Polarization tunable transmitted full-color display enabling switchable bright and dark states.

Although structural colors based on nanostructures have attracted many researchers' attentions due to their superior durability and high resolution, most previous reports focused on the static and dynamic structural colors in reflection mode and few researchers focus on the static and dynamic transmission colors for high-saturation RGB models. Here, the hybrid Al-Si3N4 nanogratings with the top SiO2 capping layer and the bottom MgF2 layer that can switch full-hue and high-saturation transmitted structural colors on and off completely by changing the polarization state are theoretically demonstrated. Meanwhile, the hybrid Al-Si3N4 nanogratings with the top capping layer and the bottom layer also achieve the transmittance spectra with the full width at half maximum of ∼58 nm and the transmittance efficiency of over 70% in the on state. The added top capping layer and bottom layer can suppress the sideband of transmittance spectra in the on state and maintain the near-zero transmittance in the off state, thus improving the switching performance between bright and dark states. The realizable high-saturation colors in the on state can take up 125% sRGB space and 80% Adobe sRGB space. More interestingly, with the incident angle varying from 0° to 50°, full-hue color can be also realized in the on state and nearly black color can be also maintained in the off state. The strategy will provide potential applications in advanced color encryption and multichannel imaging.

Electrically switchable multicolored filter using plasmonic nanograting integrated with liquid crystal for optical storage and encryption.

This study proposed the synergistic merging of twisted-nematic liquid crystals (LCs) and nanograting embedded etalon structures for plasmonic structure color generation, realizing dynamic multifunctional metadevices. Metallic nanogratings and dielectric cavities were designed to provide color selectivity at visible wavelengths. Meanwhile, the polarization for the transmission of light could be actively manipulated by electrically modulating these integrated LCs. Moreover, manufacturing independent metadevices as single storage units with electrically controlled programmability and addressability facilitated secure information encoding and secretive transfer by dynamic high-contrast images. The approaches will pave the way for the development of customized optical storage devices and information encryption.

Spark plasma sintering of MgAl2O4:Mn2+ transparent ceramic phosphors with low thermal quenching, narrow-band green emission.

MgAl2O4:Mn2+ transparent ceramics were fabricated by reactive spark plasma sintering (SPS). The ceramic samples show narrow-band green emission under the 450 nm blue light excitation, which is corresponding to 4T1(4 G)-6A1(6S) transition of Mn2+ in the tetrahedral site. The emission peak of the Mg0.93Al2O4:0.07Mn2+ ceramic sample was located at 525 nm with the full-width at half-maximum (FWHM) value of 36 nm. The internal quantum yield (IQY) of Mg0.93Al2O4:0.07Mn2+ reached 63%. The emission intensity remained ∼98% at 150 °C compared to its initial value at room temperature, showing excellent thermal quenching performance. The results indicated that MgAl2O4:Mn2+ ceramic phosphor is a promising candidate for high brightness, wide gamut display backlight applications.

Fabrication of uniform-aperture multi-focus microlens array by curving microfluid in the microholes with inclined walls.

A variety of techniques have been proposed for fabricating high-density, high-numerical-aperture microlens arrays. However, a microlens array with a uniform focal length has a narrow depth of field, limiting the ability of depth perception. In this paper, we report on a fabrication method of multi-focus microlens arrays. The method for the preparation of the mold of the microlens array is based on 3D printing and microfluidic manipulation techniques. In the preparation of the mold, curved surfaces of the photo-curable resin with different curvatures are formed in the 3D printed microholes whose walls are inclined with different angles. The replicated microlens array consists of hundreds of lenslets with a uniform diameter of 500 µm and different focal lengths ranging from 635 µm to 970 µm. The multi-focus microlens array is capable of extending the depth of field for capturing clear images of objects at different distances ranging from 14.3 mm to 45.5 mm. The multi-focus microlens array has the potential to be used in a diversity of large-depth-of-field imaging and large-range depth perception applications.

Omnidirectional and compact transmissive chromatic polarizers based on a dielectric-metal-dielectric structure.

High-performance omnidirectional transmissive chromatic polarizers based on a one-dimensional dielectric-metal-dielectric subwavelength grating structure are proposed. The incident angle-insensitive properties, azimuthal angle-insensitive properties and polarization features are investigated thoroughly to realize the proposed omnidirectional transmissive chromatic polarizers. The color difference at different angles for the proposed yellow polarizers is less than 0.9746, and the extinction ratio at different angles for the proposed cyan polarizers exceeds 26. Analysis of the power density profiles for the transverse electric (TE) and transverse magnetic (TM) polarizations show that surface plasmon resonance and high refractive index contrast properties lead to excellent polarization features and high angular tolerance.

Photocatalytic water splitting properties of Cu2+ exchanged Beta zeolites.

Photocatalytic water splitting with solar energy is the most promising and environmentally friendly hydrogen production method. Having an efficient and cost-effective photocatalyst is key to hydrogen production. Cu dopant has been shown to greatly enhance photocatalytic activities. In this work, Cu2+ ions were doped into Beta zeolite powders (Cu-Beta) by the ion exchange method. The hydrogen evolution efficiency of Cu-Beta was much higher than the raw Beta zeolites without Cu loading. After solid phase reaction, the band gap of Cu-Beta reduced from 3.48 eV to less than 2 eV, and as a result enhanced the optical absorption intensity, particularly in the visible region. The best hydrogen evolution efficiency was 102.12 µmol · g-1 · h-1 when the treated temperature was 900 °C (Cu-Beta-900). The temperature of the solid phase reaction had an important influence on the photocatalytic performance of Cu-Beta; a suitable reaction temperature can greatly improve its photocatalytic performance.

Mn4+ activated Al2O3 red-emitting ceramic phosphor with excellent thermal conductivity.

An Al2O3:Mn4+, Mg2+ red emitting ceramic phosphor, which can be effectively excited by ultraviolet and blue light, was successfully synthesized via solid-state reaction in an oxygen and air atmosphere. The ceramic sintered in oxygen atmosphere has higher optical transmittance and stronger luminescence intensity than the ceramic sintered in the air, which is more suitable for LED application. Since the structure of α-Al2O3 is very simple, it is convenient to study the factors affecting the Mn4+ luminescence. The crystal-strength parameter Dq, Racah parameters B and C, and the nephelauxetic ratio ß1 were calculated to investigate the influence of crystal field strength and nephelauxetic effect on the emission of Mn4+ in the Al2O3 host. The ratio of Dq to B was 1.74, which was lower than 2.2. This indicated that the Mn4+ ions in the α-Al2O3 host were in a weak crystal field environment. Under the 395 nm and 460 nm excitations, quantum yields (QY) of the sample were measured to be 46% and 28.7%, respectively. The density measured by the Archimedes method was 3.61 g/cm3. The ceramic also showed an excellent thermal conductivity value, which was as high as 26.27 W·m-1·K-1@30 °C.

Fabrication of large micro-structured high-numerical-aperture optofluidic compound eyes with tunable angle of view.

A large optofluidic compound eye is developed by using a straightforward, rapid, and low-cost technique. The compound eye's angle of view can be adjusted by injecting deionized water/calcium chloride solution of different volume into the optofluidic chip. Optofluidic compound eyes containing about 78,000 microlenses of 50 µm diameter are fabricated for analysis. The angle of view can be tuned up to 104°. With the compound eye's deformation, the microlenses' focal length increases, due to the variation in profile. Owing to the non-uniform strain over the compound eye, the central lenses experience more variation. Furthermore, optical imaging of the compound eye is demonstrated and sharp images can be obtained from the omnidirectional microlenses.

Thickness-dependent surface plasmon resonance of ITO nanoparticles for ITO/In-Sn bilayer structure.

Tuning the localized surface plasmon resonance (LSPR) in doped semiconductor nanoparticles (NPs), which represents an important characteristic in LSPR sensor applications, still remains a challenge. Here, indium tin oxide/indium tin alloy (ITO/In-Sn) bilayer films were deposited by electron beam evaporation and the properties, such as the LSPR and surface morphology, were investigated by UV-VIS-NIR double beam spectrophotometer and atomic force microscopy (AFM), respectively. By simply engineering the thickness of ITO/In-Sn NPs without any microstructure fabrications, the LSPR wavelength of ITO NPs can be tuned by a large amount from 858 to 1758 nm. AFM images show that the strong LSPR of ITO NPs is closely related to the enhanced coupling between ITO and In-Sn NPs. Blue shifts of ITO LSPR from 1256 to 1104 nm are also observed in the as-annealed samples due to the higher free carrier concentration. Meanwhile, we also demonstrated that the ITO LSPR in ITO/In-Sn NPs structures has good sensitivity to the surrounding media and stability after 30 d exposure in air, enabling its application prospects in many biosensing devices.

Laser induced photocatalytic activity enhancement of TiO2 thin films.

In this paper, the photocatalytic activity enhancement of TiO2 thin films was realized by laser irradiation. The H2 yield of the as-irradiated film is 79 µmol/(h*m2), which is 33% more than that of the as-deposited TiO2 film. Spectrophotometer, X-ray diffraction and Raman system were employed to characterize the samples. The results showed that both the scanning rate and line spacing of the laser modification have effects on photocatalytic activity. It suggests that a phase junction is formed between the amorphous and rutile phases. The increment of H2 generation could be attributed to the alignment of Fermi levels in the phase junction.

Tunable guided-mode resonant filter with wedged waveguide layer fabricated by masked ion beam etching.

A compact, tunable guided-mode resonant (GMR) filter whose spectral reflectance wavelength varies as a function of the spatial position on the device is experimentally demonstrated. The filter incorporates a wedge-shaped waveguide layer that is fabricated using masked ion beam etching (MIBE) technology. A ceramic plate mask consisting of an isosceles triangular window is placed between the ion source and the sample to achieve different etching times at difference locations on the film. The increment in the magnitude of the film thickness is approximately 50 nm over a length of 33 mm, which results in a primary reflectance peak whose spectral location spans the range of 684.2-725.3 nm. The device is designed using the rigorous coupled-wave analysis (RCWA) method, and the proposed device is directed toward the practical application of GMR tunable filters.

Ultrafast imaging with anti-aliasing based on optical time-division multiplexing.

Serial time-encoded amplified microscopy (STEAM) is a novel ultrafast imaging technique that is based on space-to-time-to-wavelength mapping. Nevertheless, the technique requires a high-cost electronic digitizer of several tens of gigahertz sampling rate to read out sufficient image information. To acquire a large amount of image information by using a relatively low-sampling-rate electronic digitizer, an anti-aliasing technique based on optical time-division multiplexing is proposed. A 38.88 MHz line-scan imaging system is demonstrated experimentally. By using the proposed anti-aliasing technique, a 20 GS/s sampling rate is achieved by employing a 10 GS/s electronic digitizer. Defects and scratches on the target that were not identifiable originally can be clearly distinguished after using the proposed technique. Numerical analysis shows that the image quality can be improved by 4.16 dB, compared to that not using the anti-aliasing technique and at least 2.3 dB comparing to those obtained by bilinear, bicubic, and nearest-neighbor interpolation and Lanczos resampling techniques.

[Study on the Structural, Optical an Surface Plasmon Characteristics of Mo-Doped ZnO Thin Film].

Mo-doped zinc oxide (ZnO∶Mo) films were deposited with direct current magnetron sputtering on quartz substrates at room temperature. The effects of Mo doping content on the crystal structure, surface microstructure，optical properties and plasmon characteristics of the ZnO films were investigated with X-ray diffraction(XRD),atomic force microscopy (AFM),Spectrophotometer and Raman spectrometer. The XRD pattern reveals that pure ZnO film exhibits good crystallization and c-axis oriented while heavy doping leads to increasing film defects. That results decline the film crystalline quality. When Mo doping content exceeds 3.93 Wt%, the ZnO films transform c-axis oriented into amorphous. The AFM pattern indicates that the surface of amorphous MZO film is extraordinarily flat. The Rq is 498 pm. The transmittance spectra reveal that all samples have an average transmittance of 80% in the visible light range. The optical band gap energy (Eg) increases from 3.28 to 3.60 eV as the Mo doping content increase. The absorbance spectrum indicates that ZnO surface plasmon resonance absorbance perk moves to short-wavelength as the Mo doping content increase. The Raman spectrum suggests that heavy Mo doping make the Raman scattering intensity decrease significantly. This paper obtains amorphous ZnO thin film by Mo doping. That broadens the application field of ZnO thin film materials. Meanwhile, we study the effect of Mo doping concentration on ZnO thin films surface plasmon, which provides important reference value for the preparation of oxidized zinc base photonic devices.

Electrically driving bandwidth tunable guided-mode resonance filter based on a twisted nematic liquid crystal polarization rotator.

A novel bandwidth-tunable filter is proposed based on nonpolarizing guided-mode resonance effect. The compact, electrically driving bandwidth-tunable optical filter is realized by taking advantage of the effect of bandwidth-to-polarization sensitivity and using a twisted nematic liquid crystal polarization rotator for simple and precise polarization control. The operation principle and the design of the device are presented. The center wavelength is fixed at 623.1 nm with a relatively symmetric line shape. The full-width at half-maximum bandwidth is tuned from 12 to 44.8 nm by controlling the voltage in the polarization rotator.

Stroboscopic Surface Thermal Lensing for Fast Detection of Thermal Defects in Large-Scaled Coating Films.

A stroboscopic surface thermal lensing (SSTL) system for the fast detection of thermal-induced defects in large-scaled optical coating films was constructed. The SSTL signal was generated by a set of double-modulators and captured by a high speed matrix camera, respectively. The spot size of both pump laser and probe laser expanded for larger detection area was finished in a single step. Based on the STL technique, both the mapping of amplitude and the phase of SSTL signal on the whole area of the coatings can be achieved simultaneously.

[Study of Surface Enhanced Raman Spectroscopy on Copper Films Modified by Ion Beam].

Surface-enhanced Raman Spectroscopy (SERS) was a rapid non-destructive testing. It was based on detecting molecule vibrational spectrum which was adsorbed on the metallic surface. Now it was widely used in surface adsorption, electrochemical catalysis, sensors, bio-medical testing, trace amount analysis and other fields. In our experiment, copper metallic films were deposited 50 nm on BK7 glass substrates by direct current magnetron sputtering. And then the films were employed for the Ar ion beam etching modification. The structure, morphology and optical properties was characterized by X-ray diffraction (XRD), Atomic Force Microscope (AFM), spectrophotometer and Raman spectroscopy. In the XRD graph, the peak value of modify copper film were the same with the untreated film. So the structure of copper film was not change. With increasing the power of Ar ion, the surface roughness was changed, and scattered spectrum intensity was increased by surface roughness added. With Rhodamine B (Rh B) as a probe molecule, Raman scattered spectrum was detected on modify copper film. Compared with the different samples, we can find the Raman signal was enhanced by surface roughness added. It will have some value on study the principles of SERS.

Optical bandpass/notch filter with independent tuning of wavelength and bandwidth based on a blazed diffraction grating.

We propose a multifunctional optical filter based on a blazed diffraction grating. The optical filter can function as a bandpass filter or a notch filter. A theoretical model of the filter is built for analysis. Both bandwidth and wavelength of the filter can be independently and continuously tuned. In the experimental demonstration, the wavelength can be linearly tuned within the entire C-band and partial L-band. The bandwidths of the filter can be tuned from 1.3 to 6.4 nm (-3 dB bandwidth) and from 2.4 to 11.3 nm (-10 dB bandwidth) for bandpass function and from 6.9 to 11.9 nm (-3 dB bandwidth) and from 5.1 to 8.8 nm (-10 dB bandwidth) for band-stop function, respectively. The extinction ratio of more than 35 dB is achieved.

[Performance comparison of coronene film for UV-CCD prepared by spin-coating and physical vapor deposition].

In the present paper, the methods of spin-coating and physical vapor deposition (PVD) were researched to prepare the coronene film for UV-CCD, and their properties were characterized and compared with each other. The results of the experiment show that the process of spin-coating is relatively simple, which takes advantage of materials and retains the inherent crystal structure of coronene. However, the roughness of the film is a little more than that of PVD method; the film prepared by PVD method can absorb ultraviolet more effectively and then emits fluorescence with more intensity. Compared with the method of spin-coating, the surface of PVD film is more smoothly, and the process of thermal evaporation changes the crystal structure of coronene and forms another new crystalline state according to the XRD graph. While the whole process of PVD is morecomplex and it needs larger cost of production than spin-coating method. Besides, the comparison research work provided theoretical direction for preparing the photoluminescence down-conversion film under different requirements, such as fluorescence intensity, surface roughness and cost of production.

[The research of UV-responsive sensitivity enhancement of fluorescent coating films by MgF2 layer].

A low cost and less complicated expansion approach of wavelength responses with a Lumogen phosphor coating was adopted, as they increased the quantum efficiency of CCD and CMOS detectors in ultra-violet by absorbing UV light and then re emitting visible light. In this paper, the sensitivity enhancement of fluorescence coatings was studied by adding an anti-reflection film or barrier film to reduce the loss of the scattering and reflection on the incident interface. The Lumogen and MgF2/Lumogen film were deposited on quartz glasses by physical vacuum deposition. The surface morphology, transmittance spectrum, reflectance spectrum and fluorescence emission spectrum were obtained by atomic force microscope (AFM), spectrophotometer and fluorescence spectrometer, respectively. The results indicated that MgF2 film had obvious positive effect on reducing scattering and reflection loss in 500-700 nm, and enhancing the absorption of Lumogen coating in ultraviolet spectrum. Meanwhile, the fluorescent emission intensity had a substantial increase by smoothing the film surface and thus reducing the light scattering. At the same time, the MgF2 layer could protect Lumogen coating from damaging and contamination, which give a prolong lifetime of the UV-responsive CCD sensors with fluorescent coatings.

Optical Temperature-Sensing Performance of La2Ce2O7:Ho3+ Yb3+ Powders.

In this paper, La2Ce2O7 powders co-activated by Ho3+ and Yb3+ were synthesized by a high temperature solid-state reaction. Both Ho3+ and Yb3+ substitute the La3+ sites in the La2Ce2O7 lattice, where the Ho3+ concentration is 0.5 at.% and the Yb3+ concentration varies in the range of 10~18% at.%. Pumped by a 980 nm laser, the up-conversion (UC) green emission peak at 547 nm and the red emission at 661 nm were detected. When the doping concentration of Ho3+ and Yb3+ are 0.5 at.% and 14% at.%, respectively, the UC emission reaches the strongest intensity. The temperature-sensing performance of La2Ce2O7:Ho3+ with Yb3+ was studied in the temperature range of 303-483 K, where the highest relative sensitivity (Sr) is 0.0129 K-1 at 483 K. The results show that the powder La2Ce2O7:Ho3+, Yb3+ can be a potential candidate for remote temperature sensors.