Monolithic SU-8 Waveguide Micro-Lens for Deep Tissue Imaging
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Solution Overview
Problem
Current deep tissue imaging methods, such as endoscopy using fibers or GRIN lenses, suffer from poor resolution and limited field of view, making it difficult to control and monitor single neurons deep in the brain, especially due to light scattering and the need for high bandwidth and wavelength sensitivity.
Innovation Solution
A monolithically integrated polymeric waveguide with a micro-lens is fabricated using SU-8 or other polymers, combining waveguide and lens molds with controlled temperature and capillary forces to achieve high resolution and a large field of view, allowing for precise light manipulation and imaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If endoscopy using fibers or GRIN lenses is used for deep tissue imaging, then the imaging capability is achieved, but the resolution is poor and the field of view is limited
Solution Approach 1:
The patent merges the waveguide and lens into a single monolithic integrated structure. The lens is formed directly from the waveguide material through lateral etching, eliminating the need for separate components and achieving tight integration that improves both resolution and field of view simultaneously
Solution Approach 2:
The patent changes the geometric parameters of the waveguide-lens structure by controlling the etching depth and lateral dimensions. By adjusting the lateral etch distance and lens curvature, the numerical aperture and focal length are optimized to achieve high resolution imaging with an extended field of view
2Area of stationary object
If GRIN lenses are used, then deep tissue imaging is enabled, but the field of view is much smaller than the actual size due to low index contrast
Solution Approach 1:
The patent changes the refractive index parameter by using materials with higher index contrast (such as silicon nitride over silicon dioxide, or chalcogenide glass over polymer). This increased index contrast enables the lens to achieve a larger field of view relative to its physical size while maintaining focusing capability
3Device complexity
If on-chip waveguides with high index contrast materials are used, then integration is achieved, but the cross sectional dimensions are limited to small sizes leading to high beam divergence
Solution Approach 1:
The patent introduces curvature by forming a lens structure at the waveguide tip through lateral etching. This curved lens surface collimates or focuses the diverging beam, correcting the high beam divergence inherent in small cross-section waveguides while maintaining the benefits of on-chip integration
Solution Approach 2:
The patent uses thin film materials (such as silicon nitride, chalcogenide glass, or polymer) to form the waveguide and lens structure. These thin films enable precise control of the lens curvature and thickness, allowing optimization of beam divergence while maintaining compact integrated dimensions
4Measurement precision
If conventional waveguide platforms are used, then on-chip integration is achieved, but the resolution and bandwidth are poor
Solution Approach 1:
The patent uses composite material structures combining different layers (such as silicon nitride on silicon dioxide, or chalcogenide glass on polymer). This composite structure enables simultaneous optimization of resolution (through high index contrast and precise lens formation) and bandwidth (through material dispersion characteristics and wavelength insensitivity)
Solution Approach 2:
The patent changes the material parameters by selecting materials with appropriate dispersion characteristics and refractive indices. This enables the waveguide-lens structure to maintain high resolution across a broad wavelength range, achieving both high resolution and high bandwidth performance
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The integrated waveguide with micro-lens provides ultra-high resolution imaging and a larger field of view compared to conventional methods, enabling effective deep tissue imaging and optogenetic excitation with reduced background noise and improved neural control.
Implementation Method 1
an aluminum or other reflective layer acting as a mirror is deposited on the substrate
Implementation Method 2
A polymer, e.g., SU-8 2025, is flowed into the waveguide mask/lens mold (both on the same substrate) by decreasing its viscosity and using capillary forces via careful temperature control of the substrate
Implementation Method 3
The lens numerical aperture of 0.25, focal length of about 175 μm, and spot size of about 1.6 μm are achieved considering the lens dimensions
Data Source
AI summary
A probe structure includes a monolithically integrated waveguide and lens. The probe is based on SU-8 as a guiding material. A waveguide mold is defined using wet etching of silicon using a silicon dioxide mask patterned with 45° angle with respect to the silicon substrate edge and an aluminum layer acting as a mirror is deposited on the silicon substrate. A lens mold is made using isotropic etching of the fused silica substrate and then aligned to the silicon substrate. A waveguide polymer such as SU-8 2025 is flowed into the waveguide mask+lens mold (both on the same substrate) by decreasing its viscosity and using capillary forces via careful temperature control of the substrate.