Dual Layer Grating Coupler Relaxes Alignment Tolerances
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Solution Overview
Problem
Coupling light from single mode edge emitting lasers to silicon photonics is costly and requires precise alignment, typically necessitating two lenses and a large isolator block, with stringent alignment tolerances of less than 0.5 micrometers, which complicates the packaging process.
Innovation Solution
The implementation of dual layer grating couplers that eliminate the need for lenses by using a transmit grating coupler and a receive grating coupler with a first grating and a second grating spaced apart by a gate oxide layer, allowing for optical alignment and efficient light coupling without the need for lenses, thereby simplifying packaging and increasing alignment tolerances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two lenses and a large isolator block are used to couple light from single mode edge emitting lasers to silicon photonics, then coupling efficiency is improved, but device complexity and packaging difficulty increase due to stringent alignment tolerances of less than 0.5 micrometers
Solution Approach 1:
The patent transitions from edge-coupled geometry to surface-coupled geometry, fundamentally changing the spatial dimension of light coupling. The grating coupler structures are positioned on the surface of the silicon photonic chip, allowing vertical light coupling instead of lateral coupling through edges. This dimensional change enables relaxed alignment tolerances while maintaining coupling efficiency.
Solution Approach 2:
The patent introduces grating coupler structures as intermediary elements between the laser and the silicon photonic waveguide. These gratings act as mediators that convert the laser's output mode into the waveguide's input mode through diffraction, eliminating the need for direct mechanical alignment between laser and waveguide edges.
2Reliability
If two lenses and a large isolator block are used for light coupling, then coupling efficiency is improved, but manufacturing cost increases
Solution Approach 1:
The patent extracts and eliminates the expensive optical components (lenses and isolator block) from the coupling system. By using integrated grating couplers fabricated directly on the silicon photonic chip, the solution removes the need for separate optical elements, thereby reducing component count and manufacturing cost.
Solution Approach 2:
The patent merges the coupling function into the silicon photonic chip itself through integrated grating structures. Instead of separate coupling components, the grating couplers are fabricated as part of the chip's waveguide layer, combining the functions of light coupling and waveguide transmission into a single integrated structure.
3Reliability
If precise active alignment is performed to meet alignment tolerances of less than 0.5 micrometers, then coupling efficiency is improved, but alignment tolerance is reduced
Solution Approach 1:
The patent changes the coupling geometry from lateral edge-coupling to vertical surface-coupling. This dimensional transformation inherently relaxes the lateral alignment tolerance from sub-micrometer to micrometer scale, as the vertical coupling direction provides a larger effective interaction area between the laser beam and the grating structure.
Solution Approach 2:
The grating coupler structures are designed with self-aligning characteristics through their periodic geometry and diffraction properties. The gratings automatically guide and focus the diffracted light into the waveguide mode, providing self-correction for minor misalignments and reducing the precision requirements for manual or automated alignment processes.
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 reduces the cost and size of the isolator, increases alignment tolerances by a factor of 10 or more, and enables wafer level testing of lasers, improving the efficiency and reliability of light coupling between edge emitting lasers and silicon photonics.
Implementation Method 1
The receive grating coupler may include a first grating and a second grating spaced apart from and above the first grating within the PIC
Data Source
AI summary
A system includes a grating coupled laser and a photonic integrated circuit (PIC). The grating coupled laser includes a first waveguide and a transmit grating coupler optically coupled to the first waveguide. The PIC includes a second waveguide and a receive grating coupler optically coupled to the second waveguide. The receive grating coupler is in optical alignment with the transmit grating coupler. The receive grating coupler includes a first grating and a second grating spaced apart from and above the first grating within the PIC.