An arbitrary mode converter with high precision for mode division multiplexing in optical fibers

In this paper, a high-precision arbitrary-mode converter is proposed for mode-division multiplexing optical fiber communication systems. As the kernel of this converter, a phase-only spatial light modulation based on simulated annealing algorithm is used as a spatial spectrum filter. The results demonstrate that our proposed mode converter is of high precision and is capable of converting different modes without any physical change.     

Impact of second-order PMD in a coherent optical orthogonal frequency division multiplexing system

The second-order, polarization-mode dispersion (PMD) effect for coherent optical orthogonal frequency division multiplexing (CO-OFDM) system in long-haul transmission with single-mode fiber was analyzed in detail. The closed-form expression is presented for the time impulse response of an OFDM signal affected by second-order PMD. Analysis and simulation results show that, compared with polarization-dependent chromatic dispersion (PCD), CO-OFDM system performance is mainly influenced by depolarization rate (DR) which can moderate phase noise induced by chromatic dispersion. For a fiber link of 800 km and DR of 30 ps, the system Q value is improved by about 1.3 dB over the case of no DR.     

双光纤波分复用网阻塞率研究

研究了双光纤波分复用互联网在不同网络容量使用率时的阻塞率,主要对单光纤网络使用波长变换器和双纤网络在波长数不同时对网络阻塞率的改善情况做了仿真比较,结果表明仅仅在低阻塞率时波长变换器给网络所带来的增益非常有限,双纤网络可以达到其效果。     

基于光纤光栅的波分复用系统设计

设计了两种基于光纤布拉格光栅的波分复用(WDM)系统,一种为基于光纤光栅的四路波分复用系统,另一种为结合光分插复用器(OADM)的四路波分复用系统。给出了基于Opti System的波分复用光传输系统仿真模型,对复用及解复用后的光信号进行仿真得出了光谱图,对传输性能及Q因子、误码率、眼图等参数进行分析。在第二种结构中光纤光栅作为色散补偿器、光反射器和滤波器使用,可以实现任一波长的上载和下路。两种波分复用系统眼图张开良好,误码率均低于10e-9。证明了波分复用系统的正确性和设计方案的可行性。     

Structural integrity analysis of embedded optical fibres in composite structures

The virtues of having sensors in manufactured goods for increased functionality purposes have been well documented. Benefits include sophisticated structures requiring less maintenance and repair, increased safety and reliability, and avoidance of ‘over design’. Though many schemes of sensing are available, these so-called ‘smart’ products in the near future, will increasingly rely on the optical fibres (OF) principles because of numerous inherent advantages. Optical fibres are small, lightweight, possess geometrical flexibility, Electromagnetic interference (EMI) immunity, operate over a wide range of environmental conditions, and can be configured to respond to many physical parameters.

This paper will report on the suitability of embedding OF in commonly used carbon-fibre composites. These panels will be designed, manufactured and tested for the effects of typical fibre-optic geometrical and physical parameters such as types of fibre coating polymers, fibre diameter and fibre distribution. Corroboration of these test results with finite element (FE) results will be shown. Based on tensile and compression tests on OF-embedded composites, it is shown that significant deterioration on strength is observed beyond a certain OF density level. This paper will focus on the macroscopic effect of having optical fibres in composites from a structural integrity point of view. To this end, an exposition on the theoretical considerations using continuum mechanics and energy principles is provided.     

Ag离子注入石英玻璃光学透射率研究

用Mevva离子源,将Ag离子注入到石英玻璃中形成纳米晶粒。离子注入的能量为90keV,剂量分别为5×1015、1×1016、3×1016、5×1016、1×1017ions/cm2。X光电子能谱(XPS)分析纳米Ag颗粒没有发生化学反应,说明Ag仍以金属态形式存在。光学透射率测试表明,吸收峰的位置在400nm,当剂量大于5×1016ions/cm2时,发现在440nm左右有一伴峰。分析表明400nm的峰来源于表面等离子体共振吸收,而440nm的伴峰是注入离子形成了少数非常大的纳米颗粒以及纳米颗粒之间相互作用引起的。样品退火后,表面等离子体共振吸收峰红移,而伴峰消失。随着退火的温度升高,峰位红移越大,说明纳米颗粒尺寸增大。     

Investigation of mode coupling in low and high NA step index plastic optical fibres using the Langevin equation

By employing the Langevin equation, we have examined a mode coupling in low and high NA step index plastic optical fibres. The numerical integration of the Langevin equation is based on the computer-simulated Langevin force. The solution matches the experimental data reported previously. We have shown that by solving the Langevin equation (stochastic differential equation) one can treat a mode coupling in multimode low and high NA step index plastic optical fibres, which is the result of fibre's intrinsic random perturbations.     

空间光学成像系统用高尺寸稳定光学聚酰亚胺薄膜

空间光学成像系统采用薄膜主镜解决了大口径、轻量化、空间折叠展开等难题,但大口径光学透镜的成像指标要求高、空间应用环境恶劣,对透镜基底材料的性能要求严苛,其中尺寸稳定性、空间环境适应性尤为重要。本文提出在分子结构设计基础上,通过共聚合成的方法有效改性聚酰亚胺材料,通过在分子结构中同时引入刚性链和分子链间氢键作用,在保证传统聚酰亚胺高机械性能、高热稳定性的同时,改善其热尺寸稳定性、空间环境光学稳定性。所得高尺寸稳定性光学级聚酰亚胺薄膜材料综合性能良好,是优异的空间光学成像系统薄膜主镜候选材料。     

一种实现空间光-单模光纤的自动耦合方法

精确定位耦合光斑在光纤端面上的位置是空间光与单模光纤耦合技术的关键.提出由压电陶瓷、控制器、驱动器、光电探测器、耦合透镜及反射镜组成闭环控制系统,使用光栅式扫描初步确定最佳耦合位置后再用五点跟踪法结合一维平动精确定位实现自动耦合.推导出扫描所需步长和时间,详细阐述了光栅式扫描和五点跟踪法原理.实验结果表明,该方法可以在较短时间内根据耦合入光纤的光功率大小自动搜寻到最佳位置,获得59.2%的最大耦合效率,能校正由地表震动、气流扰动等低频干扰造成的数值偏差保持较高的耦合效率.     

A flexible labour division approach to the polygon packing problem based on space allocation

This paper deals with the two-dimensional satellite module polygon packing problem. Based on the duality of material and space, it regards the polygon packing problem as a space allocation problem, which involves allocating the container space to the given polygons reasonably and efficiently. Ant colony’s labour division is essentially a kind of task allocation. Using this task allocation to achieve the space allocation in polygon packing problems, a flexible labour division approach (FLD) is proposed based on the response threshold model. According to the characteristics of space allocation in polygon packing problems, FLD designs three actions for polygons to occupy the container space. With the interaction between environmental stimulus and response threshold, each polygon takes an appropriate action to complete the space allocation and a layout that meets the requirements of satellite module layout is obtained. The results of standard test instances demonstrate the effectiveness of FLD when compared with self-organisation emergence algorithm. Moreover, experiments on the general polygon packing problem also show that FLD is competitive with other existing algorithms.     

深空光通信中恒星信标的捕获跟踪技术研究

提出一种深空光通信系统的信标捕获、跟踪方案,该方案是以恒星作为信标,根据恒星在惯性坐标系中的绝对位置信息,基于航天器和地球星历表、航天器的姿态信息来进行下行光束瞄准方向的精确控制。理论分析和计算机仿真都表明,星敏感器的测量精度和焦距,下行信号光的束散角将影响激光链路成功建立概率。下行信号光束散角为30μrad,星敏感器视场为8°×8°,焦距为143mm,恒星的中心位置测量精度达到0.10个像素时,链路成功建立的概率达到96.4%,表明该方案是可行的。     

The radiation hardness of silica optical fiber used in the LED-fiber monitor of BLM and BESIII EMC

LED-fiber system has been used to monitor BLM and BESIII EMC. A radiation hard silica optical fiber is essential for its stability and reliability. Three types of silica optical fibers, silicone-clad silica optical fiber with high OH⁻ content (SeCS), silica-clad silica optical fiber with low OH⁻ content (SCSL) and silica-clad silica opical fiber with high OH⁻ content (SCSH) were studied. In the experiment, 12 groups of fiber samples were irradiated by ⁶⁰Co and 3 groups of fiber samples were irradiated by BEPCII background radiation. Radiation hardness: the radiation hardness of SCSH is best and meets the radiation hardness requirement for LED-fiber monitor of BLM and BESIII EMC. The transmission of SeCS and SCSH decreased to around 80% under the ⁶⁰Co-irradiation of 5 Gy and 10 Gy, respectively. The radiation hardness of SeCS is worst because of its silicone cladding. Recovery characteristics: ⁶⁰Co-irradiated by the same doses, there were both more annealable and more permanent color centers formed in SeCS than SCSL, and for the same kind of fibers, as long as the irradiated doses are under a certain amount (for example, less than 5 Gy for SeCS), the higher the doses, both the more annealable and the more permanent color centers are formed.     

深空光通信中导航星表的构造

提出一种导航星表的构建方法，该方法以星跟踪器视场内最亮恒星作为信标，把信标锁定在视场中心，测量视场内其他恒星到信标的角间隔，把测量的所有恒星角间隔和信标的赤经、赤纬存储到导航星表中。基于该方法，利用史密森天文观测台恒星星表（SAO），选择星等小于6等的恒星，建立起导航星表，该星表仅包括5103颗星，其容量仅为1.2兆。相对三角形算法，该星表容量更小，可节省星载系统的存储空间，减少识别时间，提高跟踪速率。蒙特-卡诺仿真结果表明，利用该导航星表识别信标具有较好的抗干扰性，且当星跟踪器测角误差（30σ）在1μrad以内时，信标正确识别概率几乎为100％。     

光纤网时间同步性能计量校准装置研制

为解决光纤时间传递系统中存在的远距离传递准确度低的问题,分析了环回法、双纤双向时间同步、双向波分复用、双向时分复用四种主流的高精度光纤时间传递方法的基本原理和技术特点,在此基础上研制了单信道时频传递装置。该装置采用电学相位补偿法实现频率传递同步,采用环回法与时分复用相结合的方法实现时间传递同步;使用1 秒脉冲（Pulse Per Second, PPS）和100 MHz共同标记时刻信号,其中1 PPS作为时刻粗标记,100 MHz作为时刻细标记,实现高精度时间同步。经实验证明,单信道时频传递装置的不确定度约为13 ps,能够满足现有光纤时频同步网计量校准的要求。该装置在多级时间传递同步、光纤时频同步网计量校准等领域中具有广阔的应用前景,为建设高稳定性、高可靠性和高精度的授时体系提供了重要技术支撑。     

基于OFDM的大气激光通信湍流抑制关键技术研究

文章在分析无线激光通信(FSO)存在两种主要的大气信道问题的基础上,针对激光大气信道问题尤其是在复杂湍流环境下的频率选择性衰落问题和多径效应问题,提出了基于正交频分复用(OFDM)的湍流效应抑制方法,构建了FSO-OFDM系统,研究了该系统的基带模型以及信号的多载波调制与解调方法。分析了无线激光通信中存在复杂湍流环境下的大气信道问题,讨论了大气湍流影响下的平面波激光通信系统模型,建立了大气湍流影响下对数正态湍流通道的高斯光束空间光通信系统模型,推导了光波强度的概率密度函数,研究了利用信噪比概率密度函数分析各种大气湍流效应对系统性能影响的方法;设计了无线光通信系统的OFDM多载波调制方案,构建了FSO-OFDM系统基带模式模型,并基于该模型研究了其信号的调制与解调原理。最后,采用MATLAB编程实现FSO-OFDM系统,对多径干扰下的FSO通信系统进行仿真实验,进行了不同保护间隔下的误码率特性实验,验证了FSO-OFDM系统具有很强的抗多径干扰和频谱选择性衰落能力以及良好的BER性能,可有效解决码间干扰大、链路不可靠的问题,具有非常广泛的应用前景和使用价值。     

Large area double p–i–n heterostructure for signal multiplexing and demultiplexing in the visible range

Results on the use of a double a-SiC:H p–i–n heterostructure for signal multiplexing and demultiplexing applications in the visible range, are presented.Modulated monochromatic beams together (multiplexing mode), or a single polychromatic beam (demultiplexing mode) impinge in the device and are absorbed, accordingly to their wavelength, giving rise to a time and wavelength dependent electrical field modulation.Red, green and blue pulsed input channels are transmitted together, each one with a specific transmission rate. The combined optical signal is analyzed by reading out, under different applied voltages, the generated photocurrent. Results show that in the multiplexing mode the output signal is balanced by the wavelength and transmission rate of each input channel, keeping the memory of the incoming optical carriers. In the demultiplexing mode the photocurrent is controlled by the applied voltage allowing regaining the transmitted information. An electrical model gives insight into the device operation.     

A novel experimental set-up for turbidity sensing based on plastic optical fibre

A novel set-up for remote sensing the turbidity of a solution using plastic optical fibres together with a mirror is proposed. The authors have estimated turbidity of a liquid in terms of the nephelometric turbidity unit – NTU, a standard unit that relates the solution appearance with its turbidity for two proposed set-ups. Its performance was also investigated using clay sample measurements over a concentration range of 0–10 g/L. The proposed set-ups are useful for detection of suspended particles in a solution even in small quantities due to its high sensitivity, simplicity and robustness.     

Channel correlation of free space optical communication systems with receiver diversity in non-Kolmogorov atmospheric turbulence

Spatial diversity as an effective technique to mitigate the turbulence fading has been widely utilized in free space optical (FSO) communication systems. The received signals, however, will suffer from channel correlation due to insufficient spacing between component antennas. In this paper, the new expressions of the channel correlation coefficient and specifically its components (the large- and small-scale channel correlation coefficients) for a plane wave with aperture effects are derived for horizontal link in moderate-to-strong turbulence, using a non-Kolmogorov spectrum that has a generalized power law in the range of 3–4 instead of the fixed classical Kolmogorov power law of 11/3. And then the influence of power law variations on the channel correlation coefficient and its components are analysed. The numerical results indicated that various value of the power law lead to varying effects on the channel correlation coefficient and its components. This work will help with the further investigation on the fading correlation in spatial diversity systems.     

Reliability-guided Rayleigh backscattering spectrum correlation method for distributed strain measurements in optical fibres

We present a method of reliability-guided Rayleigh backscattering correlation for distributed strain measurements in optical fibres. In this method, a reference Rayleigh-backscattering-spectrum (RBS) range that is larger than the measurement RBS range is defined to extend the matching range. To obtain the best match between reference and measurement spectra, the zero-mean normalized cross correlation (ZNCC) is employed to evaluate the degree of similarity. The path for searching the maximum similarity matching pattern is guided using Newton’s iteration method. The reliability of the computed RBS shift is identified by the ZNCC coefficient distribution. The experiments show that the proposed method has high reliability in computing the RBS shift. Even at a relatively large strain (e.g. 5000?µ?), the proposed method can stably demodulate the strain within a relative error of ?1% and a spatial resolution of 1.6?cm over a 22-meter-long single-mode fibre. This shows that the proposed method has an advantage in regard to relatively large strain measurements.