Optical Resonator Filter for Wavelength and Mode Selection
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Solution Overview
Problem
Higher-order Hermite-Gaussian modes interfere with the monitoring of optical systems, particularly in fibre-optic communication, as they are not attenuated by the time the beam reaches the detector, leading to phase characteristic differences between detected and transmitted beams, and existing solutions that use fibre length to attenuate these modes increase system size.
Innovation Solution
An optical filter comprising a first lens and first and second optical elements with semi-reflective surfaces arranged to form a resonator, where the radius of curvature is between 1 and 10,000 times the distance from the semi-reflective surfaces to the focal point, allowing for the selection of both wavelength and Hermite-Gaussian modes by adjusting the relative movement of these surfaces using expansion elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a length of fibre is used to attenuate higher-order modes before detection, then mode interference is reduced, but system size increases
Solution Approach 1:
The patent extracts the harmful higher-order modes from the optical beam using a spatial filter (iris diaphragm) positioned at the focal point of a lens. This removes the need for long fibre attenuation while maintaining compact system size, as the filtering occurs immediately at the beam path rather than requiring extended propagation distance
Solution Approach 2:
The patent introduces a spatial filter (iris diaphragm) as an intermediary element between the optical components and detector. This mediator selectively blocks higher-order modes while allowing the fundamental mode to pass, achieving mode filtering without requiring long fibre lengths
2Device complexity
If higher-order modes are allowed to reach the detector, then system complexity is reduced, but measurement precision deteriorates due to phase characteristic differences
Solution Approach 1:
The patent extracts harmful higher-order modes using a spatial filter at the focal point, removing the source of phase characteristic discrepancies. This enables precise measurement of the fundamental mode phase characteristics without the complicating influence of higher-order modes, improving measurement precision while maintaining relatively simple system architecture
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 solution effectively filters higher-order modes, reducing interference in optical systems and allowing for precise monitoring by selectively attenuating unwanted modes, while maintaining a compact system design.
Implementation Method 1
The first and second semi-reflective surfaces are arranged to form a resonator
Implementation Method 2
The first lens has an optical axis, configured to focus beams propagating parallel to the optical axis at a focal point
Implementation Method 3
The first optical element has a first semi-reflective surface, the first semi-reflective surface being curved and having a first radius of curvature around a first centre of curvature on the optical axis
Data Source
AI summary
An optical filter comprising a first lens, and first and second optical elements. The first lens has an optical axis, configured to focus beams propagating parallel to the optical axis at a focal point. The first optical element has a first semi-reflective surface, the first semi-reflective surface being curved and having a first radius of curvature around a first centre of curvature on the optical axis. The second optical element has a second semi-reflective surface. The first radius of curvature is between 1 and 10,000 times the distance between the first semi reflective surface and the focal point along the optical axis. The first and second semi-reflective surfaces are arranged to form a resonator. The first lens and the first and second semi-reflective surfaces are arranged along the optical axis such that light is transmittable along an optical path through the lens and the resonator. The optical filter further comprises one or more expansion elements located outside of the optical path, and arranged such that expansion of the expansion elements causes relative movement of the first and second semi-reflective surfaces.