光纤光栅用作匹配光滤波器的研究

【作者】 闾晓琴；

【导师】 李振华； 贺安之；

【作者基本信息】 南京理工大学 ， 光学工程， 2003， 硕士

【摘要】 本文在利用耦合模理论对均匀及线性啁啾变迹光纤光栅(OFBG：Optical Fiber Bragg Grating)的反射谱进行分析的基础上，发现弱耦合条件下(耦合系数κ＜1)，均匀OFBG的反射谱具有类似与Sa~2(x)函数的分布特性，从而创新提出利用OFBG对光纤通信系统中光放大器的ASE噪声进行匹配光滤波的设想。 论文计算了通信系统中矩形光脉冲信号经强、弱OFBG、匹配光滤波器、F-P滤波器的输出光脉冲波形，经分析比较后发现：弱OFBG和理想匹配光滤波器的输出信号波形极其相似，不存在码间干扰，而F-P滤波器的输出波形存在比较严重的码间干扰。另外用计算机模拟计算了光信噪比的改善情况，研究发现：一个相同的噪声信号经弱OFBG后的光信噪比较经过F-P滤波器后的光信噪比高，由此认为，OFBG用作光滤波器对接收端前置光放大器的噪声进行滤波，比常用F-P光滤波器具有更大的优越性。 同时，建立了OFBG调谐测试装置，实现了OFBG的高精度线性调谐，两根光栅分别实现调谐范围6.320nm和5.762nm，调谐装置具有很好的重复性。 文中相关的研究成果已整理成多篇文章在相关刊物上发表。更多还原

【Abstract】 Based on the coupled mode theory, the reflect spectrum of OFBG is derived. The influenced of grating length, coupling coefficient and chirp coefficient to the maxium reflectivity and reflection bandwidth of OFBG are discussed in details. We find that under weak couple conditions (the couple coefficient K < 1), the reflect spectrum of an OFBG approximately has a characteristic of sa2(x) shape, which matched to the power spectrum of an optical communication signal. According to the above considerations, we proposed an idea to use weak OFBG as matched optical filter to filter the ASE noise of optical amplifier before the signal is detected in optical fiber communication system. The goal of the filter is to improve the sensitivity of an optical receiver by optimally filtering a communication signal.In this paper we calculated the temporal response of the matched filter, the commonly used F-P filter, as well as the matched weak OFBG filter. We find that the reflected pulse of weak OFBG closely resembles the triangular shape characteristic of a perfectly matched filter. It almost has no intersymbol interference. Whereas the pulse from a F-P transmission filter has a long decaying tail, this will lead to errors in detection. Secondly, we simulate the transmission process in computer, calculate the Optical-Signal-to-Noise-Ratio(OSNR) of output signal with the same input signal filtered by the OFBG, matched filter and F-P filter, analyze the improvement of the OSNR after filtered by them. We find it also has advantage over F-P filter. Taking the two reasons into account, we believe that the weak OFBG is superior to the widely used F-P filter.Additionally, the tuning characteristics of the OFBG are analyzed. By use of a micro-displacement set we realized a very high precision tuning. The experimental results verified the theoretical predication. The realized tuning ranges of the two OFBG are 6.320nm and 5.762nm respectively.更多还原