Abstract
Dynamic axial focusing functionality has recently experienced widespread incorporation in microscopy, augmented/virtual reality (AR/VR), adaptive optics and material processing. However, the limitations of existing varifocal tools continue to beset the performance capabilities and operating overhead of the optical systems that mobilize such functionality. The varifocal tools that are the least burdensome to operate (e.g. liquid crystal, elastomeric or optofluidic lenses) suffer from low (≈100 Hz) refresh rates. Conversely, the fastest devices sacrifice either critical capabilities such as their dwelling capacity (e.g. acoustic gradient lenses or monolithic micromechanical mirrors) or low operating overhead (e.g. deformable mirrors). Here, we present a general-purpose random-access axial focusing device that bridges these previously conflicting features of high speed, dwelling capacity and lightweight drive by employing low-rigidity micromirrors that exploit the robustness of defocusing phase profiles. Geometrically, the device consists of an 8.2 mm diameter array of piston-motion and 48-μm-pitch micromirror pixels that provide 2π phase shifting for wavelengths shorter than 1100 nm with 10–90% settling in 64.8 μs (i.e., 15.44 kHz refresh rate). The pixels are electrically partitioned into 32 rings for a driving scheme that enables phase-wrapped operation with circular symmetry and requires <30 V per channel. Optical experiments demonstrated the array’s wide focusing range with a measured ability to target 29 distinct resolvable depth planes. Overall, the features of the proposed array offer the potential for compact, straightforward methods of tackling bottlenecked applications, including high-throughput single-cell targeting in neurobiology and the delivery of dense 3D visual information in AR/VR.
Highlights
With the increasingly broad reliance on volumetric processing for improved throughput and precision in optical systems, dynamic axial focusing has recently emerged as an essential feature across several disciplines
Pixel-level fabrication MEMSCAP’s PolyMUMPs and MUMPs-PLUS platforms were used to produce the focusing array, with custom postprocessing performed for reflective layer deposition
As part of the semi-custom modifications, the Polysilicon 1 layer, which forms the body of the suspension beams, was thinned down from the 2 μm standard for the process to 0.5 μm to reduce the spring stiffness and lower the voltage drive requirements
Summary
With the increasingly broad reliance on volumetric processing for improved throughput and precision in optical systems, dynamic axial focusing has recently emerged as an essential feature across several disciplines. Varifocal tools have become common fixtures in applications including biological microscopy[1], immersive displays[2], ophthalmoscopy[3] and material processing[4]. Most of these applications involve either coherent scanning systems for volumetric recording,. While AR/VR systems typically employ broadband and incoherent light sources, high-speed varifocal tools can seize upon the 1 kHz physiological detection rate of the human eye by rapidly cycling through multiple frames. By exploiting the persistence of vision using such frame partitioning schemes, high-speed varifocal tools can alleviate the burden posed by the delivery of dense 3D visual information in AR/VR
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