OCDMA系统中新型正交码的设计及性能研究

为了得到性能较为良好的正交码,采用没有重复数字的全间隔集,进行了地址码的设计和系统仿真验证,设计出的正交码具有理想的相关性和灵活的码字容量。分析整个系统,在考虑各种噪声和多址干扰的影响下,推导出正交码的误比特率公式。自行设计并搭建了采用光纤延时线作为编解码器的异步光码多分址系统。结果表明,该正交码能够适应更多用户的需求,通过误比特率公式计算和系统仿真得到的结果都较为理想,此研究对需要大容量的光码多分址系统的进一步发展具有一定的帮助。     

Construction and performance research on variable-length codes for multirate OCDMA multimedia networks

A new kind of variable-length codes with good correlation properties for the multirate asynchronous optical code divi- sion 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.     

基于动量梯度下降优化算法的色散均衡器设计

针对梯度下降(GD)算法收敛速度较慢的问题,提出了一种基于GD优化算法的有限脉冲响应(FIR)色散均衡器.采用动量梯度下降(MGD)算法在每次更新迭代时对梯度进行指数加权平均优化(简称CMGD算法)并进行偏差修正,利用OptiSystem搭建单载波相干光传输系统并与Matlab联合仿真.仿真结果表明:在学习速率为0.1...     

A high quality factor photonic crystal channel-drop filter with a linear gradient microcavity

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.