Digitally enhanced heterodyne interferometry (DEHI) combines the sub-wavelength displacement measurements of conventional laser interferometry with the multiplexing capabilities of spread-spectrum modulation techniques to discriminate between multiple electric fields at a single photodetector. Technologies that benefit from DEHI include optical phased arrays, which require the simultaneous phase measurement of a large number of electric fields. A consequence of measuring the phase of multiple electric fields is the introduction of crosstalk, which can degrade measurement precision. This work analytically and experimentally investigates the crosstalk when using DEHI to measure the phase of an arbitrarily large number of electric fields at a single photodetector. Also considered is the practical limit the dynamic range of the photodetector and shot noise imposes on the number of electric fields that can be discriminated. We describe how to minimize crosstalk by design. Experimental results demonstrate up to 55 dB suppression of crosstalk between two electric fields with a phase measurement bandwidth of 20 kHz and 1-10 pm$/\sqrt {\textrm {Hz}}$ displacement sensitivity for audio frequencies. Additionally, we demonstrate scaling of crosstalk proportional to the square-root of the number of electric fields when using an M-sequence modulation. Based on this analysis, we estimate that digitally enhanced heterodyne interferometry should be capable of measuring the phase of several hundreds of electric fields at a single photodetector while maintaining the same measurement bandwidth.

中文翻译：

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多通道光相位计量的串扰减少

数字增强外差干涉测量法（DEHI）将常规激光干涉测量法的亚波长位移测量与扩频调制技术的复用能力相结合，以区分单个光电探测器的多个电场。受益于DEHI的技术包括光学相控阵，其需要同时测量大量电场的相位。测量多个电场的相位的结果是引入了串扰，这会降低测量精度。当使用DEHI在单个光电探测器上测量任意大量电场的相位时，这项工作将进行分析和实验研究。还考虑了实际的限制，即光电检测器的动态范围和散粒噪声强加在可以区分的电场数量上。我们描述如何通过设计使串扰最小化。实验结果表明，在相位测量带宽为20 kHz和1-10 pm的情况下，两个电场之间的串扰抑制高达55 dB$ / \ sqrt {\ textrm {Hz}} $音频的位移敏感性。此外，我们演示了使用M序列调制时，串扰的缩放比例与电场数的平方根成比例。基于此分析，我们估计数字增强的外差干涉测量法应能够在单个光电探测器上测量数百个电场的相位，同时保持相同的测量带宽。