A Lower Bound on the Second Fiber Coefficient of the Fiber Cones

Let (R, 𝔪) be a Cohen–Macaulay local ring of dimension d > 0, I an 𝔪-primary ideal of R and K an ideal containing I. When depth G(I) ≥ d ? 1 and r(I | K) < ∞, we present a lower bound on the second fiber coefficient of the fiber cones, and also provide a characterization, in terms of f ₂(I, K), of the condition depth F _K (I) ≥ d ? 1.     

60 GHz Radio over Fiber Technology for Wireless Access by employing Narrow-Angle PSK Modulation

This paper investigates two key techniques used in 60 GHz Radio over Fiber (RoF) technology for wireless access, namely, the generation of 60 GHz signals and the distribution of 60 GHz local oscillator (LO). In the proposed model, a 60 GHz PSK signal is generated by a heterodyne of two subcarriers with narrow-angle PSK (NA-PSK) modulation, whose phase shift is equal to one half that of a normal PSK signal. Then we use a 60 GHz mixer to frequency mix two PSK signals in two different bands, 60 GHz and baseband. By doing this, the modulation information can be fully eliminated, resulting in a 60 GHz LO. In the wireless terminal, coherent demodulation is realized by a self-mixing of the transmitted 60 GHz PSK signal and LO. Thus no millimeter-wave (mm-wave) band oscillator is needed in the wireless terminal.     

长周期光纤光栅的透射光谱特征

用Matlab编程的方法对长周期光纤光栅的透射光谱谱线特性进行了研究,数值模拟了长周期光纤光栅周期对光谱谱线的影响.研究结论为长周期光纤光栅的设计提供了理论依据.     

Long-exposure far-field properties of the array of mutually-injected fiber lasers

In this paper, the long-exposure far-field properties of the array of mutually-injected fiber lasers are studied to understand the effect of the multiple phase-locked states on coherent beam combining of the array. It is found that the long-exposure far-field will degenerate into the superposition of the intensities of the elementary lasers when all the phase-locked states of the array are exported with the same probability. It means that the interference pattern will be greatly weakened in the long-exposure far-field because of the export of multiple phase-locked states of the array. This result implies that the multiple phase-locked states of the array go against coherent beam combining of the array, and only some of these phase-locked states should be exported. Then, the effects of the high-order phase-locked states on the far-field are discussed. The result suggests that only the in-phase state should be exported (i.e., all the other phase-locked states should be suppressed) in order to realize high-efficiency (> 80%) coherent beam combining when the number of the elementary lasers of the array is smaller than 19.     

Differential FBG sensor for temperature-compensated high-pressure (or displacement) measurement

A differential fiber Bragg grating (FBG) sensor with a free active element bulk-modulus for high-pressure (or displacement) measurement is presented. Based on the differential measurement method and an isosceles triangle cantilever structure, problems of cross-sensitivity and chirped signal in FBG sensor are improved both theoretically and experimentally. Preliminary experiments indicate that temperature-compensated measurement results agree well with the theoretical analysis. Displacement measurement sensitivity is 1.75 pm/μm, and the estimated pressure measurement resolution can reach 0.27 MPa in case the wavelength shift measurement resolution is 0.01 nm.     

Theoretical study on instantaneous linewidth of Fourier-domain mode-locked fiber lasers

We have numerically simulated the operation of the Fourier-domain mode-locked (FDML) fiber laser based on the wavelength reconstruction method instead of numerical solving the nonlinear Schrödinger equation. We studied the influences of the filter bandwidth and the relative time delay caused by the fiber chromatic dispersion on the instantaneous linewidth of the FDML fiber laser. The results show that the instantaneous linewidth broadens as the filter bandwidth and the relative time delay increase. When the filter has the bandwidth of 0.02 nm, the narrowest and broadest instantaneous linewidths are 0.024 and 0.042 nm, respectively. We give an understanding for the oscillation of the instantaneous linewidth of FDML. The presented result can be used to evaluate the performance achievable in the FDML fiber lasers.     

Designing a plano-convex aspheric lens for fiber optics collimator

A plano-convex aspheric lens is designed to collimate the emitted light of the fiber optics. In this paper even orders of general aspheres are used to describe the aspheric surfaces sag. To determine the aspheric coefficient, the even asphere polynomial are fitted on the computed sag data. The surface sag data is determined using genetic algorithm method. The surface sag was analyzed by the commercial optical software package ZEMAX. For typical fiber optics, the numerical aperture (NA) of 0.22 was assumed. With this specification, the expected output spot diagram of 20 mm and the maximum aperture of 25.4 mm have been obtained. A comparison between here presented lens and the similar type of conventional lens has been carried out; the proposed aspheric lens corrected the spherical aberration, which led to increase in the collimated distance.     

基于氟掺杂双芯光子晶体光纤偏振光分束器的设计及研究

在光子晶体光纤二氧化硅材料中掺入氟元素、在光纤中引入七个椭圆空气孔以及三角形和矩形周期性空气圆孔,设计了一种氟掺杂双芯光子晶体光纤偏振光分束器.对该分束器结构参量进行优化,对分束器分离两正交偏振光的性能进行分析.结果表明:在优化结构尺寸下,当光纤长度为102.717μm的超短长度时,在1.55μm波长处具有超强的分离两束正交偏振光的能力,消光比可以达到126.442dB,具有60nm的有效带宽.此偏振光分束器在大容量光通信系统中具有重要的应用价值.     

基于M-Z干涉的光纤围栏系统实验研究

对基于M-Z干涉技术的光纤围栏系统进行了实验研究.讨论并分析了M-Z干涉技术在光纤围栏系统中的应用原理.利用M-Z干涉技术和互相关技术,在总计60 km的光纤上进行了单点和两点扰动的原理性实验.在采样速率为20 MHz时,理论上最高可达10 m的定位准确度.