Simultaneous optical signal-to-noise ratio and differential group delay monitoring based on degree of polarization measurements in optical communications systems

We present a simultaneous optical signal-to-noise ratio (OSNR) and differential group delay (DGD) monitoring method based on degree of polarization (DOP) measurements in optical communications systems. For the first time in the literature (to our best knowledge), the proposed scheme is demonstrated to be able to independently and simultaneously extract OSNR and DGD values from the DOP measurements. This is possible because the OSNR is related to maximum DOP, while DGD is related to the ratio between the maximum and minimum values of DOP. We experimentally measured OSNR and DGD in the ranges from 10 to 30 dB and 0 to 90 ps for a 10 Gb/s non-return-to-zero signal. A theoretical analysis of DOP accuracy needed to measure low values of DGD and high OSNRs is carried out, showing that current polarimeter technology is capable of yielding an OSNR measurement within 1 dB accuracy, for OSNR values up to 34 dB, while DGD error is limited to 1.5% for DGD values above 10 ps. For the first time to our knowledge, the technique was demonstrated to accurately measure first-order polarization mode dispersion (PMD) in the presence of a high value of second-order PMD (as high as 2071 ps(2)).     

Method for optical signal-to-noise ratio monitoring based on modulation spectrum assessment

A novel method for optical signal-to-noise ratio monitoring is presented. The method is based on twofilter narrowband filtering which, combined with the knowledge of the modulation format, allows the determination of the amount of amplified spontaneous emission noise in the channel spectrum. The major advantage of the method is simplified experimental setup. The robustness of the method against various signal impairments is discussed and assessed through simulation. It is shown that the method provides sufficient accuracy for most practical applications and is remarkably resilient against other physical phenomena reducing signal quality. In particular, the method is inherently insensitive to chromatic dispersion and polarisation-related impairments. All results are presented for 10 Gb/s return-to-zero format.     

Comparative signal-to-noise analysis of fibre-optic based optical coherence tomography systems

Several optical coherence tomography (OCT) systems are proposed using optical-fibre components and based around Fizeau sensing interferometers. The theoretical signal-to-noise ratio (SNR) is calculated for each of the proposed configurations, using a constant set of assumed values for illumination and detection parameters. The SNR values obtained are compared with values calculated for typical existing configurations based around Michelson interferometers. Fizeau-based systems incorporating a secondary processing interferometer offer the advantage over current interferometer configurations of down-lead insensitivity, which prevents signal fading and reduces thermal fringe drift. The most basic form of the Fizeau system makes inefficient use of optical power, and has a low SNR compared with the widely used Michelson configuration. However, the results of the analysis described in this paper show that the SNR for more sophisticated Fizeau configurations, incorporating optical circulators and balanced detection systems, can be as high as the value for the most sensitive existing fibre-based OCT systems. Fizeau configurations therefore offer the combined advantages of optimized SNR and down-lead insensitivity, indicating their suitability for use in relatively poorly controlled environments such as in-vivo measurements.     

偏振比法的微小颗粒粒径反演研究

在Mie散射理论的基础上推导了偏振比法微纳颗粒检测理论.该理论避免了检测光路中气体组分对颗粒测量的影响,实现了微纳颗粒的准确测量.在检测理论的基础上建立了颗粒粒径反演模型,并引入遗传算法对偏振散射光信号进行分析.通过MATLAB仿真研究,获得偏振比法颗粒粒径测量范围为0.1~0.5μm.对服从R-R分布的均匀球形颗粒群进行模拟仿真,通过加入随机噪声模拟实际测量时的外界干扰,根据反演结果对该方法的抗噪性和精度进行了评测.     

高分辨率SAR与光学图像融合的建筑物三维重建研究

分析了用于建筑物测量的高分辨率SAR叠掩及角反射器效应等成像要素,并将其与高分辨率快鸟卫星图像融合,实现了建筑物屋顶信息的提取。进一步利用SAR叠掩得到的建筑物高度信息和快鸟图像得到的建筑物屋顶信息实现了建筑物的三维重建。与实地测量数据相比较,计算结果精度较高,从而验证了这种三维重建方法的可行性。     

One-wavelength tuning method for a tunable optical filter based on a cascaded polarization interference filter

A one-wavelength tuning method is proposed to solve the tuning difficulty in a tunable optical filter based on cascaded cells. This method ensures that the optical path difference variation of all of the cells for the tuning is less than one wavelength and lowers the relative tuning accuracy requirement. Simulations show that different cells have different cross talk and loss deterioration when they undergo an error in optical path difference between the O-ray and the E-ray. An optimal error ratio in each cell is obtained. Under the error ratio, the deterioration from the random error in every cell is further simulated.     

Design of diffractive optical elements with optimization of the signal-to-noise ratio and without a dummy area

We describe a new approach to suppress undesired diffraction orders in the signal area of a Fourier plane diffractive optical element (DOE). We implement this new approach for the DOE design by a two-stage iterative Fourier transform algorithm that incorporates an adaptive optimization of the signal-to-noise ratio and does not require the introduction of a dummy output area outside the field of view. A comparison among this approach and three other approaches are presented on the basis of numerical results from several sample diffraction patterns.     

Fully automated high-performance signal-to-noise ratio enhancement based on an iterative three-point zero-order Savitzky-Golay filter

The automated processing of data from high-throughput and real-time collection procedures is becoming a pressing problem. Currently the focus is shifting to automated smoothing techniques where, unlike background subtraction techniques, very few methods exist. We have developed a filter based on the widely used and conceptually simple moving average method or zero-order Savitzky-Golay filter and its iterative relative, the Kolmogorov-Zurbenko filter. A crucial difference, however, between these filters and our implementation is that our fully automated smoothing filter requires no parameter specification or parameter optimization. Results are comparable to, or better than, Savitzky-Golay filters with optimized parameters and superior to the automated iterative median filter. Our approach, because it is based on the highly familiar moving average concept, is intuitive, fast, and straightforward to implement and should therefore be of immediate and considerable practical use in a wide variety of spectroscopy applications.     

In-band metamaterial cloak based on the interplay of absorption and transmission

A microwave metamaterial shelter with an electromagnetic narrow window over a broad absorption spectrum is experimentally demonstrated by resorting to conventional impedance-matching theory and metamaterial resonance. This device consists of a broad absorber and an embedded electric resonator, and has the ability of permitting one to "see" surroundings but not to be readily sensed by outside detectors. The origin is verified to be a dipole oscillation excited in absorbing region which can induce selective re-emission of the captured energy towards the enclosed space. The performance of "observing without being perceived" is numerically presented.     

A multi-criteria decision model to determine inspection intervals of condition monitoring based on delay time analysis

In periodic monitoring, the main problem is determining the inspection interval of condition monitoring. For this problem, the decision variable is represented by the time of next inspection of condition monitoring. There are several studies that deal with prescribing inspection intervals. But only a few of these allow the decision maker to observe simultaneously more than one aspect. This does not accord with the natural tendency of the decision maker who desires to see the decision problem from a broader perspective, by having different viewpoints or dimensions of choices. Therefore, the main objective of this paper is to propose a decision model, which can simultaneously determine inspection intervals for condition monitoring regarding the failure behavior of equipment to be inspected, features of maintainability and decision maker preferences about cost and downtime.     

基于端点检测的精确时延提取方法及其定位精度分析

针对脉冲声源定位中时延误差大的问题,提出了一种基于端点检测的精确时延提取方法.该方法首先对信号进行滤波处理和端点检测,截取有效信号段运用广义互相关法估计时延,然后利用端点检测得到的信息提取出精确的时延值,最后用单纯形替换法求解声源位置.根据精确时延提取方法,设计了声源定位方案.实验证明,该方法能有效减弱非高斯白噪声和室...     

Slow-light element for tunable time delay based on optical microcoil resonator

We propose a simple and compact slow-light element by use of an optical microcoil resonator (OMR) constituted by two microfiber coils. Based on the matrix exponential method, we solve the coupled-wave equations of the OMR with n turns of microfiber coils and obtain a general solution. Simulations indicate that a tunable slow-light propagation can be obtained by controlling the coupling coefficient between the two adjacent microfiber coils by means of regulating the voltage applied to the ferroelectric crystal. A slow-light time delay up to 62?ps with a bandwidth of 0.4?nm is performed at the wavelength around 1.5?μm.     

基于改进FISTA的高分辨率声源定位方法

为提高快速迭代收缩阈值算法(Fast Iterative Shrinkage-Thresholding Algorithm, FISTA)在反卷积波束形成中的空间分辨率以及计算速度,采用基于快速傅里叶变换的声学模型,引入过松弛方法和“贪婪”重启策略,提出两种改进的快速迭代收缩阈值算法,即基于快速傅里叶变换的过松弛单调快速迭代收缩阈值算法(Over-relaxed MonotoneFast Iterative Shrinkage-Thresholding Algorithm based on Fast Fourier Transform, FFT-OMFISTA)和基于快速傅里叶变换的“贪婪”快速迭代收缩阈值算法("Greedy" Fast Iterative Shrinkage-Thresholding Algorithm based on Fast FourierTransform, FFT-GFISTA),并应用于反卷积波束形成的求解过程中。设计了单声源和双声源的仿真与实验,验证了所提算法的有效性与优越性。结果表明,两种所提算法都具有良好的性能,都能在声源定位中实现更高的空间分辨率以及更快的计算速度。     

Detection and characterization of optical inhomogeneities with diffuse photon density waves: a signal-to-noise analysis

Diffusing photons provide information about the optical properties of turbid media. In biological tissues these optical properties may be correlated to physiological parameters, enabling one to probe effectively the physiological states of tissue for abnormalities such as tumors and hemorrhages. We show that positional uncertainty in the source and detector lead to significant random errors that degrade the optical information available from diffusing photons. We investigate the limits for the detection, localization, and characterization of optical inhomogeneities by using diffusing photons as a probe. Although detection is sufficient for tumor screening, full characterization of the optical properties is desirable for specification of the tumor. Our findings in model breast systems with realistic signal-to-noise ratios indicate that tumors as small as 0.3 cm in diameter can be unambiguously detected; however, simultaneous determination of tumor size and optical properties is possible only if its diameter is of the order of 1.0 cm or larger. On the other hand, if a priori information about the size (optical properties) is available, then the optical properties (size) of tumors as small as 0.3 cm in diameter can be determined.     

Improved design of a polarization converter based on semiconductor optical waveguide bends

By using an efficient vector finite-element-based beam-propagation method, we present an improved design of a polarization converter. This design relies on the use of a single-section deeply etched bent semiconductor waveguide with slanted sidewalls. By careful adjustment of the bend radius, the waveguide width, and the sidewall angle we obtained a nearly 100% polarization conversion ratio with no appreciable radiation loss and a bending angle of less than 180 degrees .     

Integrated optical polarization splitter based on photobleaching-induced birefringence in azo dye polymers

An integrated optical polarization splitter has been fabricated by utilizing the photobleaching-induced birefringence in an azo dye polymer. It consists of a Y-branch waveguide formed by the reactive ion etching with one of the two arms photobleached. The refractive index of the photobleached arm is decreased for the TE mode and increased for the TM mode. The performance of the splitter was measured as a function of the energy of the photobleaching beam and compared to a wave propagation simulation of the device. The measured cross talks are less than -28 dB for the TM mode and -24 dB for the TE mode at a wavelength of 1310 nm. The measured excess losses for the TE and TM modes, which measure the effect of the Y branch and the photobleaching, are 0.3 and 0.4 dB, respectively. The insertion loss was 5 dB, which includes the input fiber to waveguide coupling loss.     

Resolution improvement in microscopic imaging through turbid media based on differential polarization gating

We report a new method for microscopic imaging of an object embedded in a turbid medium, based on the differential polarization-gating mechanism. It is demonstrated that with this method, image resolution through optically thick milk suspensions can be improved by as much as 30% compared with no-gating methods. An image resolution of tens of micrometers is achieved in an optically thick turbid medium, which is approximately 10 times better than that achieved in transillumination imaging in a similar medium.     

Optical vector network analyzer for single-scan measurements of loss, group delay, and polarization mode dispersion

We present a method for measuring the complete linear response, including amplitude, phase, and polarization, of a fiber-optic component or assembly that requires only a single scan of a tunable laser source. The method employs polarization-diverse swept-wavelength interferometry to measure the matrix transfer function of a device under test. We outline the theory of operation to establish how the transfer function is obtained. We demonstrate the enhanced accuracy, precision, and dynamic range of the technique through measurements of several components.     

Solid-state urea biosensor based on the differential method

In this paper, the solid-state urea biosensor was successfully fabricated based on the differential method, which contains three parts: the SnO/sub 2//ITO glass electrode used as the pseudoreference electrode; the SnO/sub 2//ITO glass electrode used as the contrast electrode; and the urease/SnO/sub 2//ITO glass electrode used as the enzyme electrode. Correspondingly, this solid-state urea biosensor was fabricated based on the SnO/sub 2//ITO glass electrode, whose simple fabrication process reduces the cost of fabricating the solid-state biosensor. Additionally, as revealed in the experimental results, the solid-state urea biosensor has good sensing characteristics between 5 and 80 mg/dl. After fabricating a successful solid-state urea biosensor, an array sensing system was designed to enhance the precision of the solid-state urea biosensor, which comprises four parts: the biosensor system, the input buffer circuit, the differential circuit, and the weighted sum circuit. As indicated in the experimental results of the array sensing system, the sensing characteristic of the array sensing system is similar to the mean sensing characteristic from four solid-state biosensors. Therefore, the sensing signal of the solid-state urea biosensor can be averaged using the array sensing system. In summary, this study successfully investigated a solid-state urea biosensor and designed an array sensing system to increase the precision of solid-state urea biosensors.