Hybrid Optical Chip-to-Chip Coupling via Glass Substrate
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Solution Overview
Problem
Photonic integrated circuits (PICs) face challenges in signal loss and integration issues when routing across large packages, with existing optical communication methods like polymer waveguides suffering from high loss and reliability problems, and glass-based waveguides limited by density restrictions.
Innovation Solution
A glass substrate with low-index-difference direct-write waveguides and high-index-difference silicon nitride waveguides is used, allowing for low-loss, dense routing and flexible 3D routing, coupled with micromirrors for efficient light transfer between PIC dies and the glass substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If silicon photonic waveguides are routed across tens of millimeters in a multi-die package, then communication speed is maintained, but signal loss increases substantially and cost becomes prohibitively expensive
Solution Approach 1:
The patent introduces an intermediary optical waveguide system consisting of a first optical waveguide on the first substrate, a second optical waveguide on the second substrate, and a coupling structure. This intermediary system allows optical signals to be transmitted between PIC dies without requiring long-distance routing across the package, thereby reducing signal loss while maintaining communication speed.
Solution Approach 2:
The patent employs three-dimensional stacking architecture where optical waveguides are routed in multiple layers and dimensions. The coupling structure enables vertical and lateral light transfer between substrates, utilizing spatial dimensions to achieve short-distance, low-loss optical communication while maintaining high speed transmission.
2Loss of energy
If optical fibers are used to route between dies at the package level, then signal loss is reduced, but integration and handling challenges increase
Solution Approach 1:
The patent merges the optical waveguide structure directly with the PIC die substrate, creating an integrated photonic-electronic platform. The optical waveguides are fabricated using the same semiconductor manufacturing processes as the PIC circuits, enabling monolithic integration and simplifying handling while achieving low signal loss transmission.
Solution Approach 2:
The patent changes the physical parameters of the optical transmission medium by using planar optical waveguides with controlled refractive index profiles instead of traditional optical fibers. This allows the waveguides to be integrated with semiconductor fabrication processes, reducing handling complexity while maintaining low loss characteristics through optimized waveguide geometry and material composition.
3Loss of energy
If glass-based ion-exchange waveguides or direct-write waveguides are used, then signal loss is reduced, but density is restricted due to limited refractive index contrast
Solution Approach 1:
The patent employs composite material structures for optical waveguides, combining multiple layers with different refractive indices (e.g., silicon nitride, silicon oxide, tantalum oxide) to achieve high refractive index contrast. This composite approach enables dense waveguide routing while maintaining low signal loss through enhanced light confinement in the waveguide core.
Solution Approach 2:
The patent optimizes the refractive index parameters of waveguide materials and structures to achieve high index contrast without sacrificing low loss transmission. By carefully selecting and engineering material compositions and layer thicknesses, the patent achieves both high waveguide density for compact routing and low signal loss through improved light confinement efficiency.
4Quantity of substance
If silicon nitride waveguides are formed on a glass substrate, then signal loss is reduced and density is increased, but coupling to PIC dies becomes difficult
Solution Approach 1:
The patent introduces coupling structures that act as intermediaries between the silicon nitride waveguides on the glass substrate and the PIC dies. These coupling structures include mode converters and interface layers that facilitate efficient optical coupling by matching the mode profiles and refractive indices of the waveguides and PIC die waveguides, thereby reducing coupling difficulty.
Solution Approach 2:
The patent applies local quality modifications at the coupling interfaces between waveguides and PIC dies. By creating localized regions with optimized refractive index profiles, mode field distributions, and geometric configurations at the coupling points, the patent enables efficient optical coupling while maintaining the low loss and high density characteristics of the silicon nitride waveguide system throughout the majority of the transmission path.
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 enables low-loss, high-density signal propagation across the glass substrate, reducing signal loss and integration challenges, and improving the reliability of optical communication within multi-die packages.
Implementation Method 1
one or more low-index-difference direct-write waveguides and one or more high-index-difference waveguides, such as silicon nitride waveguides, formed on the surface of the glass substrate
Implementation Method 2
coupled with micromirrors for efficient light transfer between PIC dies and the glass substrate
Data Source
AI summary
Technologies for hybrid optical chip-to-chip coupling are disclosed. In an illustrative embodiment, light from a waveguide in a photonic integrated circuit (PIC) die is collimated using a micromirror and directed towards a glass substrate. Another micromirror in the glass substrate focuses the light into a waveguide defined in a bulk layer of the glass substrate. In the illustrative embodiment, the waveguide is directly written into the bulk layer using an ultrafast laser. The glass substrate also has waveguides with a large difference in the index of refraction in a layer above the bulk substrate, such as silicon nitride waveguides in silicon oxide cladding. The directly-written waveguides can be evanescently coupled to the silicon nitride waveguides. The silicon nitride waveguides can then be used for two-dimensional routing throughout the glass substrate. The light can be coupled back into a directly-written waveguide before it is transmitted to another PIC die.