Evanescent Optical Couplers for Relaxed Alignment Tolerances
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Solution Overview
Problem
Current die-to-die optical coupling techniques face challenges with sub-micron alignment requirements, which are often beyond the capabilities of high-volume packaging tools, and existing methods struggle with relaxed alignment tolerances, leading to inefficiencies in achieving high-speed data transfer in co-packaged optical and electronic integrated circuits.
Innovation Solution
The development of multi-segmented tapered evanescent optical couplers and graded refractive index (GRIN) couplers, which allow for efficient optical and electrical coupling between semiconductor dies with relaxed alignment tolerances, enabling misalignment tolerances of up to 10 microns or more, and the use of conductive micropillars, nanopillars, and micro-scale conductive pads for electrical interconnections that can self-align optical couplers during bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional die-to-die optical coupling techniques are used, then optical coupling can be achieved, but sub-micron alignment requirements are needed which are beyond the capabilities of high-volume packaging tools
Solution Approach 1:
The patent applies parameter changes by transforming the optical coupling interface from a conventional direct waveguide-to-waveguide coupling to an evanescent field coupling mechanism. This involves changing the geometric parameters of the waveguides (creating gaps of specific dimensions) and material parameters (using high-index contrast materials) to enable relaxed alignment tolerances while maintaining coupling efficiency. The evanescent field extends beyond the waveguide core, creating an overlapping field region that tolerates larger misalignments.
Solution Approach 2:
The patent segments the optical coupling interface into distinct functional regions: the evanescent field generation zone with specific gap dimensions, the coupling region where fields overlap, and the waveguide regions. This segmentation allows independent optimization of each region's parameters to achieve both relaxed alignment and high coupling efficiency, making the system manufacturable with standard packaging tools.
2Ease of manufacture
If misalignment tolerance is relaxed to enable high-volume packaging, then ease of manufacture improves, but optical coupling efficiency decreases
Solution Approach 1:
The patent employs composite material structures with high-index contrast, combining materials such as silicon nitride or silicon oxide waveguides with lower-index cladding materials. This composite structure confines the evanescent field more effectively while extending its reach, enabling both relaxed alignment tolerance and maintained coupling efficiency. The high-index core materials enhance the evanescent field strength and extension distance.
Solution Approach 2:
The patent creates a replicated evanescent field pattern across multiple waveguide interfaces, where each interface copies the same gap dimension and coupling geometry. This standardization allows mass production with consistent coupling efficiency across all channels, maintaining reliability while enabling high-volume manufacturing with relaxed alignment tolerances.
3Productivity
If multiple optical transceivers are integrated in a package to increase bandwidth, then data rate increases, but device complexity increases
Solution Approach 1:
The patent creates a universal evanescent coupling interface that can be replicated across multiple waveguide channels with identical geometry and dimensions. This universal interface design allows the same coupling structure to serve multiple transceiver channels simultaneously, increasing data rate while avoiding proportional increases in complexity. The standardized interface enables modular scaling.
Solution Approach 2:
The patent transitions from planar two-dimensional alignment to three-dimensional evanescent field overlap, where the coupling occurs through the vertical extension of the evanescent field. This dimensional change allows lateral misalignments to be tolerated while maintaining coupling, enabling higher density integration of multiple transceivers in the package without proportionally increasing alignment complexity.
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
These solutions enable high-efficiency optical coupling and electrical interconnects in a single bonding step, facilitating the integration of multiple optical transceivers in a package and achieving data rates of over 50 Tbps with improved alignment tolerances, suitable for top-of-rack switch packages and high-density integrated circuit packaging.
Implementation Method 1
evanescent optical couplers comprising: a first tapered core segment optically coupled to a first single-mode optical waveguide
Implementation Method 2
a GRIN stack optically coupled at a first end to a second end of the slotted core segment, the GRIN stack comprising a plurality of layers of one or more materials, wherein at least two layers of the plurality of layers of one or more materials have different values of refractive index
Data Source
AI summary
Die-to-die electrical interconnects, optical couplers, and related methods for electronic and photonic co-packaging are described. Optical couplers include multi-segmented tapered waveguide core segments, slotted core segments, and graded refractive index structures to significantly relax alignment tolerances between dies. Conductive nanopillars, conductive pads, and conductive micropillars can be used to make electrical connections between circuitry on the interconnected dies. The electrical connections can be used to self-align the optical couplers between the dies. Due to relaxed optical alignment tolerances, electrical interconnects and optical coupling between dies can be made in the same die-to-die bonding step.