field display.

Plasmonic distributed feedback lasing in an anodic aluminum oxide/silver/polymer hybrid membrane.

A hybrid membrane is employed as a high-order plasmonic distributed feedback (DFB) cavity to reduce the lasing threshold of polymer lasers. The hybrid membrane consists of an anodic aluminum oxide (AAO) membrane, a 25 nm thick silver layer and a free-standing polymer membrane. The AAO membrane is fabricated by a low-cost, single chemical etching method. Then, a layer of silver with a thickness of 25 nm is sputtered on the surface of the AAO. Subsequently, a polymer membrane is directly attached to the silver-plated AAO membrane, forming an AAO/silver/polymer hybrid membrane. Under optical pumping conditions, low-threshold, three-order DFB lasing is observed. The proposed laser device exhibited a dual-threshold characteristic because of the evolution from amplified spontaneous emission to DFB lasing. And a significant shift from omnidirectional emission to directional emission lasing can be observed while the pump energy density is beyond the second threshold. Furthermore, the plasmonic enhancement sourced from silver corrugation reveals important improvement effects to the DFB lasing of AAO/silver/polymer hybrid membrane for decreasing threshold, narrowing full width at half maximum (FWHM), and an increasing Q factor. This work may promote the design and production of low-cost and large-area high-order plasmonic DFB polymer lasers.

Dynamic manipulation of WGM lasing by tailoring the coupling strength.

Miniaturized lasing with dynamic manipulation is critical to the performance of compact and versatile photonic devices. However, it is still a challenge to manipulate the whispering gallery mode lasing modes dynamically. Here, we design the quasi-three-dimensional coupled cavity by a micromanipulation technique. The coupled cavity consists of two intersection polymer microfibers. The mode selection mechanism is demonstrated experimentally and theoretically in the coupled microfiber cavity. Dynamic manipulation from multiple modes to single-mode lasing is achieved by controlling the coupling strength, which can be quantitatively controlled by changing the coupling angle or the coupling distance. Our work provides a flexible alternative for the lasing mode modulation in the on-chip photonic integration.

Electrically Tunable Polymer Whispering-Gallery-Mode Laser.

Microlasers hold great promise for the development of photonics and optoelectronics. At present, tunable microcavity lasers, especially regarding in situ dynamic tuning, are still the focus of research. In this study, we combined a 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT) piezoelectric crystal with a Poly [9,9-dioctylfluorenyl-2,7-diyl] (PFO) microring cavity to realize a high-quality, electrically tunable, whispering-gallery-mode (WGM) laser. The dependence of the laser properties on the diameter of the microrings, including the laser spectrum and quality (Q) value, was investigated. It was found that with an increase in microring diameter, the laser emission redshifted, and the Q value increased. In addition, the device effectively achieved a blueshift under an applied electric field, and the wavelength tuning range was 0.71 nm. This work provides a method for in situ dynamic spectral modulation of microcavity lasers, and is expected to provide inspiration for the application of integrated photonics technology.

Dual chaos encryption for color images enabled in a WGM-random hybrid microcavity.

Chaotic cryptography as an important means for digital image encryption has become a great cryptographic project in the current information age. As a novel microcavity laser, a random laser (RL) has a natural advantage for a chaotic system, relying on its spectral randomness. Nevertheless, this encrypted image generally suffers from outline exposition when an unsuitable key from a single RL spectrum is employed. Herein, to realize reliable dual chaotic encryption, an internally integrated hybrid microcavity in random and whispering-gallery-mode (WGM) is reported. Within this coupled microcavity, the rhodamine-6G-doped inner-wall of the fiber serves as the gain medium and the optical cavities for WGM lasing; an RL mode is enabled by scattered particles and the gain medium (Rh6G). Interestingly, the smooth inner wall of the fiber with a high-quality (Q) factor and tight optical confinement make WGM lasing occur earlier than RL. What is more, a fast energy transfer process from the WGM laser to Ag nanoparticles and the resultant localized surface plasmon resonance effects from Ag NPs to RL jointly promote the output of the random laser. As a result, a free transformation from the WGM laser to RL is successfully modulated by varying the pump power alone, thus providing two initial values for dual chaos image encryption. This work provides an in-depth understanding of a WGM-random inner-coupled cavity and promotes the application of a hybrid microcavity in the field of information security.

WGM lasing in irregular cavities with arbitrary boundaries.

Because of its limited light field mode and high Q value, the whispering-gallery-mode (WGM) cavity has been widely studied. In this study, we propose a simple, rapid, low-cost and no-manufacturing technology method that we call the drip-coating method to obtain an irregular cavity with arbitrary boundaries. By using polyvinyl alcohol (PVA) solution doped with rhodamine 6G, the irregular cavity with arbitrary boundaries was drip-coated on a high-reflection mirror, forming a WGM laser. The sample was pumped with a 532 nm pulsed laser, and the single-mode WGM and multi-WGM lasing were obtained. All WGMs are the vertical oscillation modes, which originate from both the total internal reflection of the PVA/air interface and vertical reflection of the PVA/mirror interface. The other boundaries of the cavity were not involved in the reflection and could have any shape. The mechanism of producing single-mode lasing is due to the action of the loss-gain cavity. Multi-WGM lasing is attributed to at least two groups of different WGMs existing in an irregular cavity. This can be confirmed by using a microsphere model and intensity correlation method. These results may provide an alternative for the design of WGM lasers.

Multifunctional Sensing Based on an Ultrathin Transferrable Microring Laser.

An ultrathin-film microring laser was fabricated using inkjet printing and a simple lift-off technique. Whispering-gallery-mode lasing was observed under optically pumped conditions in the film. The freestanding laser can be transferred to arbitrary surfaces for multifunctional applications, such as acoustic and relative humidity sensing. Using the first eigenmode of a membrane vibration, an acoustic sensor with a 0.15 Pa limit of detection was demonstrated via laser bandwidth broadening. A relative humidity sensor with a 1.1% limit of detection via wavelength shifts was demonstrated by placing the device on an optical fiber facet. These cost-effective, transferrable, multifunctional laser sensors will have many additional applications.

Dual-color plasmonic random lasers for speckle-free imaging.

A dual-color plasmonic random laser under single-excitation is achieved in an ultrathin membrane doped with binary quantum dots and gold nanorods. The gold nanorods tune the luminescence lifetime and emission efficiency of quantum dots. Under single excitation, low-threshold random lasing is observed. Green random lasing at 547 nm is 'turned on' and red random lasing at 630 nm is greatly enhanced by the transversal and longitudinal surface plasmon resonance of the gold nanorods, respectively. Speckle-free color imaging is achieved by using the proposed dual-color random laser source. These properties would facilitate the development of random lasers in fields of illumination and imaging.

Low-cost biosensors based on a plasmonic random laser on fiber facet.

Low-cost and miniaturized biosensors are key factors leading to the possibility of portable and integrated biomedical system, which play an important role in clinical medicine and life sciences. Random lasers with simple structures provide opportunities for detecting biomolecules. Here, low-cost biosensors on fiber facet for label-free detecting biomolecules are demonstrated based on a plasmonic random laser. The random laser is achieved resorting to a self-assembled plasmonic scattering structure of Ag nanoparticles and polymer film on fiber facet. Refractive index sensitivity and near-surface sensitivity of the biosensor are systematically studied. Furthermore, the biosensor is used to detect IgG through specific binding to protein A, exhibiting the detecting limit of 0.68 nM. It is believed that this work may promote the applications of a plasmonic random laser bio-probe in portable or integrated medical diagnostic platforms, and provide fundamental understanding for the life science.

Chromaticity-tunable white random lasing based on a microfluidic channel.

The color and/or chromaticity controllability of random lasing is a key factor to promote practical applications of random lasers as high luminance sources for speckle-free imaging. Here, white coherent random lasing with tunable chromaticity is obtained by using broadband enhancement Au-Ag nanowires as scatterers and the resonance energy transfer process between different dyes in the capillary microfluidic channel. Red, green and blue random lasers are separately fabricated with low thresholds, benefiting from the plasmonic resonance of the nanogaps and/or nanotips with random distribution and sizes within Au-Ag nanowires and positive optical feedback provided by the capillary wall. A white random laser system is then designed through reorganizing the three random lasers. And, the chromaticity of the white random laser is flexibly tunable by adjusting pump power density. In addition, the white random laser has anisotropic spectra due to the coupling role between the lasers. This characteristic is then utilized to obtain different random lasing with different chromaticity over a broad visible range. The results may provide a basis for applying random laser in the field of high brightness illumination, biomedical imaging, and sensors.

Tunable polymer lasing in chirped cavities.

Continuously tunable polymer lasing was achieved in one-dimensional, two-dimensional, and compound chirped cavities. The chirped cavity was simply fabricated by using interference lithography and spin coating. Two-dimensional and compound chirped cavities were obtained by employing oblique exposure and double exposure, respectively. The tunability range of two-dimensional chirped cavities was much wider than that of one-dimensional chirped cavities, which varied from 557 nm to 582 nm. The interaction between lasing modes was studied in the compound cavity by introducing an additional nanostructure into the two-dimensional chirped cavities. The threshold of the compound chirped cavities changed with the coupling strength between lasing modes. These results may be helpful for designing compact polymer laser sources.

Tailoring Whispering Gallery Lasing and Random Lasing in A Compound Cavity.

A compound cavity was proposed to achieve both whispering gallery mode (WGM) lasing and random lasing. The WGM-random compound cavity consisted of a random structure with an annular boundary, which was fabricated by a method combining both inkjet printing and metal-assisted chemical etching methods. An ultrathin polymer membrane was attached to the WGM-random compound cavity, forming a polymer laser device. A transformation from WGM lasing to random lasing was observed under optical pumping conditions. The laser performance could be easily tailored by changing the parameter of the WGM-random compound cavity. These results provide a new avenue for the design of integrated light sources for sensing applications.

Design, synthesis, and biological evaluation of novel tetrahydroprotoberberine derivatives (THPBs) as proprotein convertase subtilisin/kexin type 9 (PCSK9) modulators for the treatment of hyperlipidemia.

Proprotein convertase subtilisin/kexin type 9 (PCSK9) modulators may attenuate PCSK9-induced low-density lipoprotein receptor (LDLR) degradation in lysosome and promote the clearance of circulating low-density lipoprotein cholesterol (LDL-C). A novel series of tetrahydroprotoberberine derivatives (THPBs) were designed, synthesized, and evaluated as PCSK9 modulators for the treatment of hyperlipidemia. Among them, eight compounds exhibited excellent activities in downregulating hepatic PCSK9 expression better than berberine in HepG2 cells. In addition, five compounds 15, 18, 22, (R)-22, and (S)-22 showed better performance in the low-density lipoprotein, labeled with 1,1'-dioctadecyl-3,3,3',3'-tetramethyl-indocarbocyanine perchlorate (DiI-LDL) uptake assay, compared with berberine at the same concentration. Compound 22, selected for in vivo evaluation, demonstrated significant reductions of total cholesterol (TC) and LDL-C in hyperlipidemic hamsters with a good pharmacokinetic profile. Further exploring of the lipid-lowering mechanism showed that compound 22 promoted hepatic LDLR expression in a dose-dependent manner in HepG2 cells. Additional results of human ether-à-go-go related gene (hERG) inhibition assay indicated the potential druggability for compound 22, which is a promising lead compound for the development of PCSK9 modulator for the treatment of hyperlipidemia.

Pump Polarization and Size Effects on the Performance of Polymer Lasers.

The parameters of a pump have a marked influence on the performance of distributed feedback polymer lasers. Our polymer laser consisted of a grating and a polymer film. We fabricated the grating using interference lithography. The polymer film was spin coated on the grating. A half-wave plate was used to change the pump polarization, and an x-y slit was used to change the pump size. The direction of grating lines were parallel to the x axis of the slit. The laser performance was modified by changing the polarizations and sizes of the pump beam. The lasing threshold increased more rapidly with decreasing pump size in the y direction than in the x direction. The influence of the pump polarization on the lasing threshold for decreasing pump size in the x direction was greater than that for decreasing pump size in the y direction. These results may be useful for the miniaturization of distributed feedback polymer lasers.

Controlling the Performance of Polymer Lasers via the Cavity Coupling.

The polarization and threshold of distributed feedback (DFB) polymer lasers were controlled by adjusting the cavity coupling. The cavity of DFB polymer lasers consisted of two gratings, which was fabricated by a two-beam multi-exposure holographic technique. The coupling strength of the cavity modes was tuned by changing the angle between the two gratings. The threshold of the polymer lasers decreased with reducing the coupling strength of the cavity modes. A minimum threshold was observed at the lowest coupling strength. Moreover, the azimuthally polarized output of the polymer lasers was modified by changing the cavity coupling. These results may provide additional perspectives to improve the performance of DFB polymer lasers.

Effects of Cavity Structure on Tuning Properties of Polymer Lasers in a Liquid Environment.

The effect of cavity structures on the tuning properties of polymer lasers was investigated in two common distributed-feedback cavities. The configurations of the two cavities are substrate/grating/active waveguide and substrate/active waveguide/grating, respectively. The polymer lasers were operated in the liquid environment, and the laser wavelength was tuned dynamically by changing the refractive index of the liquid. Polymer lasers based on the substrate/grating/active waveguide structure showed a higher tunability than those based on the substrate/active waveguide/grating structure due to a larger electric field distribution of the laser mode in the liquid environment. It is expected that these results will be useful in the development of tunable laser sources.

Flexible Random Laser Using Silver Nanoflowers.

A random laser was achieved in a polymer membrane with silver nanoflowers on a flexible substrate. The strong confinement of the polymer waveguide and the localized field enhancement of silver nanoflowers were essential for the low-threshold random lasing action. The lasing wavelength can be tuned by bending the flexible substrate. The solution phase synthesis of the silver nanoflowers enables easy realization of this type of random lasers. The flexible and high-efficiency random lasers provide favorable factors for the development of imaging and sensing devices.

Hybrid lasing in a plasmonic cavity.

Distributed feedback lasing and surface plasmon lasing were achieved in a single laser device. The laser cavity consisted of a four-layer structure including two metal films, a grating, and a gain material; the cavity was fabricated by combining interference lithography and metal evaporation. A hollow structure was employed to overcome the Joule losses of the metal film. The total thickness of the multilayer structure was 350 nm. The lasing threshold for this hybrid lasing was decreased significantly owing to the coupling between the SP mode in two metal films and the waveguide mode. The combination of SP lasing and distributed feedback lasing could benefit the design of biosensors, all-optical circuits, and electrically pumped devices.