( Invited ) Improving Biological Inspection Via Novel Nonlinear Vibration-Enhanced Fiberoptic MEMS Imaging System

Abstract

Miniaturized, high-resolution optical imaging systems are essential for advancing minimally invasive diagnostics and endomicroscopy. This work presents a nonlinear vibration-enhanced fiber-optic MEMS scanner that overcomes key limitations of conventional MEMS micromirror-based scanners, including large footprint, optical complexity, and fabrication cost. The proposed device exploits resonant nonlinear vibrational dynamics of a tapered optical fiber to generate controlled two-dimensional (2-D) scan patterns using a single electrical driving signal . Experimentally, the scanner demonstrates stable circular and spiral scan trajectories with enhanced field-of-view (FOV) and spatial resolution sufficient to resolve features on the order of ~5 µm. Integration with a field-programmable gate array (FPGA) enables real-time control of scanning and illumination for micro-display visualization, highlighting the potential of this compact platform for fiber-based microscopy applications. Optical endomicroscopy plays a critical role in clinical diagnostics by enabling real-time, micron-scale visualization of tissue morphology in vivo . Conventional miniature imaging systems commonly rely on MEMS micromirrors to raster an optical beam across a sample. However, such approaches often suffer from size constraints, complex optical alignment, and limited scalability for ultra-compact probes. In addition, MEMS micromirror scanners require mirror apertures larger than the incident beam to avoid clipping and diffraction, as well as multi-step silicon microfabrication processes that increase cost and reduce mechanical robustness. These limitations motivate alternative scanning architectures that reduce optical complexity while maintaining high spatial resolution. To address these challenges, a hybrid fiber-optic MEMS scanner is developed that leverages nonlinear vibrational dynamics of a tapered optical fiber to achieve 2-D scanning using a single electrical input. By replacing the conventional scanning mirror with a resonantly driven optical fiber, the system significantly reduces optical and mechanical complexity while enabling compact form factors suitable for fiber-based microscopy and endoscopic imaging. The MEMS scanner consists of a five-layer stainless-steel bimorph structure with four piezoelectric actuation pads arranged symmetrically on either side of a central connecting arm, to which a tapered optical fiber is epoxied. The 60 µm-thick stainless-steel substrate provides enhanced mechanical robustness compared to silicon while remaining compatible with microfabrication processes. Lead zirconate titanate (PZT) thin films (~5 µm) are deposited on both sides of the substrate using aerosol-jet printing, followed by electron-beam deposition of titanium and platinum electrodes. When equal-phase driving signals are applied to opposing PZT pads, vertical vibration of the fiber is induced, while introducing a phase difference produces horizontal vibration. At specific resonant frequencies, fabrication-induced asymmetries in the tapered fiber and actuator structure give rise to nonlinear vibrational modes, transforming nominal one-dimensional motion into stable two-dimensional scan trajectories. This mechanism enables circular and spiral scanning without requiring independent orthogonal actuators or complex drive electronics. For experimental validation, the scanner was mounted on a 3D-printed holder and driven using an FPGA-based controller that provided synchronized actuation signals and optical modulation. Light from an LED source was coupled into the tapered fiber, and the resulting scan patterns were captured using a 200× microscope camera. The fiber tip was tapered using a CO₂ laser, reducing the emitted spot size from approximately 125 µm to ~5 µm, resulting in a substantial improvement in spatial resolution. At a carrier frequency of approximately 7.0 kHz with a 10 Hz amplitude modulation, the scanner produced a stable spiral scan with a diameter of ~60 µm at a frame rate of 10 frames s⁻¹. These results demonstrate that a single electrical drive signal, when operated near nonlinear resonance, can generate effective 2-D scanning suitable for microscopy-scale imaging. Overall, the results highlight the effectiveness of exploiting nonlinear resonance in fiber-optic MEMS systems to generate complex scan trajectories while significantly simplifying actuation and control. Compared to conventional dual-axis MEMS micromirror scanners, the proposed approach reduces system footprint, power consumption, and control complexity. The combination of aerosol-jet-printed piezoelectric actuation, tapered fiber optics, and FPGA-based control enables a compact, robust, and scalable scanning platform for fiber-based microscopy and endomicroscopy applications. Miniaturized, high-resolution optical imaging systems are essential for advancing minimally invasive diagnostics and endomicroscopy. This work presents a nonlinear vibration-enhanced fiber-optic MEMS scanner that overcomes key limitations of conventional MEMS micromirror-based scanners, including large footprint, optical complexity, and fabrication cost. The proposed device exploits resonant nonlinear vibrational dynamics of a tapered optical fiber to generate controlled two-dimensional (2-D) scan patterns using a single electrical driving signal . Experimentally, the scanner demonstrates stable circular and spiral scan trajectories with enhanced field-of-view (FOV) and spatial resolution sufficient to resolve features on the order of ~5 µm. Integration with a field-programmable gate array (FPGA) enables real-time control of scanning and illumination for micro-display visualization, highlighting the potential of this compact platform for fiber-based microscopy applications. Optical endomicroscopy plays a critical role in clinical diagnostics by enabling real-time, micron-scale visualization of tissue morphology in vivo . Conventional miniature imaging systems commonly rely on MEMS micromirrors to raster an optical beam across a sample. However, such approaches often suffer from size constraints, complex optical alignment, and limited scalability for ultra-compact probes. In addition, MEMS micromirror scanners require mirror apertures larger than the incident beam to avoid clipping and diffraction, as well as multi-step silicon microfabrication processes that increase cost and reduce mechanical robustness. These limitations motivate alternative scanning architectures that reduce optical complexity while maintaining high spatial resolution. To address these challenges, a hybrid fiber-optic MEMS scanner is developed that leverages nonlinear vibrational dynamics of a tapered optical fiber to achieve 2-D scanning using a single electrical input. By replacing the conventional scanning mirror with a resonantly driven optical fiber, the system significantly reduces optical and mechanical complexity while enabling compact form factors suitable for fiber-based microscopy and endoscopic imaging. The MEMS scanner consists of a five-layer stainless-steel bimorph structure with four piezoelectric actuation pads arranged symmetrically on either side of a central connecting arm, to which a tapered optical fiber is epoxied. The 60 µm-thick stainless-steel substrate provides enhanced mechanical robustness compared to silicon while remaining compatible with microfabrication processes. Lead zirconate titanate (PZT) thin films (~5 µm) are deposited on both sides of the substrate using aerosol-jet printing, followed by electron-beam deposition of titanium and platinum electrodes. When equal-phase driving signals are applied to opposing PZT pads, vertical vibration of the fiber is induced, while introducing a phase difference produces horizontal vibration. At specific resonant frequencies, fabrication-induced asymmetries in the tapered fiber and actuator structure give rise to nonlinear vibrational modes, transforming nominal one-dimensional motion into stable two-dimensional scan trajectories. This mechanism enables circular and spiral scanning without requiring independent orthogonal actuators or complex drive electronics. For experimental validation, the scanner was mounted on a 3D-printed holder and driven using an FPGA-based controller that provided synchronized actuation signals and optical modulation. Light from an LED source was coupled into the tapered fiber, and the resulting scan patterns were captured using a 200× microscope camera. The fiber tip was tapered using a CO₂ laser, reducing the emitted spot size from approximately 125 µm to ~5 µm, resulting in a substantial improvement in spatial resolution. At a carrier frequency of approximately 7.0 kHz with a 10 Hz amplitude modulation, the scanner produced a stable spiral scan with a diameter of ~60 µm at a frame rate of 10 frames s⁻¹. These results demonstrate that a single electrical drive signal, when operated near nonlinear resonance, can generate effective 2-D scanning suitable for microscopy-scale imaging. Overall, the results highlight the effectiveness of exploiting nonlinear resonance in fiber-optic MEMS systems to generate complex scan trajectories while significantly simplifying actuation and control. Compared to conventional dual-axis MEMS micromirror scanners, the proposed approach reduces system footprint, power consumption, and control complexity. The combination of aerosol-jet-printed piezoelectric actuation, tapered fiber optics, and FPGA-based control enables a compact, robust, and scalable scanning platform for fiber-based microscopy and endomicroscopy applications.