DFB Laser Bragg Grating Layout for Stable Single-Mode Output
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Solution Overview
Problem
Existing distributed feedback lasers face challenges in achieving single-mode operation and precise control over the emitted wavelength due to random phase conditions caused by fabrication constraints, leading to variable performance and reduced single-mode yield.
Innovation Solution
A method for fabricating distributed feedback lasers with a mirror section having higher coupling strength by using a single grating mask to define both the first and second Bragg gratings, allowing precise control of the phase shift and spacing between them, which enhances the reflectivity and power distribution, enabling accurate wavelength control and increased single-mode yield.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a Bragg grating is added to the laser section to select wavelength, then wavelength selectivity is improved, but dual-mode operation occurs reducing single-mode yield
Solution Approach 1:
The patent introduces asymmetry by adding a mirror section with a second Bragg grating that is coplanar with the active layer, creating an asymmetric optical path. This asymmetry breaks the degeneracy of the two modes and enables single-mode operation while maintaining wavelength selectivity through the first Bragg grating in the laser section.
2Reliability
If HR and AR coatings are added to favor one mode, then single-mode operation is achieved, but the position of the rear facet cannot be precisely controlled due to fabrication constraints
Solution Approach 1:
The patent uses the same active layer to serve dual purposes: as the light-emitting medium and as the layer containing the second Bragg grating in the mirror section. This self-service approach eliminates the need for separate precision alignment of the rear facet, as the second grating is automatically positioned relative to the active layer through the single-mask fabrication process.
3Reliability
If a mirror section with DBR and coplanar second Bragg grating is added, then single-mode yield and wavelength control are improved, but coupling strength is low requiring long mirror sections
Solution Approach 1:
The patent changes the key parameter of grating orientation by making the second Bragg grating coplanar with the active layer, rather than placing it in a separate layer. This parameter change increases the optical overlap and coupling strength between the grating and the active layer, allowing for shorter mirror section lengths while maintaining high single-mode yield and wavelength control.
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 results in a DFB laser with higher coupling strength, improved power distribution, and precise wavelength control, increasing the single-mode yield and reducing the laser's footprint and cost, while being compatible with various structures and applications.
Implementation Method 1
a first Bragg grating arranged in a planar layer substantially parallel to the active layer but not coplanar with the active layer and on a side of the active layer opposite to the planar substrate
Implementation Method 2
a second Bragg grating arranged in a planar layer that is coplanar with the active layer
Data Source
Figure 1
Figure 2A~2C
Figure 3A~3C
AI summary
According to a first aspect, the present disclosure relates to distributed feedback (DFB) laser comprising a planar substrate (101); a laser section (110) comprising a front facet (111), an active layer (102) substantially parallel to the planar substrate (101) but not coplanar with said planar substrate and configured to emit light through said front facet (111), and a first Bragg grating (115) arranged in a planar layer substantially parallel to the active layer (102) but not coplanar with said active layer and on a side of the active layer (102) opposite to the planar substrate (101); and a mirror section (120) optically coupled to said laser section (110), comprising a second Bragg grating (125) configured to reflect light towards said front facet (111); wherein said second Bragg grating (125) is arranged in a planar layer that is coplanar with said active layer (102).