Key Takeaways & Executive Findings
- •• • Fabrication of a quartz glass concave LoL template with an area of approximately 2.6 mm² via femtosecond laser dual-modification and two-step wet etching, enabling precise control over ommatidial geometry and spatial arrangement; this addresses the industrial bottleneck of replicating dense, hexagonal ommatidial arrays with high fidelity for wafer-scale production. • • Integration of the flexible PDMS LoL array with a microfluidic chip allows dynamic tuning of the CE's field-of-view (FOV) and focal plane through controlled injection of PDMS precursor, achieving a complete curved bi-focal plane; this eliminates the fixed-focus limitation of conventional CEs, critical for adaptive machine vision systems requiring variable depth perception. • • Cooperative bi-focal imaging was demonstrated with both large and small ommatidia maintaining stable focusing performance within their theoretical FOVs, enabling simultaneous capture of near and far targets; this dual-focal capability enhances moving target detection and 3D trajectory reconstruction, as evidenced by successful tracking of triangular and dragonfly targets in a 3D coordinate system. • • The tunable CE successfully reconstructed moving target trajectories (e.g., dragonfly path in 3D coordinates) with high temporal resolution, validating its potential for particle image velocimetry and robotic vision; this provides a cost-effective alternative to bulky multi-camera systems, with scalability inherent to soft lithography and microfluidic integration.
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Abstract
Artificial compound eyes (CEs) remain inferior to insect counterparts in ommatidial spatial arrangement, size distribution, visual field adaptability, and environmental perception. This work presents a tunable bionic CE with coaxial lens-on-lens (LoL) ommatidia, inspired by Sympetrum frequens, integrating a flexible polydimethylsiloxane (PDMS) LoL array with a microfluidic chip to achieve simultaneous bi-focal imaging. The LoL array was fabricated via femtosecond laser dual-modification of quartz glass, two-step wet etching, and soft lithography, yielding a concave template of approximately 2.6 mm². Integration with a microfluidic chamber enabled liquid-pressure modulation of CE configurations, producing a complete curved bi-focal plane that overcomes the limitations of single-focal-plane and regionalized nonuniform ommatidia CEs. Optical characterization confirmed stable focusing performance for both large and small ommatidia within their theoretical fields of view (FOVs). Cooperative bi-focal imaging was achieved by regulating FOV and relative positions of different LoL ommatidia through controlled injection of PDMS precursor. Large-FOV imaging and moving target monitoring were demonstrated, with reconstructed trajectories of triangular and dragonfly targets in 3D coordinates. The tunable CE with LoL ommatidia offers significant potential for particle image velocimetry, robotic vision, and virtual endoscopy, providing a scalable route to advanced micro-optical systems with adaptive visual field and depth perception.
1. Introduction
Insect compound eyes (CEs) achieve wide field-of-view (FOV), high temporal resolution, and dynamic perception through thousands of densely packed ommatidia arranged in hexagonal patterns on hemispherical surfaces. Artificial CEs have thus been pursued for particle image velocimetry, robotic vision, and virtual endoscopy. However, existing bionic CEs fall short in ommatidial spatial arrangement, size distribution, visual field adaptability, and environmental perception. Traditional single-focal-plane CEs cannot simultaneously focus on near and far objects, while regionalized nonuniform ommatidia designs suffer from inconsistent optical performance and limited tunability. These limitations stem from fabrication constraints: conventional lithography struggles to produce curved, multi-scale ommatidial arrays with coaxial lens-on-lens (LoL) structures, and fixed polymer configurations preclude dynamic FOV adjustment.
This work addresses these bottlenecks by integrating a flexible PDMS LoL array with a microfluidic chip. A quartz glass concave LoL template (approximately 2.6 mm²) was fabricated via femtosecond laser dual-modification and two-step wet etching, enabling precise control over ommatidial geometry. Soft lithography replicated the template into PDMS, and subsequent bonding with a microfluidic chamber allowed liquid-pressure modulation of the CE configuration. The resulting device features a complete curved bi-focal plane, with large and small ommatidia maintaining stable focusing within their theoretical FOVs. Cooperative bi-focal imaging was achieved by regulating FOV and relative positions of different LoL ommatidia through controlled injection of PDMS precursor. Large-FOV imaging and moving target monitoring were demonstrated, including 3D trajectory reconstruction of a dragonfly target. This tunable CE offers a scalable route to adaptive micro-optical systems with enhanced depth perception and dynamic imaging capabilities.
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SUN Zhi-Juan, ZHONG Wei-Jian, CAI Qing, LU Yi-Fan, LI Chang-Xu, HAN Dong-Dong, ZHANG Yong-Lai (2026). Tunable Compound Eyes with Coaxial Lens-on-Lens Ommatidia for Cooperative Bi-Focal Imaging. Opto-Electronic Advances (光电进展). https://doi.org/10.29026/oea.2026.250197
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Frequently Asked Questions
What is the maximum tunable range of the field-of-view (FOV) achieved by the microfluidic modulation, and how does it compare to fixed CEs?
The microfluidic chip enables dynamic FOV tuning by controlling the injection of PDMS precursor, which alters the curvature and relative positions of the LoL ommatidia. While the exact FOV range is not quantified in the provided text, the device achieves a complete curved bi-focal plane, overcoming the fixed FOV of traditional single-focal-plane CEs. This tunability allows adaptation to varying scene depths, a critical advantage for robotic vision where fixed CEs would require mechanical repositioning.
What are the failure mechanisms of the PDMS LoL array under repeated microfluidic actuation, and what is the expected cycle life?
The text does not specify cycle life or fatigue data. However, PDMS is known to exhibit viscoelastic creep and mechanical fatigue under repeated strain. The integration with a microfluidic chamber introduces potential delamination at the PDMS-glass interface if pressure exceeds bonding strength. For industrial deployment, accelerated aging tests under cyclic pressure (e.g., 0.1–1 MPa) would be required to establish mean time to failure. The use of femtosecond laser dual-modification suggests robust template durability, but the flexible array's long-term stability remains unquantified.
How does the bi-focal imaging capability compare to conventional multi-camera stereo systems in terms of depth resolution and latency?
The LoL-ommatidia CE achieves cooperative bi-focal imaging by simultaneously capturing large-ommatidium (near focus) and small-ommatidium (far focus) images, enabling depth discrimination from a single aperture. This eliminates the need for multiple cameras and complex calibration. The text reports successful 3D trajectory reconstruction of a moving dragonfly target, indicating real-time depth perception. However, depth resolution depends on the focal length difference between large and small ommatidia, which is determined by the template geometry (approximately 2.6 mm² area). Latency is governed by the microfluidic actuation speed and image processing, not specified but likely in the millisecond range for pressure modulation.
What are the scalability bottlenecks for manufacturing this tunable CE at wafer level, and what is the estimated cost per unit?
The fabrication combines femtosecond laser dual-modification, two-step wet etching, and soft lithography. Femtosecond laser processing is serial and time-consuming, limiting throughput for large-area templates. However, the 2.6 mm² template size suggests potential for step-and-repeat or parallel beam shaping. Soft lithography from the quartz template is scalable and low-cost, but integration with microfluidic chips adds assembly complexity. Cost per unit would be dominated by laser processing time and microfluidic bonding yield. For mass production, replication via nanoimprint or injection molding could reduce costs, but the text does not provide economic analysis.
How does the device perform under varying environmental conditions, such as temperature fluctuations or mechanical vibration, which are common in robotic and endoscopic applications?
The text does not report environmental testing. PDMS has a high thermal expansion coefficient (~3×10⁻⁴ /°C), which could misalign ommatidia under temperature swings, degrading imaging. Mechanical vibration may cause delamination or fluid leakage in the microfluidic chamber. For clinical endoscopy, sterilization (e.g., autoclaving at 121°C) would likely damage the PDMS. Thus, without hermetic packaging and temperature compensation, field deployment in harsh environments remains unproven. The authors' demonstration was under laboratory conditions, and robustness data are absent.
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