低相干光干涉法延时测量中的误差分析

Time Delay Error in Optical Low Coherence Interferometry

低相干光干涉法通过测量宽谱光通过待测器件之后的相位变化得到其相对延时量。采集宽谱光时域干涉数据，利用傅里叶变换提取出频域相位信息后再进行相位展开、多项式拟合处理，所得相位曲线对频率求导可得待测延时曲线。延时测量误差来源于干涉信号强度误差和纯相位误差。理论分析和仿真计算表明，延时误差与相位误差成正比；强度噪声引起的相位误差与噪声强度成正比，且该类噪声可通过曲线拟合算法得到有效抑制。实验表明，温度等环境因素引起的纯相位误差是延时测量误差的主要因素。实验上，对约19m光子晶体光纤于1540～1560nm波段的相对延时进行了测量，达到了0．14ps的精度。

Relative time delay of the optical device under test （DUT） is measured by optical low coherence interferometry by measuring the phase change of a broadband light after passing through it. The interference patterns of broadband light are recorded and analyzed using Fourier transform （FT） to calculate the phase change of the broadband light in frequency domain. The polynomial fitting algorithm is used to smooth the calculated phase curve. The derivation of phase delay curve versus frequency is the measured time delay. Measurement error of time delay comes from the intensity noise and pure phase noise of interference patterns. Theoretical analysis and simulation calculations show that the time delay error is directly proportional to phase error, and the phase error due to intensity noise is directly proportional to the noise too and it can be eliminated by polynomial fitting algorithm. Experimental results show that the instability of the phase characteristic of the DUT is mainly due to temperature variation, which is also the main source of measurement error. The relative time delay of a section of photonic crystal fiber （PCF） about 19 m from 1540 to 1560 nm is measured and the best precision reaches sub-picoseconds.