PaMIr: Phase Modulation Interferometry (resubmission)

距离是人类用来描述世界的最基本的属性之一，人类已经学会了用各种各样的方法来测量距离，从前臂的长度到光子的波长，甚至是电子或原子的波长。在现代工业社会中，长度测量深深嵌入到所有生产过程中，对范围，分辨率，速度和绝对精度的要求不断增长。在现代生产机器中，如数控铣床或车床，这些测量不仅必须以微米级的分辨率进行，而且在这些机器中，有几十个距离必须快速同时测量，同时它们也以每秒几米的高速变化。牛津大学开发了一种名为频率扫描干涉测量（FSI）的技术，能够以高精度（每米超过半微米）和每秒270万次测量的高时间分辨率测量绝对距离。这项技术正在与工业合作伙伴（Etalon AG）成功商业化，并在工业和科学中得到了许多应用。然而，目前商用的FSI还不能连续测量快速移动的目标。牛津大学的Reichold教授小组最近开发了一种快速测量快速移动目标距离的新方法，称为相位调制干涉测量法（PaMIr）。在PaMIr技术中，测量干涉仪中使用的激光在高频处进行相位调制，得到的干涉信号在不同频率处进行多次解调。由此产生的信号可以重建测量干涉仪的长度变化。PaMIr方法原则上与用于FSI测量的仪器向后兼容，并将保持FSI的独特功能，例如同时测量许多距离和每个测量通道的低成本。这种兼容性允许测量从用FSI测量的绝对距离开始，然后可以用PaMIr方法高速跟踪。PaMIr项目旨在与ettalon和VadaTech合作，将PaMIr的基本原理发展到可以在商业仪器中实施的状态。为此，我们必须根据现代生产机器的应用需要，以在线方式使用复杂的算法分析来自每个PaMIr测量干涉仪的快速数据流，延迟低于0.1毫秒。PaMIr仪器必须以每秒1.25亿个样本的速度同时数字化所有干涉仪信号，并将这些数据流馈送到基于现场可编程门阵列（fpga）的快速并行处理单元。我们将对这些fpga进行编程，以将PaMIr算法并行应用于所有通道，并且具有低延迟，这是一项艰巨的任务。为了有效地做到这一点，并以商业上适用的方式，我们需要了解和控制各个层面的DAQ系统硬件，这就是牛津大学与世界领先的数据采集设备制造商（VadaTech）合作的原因。与VadaTech和Etalon一起，我们已经开发了第一个用于FSI的光学读出系统。我们将在此基础上进一步改进其性能，以满足PaMIr的要求。最终，我们希望将PaMIr技术授权给ettalon AG，使该技术可用于工业和科学应用，并将我们开发的固件授权给VadaTech，以允许使用他们的DAQ系统作为多通道数字锁相放大器或PLL和PID控制器。

Distances are one of the most fundamental properties that humanity uses to describe the world and has learned to measure in an amazing variety of ways using everything from the length of your forearm to the wavelengths of photons or even electrons or atoms.In modern industrial societies length measurements are deeply embedded into all production processes and the requirements for range, resolution, speed and absolute accuracy are constantly growing. In modern production machines such as CNC mills or lathes these measurements have to be performed not only with micrometer resolution but in these machines there are dozens of distances that have to be measured rapidly and simultaneous while they are also changing at high speeds of meters per second. The University of Oxford has developed a technology called Frequency Scanning Interferometry (FSI) capable of measuring absolute distances with high accuracy (better than half a micrometer per meter) and high time resolution of 2.7 million measurements per second. This technology is being successfully commercialised with an industrial partner (Etalon AG) and has found many applications in industry and science. The current commercially available state of FSI is however not yet capable of measuring fast moving targets in a continuous form. The group of Prof Reichold at the University of Oxford has recently developed a novel method for rapid distance measurements of fast moving targets referred to as Phase Modulation Interferometry (PaMIr). In the PaMIr technique the laser light used in the measurement interferometers is phase modulated at high frequencies and the resulting interference signal is demodulated multiple times at different frequencies. From the resultant signals it is possible to reconstruct the change in length of measurement interferometer. The PaMIr method is in principle backward compatible with the instrumentation used for FSI measurements and will maintain the unique feature of FSI such as simultaneous measurements of many distances and a low cost per measurement channel. This compatibility allows a measurement to start at an absolute distance measured with FSI which can then be tracked at high speed with the PaMIr method.The PaMIr project aims to develop the basic PaMIr principles to a state ready for implementation in a commercial instrument in a collaboration with Etalon and VadaTech. To do so we will have to analyse the rapid flow of data from each PaMIr measurement interferometer with complex algorithms in an on-line way with a latency below 0.1 milliseconds as needed for applications in modern production machines. The PaMIr instrument will have to simultaneously digitise all interferometer signals at a rate 125 million samples per second and feed these data streams into fast parallel processing units based on Field Programmable Gate Arrays (FPGAs). We will program these FPGAs to apply the PaMIr algorithms to all channels in parallel with low latency which is a formidable task. To do this efficiently and in a commercially applicable way we need to know and control the hardware of the DAQ system at all levels which is why Oxford has teamed up with a world leading manufacturer of data acquisition equipment (VadaTech). Together with VadaTech and Etalon we have already developed a first optical readout system for FSI. We will build on this development and further improve its performance to meet the PaMIr requirements. Ultimately we expect to license the PaMIr technology to Etalon AG to make the technique commercially available for industrial and scientific application alike and to license the firmware we develop to VadaTech to allow the use of their DAQ systems as multi-channel digital lock-in amplifiers or PLL and PID controllers.