A Review of Various Methods for Distance Measurements with Light

Physical and Analytical Chemistry Seminar

Lecturer: Yakir Ishay

29-28 Oct 2019 @ 15:30

Location: Faculty Seminar Room


One the most accurate methods for distance measurements involve the intrinsic nature of light in various ways. In most cases, the accuracy manifests through a measurement uncertainty up to several nanometers. The ability to make use of light for measuring distances with such accuracy is of great importance for lots of applications. Among others, these include 3D stereovision, building blocks for 3D cameras, robot and computer vision, object detection and tracking, molecular inspection, investigation of small biological tissues, wafer defects mappings, various spectroscopy methods and these are only few examples. Practically, measuring distances with great accuracy can also be performed by non-optical methods such as, Scanning Electron Microscopy (SEM), which uses electron beams (or the reflected electron beams) to measure distance, sound waves (e.g. sonar systems) and mechanical based methods. In this seminar, we are focusing on the optical methods for distance measurements that very often involves simpler measuring setup and process. Essentially, the optical methods can be divided into two main categories: passive and active methods. The passive methods correspond to measuring systems that do not illuminate the target directly, that is the light is either reflected or produced by the target itself. This is in contrast to active methods that illuminate the target directly. Among these two categories there exist five main techniques: (1) Geometrical based techniques, which include triangulation and structured light technique, (2) Time of Flight (TOF) , which include direct and indirect TOF.  The main idea is to relies on the speed of light to measure the TOF either directly with clocks (direct TOF) or indirectly (indirect TOF) by comparing the phase of the intensity-modulated emitted and reflected light, and  (3) Interferometry based techniques, which employs the wave nature of light and the ability of waves to interfere. This seminar reviews the basic ideas behind these quantitative methods of measuring the distance, shape, or size of an object with light. Hence, the general methods/techniques discussed are:

  • Triangulation
  • Structured Light
  • Direct and indirect time of flight
  • Interferometry



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