Faceted Lens Rear Surface for Low-Noise Optical Transmitter
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Solution Overview
Problem
Optical feedback from fibers to lasers in fiber communications causes jitter in signal timing, particularly affecting single-mode and multi-mode lasers, necessitating a reduction in feedback to improve laser operation and modal bandwidth.
Innovation Solution
An optical subassembly with a lens having an angled rear surface with facets, which reduces feedback by misaligning the light beam incidence on the fiber, minimizing the coupling into innermost modes and reducing interference noise through an offset and angled launch configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional optical subassembly with a flat lens rear surface is used, then the structure is simple and easy to manufacture, but optical feedback from the fiber causes jitter in signal timing and reduces laser operation stability
Solution Approach 1:
The patent applies asymmetry by changing the lens rear surface from a flat symmetric shape to an asymmetric shape with multiple facets at different angles. This asymmetric faceted structure causes the reflected light beam to return to the VCSEL at a different angle than the incident beam, thereby reducing optical feedback effects while maintaining manufacturing feasibility through standard lens molding techniques.
Solution Approach 2:
The patent changes the geometric parameters of the lens rear surface by introducing facets with specific angle ranges (e.g., 10-45 degrees relative to the optical axis). This parameter modification alters the light reflection characteristics, causing the reflected beam to be angularly displaced from the incident beam path, thus reducing feedback without requiring complex additional components.
2Reliability
If the VCSEL is tilted to reduce feedback, then optical feedback is reduced, but the laser alignment becomes complex and manufacturing precision requirements increase
Solution Approach 1:
The patent introduces the faceted lens rear surface as an intermediary element between the VCSEL and the fiber. This intermediary structure performs the feedback reduction function that would otherwise require tilting the VCSEL itself. The facets act as a mediator that redirects the reflected light away from the laser source, achieving the same effect as VCSEL tilting but without the alignment and manufacturing precision challenges.
3Productivity
If an offset launch configuration is used, then coupling into innermost modes is minimized and modal bandwidth is enhanced, but the optical subassembly structure becomes more complex
Solution Approach 1:
The patent merges the feedback reduction function and the modal bandwidth enhancement function into a single integrated component - the faceted lens. The same faceted rear surface structure that redirects reflected light to reduce feedback also creates the offset and angled launch conditions needed to minimize coupling into innermost fiber modes and enhance effective modal bandwidth, thereby achieving multiple benefits without proportionally increasing complexity.
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 effectively minimizes optical feedback and enhances the effective modal bandwidth by ensuring the reflected light beam is incident on the VCSEL at a different angle, reducing noise and jitter in the signal, without requiring the laser to be tilted or misaligned, thus improving signal quality.
Implementation Method 1
a lens that has an optical axis and that is located on a proximal end of the optical sub-assembly for focusing a light beam travelling through the optical subassembly
Implementation Method 2
the lens rear surface includes one or more facets that are angled with respect to the fiber axis of the optical subassembly... ensuring the reflected light beam is incident on the VCSEL at a different angle
Data Source
AI summary
A device comprising: an optical subassembly has a lens rear surface including one or more facets for scattering at least some of the light transmitted through the lens rear surface.