Miniaturized digital holography sensor for distal three-dimensional endoscopy

Abstract

A miniaturized sensor head for endoscopic measurements based on digital holography is described. The system was developed to measure the shape and the three-dimensional deformation of objects located at places to which there is no access by common measurement systems. A miniaturized optical sensor, including a complete digital holographic interferometer with a CCD camera, is placed at the end of a flexible endoscope. The diameter of the head is smaller than 10 mm. The system enables interferometric measurements to be made at speeds of as many as five reconstructions per second, and it can be used outside the laboratory under normal environmental conditions. Shape measurements are performed with two wavelengths for contouring, and the deformation is measured by digital holographic interferometry. To obtain full three-dimensional data in displacement measurements we illuminate the object sequentially from three different illumination directions. To increase the lateral resolution we use temporal phase shifting.

Three-Dimensional Displacement and Strain Measurements by Windowed Phase-Shifting Digital Holographic Interferometry

“…In order to measure three-dimensional displacement components, a three-directionalillumination method or three-directional-observation method is usually employed (Zhang et al, 1998;Kolenovic et al 2003). However, in order to analyze strain distributions, the displacement is spatially differentiated which requires accurate measurement of displacement distributions.…”

“…It is useful to analyze threedimensional displacement and strain distributions of an object. (Zhang et al, 1998;Kolenovic et. al., 2003) In this study, the Windowed PSDHI is extended to analyze threedimensional displacement components.…”

Time-of-Flight 3-D Endoscopy

“…Utilizing a miniaturized digital holography system 512×512 3D points can be obtained at 5 fps [8]. The authors successfully address non-medical application fields but do not comment on the applicability under sterile conditions.…”

Investigation of hidden diffuse surfaces using phase-shifting endoscopic digital speckle pattern interferometry

“…Since the invention of DSPI, many optical setups of DSPI have been developed, but most of them are only used to investigate the outer surfaces because of the convenience of observation and illumination. However, the tests of the inner surfaces of cavities with small access apertures or hidden surfaces that are not easy to be observed are in great demand in industry [4,5] . For example, it is very important in modern society to carry out a nondestructive inspection of the inner surfaces of a tube or tank, to measure the heat-deduced deformations of the hidden surfaces of an engine, or to investigate the changes inside a human body.…”