In this paper, a new two-dimensional variable weight optical orthogonal code (2D-VWOOC) for optical code division multiple access (OCDMA) system is constructed. It takes the C as the frequency hopping sequence and the strict variable weight optical orthogonal code (SVWOOC) as the time spreading sequence. The code can meet the different quality of service (QoS) requirements of different users. Under the same time spread sequence, the bit error rate (BER) of QCHC/SVWOOC is 3-9 orders of magnitude lower than that of other similar 2D-VWOOCs. In Optisystem simulation, when the transmission rate of the system is 14 Gbits/s, the BER of users with code weight 4 is 7 orders of magnitude lower than that of users with code weight 2, and a clear and correct eye diagram can be obtained.

在保证误码率较低的前提下, 为了获得较大的码容量, 现以扩展二次素数码作为扩时序列, 以二次全等跳频码作为跳频序列, 构造出了一种新的二维光正交码ESPC/QCHC。分析了ESPC/QCHC的码字性能, 得到了该码字的平均互相关表达式。对该码字的码字容量进行理论分析, 并对其误码率进行了MATLAB仿真。结果表明, 当码重(或码长)一定时, 增加频率片数会降低误码率; 同其他几种以素数码作为扩时序列构造出的二维光正交码相比, 该码字有较低的误码率, 较大的码容量。最后在Optisystem7.0中对ESPC/QCHC在光码分多址系统中的误码率进行仿真分析, 验证了其有较好的误码性能。

We design a channel-drop filter (CDF) with a linear gradient microcavity in a two-dimensional (2D) photonic crystal (PC). The model of three-port CDF with reflector is used to achieve high quality factor (Q-factor) and 100% channel-drop efficiency. The research indicates that adjusting the distance between reference plane and reflector can simultaneously influence the Q-factor due to coupling to a bus waveguide and the phase retardation occurring in the round trip between a microcavity and a reflector. The calculation results of 2D finite-difference time-domain (FDTD) method show that the designed filter can achieve the drop efficiency of 96.7% and ultra-high Q-factor with an ultra-small modal volume.

利用二维正方晶格介质柱型光子晶体(PC), 设计了一款由4个线性渐变型微腔和异质结构光子晶体反射器组成的多信道下路滤波器。利用平面波展开法(PWE)以及二维时域有限差分法(2D-FDTD)分析了该异质结构滤波器的工作机制, 并进一步探究了微腔参考面与异质结界面之间距离对下路效率的影响。研究表明, 滤波器中的异质结反射器可以实现接近100%的反射, 从而大幅度地提高了三端口滤波器的滤波效率。设计的多信道滤波器各个通道都能有效地实现下路滤波功能, 其信道间隔为10 nm, 滤波效率均在90%以上, 透射谱半高宽均在0.54 nm以下, 实现了较高的品质因子特性。该滤波器尺寸只有15.15 μm×13.91 μm, 且滤波效率很高, 适于在波分复用系统中进行复用与解复用, 在未来光路集成应用中具有良好的应用前景。

采用平面波展开法,研究铜币形空气孔二维三角晶格光子晶体的完全带隙随结构参量变化的规律.研究表明:铜币形散射子结合了空气孔型和介质柱型两种光子晶体的优点,有利于获得更宽的完全带隙.该光子晶体大完全带隙对由制备工艺上引起的材料掺杂和空气孔半径的偏离具有一定的稳定性.为了获得完全带隙,组成光子晶体的两种介质要有足够大的介电常数对比度,铜币形空气孔二维三角晶格光子晶体在ε=11.8时出现完全带隙.对参量分组优化发现,在ε=22.75,R=0.483 μm,d=0.195 μm,φ=90°,G=1.3时,完全带隙的宽度Δωa /2πc获得最大值0.136 1,带隙率为33.55%

A new kind of variable-length codes with good correlation properties for the multirate asynchronous optical code division multiple access (OCDMA) multimedia networks is proposed, called non-repetition interval (NRI) codes. The NRI codes can be constructed by structuring the interval-sets with no repetition, and the code length depends on the number of users and the code weight. According to the structural characteristics of NRI codes, the formula of bit error rate (BER) is derived. Compared with other variable-length codes, the NRI codes have lower BER. A multirate OCDMA multimedia simulation system is designed and built, the longer codes are assigned to the users who need slow speed, while the shorter codes are assigned to the users who need high speed. It can be obtained by analyzing the eye diagram that the user with slower speed has lower BER, and the conclusion is the same as the actual demand in multimedia data transport.

A construction scheme of variable-weight optical orthogonal codes (VW-OOCs) for asynchronous optical code division multiple access (OCDMA) system is proposed. According to the actual situation, the code family can be obtained by programming in Matlab with the given code weight and corresponding capacity. The formula of bit error rate (BER) is derived by taking account of the effects of shot noise, avalanche photodiode (APD) bulk, thermal noise and surface leakage currents. The OCDMA system with the VW-OOCs is designed and improved. The study shows that the VW-OOCs have excellent performance of BER. Despite of coming from the same code family or not, the codes with larger weight have lower BER compared with the other codes in the same conditions. By taking simulation, the conclusion is consistent with the analysis of BER in theory. And the ideal eye diagrams are obtained by the optical hard limiter.

Aiming at the defects of passive optical network (PON) monitoring based on optical time domain reflectometry (OTDR) technology, we research the non-OTDR monitoring technology. The coding scheme based on periodic encoder monitoring is discussed, and its limitation is analyzed. On this basis, the monitoring technology based on optical code division multiple access (OCDMA) is put forward. We analyze the feasibility of monitoring scheme based on PON of OCDMA, design a monitoring plan, and then use OptiSystem to simulate the design. The results of simulation and bit error rate (BER) analysis show that this monitoring technology can overcome the deficiencies of OTDR and distinguish the monitoring signals of different fiber branches clearly, which meets the demands for high beam split ratio of multi-user communication.

An electric encoded/optical transmission system of code division multiple access (CDMA) is proposed. It encodes the user signal in electric domain, and transfers the different code slice signals via the different wavelengths of light. This electric domain encoder/decoder is compared with current traditional encoder/decoder. Four-user modulation/ demodulation optical CDMA (OCDMA) system with rate of 2.5 Gbit/s is simulated, which is based on the optical orthogonal code (OCC) designed in our laboratory. The results show that the structure of electric encoding/optical transmission can encode/decode signal correctly, and can achieve the chip rate equal to the user data rate. It can overcome the rate limitation of electronic bottleneck, and bring some potential applications in the electro-optical OCDMA system.

基于倾斜光纤光栅耦合模理论，采用数值分析法研究了前后向导模耦合时倾斜角度和调制深度对倾斜光纤光栅反射谱的影响，以及导模和辐射模耦合时针对不同的入射光偏振态在倾斜角度、调制深度、光栅长度等不同时倾斜光纤光栅透射谱(或反射谱)的特性.研究结果表明，在前后向导模耦合时，不同偏振态入射光的光谱几乎相同；而对于辐射模耦合，由于反射谱的包络受消光系数的调制，而不同偏振态入射光的消光系数不同，并且倾斜角度越大不同偏振态的入射光的消光系数差别越大，故在研究辐射模耦合时需要将偏振态予以考虑.