Low-Fill Factor Top Contact for Interband Cascade Laser Loss Reduction
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Solution Overview
Problem
Interband cascade lasers (ICLs) face significant internal loss due to the overlap of the lasing mode with the metal contact, which degrades slope efficiency and wallplug efficiency, especially when the top cladding layer is thin or the grating is etched deeply to enhance optical coupling.
Innovation Solution
The implementation of a low-fill-factor top contact structure by creating spaced-apart contact openings in a dielectric layer on the laser ridge, reducing the percentage of the ridge's top surface available for electrical contact, thereby minimizing the overlap of the lasing mode with the metal contact and reducing internal loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the top cladding layer is made thin or the grating is etched deeply to enhance optical coupling, then the coupling to the DFB grating is improved, but the internal loss increases due to greater overlap of the lasing mode with the metal contact
Solution Approach 1:
The top contact structure is segmented into multiple discrete contact regions rather than a continuous metal layer. This segmentation allows the optical mode to couple effectively to the grating while minimizing the continuous overlap with metal, thereby reducing internal loss while maintaining electrical contact functionality
Solution Approach 2:
The metal contact is extracted from directly covering the entire top surface of the ridge. By removing the metal contact from portions of the top surface, the patent reduces the overlap between the lasing mode and metal contact, thereby reducing internal loss while maintaining necessary electrical contact through selective placement
2Reliability
If a conventional top contact structure is used with full surface coverage, then electrical contact is maximized, but the overlap of the lasing mode with the metal contact increases internal loss
Solution Approach 1:
The continuous metal contact layer is divided into discrete segmented contact regions. This segmentation maintains sufficient electrical contact quality by providing multiple contact points while reducing the overall overlap area between the metal contact and the optical mode, thereby reducing internal loss
Solution Approach 2:
Different regions of the top surface are assigned different functions: some regions have metal contact for electrical conduction, while other regions are left free of metal to minimize optical loss. This local differentiation optimizes both electrical contact quality and reduces internal loss by placing metal only where electrically necessary
Data Source
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AI summary
A DFB laser having a reduced fill factor and reduced loss. A plurality of spaced-apart contact openings are etched into a dielectric layer situated on top of a laser ridge having a DFB grating layer so that electrical contact between the metal top contact layer and the DFB gratings is made only in the etched openings, since all other areas of the top surface of the DFB-grated laser ridge are insulated from the metal contact layer by the dielectric. The size and shape of contact openings and their spacing are configured so that the ratio of the total area of the openings to the total area of the laser ridge provides a fill factor of less than 100%.