DFB Laser Single Facet U-Turn Waveguide Design
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Solution Overview
Problem
Distributed feedback (DFB) lasers face instability due to grating phase changes from mechanical processes in HR/AR configurations and low efficiency in AR/AR configurations, where light is not efficiently transmitted to photonic chips.
Innovation Solution
A DFB laser design with a U-turn region and anti-reflective (AR) coated facet, where the waveguide ends terminate on the same facet, eliminating grating phase changes and enhancing optical efficiency by aligning both ends with optical couplers in a photonic chip.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a second facet with a total reflector (HR coating) is used in HR/AR DFB laser configuration, then light reflection is improved (more than 90% reflected), but manufacturing precision deteriorates (mechanical cleaving process has high tolerances causing uncertain phase)
Solution Approach 1:
The patent removes the second facet with total reflector from the laser structure, extracting the problematic component that caused phase instability. Instead of using HR/AR facet configuration, the invention uses a single facet with AR coating and implements feedback through a grating structure, eliminating the manufacturing precision issues associated with mechanical cleaving of a second facet.
Solution Approach 2:
The patent introduces a grating structure as an intermediary element to provide optical feedback. The grating acts as a mediator that replaces the need for a second HR facet, providing stable phase reference through its periodic structure while maintaining high reflection efficiency without requiring precise mechanical fabrication.
2Manufacturing precision
If two facets with partial reflectors (AR coating) are used in AR/AR DFB laser configuration, then manufacturing precision is improved (inherently less susceptible to grating phase changes), but efficiency deteriorates (significant amounts of light exit from both facets)
Solution Approach 1:
The patent merges the functions of both AR facets into a single facet structure. By combining the phase stability benefit of AR coating with a single facet design and using a grating-based feedback mechanism, the invention achieves both phase stability and high light transmission efficiency, as substantially all light exits through the single AR-coated facet.
3Loss of energy
If HR/AR DFB laser configuration is used, then light transmission efficiency is improved (almost all light exits through AR coated facet), but stability deteriorates (grating phase change causes mode hopping)
Solution Approach 1:
The patent extracts the second HR facet from the structure, removing the source of phase instability. By using only a single AR-coated facet with grating-based feedback, the invention eliminates the mode hopping issue while maintaining high light transmission efficiency through the single facet.
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 design stabilizes the laser operation, avoids mode hopping, and ensures high optical efficiency by transmitting substantially all light to the photonic chip, maintaining narrow line width and stability over a wide range of conditions.
Implementation Method 1
a facet coated with an anti-reflective (AR) coating
Implementation Method 2
a waveguide extending through the facet, the intermediate region, and the U-turn region
Implementation Method 3
a grating disposed over a second portion of the waveguide in at least one of the intermediate region and the U-turn region
Implementation Method 4
A first portion of the waveguide in the U-turn region changes direction such that the waveguide exits the U-turn region in an opposite direction than the portion of the waveguide entered the U-turn region
Data Source
AI summary
The embodiments herein describe a single-frequency laser source (e.g., a distributed feedback (DFB) laser or distributed Bragg reflector (DBR) laser) that includes a feedback grating or mirror that extends along a waveguide. The grating may be disposed over a portion of the waveguide in an optical gain region in the laser source. Instead of the waveguide or cavity being linear, the laser includes a U-turn region so that two ends of the waveguide terminate at the same facet. That facet is coated with an anti-reflective (AR) coating.