Tapered Waveguide EML for Reliable Butt-Coupling
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Solution Overview
Problem
The discontinuity between adjoining multi-quantum well blocks in electroabsorption modulated lasers (EMLs) leads to weaknesses and failures due to peak temperature profiles at the butt-coupled interface, requiring precise control of the butt-coupling process and complex techniques like proton implantation or quantum well intermixing, which are not suitable for mass production.
Innovation Solution
A compound laser structure with tapered waveguides and electrical isolation regions is introduced, where the cross-section of the laser emitter and modulator tapers towards the butt-coupled interface, reducing optical intensity and promoting efficient light propagation, thereby minimizing heat buildup and improving device reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a butt-coupled interface is used to join MQW blocks, then device integration is achieved, but crystalline discontinuity and temperature peaks cause device failure at the interface
Solution Approach 1:
The patent introduces an intermediate tapered section between the DFB laser and EAM modulator blocks. This tapered waveguide section acts as a mediator that gradually transitions the optical mode size, reducing the optical intensity at the butt-coupled interface and thereby improving interface reliability while maintaining device integration.
Solution Approach 2:
The patent applies local quality by creating a tapered waveguide section with varying width along its length. The waveguide width is smaller near the butt-coupled interface and gradually increases towards the DFB laser, creating a non-uniform structure that locally modifies the optical intensity distribution to protect the vulnerable interface region.
2Ease of manufacture
If conventional constant-width waveguides are used, then manufacturing is simplified, but optical intensity concentration at the interface causes temperature peaks and device breakdown
Solution Approach 1:
The patent implements local quality by creating a tapered waveguide section with non-uniform width. The waveguide width varies along the propagation direction, being smaller near the butt-coupled interface and gradually increasing towards the DFB laser, which locally reduces optical intensity and temperature at the critical interface region.
3Temperature
If techniques like proton implantation or quantum well intermixing are used to distribute absorption, then temperature distribution is improved, but manufacturing complexity and difficulty increase significantly
Solution Approach 1:
The patent applies parameter changes by modifying the geometric parameter of the waveguide (width) along its length to create a tapered profile. This geometric parameter change naturally redistributes the optical intensity and absorption profile without requiring complex material processing techniques like proton implantation or quantum well intermixing, thereby improving temperature distribution while maintaining manufacturing simplicity.
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 tapered waveguide design reduces light intensity and heat at the butt-coupled interface, enhancing the reliability and performance of EMLs by distributing optical intensity more evenly and reducing saturation, leading to higher optical output power.
Implementation Method 1
the mode field diameter of the waveguide in the region of the intermediate location is smaller than the mode field diameter of the waveguide at either side of the intermediate location. This can reduce optical intensity in certain parts of the device in the region of the intermediate location.
Implementation Method 2
one block forming part of a distributed feedback (DFB) laser... The laser emitter may have a first end further from the modulator and a second end closer to the modulator
Implementation Method 3
electroabsorption modulated laser (EML)... one block forming part of an electroabsorption modulator (EAM)
Data Source
Figure 1~2
AI summary
A compound laser structure comprising a substrate and an active waveguide structure. A laser emitter is defined on a first area of the substrate and an optical modulator is defined on a second area of the substrate. The modulator is optically coupled to the laser emitter along a coupling axis. The waveguide structure is configured so that its cross-section perpendicular to the coupling axis tapers so as to be smaller at an intermediate location between the laser emitter and the waveguide structure than at locations on either side of the intermediate location along the coupling axis. Such a laser can be particularly reliable.