Aspherical Lens with Helical Sag for Low-Feedback Optical Coupling
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Solution Overview
Problem
Existing optical subassemblies for fiberoptic communications are sensitive to misalignment, leading to increased optical feedback and power loss due to complex lenses creating large spots at the fiber tip, which results in high manufacturing costs and reliability issues.
Innovation Solution
An optical subassembly with a lens having a surface sag consisting of a superposition of a rotationally symmetrical and a rotationally asymmetrical sag component, where the asymmetrical component forms a donut-shaped spot around the light source aperture, reducing backreflection, and the symmetrical component is either spherical or aspherical without a cone component, integrated within a monolithic housing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If complex lenses with diffractive surfaces or conical components are used to reduce optical feedback, then optical feedback into the light source is reduced, but the spot size at the fiber tip increases leading to increased sensitivity to misalignment and clipping losses
Solution Approach 1:
The patent applies asymmetry by introducing a rotationally asymmetrical sag component (such as an astigmatic or coma term) to the lens surface profile. This asymmetry creates an elliptical or asymmetric spot pattern at the fiber tip that is intentionally designed to avoid the fiber center, thereby reducing optical feedback while maintaining a compact overall spot size that is less sensitive to misalignment.
Solution Approach 2:
The patent applies local quality by creating a non-uniform light distribution pattern where the intensity is deliberately reduced at the fiber center (where feedback occurs) while maintaining higher intensity in the peripheral regions. This is achieved through the specific combination of rotationally symmetrical and asymmetrical sag components that generate a tailored intensity profile across the spot area.
2Object-affected harmful factors
If complex lenses are used to reduce optical feedback, then optical feedback is reduced, but manufacturing precision requirements increase due to tight tolerances for assembly
Solution Approach 1:
The rotationally asymmetrical sag component introduces controlled asymmetry that creates a robust optical pattern less sensitive to manufacturing variations. The specific mathematical form of the asymmetry (astigmatic or coma terms) is chosen to provide tolerance to alignment errors while achieving the feedback reduction goal.
Solution Approach 2:
The patent changes the surface sag parameters by combining rotationally symmetrical components (spherical or aspherical) with rotationally asymmetrical components. This parameter combination creates an optical system with relaxed tolerances compared to conventional symmetric designs, as the asymmetric pattern provides inherent immunity to certain types of misalignment and manufacturing variations.
3Ease of manufacture
If conventional spherical or aspherical lenses are used, then manufacturing is simpler, but optical feedback into the light source is not sufficiently reduced
Solution Approach 1:
The patent applies composite materials by combining multiple sag components (rotationally symmetrical spherical or aspherical terms with rotationally asymmetrical astigmatic or coma terms) into a single lens surface profile. This composite approach allows the lens to achieve both manufacturability (through the spherical/aspherical base) and effective feedback reduction (through the asymmetrical components) simultaneously.
Solution Approach 2:
The patent uses spheroidality by incorporating aspherical terms in the rotationally symmetrical sag component, which allows for better control of the light distribution pattern while maintaining manufacturing feasibility. The aspherical curvature works in combination with the asymmetrical terms to achieve the desired optical 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 solution significantly reduces optical feedback into the light source while maintaining a compact spot size at the fiber tip, allowing for relaxed manufacturing tolerances and cost savings by minimizing the need for precise alignment, thus enhancing the reliability and efficiency of light coupling.
Implementation Method 1
a lens for coupling light emitted from the light source aperture into the optical waveguide aperture
Implementation Method 2
the rotationally asymmetrical sag component is for lessening coupling of light reflected from the waveguide back into the light source aperture
Data Source
AI summary
An optical subassembly for low-feedback coupling of light from a light source into an optical waveguide such as an optical fiber is described. The optical subassembly has an aspherical lens with surface sag having a rotationally symmetrical sag component without having a cone sag component, and a rotationally asymmetrical helical component for reducing coupling of light reflected from the optical fiber tip back into the laser aperture by causing a significant portion of the reflected light to encircle the laser aperture. The lens shape and the height of the helix are selected so that tight focusing onto the fiber tip is preserved, while the optical feedback is reduced.