High-sensitivity Bloch surface wave sensor with Fano resonance in grating-coupled multilayer structures

A new type of device consisting of a lithium niobate film coupled with a distributed Bragg reflector(DBR)was theoretically proposed to explore and release Bloch surface waves for applications in sensing and detection.The film and grating made of lithium niobate(LiNbO_(3))were placed on both sides of the DBR and a concentrated electromagnetic field was formed at the film layer.By adjusting the spatial incidence angle of the incident light,two detection and analysis modes were obtained,including surface diffraction detection and guided Bloch detection.Surface diffraction detection was used to detect the gas molecule concentrations,while guided Bloch detection was applied for the concentration detection of biomolecule-modulated biological solutions.According to the drift of the Fano curve,the average sensor sensitivities from the analysis of the two modes were 1560°/RIU and 1161°/RIU,and the maximum detection sensitivity reached2320/RIU and 2200°/RIU,respectively.This study revealed the potential application of LiNbO_(3)as a tunable material when combined with DBR to construct a new type of biosensor,which offered broad application prospects in Bloch surface wave biosensors.

A sliding-mode triboelectric nanogenerator with chemical group grated structure by shadow mask reactive ion etching

With the support by the National Natural Science Foundation of China,a collaboration by the research groups led by Prof.Cheng Gang(程纲)from Henan University and Prof.Wang Zhonglin(王中林)from Beijing Institute of Nanoenergy and Nanosystems,Chinese Academy of Sciences,invents'a sliding-mode triboelectric nanogenerator with chemical group grated structure by shadow mask reactive ion etching',which was published in ACS Nano(2017,11(9):8796-8803).

Large-area periodic lead halide perovskite nanostructures for lenticular printing laser displays

Lenticular printing technique provides a promising way to realize stereoscopic displays,especially,when microscopic optical structures are integrated into light-emitting materials/devices.Here,we fabricated large-area periodic structures with a spatial resolution at a wavelength scale from hybrid perovskite materials via a space-confined solution growth method.It takes advantages of both high refractive index contrast and high luminescence brightness,which allows the optical modulation on not only the reflection of illumination,but also the light emission from hybrid perovskites.The distributed feedback within these periodic structures significantly improves the degree of polarization and directionality of laser actions while their threshold is also reduced.These findings enable us to present a prototype of lenticular printing laser displays that vary emission colors at different view angles,which may find applications in creating high-resolution and high-contrast holographical images.

Impact of the CoFe microstructure etched surface oxidation on Co spin and orbital moment

Patterned ferromagnetic thin film shows promising applications in ultra-high density magnetic storage,magnetoresistive transducer,magnetic random access memory and many other devices.Since the performance of these devices is closely associated with the magnetic properties of the etched patterns,it is necessary to study the effects of freshly etched surface oxidation on the magnetic properties of the patterned microstructures.In the current work,were carried out an X-ray Magnetic Circular Dichroism(XMCD) study on a 50 nm Co 0.9 Fe 0.1 continuous thin film and a related patterned Co 0.9 Fe 0.1 grating structure etched with a 2 μm period.Based on the sum rules,the spin and orbital moments were calculated for these two samples,respectively.The results indicated that the spin and orbital moments of grating structure(1.34μ B and 0.24μ B,respectively) decreased 17.3% compared with the corresponding continuous film(1.62μ B and 0.29μ B,respectively).We proposed that the moment decreasing of the patterned grating structure was mainly caused by the etched surface oxidation during the pattern manufacture process.The oxidation ratio of Co element in the patterned grating structure is 14.4% calculated from X-ray absorption spectroscopy(XAS) measurement.Considering the oxidation ratio,we amend the spin and orbital moment of Co and the amended result is basically in accordance with that of continuous film,demonstrating that the difference of the spin and orbital moments between the sub-micron grating unit and the continuous film is really caused by the oxidation.

Multiple directional enhanced light source through a periodic metal grating structure

In recent years, semiconductor quantum dots （QDs） have been widely used as photon sources in quantum optics due to their special properties, such as high quantum effi- ciency, narrow and tunable emission spectrum, easy manipulation, and so on. The spontaneous emission of QDs also depends on the surrounding environment.

A flat-topped etched diffraction grating demultiplexer with low polarization-dependent loss using a tapered MMI structure

A flat-topped etched diffraction grating (EDG) demultiplexer with a low polarization-dependent loss (PDL) is designed. A design and simulation method based on the method of moment (MoM) is proposed. A 65-channcl EDG demultiplexer with channel spacing of 100 GHz is considered as a design example. A tapered multi-mode interferometer (MMI) is used to flatten the passband of the EDG demultiplexer. The numerical results show that the exit width of the tapered waveguide impacts the loss of the TE case more than that of the TM case. Based on this fact, the exit width of the taper is optimized to obtain the lowest PDL. The tapering angle is also optimized where the minimal ripple is obtained. The designed EDG demultiplexer has an excellent flat-topped spectral response and a very low PDL.

Bragg Grating Tuning Package Based on a Clamped Beam Structure

It is reported that simple beam structure used for FBG tuning can cause FBG chirping. A novel tuning method utilizing the clamped beam structure under pure bending is introduced. In this paper, we experimentally and theoretically demonstrate that new method can tune the Bragg wavelength without chirp. Further integration of this package can be used for FBG athermal/MEMS packaging.

Enhanced sum-frequency generation from etchless lithium niobate empowered by dual quasi-bound states in the continuum

The miniaturization of nonlinear light sources is central to the integrated photonic platform,driving a quest for high-efficiency frequency generation and mixing at the nanoscale.In this quest,the high-quality(Q)resonant dielectric nanostructures hold great promise,as they enhance nonlinear effects through the resonantly local electromagnetic fields overlapping the chosen nonlinear materials.Here,we propose a method for the enhanced sum-frequency generation(SFG)from etcheless lithium niobate(LiNbO_(3))by utilizing the dual quasi-bound states in the continuum(quasi-BICs)in a one-dimensional resonant grating waveguide structure.Two high-Q guided mode resonances corresponding to the dual quasi-BICs are respectively excited by two near-infrared input beams,generating a strong visible SFG signal with a remarkably high conversion efficiency of 3.66×10^(-2)(five orders of magnitude higher than that of LiNbO_(3)films of the same thickness)and a small full-width at half-maximum less than 0.2 nm.The SFG efficiency can be tuned via adjusting the grating geometry parameter or choosing the input beam polarization combination.Furthermore,the generated SFG signal can be maintained at a fixed wavelength without the appreciable loss of efficiency by selectively exciting the angle-dependent quasi-BICs,even if the wavelengths of input beams are tuned within a broad spectral range.Our results provide a simple but robust paradigm of high-efficiency frequency conversion on an easy-fabricated platform,which may find applications in nonlinear light sources and quantum photonics.

Surface-plasmon-enhanced light transmission intensity with a basic grating in GaNbased LED

The transmitting light in GaN-based LED with 30 nm thickness metal film grating is investigated. We proposed a basic grating structure model to enhance light intensity in GaN material, which was simpler and cheaper. We calculated and analyzed the structure with different parameters, and studied the numerical simulation results of Ag-films/Al-films/Au-films. With a simple A1 or Ag basic grating structure, the 7.4-7.6 times intensity of 550 nm light can be obtained easily, and the enhancement efficiency is better than others.

Periodic structural defects in Bragg gratings and their application in multiwavelength devices

In this paper, we present the finding that periodic structural defects(PSDs) along a Bragg grating can shift the Bragg wavelength. This effect is theoretically analyzed and confirmed by numerical calculation. We find that the Bragg wavelength shift is determined by the defect size and the period of the defects. The Bragg wavelength can be well tuned by properly designing the PSDs, and this may provide an alternative method to fabricate grating-based multiwavelength devices, including optical filter arrays and laser arrays. In regards to wavelength precision, the proposed method has an advantage over the traditional methods, where the Bragg wavelengths are changed directly by changing the grating period. In addition, the proposed method can maintain grating strength when tuning the wavelength since only the period of defects is changed. This will be a benefit for devices such as arrays.

Subwavelength ripple formation on planar and nonplanar surfaces by femtosecond laser scanning

The self-formation of periodic subwavelength ripples by linear polarized femtosecond laser scanning planar and non-planar tungsten targets on the employed laser wavelength, scanning speed, and energy fluence are examined systematically. The results show that, for a certain laser wavelength, the scanning conditions have no obvious effect to the morphological features of grating structures in the threshold range of laser fluence. The spatial structured period of gratings can be self-consistently interpreted by recently presented physical model of surface two-plasmon resonance. The subwavelength structures on cylindrical surface would be a good method to realize unique surface functions on complex surface of micro-devices.