2D MEMS electrostatic cantilever waveguide scanner for potential image display application

Abstract

Abstract. This paper presents the current status of our micro-fabricated SU-8 2D electrostatic cantilever waveguide scanner. The current design utilizes a monolithically integrated electrostatic push-pull actuator. A 4.0 μm SU-8 rib waveguide design allows a relatively large core cross section (4μm in height and 20 μm in width) to couple with existing optical fiber and a broad band single mode operation (λ= 0.7μm to 1.3μm) with minimal transmission loss (85% to 87% output transmission efficiency with Gaussian beam profile input). A 2D scanning motion has been successfully demonstrated with two fundamental resonances found at 202 and 536 Hz in vertical and horizontal directions. A 130 μm and 19 μm, corresponding displacement and 0.062 and 0.009 rad field of view were observed at a +150V input. Beam divergence from the waveguide was corrected by a focusing GRIN lens and a 5mm beam diameter is observed at the focal plane. The transmission efficiency is low (~10%) and cantilever is slightly under tensile residual stress due to inherent imperfection in the process and tooling in fabrication. However, 2D light scanning pattern was successfully demonstrated using 1-D push-pull actuation.

Design and Fabrication of a Push-Pull Electrostatic Actuated Cantilever Waveguide Scanner

“…The device was successfully fabricated (Figure 15a,c) [22]. Initially, due to its large aspect ratio and residual stress, the cantilever waveguide appeared bent (Figure 15b) [22]. This problem was quickly resolved by carefully controlling the baking procedure.…”

“…The basic operating principle of this 2D scanner is shown in Figure 2 [22]. The scanner motion is generated by the pair of push-pull electrostatic actuators.…”

“…The fabrication procedure of the electrostatic scanner is shown in Figure 13 [22]. A 4-inch silicon wafer with a standard thickness of 525 ± 25 μm served as the substrate for the device fabrication.…”

“…An 8.0 mm × 8.0 mm × 1.0 mm acrylic-based photopolymer holder was designed and fabricated using a multi-material three-dimensional printing system (X-axis: 600 dpi; Y-axis: 600 dpi; Z-axis: 1600 dpi, Connex350, Stratasys Ltd.) [22] to secure the MEMS device. A gradient index (GRIN) lens (4.85 mm length × 2 mm diameter GRIN lens rod by GRINTECH GmbH, Jena, Germany, working distance = 20 mm, beam width = 20 µm, view angle = ±30°, and NA = 0.5) was installed and secured in a tube structure formed by the assembly of the upper and the lower part of the holder as shown in Figure 14.…”

“…Most of the resonant scanner designs reported so far, including our previous designs, operate at resonance to achieve high line resolution and high FOV [15,16,17,18,19,20,21,22]. However, this design presents several challenges, such as achieving a large frequency difference between the two resonant operating frequencies.…”