Characteristics of thermally expanded core fiber

Thermally expanded core (TEC) fiber is expected to reduce fiber-to-fiber and fiber-to-laser diode connection loss. This paper describes the characteristics of TEC fiber theoretically and experimentally. We reveal theoretically that when fabricating TEC fiber the mode field diameter (MFD) is enlarged more effectively by increasing the heating temperature rather than the heating time. In the 1300-1600°C temperature range with heating times between 0 and 60 min, it is necessary to control the temperature accurately so that no deviation from the target temperature is more than ±30°C. This is in order to ensure that any connection loss caused by MFD mismatch is less than 0.1 dB. We show experimentally that the propagation loss of TEC fiber is dependent on the heating region and wavelength by using a micro burner with a propane/oxygen flame. Based on the relationship between the loss characteristics and the expanded MFD, we suggest a method for nondestructively measuring the MFD in TEC fibers     

Interleavers for turbo codes using permutation polynomials over integer rings

A class of deterministic interleavers for turbo codes (TCs) based on permutation polynomials over /spl Zopf//sub N/ is introduced. The main characteristic of this class of interleavers is that they can be algebraically designed to fit a given component code. Moreover, since the interleaver can be generated by a few simple computations, storage of the interleaver tables can be avoided. By using the permutation polynomial-based interleavers, the design of the interleavers reduces to the selection of the coefficients of the polynomials. It is observed that the performance of the TCs using these permutation polynomial-based interleavers is usually dominated by a subset of input weight 2m error events. The minimum distance and its multiplicity (or the first few spectrum lines) of this subset are used as design criterion to select good permutation polynomials. A simple method to enumerate these error events for small m is presented. Searches for good interleavers are performed. The decoding performance of these interleavers is close to S-random interleavers for long frame sizes. For short frame sizes, the new interleavers outperform S-random interleavers.     

A note on the relationship between the conjugate gradient method and polynomials orthogonal over the spectrum of a linear operator

The relationship between the conjugate gradient method and polynomials orthogonal over the spectrum of a linear operator is discussed. It is shown that as a byproduct of the conjugate gradient construction, two sets of polynomials are generated which are orthogonal with respect to a positive real measure over the spectrum of a self-adjoint operator. The roots of these polynomials can, under certain circumstances, be used to track the eigenvalues or singular values of the relevant operator.     

A comparison of performance of three orthogonal polynomials in extraction of wide-band response using early time and low frequency data

The objective of this paper is to generate a wideband and temporal response of three-dimensional composite structures by using a hybrid method that involves generation of early time and low-frequency information. The data in these two separate time and frequency domains are mutually complementary and contain all the necessary information for a sufficient record length. Utilizing a set of orthogonal polynomials, the time domain signal (be it the electric or the magnetic currents or the near/far scattered electromagnetic field) could be expressed in an efficient way as well as the corresponding frequency domain responses. The available data is simultaneously extrapolated in both domains. Computational load for electromagnetic analysis in either domain, time or frequency, can be thus significantly reduced. Three orthogonal polynomial representations including Hermite polynomial, Laguerre function and Bessel function are used in this approach. However, the performance of this new method is sensitive to two important parameters-the scaling factor l/sub 1/ and the expansion order N. It is therefore important to find the optimal parameters to achieve the best performance. A comparison is presented to illustrate that for the classes of problems dealt with, the choice of the Laguerre polynomials has the best performance as illustrated by a typical scattering example from a dielectric hemisphere.     

Use of discrete Laguerre sequences to extrapolate wide-band response from early-time and low-frequency data

Extrapolation of wide-band response using early-time and low-frequency data has been accomplished by the use of the orthogonal polynomials, such as Laguerre polynomials, Hermite polynomials, and Bessel-Chebyshev functions. It is a good approach to reduce the computational loads and obtain stable results for computation intensive electromagnetic analysis. However, all the orthonormal basis functions that have been used are all continuous or analog functions, which means we have to sample the polynomials both in time and frequency domains before we can use them to carry out the extrapolation. The process of sampling will introduce some errors, especially for high degrees or small scaling factors and, hence, may destroy the orthogonality between the polynomials of various degrees in a discrete sense. In this paper, we introduce the discrete Laguerre functions, which are directly derived using the Z transform and, thus, are exactly orthonormal in a discrete sense. The discrete Laguerre polynomials are fundamentally different from its continuous counterparts, except asymptotically when the sampling interval approaches zero. The other advantage of using these discrete orthonormal functions is that they do not give rise to the Gibbs phenomenon unlike its continuous counterpart. Using it in the extrapolation, the range or convergence can be extended both for the scaling factor and order of expansion, and at the same time, the quality of performance can be improved. Since the error of extrapolation is sensitive to the scaling factor, an efficient way to estimate the error as a function of the scaling factor is explained and its feasibility for any problem is validated by numerical examples of antennas.     

The measurement of non-Gaussian mode fields by the far-field axial scanning technique

A new measurement technique is proposed for determining the second Petermann definition of mode field diameter (MFD) for single-mode fibers with both near-Gaussian and non-Gaussian radial field distributions. The method involves measuring the power passed through a circular aperture as it is scanned along the far-field optical axis of a fiber. Using this technique, it is possible to select those acceptance angles that are most critical to the accurate determination of MFD for a particular fiber design. Also, the aperture can be positioned close enough to the fiber endface so that collection of the total far-field power is assured. Measurements of MFD for conventional and disperson-modified single-mode fibers have been made at 1.3 μm and 1.55 μm with a precision of +/-0.05 μm and a comparison with the far-field angular scanning method gives agreement ot within 1 percent for both fiber types.     

Improvements to the variable aperture method for measuring themode-field diameter of dispersion-shifted fibers

The variable aperture system for measuring single-mode fiber mode-field diameter is modified to provide accurate measurements of dispersion-shifted fibers. The system's numerical aperture (NA) is increased by using a spherical mirror and a large aperture wheel with 23 apertures out to 0.556 NA. Petermann's second mode-field diameter (MFD) definition is calculated with Simpson's rule numerical integration. The industrialized high-NA variable aperture method in the far field (VAMFF) system is accurate to within 1%, with a measurement standard deviation of less than 0.5%. Flexibility for measuring various fiber designs over a range of wavelengths is also a key feature. It is concluded that the industrialized high-NA VAMFF system is an excellent MFD measurement bench because of its precision, accuracy, and versatility     

Design and Implementation of a Micromanipulation System Using a Magnetically Levitated MEMS Robot

Magnetic levitation of microrobots is presented as a new technology for micromanipulation tasks. The microrobots were fabricated based on microelectromechanical systems technology and weigh less than 1 g. The robots can be positioned in 3-D using magnetic field. It is shown that microrobots can be produced using commercially available magnets or electrodeposited magnetic films. A photothermal microgripper is integrated to the microrobots to perform micromanipulation operations. The microgrippers can be actuated remotely by laser focusing that makes the microrobot free of any wiring. This leads to increased motion range with more functionality in addition to dust-free motion and ability to work in closed environments. The 3-D motion capability of the microrobots is verified experimentally and it was demonstrated that the microgrippers can be operated in a vertical range of 4 mm and a horizonal range of 4 mm $,times,$5 mm. Micromanipulation experiments such as pick-and-place, pushing, and pulling were demonstrated using objects with 100 $mu$ m and 1 mm diameter.      

Ability of the Lapicque and Blair strength-duration curves to fitexperimentally obtained data from the dog heart

The objective of this study was to determine the ability of the empirical Lapicque and theoretically derived Blair expressions for excitation to fit experimentally obtained threshold current values to evoke a ventricular extrasystole using rectangular-wave stimuli applied to the dog heart. The data points were fitted to both expressions and the ability of each to predict the measured values was determined. The Levenberg-Marquardt (L-M) algorithm was used to fit the Lapicque and Blair expressions. The Lapicque data were also fitted to the linear charge-duration expression of Weiss (W). It was found that the ratio of the predicted to measured current was slightly different from one 0.95 (L-M) and 1.06 (W) for the Lapicque and 0.92 (L-M) for the Blair expression. Thus, there appears to be little difference between the ability of the expressions to fit the same experimentally obtained data. The L-M Lapicque fit is best for the short durations range; the Weiss-Lapicque fit overestimates in the short duration range and underestimates near chronaxie. The L-M Blair fit is best for the short duration range and poor for the durations near the membrane time constant.     

70-GHz-Band OFDM Transceivers Based on Self-Heterodyne Scheme for Millimeter-Wave Wireless Personal Area Network

70-GHz-band orthogonal frequency-division multiplexing (OFDM) transceivers were developed by combining self-heterodyne transmission with two-element diversity reception. The transceivers were used to study and demonstrate a millimeter-wave wireless personal network that enables cost-effective broadband data transmissions in a multipath channel environment. A 100-MHz sampling OFDM modulator/demodulator was developed for the baseband part. It has a payload data rate of 100 Mb/s using quadrature phase-shift keying (QPSK) modulation and a coding rate of 3/4 (many other modulations and coding rate are available). The bit error rate was experimentally evaluated when a pair of devices was placed on a wooden table under line-of-sight path conditions. The results showed that the combined use of the self-heterodyne technique and two-element diversity receiver successfully avoids serious signal fading at unpredictable transmission distances. The transceiver with QPSK modulation and coding rate of 1/2 for forward error correction achieves error-free data transmission over a distance of up to 3.4 m. In addition, a successful transmission in 64 quadrature amplitude modulation mode was demonstrated, although the communication range was quite short.     

用方形区域内的标准正交多项式重构波前

提供了一种方形区域上归一化Zernike正交基的生成方法。它采用线性无关组Gram-Schimdt正交组构造方法,根据线性代数内积、欧氏空间及其正交性和范数的相关概念,对标准Zernike多项式进行正交处理,得到了一组新的正交多项式Z-square多项式。采用该正交基实现了方形区域内波前模式的拟合,它不仅可由Z-square模式的集合直接对波前进行表示,而且也可以通过线性反变换,将Z-square多项式表示成标准的Zernike模式的线性组合,使被分解的波前模式与像差之间有明确的对应关系。实验表明,它不仅可以对透镜设计中的波前像差函数进行有效的拟合,而且也能对Hartmann-Shack波前传感器测试得到的实际相位数据进行拟合。     

Polynomial based analog source-channel codes - [transactions papers]

In many communication applications one is interested in transmitting a time-discrete analog-valued (i.e. continuous alphabet) source over a time-discrete analog channel. We study this problem in the case of bandwidth expansion, in the sense that one source sample, X, is transmitted over N-orthogonal channels. An analog source-channel code based on orthogonal polynomials is proposed and analyzed. The code can be generated using a Gram-Schmidt procedure, to fit virtually any source distribution.     

Two-dimensional stability and orthogonal polynomials on the hypercircle

This paper is concerned with a possible extension of a well-known stabilization technique for one-variable recursive digital filters to the two-dimensional case, as recently conjectured. It is shown that this problem is equivalent to considering a new class of orthogonal polynomials, the two-variable orthogonal polynomials on the hypercircle, the properties of which are investigated. As a result, the zeros of these polynomials are proved not to lie necessarily in an appropriate region compatible with the proposed conjecture, which therefore turns out to be in error.     

基于运动补偿和正交解耦合的双基SAR成像算法

复杂的应用场景下,平台速度不能保持恒定.加速度的存在增加了双基合成孔径雷达距离和方位向的耦合,使成像处理更加困难.论文提出了一种二维频谱的正交解耦合方法,以解决加速度下的双基SAR成像问题.首先利用Chebyshev多项式将斜距展开成幂级数形式,然后利用驻留相位原理和级数反演法(Method of Series Re-...     

一种有效的分段光滑信号逼近方法

传统的Fourier变换,连续小波变换等方法在逼近具有分段光滑特性的非连续信号时,因 Gibbs现象的干扰会产生比较大的误差。本文提出了一种有效的分段光滑信号逼近方法。首先根据给定信号的分段点位置,构造一组标准正交分段多项式系,该函数系具有正交性,收敛性及再生性。然后将信号在该函数系下进行正交分解及重构,即可得到该信号的最佳平方逼近结果。数值实验表明,本文方法比传统的正交基具有更好的逼近结果。     

改进的多项式图像配准方法

针对多项式方法进行图像配准的一些缺点,本文将正交多项式应用到图像配准方法中,并提出一种加权的正交多项式方法,然后对这些方法进行了讨论和比较。结果表明:正交多项式方法进行图像配准具有很强的灵活性;加权的正交多项式方法具有很好的局域性。最后利用实验结果对这些方法进行了验证和比较。     

Generating High-Accuracy Simulation Models Using Problem-Tailored Orthogonal Polynomials Basis

The problem of computing high-accuracy simulation models for systems described by tabulated frequency data is of paramount importance in the modeling arena. Standard algorithms for this task involve generating rational function approximations to the data. However, for complicated data sets, high-order approximations are required. Unfortunately, numerical conditioning problems arise when attempting to fit high-order rational approximations to the data, effectively limiting the accuracy of the models that can be generated. While robust fitting schemes based on orthogonal polynomial exist, they usually pose strict constraints on the data points, which are either hard or even impossible to guarantee. Furthermore, the approximation must still be translated such that it can directly be used inside a simulator. In this paper, we present an algorithm for robustly generating such a model using only the data given. The model is supported on a problem-tailored orthogonal polynomial basis. We also present a method for directly generating a state-space model associated with a rational function described in terms of such polynomials, effectively making the model amenable for simulation. An extension to the MIMO case is described and it is shown that the method is easily included with existing passivity enforcing procedures. Finally, we demonstrate the proposed technique by constructing approximations to several real-world data sets     

磁致伸缩效应光纤微分干涉电流传感器

基于磁致伸缩效应，利用微分干涉仪，设计了一种光纤电流传感器，可用于高精度，高灵敏度电流和磁场的测量，分析了用磁致伸缩效应实现光纤电流传感器的原理，建立了基于磁致伸缩效应传感头的数学模型，并通过实验对光纤电流传感器的输入－输出特性，直流偏置特性和精确度等进行了研究，在8－200A的电流测量范围内，测量比差约为0．5％。     

一种手持式电子磁罗盘航向误差校正方法

针对传统的磁罗盘补偿方法计算量大、需要标定设备的问题,提出了一种利用陀螺仪相对航向辅助校准的方法。在分析磁罗盘误差的基础上建立了误差模型,采用梯度下降法解出姿态信息对磁场数据进行倾斜补偿,在陀螺仪相对航向角的辅助下,采用最小二乘法拟合经过倾斜补偿后的磁场数据求解出误差模型的系数。实验数据表明,该算法能够有效的对磁罗盘误差进行补偿,可以将磁罗盘的航向角测量误差控制在1°之内。     

基于正交多项式拟合的风廓线雷达风谱识别

风廓线雷达是一种以大气湍流为主要探测对象的晴空测风雷达,由于大气湍流对电磁波的散射非常微弱,湍流回波常常被淹没,特别是在降水条件下更是如此。为了能准确识别湍流回波提高谱矩估计精度,文中提出了基于正交多项式拟合的风谱识别方法。结果表明,该方法在降水天气下能很好地保留湍流回波信息,在风廓线雷达谱数据处理中取得了良好的效果,具有很大的实用价值。