采用双光束干涉曝光法制作大尺寸全息光栅时, 由于温度变化、空气流动、振动等因素的干扰, 曝光条纹相对于光栅基板存在平移和周期变化, 从而造成光栅对比度下降。分析了大尺寸光栅曝光过程中条纹的动态变化情况, 结果表明：3 h内条纹平移和周期变化的均方根值分别为1.87、1.20个条纹周期, 对比度的数值模拟结果分别为12.83%、67.37%.构建了由三组条纹监视系统、计算控制系统和两组压电位移台组成的曝光条纹锁定系统, 实现了条纹平移和周期的同时锁定.锁定之后得到的光栅槽型和对比度明显优于未锁定时的情形, 锁定精度为：平移3σ值为0.009个条纹周期, 对比度为99.99%, 周期变化均方根值为0.017个条纹周期, 对比度为99.77%, 满足大尺寸光栅曝光对条纹稳定性的要求.

The position and period of grating fringes will vary against the substrate during double beam interference exposure due to temperature variation, air flow, vibration and other factors in the fabrication of largesize holographic gratings. It will result in the decrease of grating contrast. The dynamic change of fringes was analyzed during largesize grating exposure. The RootMeanSquare (RMS) errors of fringe translation and period in 3 hours are 1.87 and 1.20 period respectively. The corresponding simulative grating contrasts are 12.83% and 67.37% respectively. A fringe locking system composed of three monitoring subsystems, a computation and control subsystem and two piezo nanopositioners was set up. The translation and period of fringes can be locked at the same time. The groove shape and contrast of gratings are improved significantly after locking. The precision of this fringe locking system: the 3σ value of fringe translation and corresponding contrast are 0.009 period and 99.99% respectively; the RMS error of period change and corresponding contrast are 0.017 period and 99.77% respectively. This locking system satisfies the requirements of fringe stability for the exposure of largesize gratings.