Focal length hysteresis of a double-liquid lens based on electrowetting

Abstract

In this paper, an extended Young equation especially suited for an ideal cylindrical double-liquid variable-focus lens is derived by means of an energy minimization method. Based on the extended Young equation, a kind of focal length hysteresis effect is introduced into the double-liquid variable-focus lens. Such an effect can be explained theoretically by adding a force of friction to the tri-phase contact line. Theoretical analysis shows that the focal length at a particular voltage can be different depending on whether the applied voltage is increasing or decreasing, that is, there is a focal length hysteresis effect. Moreover, the focal length at a particular voltage must be larger when the voltage is rising than when it is dropping. These conclusions are also verified by experiments.

Effect of the Liquid Density Difference on Interface Shape of Double-Liquid Lens

“…(8) is the relationship between the liquid density difference and the interface shape of a double-liquid lens. The interface shape is completely spherical when the density difference of the two liquids is zero [7].…”

“…The liquid lens has the advantage of being able to change focal length without mechanically moving the lens, which can provide considerable power savings and can eliminate wear associated with moving parts [1], so it is widely used in a large variety of application areas, such as mobile phones [2], surgical instruments [3], miniature cameras [4], and so on. The doubleliquid lens [4][5][6][7] based on the electrowetting effect is highly regarded because of its outstanding performance [7].…”

1 × 4 optical switch based on electrowetting

“…With the development of liquid photonic devices, optical switches have attracted more and more attention because of their wide applications in communications and displays. In the past few decades, many researchers have proposed a variety of liquid optical switches based on manipulating the shape of a liquid droplet or the position of the liquid, which can be divided into several categories with the different driving methods .…”

Adaptive Liquid Lens Actuated by Droplet Movement

“…According to the difference of the filled materials, it can be roughly classified into two categories: liquid crystal (LC) lens [1][2][3][4][5] and liquid lens [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24]. An adaptive LC lens usually employs an OPEN ACCESS inhomogeneous electric field to make the LC molecules reorient to produce a gradient refractive index profile.…”

“…Since the response time depends on the LC layer thickness and the size of the LC lens, it is more suitable for making microlens which constrains the real applications in imaging systems. There are three common operating mechanisms to design a liquid lens: electrowetting effect [6][7][8][9][10][11][12][13][14], dielectric force [15][16][17][18], and fluidic pressure [19][20][21][22][23][24].…”