Non-uniform grating for STED doughnut beam generation
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Solution Overview
Problem
Current semiconductor processing techniques find it difficult to fabricate spiral zone plates with continuously varying thickness, which are necessary for producing doughnut-shaped depletion beams in Stimulated Emission Depletion (STED) imaging, limiting the resolution and efficiency of STED microscopy.
Innovation Solution
A non-uniform grating with a varying duty cycle and period is used to produce a doughnut-shaped intensity profile, acting as a spiral phase plate, which can create a phase shift that varies linearly across a 2π range, allowing for the production of a doughnut-shaped depletion beam without requiring continuous thickness variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a spiral zone plate with continuously varying thickness is used to produce a doughnut-shaped depletion beam, then the resolution of STED imaging is improved, but the difficulty of fabrication using semiconductor processing techniques increases
Solution Approach 1:
The continuous thickness variation of the spiral zone plate is segmented into discrete thickness levels corresponding to different grating periods. This segmentation allows the optical phase modulation function to be achieved through discrete grating structures that can be fabricated using standard semiconductor processing techniques, while still maintaining the spiral phase plate functionality for doughnut-shaped beam generation
Solution Approach 2:
The invention changes the parameter representation from continuous thickness variation to discrete grating period variation. By modulating the grating period as a function of angular coordinate rather than using continuous thickness changes, the system achieves the same optical phase shift effect with structures that are compatible with semiconductor fabrication processes
2Ease of manufacture
If a non-uniform grating with varying duty cycle and period is used to produce a doughnut-shaped intensity profile, then the ease of manufacture is improved, but the device complexity increases
Solution Approach 1:
The non-uniform grating structure serves multiple functions simultaneously: it acts as a diffraction grating for beam shaping, implements spiral phase modulation for doughnut-shaped profile generation, and can be integrated with semiconductor processing techniques. This multi-functionality reduces the need for separate optical components while achieving the desired beam profile
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
This approach enables the creation of a doughnut-shaped depletion beam, enhancing the resolution of STED imaging to sub-wavelength sizes, such as 20 nm, while also potentially focusing both depletion and excitation beams using a single integrated optical element.
Implementation Method 1
a non-uniform grating has a duty cycle or period that varies with angle as required to act as a spiral phase plate or otherwise to produce a doughnut-shaped intensity profile in an output beam
Implementation Method 2
the duty cycle or period of the grating can be varied as required to produce a phase shift that varies with an angular coordinate in a manner that causes total destructive interference of light output from the grating at a central axis
Implementation Method 3
regions 120 that differ in refractive index from the rest of substrate 110
Data Source
AI summary
A system includes a non-uniform grating having a first region with a first refractive index and second regions with a second refractive index. A pattern of the second regions varies with an angular coordinate such that phase shifts of an incident beam created by the grating cause destructive interference that creates an intensity minimum within an output beam from the grating.