基于亚波长二维光栅的入射角不敏感颜色滤光片研究

提出了一种基于二维亚波长光栅的具有非偏振光入射下入射角不敏感特性的反射式颜色滤光片. 采用严格耦合波分析方法详细分析了光栅周期、光栅层厚度以及固定光栅占空比下光栅的结构尺寸对反射率峰值、反射带位置及带宽的影响. 结合入射角不敏感特性, 经过优化设计得到了光栅的最终结构参数, 获得了中心波长424 nm, 峰值反射率56%, 带宽45 nm的反射滤光片.模拟结果表明, 在非偏振光入射下, 此滤光片的反射光谱表现出显著的入射角不敏感特性. 当入射角高达60°时反射带的中心波长偏移6 nm 反射率下降6%带宽增加8 nm 其参数没有较大变化通过调整光栅的结构参数可在400–520 nm范围内调节滤光片的中心波长以获得不同颜色的入射角不敏感滤光片. 关键词： 反射式滤光片 二维亚波长光栅 入射角不敏感 严格耦合波分析     

Effect of grating on IR LED device performance

The electroluminescence in the range of 3–4.5 μm and 6–10 μm from a Sb-based type II interband quantum cascade structure is reported. We measured the light emission from the top surface of the LED device with different grating structures. We used different etch depths for the grating formation. The light–current–voltage (LIV) characteristics measured at both room and cryogenic temperatures show that the device with 45° angle grating and 1.0 μm deep etch onto the GaSb surface has the highest emission power.     

Light trapping in amorphous silicon solar cells with periodic grating structures

We report on the design of amorphous silicon solar cells with the periodic grating structures. It is a combination of an anti-reflection structure and the metallic reflection grating. Optical coupling and light trapping in thin-film solar cells are studied numerically using the Rigorous Coupled Wave Analysis enhanced by the Modal Transmission Line theory. The impact of the structure parameters of the gratings is investigated. The results revealed that within the incident angles of ? 40^° to + 40^° the reflectivity of the cell with a period of 0.5 μm, a filling factor of 0.1 and a groove depth of 0.4 μm is 4%–22.7% in the wavelength range of 0.3–0.6 μm and 1%–20.8% in the wavelength range of 0.6–0.84 μm, the absorption enhancement of the a-Si layer is 0.4%–10.8% and 20%–385%, respectively.     

A 100 kHz Narrow-Pulse-Width Mid-Infrared Optical Parametric Oscillator Based on PPMgLN Crystal

We report a narrow pulse width optical parametric oscillator based on periodically poled MgO:LiNbO₃ (PPMgLN) with a high repetition rate under quasi-phase matched conditions. When the maximum pumping power of the 1,064-nm laser was 14.57 W, the acousto-optical (A-O) Q-switch repetition rate was 100 kHz, and the PPMgLN crystal grating period was 29.5 μm. A 1,474-nm signal light output power of 4.21 W and a 3,828 nm idler light output power of 1.547 W were obtained, corresponding to a pulse width of 9.52 ns and 9.65 ns, respectively. The overall optical–optical conversion efficiency was 39.5%. Additionally, by changing the temperature from 25°C to 150°C, a tunable signal wavelength of 1,474–1,499 nm and idler wavelength at 3,676–3,828 nm of the output laser were achieved.     

Diffraction efficiency and electron microscopy of large amplitude holographic gratings

The diffraction efficiency of Ag coated holographic gratings was measured as a function of the grating amplitude, H, for a He-Ne laser incident at 30° and 70° in the plane perpendicular to the grating grooves. The grating amplitude was determined using a scanning electron microscope. It was found that the diffraction efficiency of s polarized light increased monotonically with increasing H for H < 250 nm. In contrast, for the same amplitude range, the diffraction efficiency of p polarized light oscillated through two maxima at H = 90 nmand 220 nm. These results were compared to the theoretical calculations of Heitmann and found to agree within 10% for H < 60 nm in the s polarization case and for H < 15 nm in the p polarization case. For larger H, the data deviated significantly, presumably due to a breakdown of the small amplitude assumption on which the calculations were based.     

Grating-coupled external-cavity short-wavelength (λ ≈ 3.9 μm) InGaAs/InAlAs/AlAs quantum-cascade lasers

In this work, the tunability properties of short-wavelength (λ ~ 3.9 μm) quantum-cascade lasers (QCLs) were studied, which is a first in the world at such short wavelengths. The experimental setup of an external cavity (EC) QCL was arranged in a Littrow configuration. A tuning range over 75 cm^?1 has been achieved by using an uncoated 23 μm stripe-width QCL at room temperature. A single-mode operation could be obtained at 2527 and 2544 cm^?1 at different grating angles by using an anti-reflection (AR) coated 23 μm ridge. A 5 μm stripe-width QCL without an AR coating could be tuned over 160 cm^?1.     

LD end-pumped c-Cut Nd:YVO<Subscript>4</Subscript>/KTP self-Raman laser at 560 nm

Intra-cavity sum frequency generation (SFG) of c-cut Nd:YVO₄ self-Raman laser was investigated for the first time. A 4 × 4 × 10 mm³ KTP crystal with a type-II phase-matching cutting angle (θ = 83.4°, φ = 0°) was used for SFG between the fundamental light at 1066 nm and first-Stokes light at 1178 nm. The laser system with different curvature radii of output couplers and different pulse repetition frequencies were investigated. At a pump power of 14 W and pulse repetition frequency of 20 kHz, the average output power of yellow-green laser at 560 nm up to 840 mW was achieved, corresponding to a slope efficiency of 7.6% and a conversion efficiency of 6% with respect to diode pump power.     

All-solid multi-core fiber-based multipath Mach–Zehnder interferometer for temperature sensing

A novel multipath Mach–Zehnder interferometer (m-MZI) is proposed and experimentally demonstrated, which is fabricated by fusion splicing a segment of all-solid multi-core fiber (MCF) between two sections of single mode fiber-28 with a well-controlled lateral offset at the splice points. Beam propagation method-based simulation results demonstrated light passing throw MCF from multiple paths. Experiments with different lengths of MCF were implemented to investigate our proposed m-MZI’s response to temperature and strain. Compared with previously reported optical fiber modal interferometers, higher phase sensitivity can be obtained in our scheme due to the multipath interference configuration embedded in one fiber. A very high temperature sensitivity of 130.6 pm/°C has been achieved, and the maximum strain sensitivity is less than 0.284 pm/με in all experiments. A record low strain-to-temperature cross-sensitivity of 6.2 × 10^?4 °C/με has been realized, and it shows great significance of this in-fiber integrated multipath Mach–Zehnder interferometer in practical temperature sensing applications.     

Gamma-ray angular correlations perturbed by a stochastic Gaussian-Markov process

Self-broadening of principal series lines of rubidium has been studied using a steel absorption tube heated up in an electric furnace. Line profiles were obtained with a grating spectrograph of high resolution in the temperature range 350–420 °C corresponding to number densities of 18.6–119 · 10¹⁵ cm^?3. The half-widths of the lines disagree with classical impact calculations using dipol-dipol interaction but approach nearly the asymptotic value of the quantum-mechanical polarization theory of Reinsberg.     

Measurement of the polarization correlation parameter C nn in the pp elastic scattering with an unpolarized proton target and an unpolarized 1-GeV proton beam

The polarization correlation parameter C _nn in the elastic proton-proton scattering was for the first time measured with a high statistical accuracy at 1 GeV using an unpolarized proton beam incident on an unpolarized proton target. Both outgoing protons from the reaction were detected in coincidence by means of a two-arm focusing magnetic spectrometer installed at nonsymmetric angles corresponding to the center-of-mass scattering angle Θ_cm = 62.25°. The correlation parameter C _nn , as well as polarizations P ₁ and P ₂ of the secondary protons, were measured by means of multiwire proportional chamber polarimeters placed at the focal planes of each spectrometer arm. The obtained data are compared with the predictions of the phase-shift analysis. The connection with the experiment on C _nn and polarization measurements in the (p, 2p) reaction on ⁴He and other light nuclei in similar kinematics is discussed     

Polarization and Color Separator Using Binary Phase Grating with Subwavelength Period

A data projector using three liquid crystal display panels has a complex optical system. The illuminating optics separate the beam from a light source into three primary colors and separate those into opposite polarizations using multi-layer films and prisms. A reflection grating with the period of subwavelength has high diffraction efficiency for p polarized light and high regularly reflectance for s polarized light. The diffraction angle of a grating largely depends on the wavelength, because a diffractive optical element (DOE) has large chromatic dispersion. The grating with the period of subwavelength can separate the unpolarized light into polarization components effectively using its polarization dependency and can separate white light into color components using its chromatic dispersion simultaneously. The grating makes the optical system simpler and smaller than those with conventional devices. In this paper the efficiency of polarization separation for the grating is calculated by a rigorous analytical method. Next, the condition for color separation is calculated by Snell#x0027;s law, and an optical system using a grating that performs polarization and color separation is proposed. Experimental results of the DOE fabricated are well matched with those of this simulation.     

Design of High-Efficiency Diffraction Gratings Based on Rigorous Coupled-Wave Analysis for 800nm Wavelength

We report on the design of a high diffraction efficiency multi-layer dielectric grating with wide incident angle and broad bandwidth for 80Ohm. The optimized grating can achieve 〉 95% diffraction efficiency in the first order at an incident angle of 5° from Littrow and a wavelength from 77Ohm to 83Ohm, with peak diffraction efieieney of 〉 99.5% at 80Ohm. The electric field distribution of the optimized multi-layer dielectric grating within the gratings ridge is 1.3 times enhancement of the incidence light, which presents potential high laser resistance ability. Because of its high-effieieney, wide incident, broad bandwidth and potential high resistance ability, the multi-layer dielectric grating should have practical application in Ti：sapphire laser systems.     

用于高能啁啾脉冲压缩的光子晶体光栅的设计

 为了克服目前高能短脉冲装置压缩光栅的损伤阈值无法满足要求的问题,针对星光Ⅲ装置皮秒激光束的压缩器,设计了由熔石英材料构成的、具有较高损伤阈值的光子晶体光栅,该光栅由2维光子晶体和表面光栅结构两部分组成,具有高反射效率和强角色散的能力。计算结果显示:经过优化设计的光子晶体光栅在波长1 053 nm,57°～77°的入射范围内,-1级衍射效率超过了92%,而当入射角为71°时,在1 040～1 090 nm光谱范围内,-1级衍射效率超过92%,性能满足使用要求。     

The charge states’ conversion of the activator ions in CaF2:Eu nanophosphors

According to stationary X-ray-excited luminescence spectra and thermally stimulated luminescence spectra of CaF₂:Eu nanophosphors, it was found that Eu³⁺?→?Eu²⁺ conversion can occur during thermal annealing of fine-grained (d?=?25?nm) nanoparticles in the 200–800°C range, which is accompanied by an increase in their size within 40–189?nm. An important role of the exciton mechanism of Eu²⁺ luminescence excitation was revealed according to the temperature dependence of X-ray-excited luminescence spectra of CaF₂:Eu nanoparticles of 114?nm size. The maximum of the X-ray-excited luminescence light output of CaF₂:Eu nanophosphors in the Eu²⁺ ions’ emission band was traced out at 400–500°C annealing temperature and at the size of nanoparticles of 114–180?nm. The subsequent growth of the annealing temperatures, particularly in the 800–1000°C range, causes the reduction of X-ray-excited luminescence light output because of the increment of lattice defects’ concentration due to a sharp increase in the size of nanoparticles and their agglomeration.     

Spectral beam combining of fiber lasers based on a transmitting volume Bragg grating

Based on the principle of spectral beam combining using a transmitting volume Bragg grating, a simple experimental setup was designed, in which an approach to control the incidence angles of beams using a focusing lens is presented. The experimental results for the spectral beam combining of two fiber lasers are reported. The gain media used in this experiment were large-mode area Er³⁺/Yb³⁺ co-doped double-clad fibers, pumped by semiconductor lasers. The output powers of the two fiber lasers were 0.39 and 0.53 W, respectively. With a grating diffraction efficiency of about 60%, a maximum combined power of 0.64 W with an absolute combining efficiency of about 69.6% was achieved.     

High-efficiency optical coupling to planar photodiode using metal reflector loaded waveguide grating coupler

For the realization of optoelectronic integrated circuits, it is required to incident light perpendicularly to a planar Si photodiode. We propose a high-efficient vertical optical coupler using an amorphous Si optical waveguide grating coupler with top reflector, which is transparent at 850 nm wavelength range. The optical waveguide (width of 300 nm $\times $ height of 100 nm) coupler is analyzed by using finite element method. The coupling efficiency of 80 % is calculated at the grating period of 380 nm, the duty ratio of 0.75 and the depth of 35–65 nm with top metal reflector.     

Nanoscale plasmonic devices for dynamically controllable beam focusing and scanning

We have performed simulations to investigate the variable focusing and scanning capability of metallic nano-slit configurations. In a symmetric nanorod configuration inside an aperture with adjustable offset of the center rod, the focal position is found to be variable in the 0.5–3.5 μm range. In a ladder configuration of the rods, the transmitted beam is found to be deflected up to 23°. Horizontal displacement of rods allows for finer control of angular scanning up to 4°. Such slit geometries offer the potential to be controlled by using nano-positioning systems for applications in dynamic beam shaping and scanning on the nanoscale.     

Scaling of the discharge heated copper vapor laser

Optimum working temperature of 1650 ± 50°C was determined for the longitudinal copper vapor laser. Using neon in the pressure range 20–200 torr we were able to operate lasers of volumes up to 600 cm³ at optimum temperature. Power output was proportional to tube volume and efficiency to the square of tube radius. Average power of 19.5 W was obtained at 4 kHz with 0.7% efficiency.     

Low temperature polarization effects in ice

When an initially unpolarized HF doped ice specimen is warmed at a constant rate in an applied electric field two peaks are observed in the current. The low temperature peak occurs near 100°K and the temperature at which this peak occurs is seen to increase as the HF concentration decreases. The second peak appears to occur randomly in the temperature range 125–135°K. These peaks are also observed if the sample is cooled in an applied electric field and then warmed at a constant rate with the field removed. It is suggested that the first peak is due to a dielectric relaxation process which is governed by the L defects released from the HF molecules. This release of L defects is shown to obey the law of mass action with an activation energy for liberation of an L defect of 0.12±0.06 eV and a dissociation constantk _o ^L≈10²⁹ m^?3. A simple theoretical model of ice is also developed which predicts the current reversal phenomenon observed by Dengelet al. [11] suggesting that it is due to dipole relaxation and not to ferroelectric ordering.     

Monoclinic HfO2:Eu X-ray phosphor

HfO₂ and HfO₂:Eu powders were synthesized with Pechini method at temperatures in the range of 600–1500 °C. Structural, radioluminescence and photoluminescence properties of the powders were investigated. The highest light output of about 20% of the efficiency of commercial GOS:Eu was found for materials containing 0.5% of Eu and prepared at 1500 °C. The data shows, that further improvement of light output could be obtained if materials are processed at yet higher temperatures. Emission spectra indicate that Eu³⁺ experiences variety of symmetries of its surroundings. Undoped materials produce broad band emission peaking at 480 nm and showing a significant afterglow.