Undercut Cavity Prevents Underfill From Optical Interface
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Solution Overview
Problem
Conventional photonic integrated circuits (PICs) face issues with underfill adhesives flowing onto the fiber/waveguide optical interface, which can degrade the quality of edge-coupling interfaces during fabrication and assembly.
Innovation Solution
Incorporating a cavity in the electrical substrate under the edge coupler of the PIC chip to prevent underfill adhesive from reaching the optical interface, with the adhesive filling the cavity and creating an undercut section that impedes capillary action, ensuring the adhesive does not impact the optical coupling quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If underfill adhesive is applied to mechanically stabilize the PIC on the electrical substrate, then mechanical stability is improved, but the adhesive may flow onto the fiber/waveguide optical interface and degrade coupling quality
Solution Approach 1:
The patent divides the substrate surface into distinct functional zones: a first region for mechanical bonding with the PIC chip and a second region for optical fiber coupling. This spatial segmentation prevents adhesive from contaminating the optical interface while maintaining mechanical stability through targeted adhesive application in the first region only.
Solution Approach 2:
The patent applies adhesive with different properties to different regions: in the first region, adhesive is applied to provide strong mechanical bonding, while the second region is kept free of adhesive to maintain optical coupling quality. This local differentiation of adhesive presence resolves the contradiction between mechanical stability and optical precision.
2Reliability
If adhesive is applied extensively to ensure complete coverage for mechanical stabilization, then bonding reliability is improved, but adhesive contamination of the optical interface increases
Solution Approach 1:
The substrate is segmented into a first region for adhesive application and a second region excluded from adhesive. This segmentation ensures complete adhesive coverage in the bonding region for reliability while preventing contamination in the optical region, resolving the contradiction between bonding reliability and contamination prevention.
Solution Approach 2:
The patent extracts the adhesive application from the optical interface region by defining a second region that is explicitly excluded from adhesive coverage. This extraction eliminates the harmful contamination effect while preserving bonding reliability in the first region through dedicated adhesive application.
3Strength
If the PIC is firmly bonded to the substrate using underfill adhesive, then mechanical support is improved, but the adhesive may interfere with the optical coupling at the edge interface
Solution Approach 1:
The patent segments the bonding interface into a first region where adhesive provides strong mechanical support and a second region where the edge coupling interface remains free of adhesive. This spatial segmentation ensures mechanical strength through comprehensive adhesive bonding in the first region while protecting edge-coupling quality by excluding adhesive from the second region.
Solution Approach 2:
Different local conditions are created: the first region has adhesive presence for mechanical strength, while the second region has adhesive absence for optical precision. This local quality differentiation resolves the contradiction between mechanical support strength and edge-coupling interface 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 solution effectively prevents the underfill adhesive from entering the optical interface, maintaining the quality of edge-coupling between the PIC chip and the optical fiber, thereby stabilizing the PIC on the substrate without compromising optical coupling.
Implementation Method 1
a layer of adhesive binding the PIC chip to the planar surface of the electrical substrate
Implementation Method 2
the adhesive filling the cavity and creating an undercut section that impedes capillary action
Data Source
AI summary
An underfill adhesive may be used to mechanically stabilize a photonic integrated circuit chip (PIC) onto an electrical substrate; however, when the PIC is optically coupled to an external optical fiber at or near an edge of the chip, e.g. using an edge coupler, the underfill may flow into the optical interface impacting optical coupling quality. A photonic integrated circuit apparatus according to the disclosure comprises an electrical substrate, which includes a cavity underneath the edge coupler for preventing underfill material from entering the optical interface by impeding capillary action thereof.