We present a highly miniaturized endoscopic point distance sensor based on a spatial confocal measurement principle.1 The sensor uses a new technique called spatial confocal point distance measurement. A special feature of the proposed sensor design is the high degree of miniaturization through femtosecond direct laser writing and the use of optical fiber bundles, which enable an endoscopic application. We show the complete sensor measurement principle, sensor head design, experimental setup, and experimental results.
Increasing miniaturization requires improved and highly miniaturized optical 3D metrology systems. In this paper a basic measurement principle and a proposed optical design of a highly miniaturized endoscopic spatial confocal point distance sensor are presented. The sensor uses a, to our knowledge new technique called spatial confocal point distance measurement. A special feature of the proposed sensor design is the high degree of miniaturization, through femtosecond direct laser writing and the use of optical fiber bundles, which enable an endoscopic application.
Spatial carrier interferometry is a well-known single frame wavefront phase measuring technique. In this
technique a large relative tilt is placed between the test and reference beams producing a high frequency
carrier fringe pattern which is modulated by the desired measurement wavefront. Implementation of spatial
carrier interferometry is relatively easily accomplished on most advanced laser interferometers. Since it is a
single frame technique, it provides robust vibration immunity, enabling measurements involving long paths or
mechanically decoupled elements as well as metrology into vacuum chambers and overall environmental
immunity. One of the major limitations of this technique is the degradation in measurement accuracy
resulting from the large wavefront tilt applied between the test and reference beams. As a result of the large
relative beam angle, the test and reference beams do not follow exactly the same path through the
interferometer, resulting in what is generally known as retrace error. In this paper an automated calibration
technique is introduced which determines the retrace error in a measurement setup without the use of a
calibration artifact. This technique works well when measuring both flat and spherical test surfaces. In both
cases, the difference between the calibrated wavefront and the wavefront measured on-axis with temporal
phase shifting is less than .05 waves. This process allows nanometer-level measurement of precision optics
even in difficult environments.