An endoscopic system adopting a liquid crystal lens with an electrically tunable depth-of-field

Abstract

Conventional endoscopic systems consisting of several solid lenses suffer from a fixed and limited depth-of-field (DOF). For practical applications, conventional endoscopes mechanically change the distance between the solid lenses of a lens module in order to change the focusing plane and DOF to see clearly in a scene. In this paper, we demonstrate an electrically tunable endoscopic system adopting a liquid crystal lens. By means of tunable focusing properties of the LC lens as a positive lens and a negative lens, the object at different objective distances can be imaged to the image sensor clearly and the corresponding depth-of-field can also help to enlarge the total spatial depth perception in a scene. The optical mechanism is discussed. In the experiments, under adjustment of three discrete lens powers of the LC lens, the viewing range or total spatial depth perception of the endoscopic system is from 76.4 mm to 12.4 mm which is 2x improved compared to the conventional one without LC lens. We believe this study can be extended to the applications of industrial and medical endoscopes.

Extending the depth of field with chromatic aberration for dual-wavelength iris imaging

“…Changing the geometrical focus in real time using a liquid lens has been proven experimentally. Chen and Lin introduce a concept of an electrically tuneable liquid lens capable of producing three different lens powers and increasing the spatial depth perception to twice that of a conventional endoscope without the image post processing [13]. Liu and Hua require restoring algorithms for the variable focal objective for deconvolving the captured image to produce an EDOF effect [14].…”

Extending the Depth of Field in a Fixed Focus Lens Using Axial Colour

“…7 An electrically tuneable liquid lens has been shown to be capable of producing three different lens powers and increasing the spatial depth perception to twice that of a conventional endoscope without image post processing. 8 An EDOF effect can be produced by introducing a variable focal objective. This approach requires restoration algorithms for deconvolving the captured image.…”

Motion‐free endoscopic system for brain imaging at variable focal depth using liquid crystal lenses

“…It is easy thus to calculate, using the values of a typical LC mixture (Δε ≈ 16.5, and K ≈ 21 • 10 -12 N), that the value of V th is approximately 1.2 V. This, in turn, means that the lens geometry requires a voltage that is at least 10 times higher in order to initiate the reorientation of the director, while an even higher voltage is required to operate the lens (V LC > V th ) [24]. To reduce the voltage required to operate the lens, the electrodes must be brought closer together by reducing the thickness of the middle substrate.…”