Highly sensitive Si nanowire-based optical sensor using a Mach-Zehnder interferometer coupled microring

A Mach-Zehnder interferometer (MZI) coupled microring is demonstrated experimentally to obtain a high sensitivity as well as a large range for measuring change in refractive index. For the present MZI-coupled microring, there is a major resonance wavelength with a high extinction ratio (16-36 dB) in a very large wavelength span. Consequently, a very large quasi-free spectral range (>120 nm) is achieved, which helps to obtain a large measurement range. The MZI-coupled microring sensor is used for measuring the change of the ambient refractive index ranging from 1.0 to 1.538, and the sensitivity is as high as 111 nm/refractive index unit.     

Tunable spectral enhancement of fiber supercontinuum

We demonstrate tunable spectral enhancement of the supercontinuum generated in a microstructured fiber with a fiber long-period grating. The long-period grating leads to phase distortion and loss that, with subsequent high-intensity propagation in uniform fiber, evolves into an enhancement around the grating's resonant wavelengths. Wavelength tunability is achieved by varying the temperature or the ambient refractive index, and the spectral peak can be extinguished by immersing the grating in index-matching oil.     

关于镀有LB膜长周期光纤光栅的谐振波长的研究

理论上详细分析了长周期光纤光栅谐振波长随外界环境折射率变化而变化的光谱特性，分析结果可较好地解释镀有LB膜(Langmuir-Blodgett thin-film)的长周期光纤光栅的谐振波长与膜厚之间的关系。分析研究表明．通过减小纤芯直径和改变芯与包层折射率差等方法可调整光纤光栅的谐振波长，使其从一般光纤光栅谐振波长所处的近红外区转到可见光区，以利于光纤光栅配套仪器系统的调试并使系统成本降低，从而为长周期光纤光栅传感技术的发展和应用奠定基础。     

The signal-to-noise ratio for speech intelligibility—An auditorium acoustics design index

The Signal-to-Noise Ratio devised by Lochner and Burger contributed an objective design index for predicting speech intelligibility. Their index provided a measure of useful and detrimental reflected speech energy according to the integration and masking characteristics of hearing, and enabled predictions to be made from impulse measurements in models. However, it was found necessary to extend the Signal-to-Noise Ratio theory to account for the effect of fluctuating ambient background noise on speech intelligibility. A modified Signal-to-Noise Ratio was derived from a best-fitting empirical correlation with speech intelligibility in a series of measurements in existing auditoria. In the modified Signal-to-Noise Ratio ambient background noise is no longer considered in terms of its steady state characteristics but more specifically in terms of its transient and spectral characteristics given by the concept of the L₁₀ PNC level. The index has been applied as design criteria to prediction and to evaluation techniques.     

基于LCD显示器光谱特性的图像颜色一致性研究

为了解决环境光和显示器色温对LCD显示器图像颜色再现有较大影响的问题,提出一种基于LCD显示器光谱特性的图像颜色一致性方法。通过测量在不同环境光和色温下99个行业认可颜色的光谱,总结出不同环境光和色温对LCD显示器图像颜色再现的光谱规律。利用不同环境光下的光谱叠加性及不同色温下的光谱对应规律,实现了不同环境光和色温下的LCD显示器图像颜色一致性,一致性后的图像平均主观评价Z得分为0.50。研究结果表明,该方法能够很好地解决不同环境光和色温下的LCD显示器图像颜色的一致性问题。     

Total annoyance from an industrial noise source with a main spectral component combined with a background noise

When living close to an industrial plant, people are exposed to a combination of industrial noise sources and a background noise composed of all the other noise sources in the environment. As a first step, noise annoyance indicators in laboratory conditions are proposed for a single exposure to an industrial noise source. The second step detailed in this paper involves determining total annoyance indicators in laboratory conditions for ambient noises composed of an industrial noise source and a background noise. Two types of steady and permanent industrial noise sources are studied: low frequency noises with a main spectral component at 100 Hz, and noises with a main spectral component in middle frequencies. Five background noises are assessed so as to take into account different sound environments which can usually be heard by people living around an industrial plant. One main conclusion of this study is that two different analyses are necessary to determine total annoyance indicators for this type of ambient noise, depending on the industrial noise source composing it. Therefore, two total annoyance indicators adapted to the ambient noises studied are proposed.     

Humidity-induced spectral shift in a cross-dispersion echelle spectrometer and its theoretical investigation

The relationship between ambient relative humidity H and the position shift of a spectral line was in-vestigated both experimentally and theoretically. An echelle-based ICP emission spectrometer equipped with a CID detector was used for experimental verification of the derived model. The shift of a spectral line is quanti-tatively described by two defined spectral shift functions. △λx (x,λ, H) (in the x direction of the CID detec-tor) and △λy(y, λ, H) (in the y direction of the CID detector). Experimental results indicate that △λx(x, λ, H) does not change with a variation in ambient relative humidity, but △λy(y, λ, H) does. A spectral shift e-quation, i.e. an empirical second-order polynomial equation, can be used to describe the relationship between △λy(y, λ, H) and H. Based on the classical dipole model, classical mechanics and electrodynamics the empiri-cal spectral-shift equation involving △λx(y, λ, H) and H was theoretically deduced. The theoretical result is in good agreement with the experimental findings. The theoretical results indicate that the coefficients of the em-pirical spectral-shift equation are related to the basic physical parameters of materials and the geometric config-uration of the echelle CID ICP-AES, and also provide physical meaning to the coefficients of the empirical shift equation obtained experimentally.     

承压类特种设备用钢光谱分析

对类型标准化样品、环境温度、环境湿度、样品表面温度、样品表面粗糙度等影响光谱分析准确度的因素进行了研究,提出了类型标准化样品需选择其各元素含量与分析样品的各元素含量尽量接近,并保证分析环境与漂移校正、类型标准化校正的环境一致的前提下,通过控制分析样品的表面温度、粗糙度,可以明显提高光谱分析的准确度.     

Wind-generated ambient noise in a topographically isolated basin: a pre-industrial era proxy

During the mid-1980s, calibrated measurements of ambient noise and wind speed were made in the Tongue of the Ocean in the Bahamas to quantify the spectra and statistics of wind-generated noise. This deep basin is topographically isolated from the Atlantic Ocean and, therefore, largely acoustically decoupled from the Atlantic Ocean deep sound channel. The quantitative effects of contaminating (non-surface wind-generated) noise sources within the basin were eliminated by careful measurement and robust statistical analysis methodologies. Above 500 Hz, the spectral slopes are approximately -5 dB per octave and independent of wind speed. Below 500 Hz, the ambient noise is no longer a linear function of wind speed. Below 100 Hz and for wind speeds greater than 18.5 knots (kt), the ambient noise is independent of frequency. The minimum observed ambient noise level falls 13 dB below Urick's "light shipping" level at 30 Hz and 2-5 dB below Wenz's sea state zero level through the wind-dominated portion of the spectrum. The basin's geographical isolation and the rigorous measurement and analysis methodologies employed make this two-decade-old data set a reasonable and justified proxy for pre-industrial era ocean noise levels in the 20 Hz to 20 kHz frequency band.     

Optical properties of aluminium nitride films obtained by pulsed laser deposition: an ellipsometric study

Aluminium nitride (AlN) films obtained by pulsed laser deposition (PLD) at different low ambient nitrogen pressure have been optically investigated by spectral ellipsometry within the 300–800 nm wavelength range, Sellmeier and Wemple–DiDomenico approximation approaches have been applied for the ellipsometric data analysis. Optical parameters such as refractive index and single oscillator energies of deposited films were estimated and their dependence on the N₂ pressure was studied. The obtained refractive index values of AlN films are around 2 in a wide wavelength region above 400 nm and suggest the growth of a polycrystalline structure. The relatively low (<3.4 eV) threshold energies indicate the formation of a defective and disordered structure, formed during the deposition process. PACS 78.20.-e; 78.20.Ci; 78.66.Fd     

田间黄花梨糖度的可见/近红外光谱检测方法

提出了一种可克服背景光对田间光谱测量影响的方法。采集田间水果光谱时,环境背景光的干扰强,难以获取样品有效光谱信息。在田间采用套袋方式遮挡现场光线能得到较理想的结果,但检测效率低,仪器暗场校正和参考光谱校正等方法有利于减小模型误差,但不能有效消除环境光照的干扰。通过在测量探头前加装快门,打开快门时测得样品在仪器光源和背景光共同作用下的现场光谱,关闭快门时测得样品仅在现场环境光线作用下的背景光谱,将背景光谱从现场光谱中扣除进行背景光校正。利用偏最二乘法建立田间(背景光校正前、后)以及室内样品光谱建立黄花梨糖度预测模型,预测值与真实值的相关系数分别为0.1,0.69,0.92,均方根误差分别为0.89。Brix,0.42。Brix,0.27。Brix,预测集的RPD分别为0.79,1.69,2.58,结果表明实验所采用的背景光校正方法可有效减小田间环境光照对黄花梨可见/近红外光谱采集的影响,可用于田间水果的近红外光谱采集,有利于充分发挥可见/近红外光谱技术在果实采收前的田间管理、采收成熟度检测等方面的潜力。     

Early stage expansion and time-resolved spectral emission of laser-induced plasma from polymer

In the nanosecond laser ablation regime, absorption of laser energy by the plasma during its early stage expansion critically influences the properties of the plasma and thus its interaction with ambient air. These influences can significantly alter spectral emission of the plasma. For organic samples especially, recombination of the plasma with the ambient air leads to interfering emissions with respect to emissions due to native species evaporated from the sample. Distinguishing interfering emissions due to ambient air represents a critical issue for the application of laser-induced breakdown spectroscopy (LIBS) to the analysis of organic materials. In this paper, we report observations of early stage expansion and interaction with ambient air of the plasma induced on a typical organic sample (nylon) using time-resolved shadowgraph. We compare, in the nanosecond ablation regime, plasmas induced by infrared (IR) laser pulses (1064 nm) and ultraviolet (UV) laser pulses (266 nm). Nanosecond ablation is compared with femtosecond ablation where the post-ablation interaction is absent. Subsequent to the early stage expansion, we observe for each studied ablation regime, spectral emission from CN, a typical radical for organic and biological samples. Time-resolved LIBS allows identifying emissions from native molecular species and those due to recombination with ambient air through their different time evolution behaviors.     

Method of Designing a Corrugated Optical Waveguide Filter

The method of designing a corrugated optical waveguide filter is proposed to yield an arbitrary spectral profile of the reflection coefficient. It gives the functional dependence of the corrugation depth on distance along the wave propagation direction. The basis of the theory of the method is a combination of the effective index approach and the Fourier transformation technique. It represents the spectral profile of the reflection coefficient approximately to Fourier transformation of the spatial profile of the effective refractive index. Examples are presented to illustrate how to apply the technique.     

Low-loss multilayered metamaterial exhibiting a negative index of refraction at visible wavelengths

We experimentally demonstrate a low-loss multilayered metamaterial exhibiting a double-negative refractive index in the visible spectral range. To this end, we exploit a second-order magnetic resonance of the so-called fishnet structure. The low-loss nature of the employed magnetic resonance, together with the effect of the interacting adjacent layers, results in a figure of merit as high as 3.34. A wide spectral range of negative index is achieved, covering the wavelength region between 620 and 806 nm with only two different designs.     

Spectral changes of stochastic beams scattered on a deterministic medium

It is well known that scattering of a polychromatic plane wave by a random medium, i.e., by a medium whose refractive index varies randomly with position, may produce frequency shifts of spectral lines. It has been a common perception that a random medium is required for generation of such spectral shifts by scattering. In this Letter we show that such a phenomenon occurs even when the refractive index of the medium is a deterministic function of position. We also show that this phenomenon may be used to obtain information about the structure of a deterministic medium.     

Study of the feasibility of optical coatings with a continuous refractive index profile

The effect of the instability of deposition rates on the spectral characteristics of optical coatings with a continuous refractive index profile was studied. A correlation between the error level in the experimental data and the accuracy of the reproducibility of spectral characteristics of these coatings was found.     

基于Hyperion高光谱数据的温带森林不同冠层结构的光谱特征分析

冠层是植被进行生态过程的主要层次,森林冠层结构影响冠层生化组分的遥感反演,因此对其光谱特征的分析有助于提高冠层生化组分反演的精度。以长白山温带阔叶红松林为研究对象,利用Hyperion高光谱数据提取不同林冠反射率,运用连续统去除和光谱一阶微分法进行光谱变换,定量分析森林冠层的光谱特征。通过计算样方阔叶树种优势度(BFDI),以及一系列光谱指数(NIR,NDVI,EVI,NDNI,SPRI*NDVI和SPRI*EVI),探讨冠层结构组成对其光谱特征及光谱指数的影响。结果表明：(1)相比阔叶林冠层,针阔混交林、美人松林和樟子松林冠层光谱的红边有左移趋势,斜率明显下降,蓝边、黄边斜率特征也相应减弱,近红外波段反射率明显下降,可见光波段的归一化反射率有上升趋势,表明不同林冠,尤其针叶林与阔叶林林冠之间的光谱特征差异明显。(2)BFDI对冠层NIR反射率和三边斜率有明显的影响,与光谱指数显著相关(P<0.01),表明BFDI影响森林光谱指数。BFDI与NDVI,EVI,SPRI*EVI,NIR,SPRI*NDVI,NDNI的R2分别达到0.90,0.83,0.83,0.81,0.68,0.59,揭示了BFDI对于冠层绿度、叶面积指数、植被生产力以及冠层叶氮浓度等植被参数存在一定影响。研究表明,利用星载高光谱数据结合地面样方调查可以很好地阐明林冠结构组成对于光谱特征的影响,也对优化植被冠层生化组分和森林生态系统生产力的遥感反演具有借鉴意义。     

High efficiency organic light-emitting display using selective spectral photo-recycling

Here, we introduce a selective photo-recycling scheme for organic light-emitting diode (OLED) displays. The conventional photo-recycling method, which uses a recycling film named DBEF, diminishes the ambient contrast ratio of the OLED display, so it is not suitable for display applications. The selective recycling scheme, which uses a cholesteric liquid crystal (CLC) layer that recycles light only in a specific spectral range, can minimize the deterioration of the ambient contrast ratio while improving the photo-efficiency. We found that the aperture ratio of the OLED display influences the recycling efficiency significantly, and that a thin CLC layer diminishes the ambient contrast ratio less than a thick CLC layer while it still recycles the emitted light. By recycling the blue spectral range, one can improve the lifetime of blue OLE material, which has the shortest lifetime, or reduce the size of the blue pixel, which has the largest size among red, green, and blue pixels.     

The inertial range spectrum for a caviton model of Langmuir turbulence

We calculate the spectral index for the Langmuir turbulence spectrum, assuming that the bulk of the energy is contained within a set of strongly flattened, non-interacting cavitons which are subject to supersonic collapse, which preserves the plasmon number in the caviton, as well as an intability, also plasmon conserving, causing splitting. The spectral index, which in the absence of splitting is $\text{-5}\text{2}$, increases when there is splitting, corresponding to a considerable flattening of the spectrum in the inertial range; if the splitting leads to two new cavitons, the resulting index is -1.73.     

反常吸收与高质量的远红外光谱

在水汽含量恒定但相对湿度较大的情况下,远红外光谱仪得不到理想的100%线。这表明过高的水汽含量将会导致反常吸收现象。反常吸收的出现将严重影响远红外光谱的质量。研究了光谱仪内部空气相对湿度和光谱分辨率对反常吸收的影响,发现降低水汽含量和采用适当光谱分辨率可以有效抑制反常吸收现象,对获得高质量的远红外光谱很有益处。在无反常吸收现象发生的实验条件下,采用"湿度中和法"在空气湿度波动的情况下也可以得到理想的100%线,这为快速获得高质量的远红外光谱提供了新测量方法。