H-Shaped Window Etched-Facet Semiconductor Lasers
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Solution Overview
Problem
The fabrication of ridge waveguide edge-emitting lasers faces challenges in achieving high facet quality and stable facet coating due to the non-planar ridge structure, which complicates the etching process and coating application, leading to issues like reflection loss and uneven coating thickness.
Innovation Solution
The proposed solution involves forming an edge-emitting optical semiconductor structure with a ridge waveguide extending between etched end facets in windows, where the windows have alcoves to create a planar surface for etching, allowing for a vertical etching profile and avoiding the 'shadowing effect, thus enabling precise coating control and improved facet quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a ridge waveguide structure is used for edge-emitting lasers, then the fabrication process is less complex and aluminum-containing MQW layers can be used without etching or oxidation issues, but the non-planar ridge structure causes poor facet quality and unstable facet coating due to mask edge disturbance and shadowing effect
Solution Approach 1:
The window structure is segmented into multiple regions including a central window region and opposing alcove regions. This segmentation allows the etching process to create a planar surface at the window level while maintaining the ridge waveguide structure, separating the functions of optical access and waveguide confinement.
Solution Approach 2:
The invention transitions from a two-dimensional ridge structure to a three-dimensional window structure with alcoves. The window extends through multiple layers creating vertical and lateral dimensions, providing a planar etching surface while maintaining the ridge waveguide's optical confinement function.
2Productivity
If conventional ICP etching is used on ridge waveguide structures, then etching can be performed after waveguide formation, but the mask edge is disturbed by the non-planar ridge structure resulting in poor facet quality
Solution Approach 1:
The window structure with alcoves is formed preliminarily before the final facet etching. This preliminary structure creation provides a planar reference surface that guides subsequent etching operations, ensuring mask alignment and achieving vertical etch profiles without disturbing the ridge structure.
Solution Approach 2:
The window structure acts as an intermediary element between the ridge waveguide and the etching process. It provides a planar interface for mask deposition and etching while protecting the underlying ridge structure, mediating the interaction between the non-planar ridge and the planar etching requirements.
3Reliability
If coating is applied to ridge waveguide facets, then optical feedback can be achieved, but the non-planar ridge structure causes shadowing effect that inhibits precise control of coating layer thickness
Solution Approach 1:
The window structure segments the optical path into distinct regions: the central window region for light propagation and the opposing alcove regions for optical feedback. This segmentation allows separate optimization of each region's coating requirements, enabling precise thickness control.
Solution Approach 2:
The invention adds vertical dimensionality with the window extending through multiple layers. This creates a three-dimensional optical cavity where coating thickness can be precisely controlled on horizontal surfaces while the vertical extent provides the necessary optical feedback path length.
4Manufacturing precision
If multi-mask layers with BCB etch-back are used to planarize the ridge, then a planar surface can be achieved for etching, but the process becomes complicated and time-consuming with multiple steps and BCB residue removal issues
Solution Approach 1:
The invention extracts the planarization function from the complex multi-mask BCB etch-back process. By designing the window structure to inherently provide a planar etching surface through its geometric configuration rather than through iterative planarization steps, the solution removes the need for BCB coating, thermal curing, etch-back, and residue removal operations.
Solution Approach 2:
Instead of planarizing the ridge structure to enable etching, the invention inverts the approach by creating a window structure that provides its own planar reference surface. The etching process then proceeds on this planar window surface rather than attempting to make the ridge planar, fundamentally reversing the conventional sequence and methodology.
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 high facet quality and stable facet coating, reducing reflection loss and enabling efficient optical feedback, while simplifying the fabrication process by avoiding complex multi-mask layers and residue issues.
Implementation Method 1
The facets in an etched-facet laser are commonly etched by an inductively coupled plasma (ICP) process using a protection mask.
Implementation Method 2
either a highly reflective (HR) coating for Fabry-Perot (FP) lasers or an anti-reflective (AR) coating for Distributed Feedback (DFB) lasers must be applied
Data Source
AI summary
An edge-emitting optical semiconductor structure has a substrate, an active multiple quantum well (MQW) region formed on the substrate, and a ridge waveguide extending between first and second etched end facets. The first etched end facet is disposed in a first window, while the second etched end facet is disposed in a second window. The first etched end facet extends between a pair of alcoves in the first window, and the second etched end facet extends between a pair of alcoves in the second window. An integrated device in which two such structures are provided has an H-shaped window where the two structures adjoin each other. The structure can be fabricated using a process that involves a first mask to form the ridge waveguide and then a second mask and an etching process to form the windows.