DFB Laser Diode Grating Coupling via Phosphorous Intermediate Layer
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Solution Overview
Problem
Conventional semiconductor laser diodes with distributed feedback (DFB-LD) face challenges in achieving high coupling efficiency due to the thickness requirements of the AlGaInAs layer, which can lead to increased distance between the grating and the active layer, resulting in reduced side mode suppression ratio (SMSR) and lower coupling efficiency κL.
Innovation Solution
Incorporating an intermediate layer made of a group III-V compound semiconductor containing phosphorous between the AlGaInAs layer and the active layer, which accelerates mass transportation during growth, allowing for a thinner total thickness and improved burying of the periodic undulation without compromising the flatness of the surface, thereby enhancing coupling efficiency κL.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If the AlGaInAs layer is made thicker to bury the periodic undulation and achieve a flat surface, then the surface flatness is improved, but the distance between the grating and the active layer increases, reducing the coupling efficiency
Solution Approach 1:
The patent divides the burying layer into two distinct segments: an AlGaInAs layer and an intermediate layer containing phosphorous. This segmentation allows each layer to perform its specific function - the AlGaInAs layer provides the primary burying function while the phosphorous-containing intermediate layer accelerates mass transportation to achieve flatness, thereby reducing the total thickness needed while maintaining surface quality.
Solution Approach 2:
The intermediate layer containing phosphorous acts as a mediator between the AlGaInAs layer and the active layer. This intermediary layer accelerates mass transportation during growth, enabling the system to achieve a flat surface with a thinner total burying layer thickness, thus reducing the distance between the grating and active layer while maintaining surface flatness.
2Reliability
If the depth of periodic undulation is increased to achieve larger coupling efficiency, then the coupling efficiency increases, but a thicker AlGaInAs layer is required to compensate the undulation and make the surface flat
Solution Approach 1:
The patent segments the burying structure into multiple functional layers, allowing the AlGaInAs layer to focus on providing sufficient burying depth for large undulation depth while the phosphorous-containing intermediate layer handles the surface flatness requirement through accelerated mass transportation, enabling independent optimization of both undulation depth and layer thickness.
Solution Approach 2:
The patent changes the chemical composition parameter by introducing phosphorous into the intermediate layer, which fundamentally alters the mass transportation characteristics during growth. This parameter change enables the system to achieve surface flatness with reduced total thickness, allowing larger undulation depths to be used for enhanced coupling efficiency without proportionally increasing the AlGaInAs layer thickness.
3Length of moving object
If the AlGaInAs layer is made thinner to reduce the distance between grating and active layer, then the coupling efficiency improves, but the surface flatness may be compromised
Solution Approach 1:
The phosphorous-containing intermediate layer serves as a mediator that enables the system to use a thinner AlGaInAs layer while still achieving surface flatness. The intermediate layer's accelerated mass transportation compensates for the reduced thickness, maintaining surface quality even when the primary AlGaInAs burying layer is made thinner to reduce the distance to the active layer.
Solution Approach 2:
By changing the composition parameter (adding phosphorous) and controlling the growth temperature, the patent creates an intermediate layer with superior mass transportation properties. This parameter change allows the system to achieve surface flatness with a thinner total burying layer, enabling reduced distance between grating and active layer while maintaining surface quality.
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 configuration enhances the coupling efficiency κL between the optical grating and the active layer, reducing the failure in side mode suppression ratio (SMSR) and maintaining a flat surface, thus improving the overall performance of the DFB-LD.
Implementation Method 1
the intermediate layer contains the phosphorous as the group V element, accordingly, a mass transportation may be accelerated during the growth of the intermediate layer, which facilitates the burying of the periodic undulation without making the total thickness of the AlGaInAs layer and the intermediate layer thick
Data Source
AI summary
The present invention is to provide a DFB-LD with a larger coupling efficiency between the grating and the active layer. The DFB-LD of the invention provides an n-type InP substrate, an n-type InP buffer layer, an AlGaInAs layer, a intermediate layer made of a material belonging to a group III-V compound semiconductor and containing phosphorous, and an active layer. The InP substrate and the InP buffer layer form a periodic undulation of the grating. Because of the AlGaInAs layer just provided on the InP buffer layer, the AlGaInAs layer and the intermediate layer can be thinned to get a flat top surface, which enhances the coupling efficiency between the grating and the active layer.