Liquid Combination with High Refractive Index Contrast and Fast Scanning Speeds for Electrowetting Adaptive Optics

Abstract

Electrowetting adaptive optical devices are versatile, with applications ranging from microscopy to remote sensing. The choice of liquids in these devices governs its tuning range, temporal response, and wavelength of operation. We characterized a liquid system, consisting of 1-phenyl-1-cyclohexene and deionized water, using both lens and prism devices. The liquids have a large contact angle tuning range, from 173 to 60°. Measured maximum scanning angle was realized at ±13.7° in a two-electrode prism, with simulation predictions of ±18.2°. The liquid’s switching time to reach 90° contact angle from rest, in a 4 mm diameter device, was measured at 100 ms. Steady-state scanning with a two-electrode prism showed linear and consistent scan angles of ±4.8° for a 20 V differential between the two electrodes, whereas beam scanning using the liquid system achieved ±1.74° at 500 Hz for a voltage differential of 80 V.

Lidar system with nonmechanical electrowetting-based wide-angle beam steering

“…The device has two separated electrodes and it is filled with two immiscible liquids as shown in Figs. 1(a) and 1(b) [28]. Applying a differential AC voltage to the two electrodes alters the contact angle at the liquid-liquid interface, tilting the liquid-liquid interface; hence resulting in a tunable prism.…”

“…A brief description of the EWOD prism fabrication process is presented; more details can be found in [23,28,37]. A three-dimensional printed mask is placed on a cylindrical glass tube (inner diameter 3.95 mm, height 5 mm) to create separated electrodes for a two-electrode device.…”

“…The EWOD prism is first filled with de-ionized water (DI water, n = 1.33) followed by 1-Phenyl-1-cyclohexene (PCH, n = 1.57) as shown in Fig. 1(b) [28]. Our previous studies on EWOD prisms used 1 wt% sodium dodecyl sulfate (SDS) solution and dodecane.…”

“…Unfortunately, this combination had a limited beam steering angle of ±2.2 • [23,37]. With the new liquid combination of DI water and PCH, beam steering of up to ±13.7 • is possible [28].…”

“…Typical mechanical solutions for scanning include mirror-based gimbals, oscillating/rotating mirrors (galvanometers) [10], rotating polygons [10], rotating prisms [10,11], and microelectromechanical systems (MEMS) mirrors [12,13]. Nonmechanical beam steering choices include acousto-optic deflectors [14,15], electro-optic deflectors [14,15], liquid crystal spatial light modulators (SLM) [16][17][18][19], solid-state beam steering based on phasedarrays [20,21], and liquid-based prisms [22][23][24][25][26][27][28]. Mechanical beam scanners are robust and reliable, although they commonly suffer from drawbacks such as movable parts prone to failure, large power requirements, heavy weights, large sizes, and high costs.…”