Grating Coupler Refractive Index Design for Alignment Tolerance
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Solution Overview
Problem
Hybrid integration of active and passive optical chips requires precise alignment for efficient optical coupling, which is challenging due to the narrow waveguides and fast diverging beams, necessitating a solution for increased tolerance and coupling efficiency.
Innovation Solution
A novel grating coupler system with a substrate, grating structure, and cladding layer configuration that diffracts light at specific angles for efficient coupling between active and passive optical chips, utilizing refractive index differences and sub-gratings to enhance coupling efficiency and tolerance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If direct waveguide-to-waveguide coupling is used, then coupling efficiency can be high, but alignment precision requirements are extremely strict (sub-micron accuracy)
Solution Approach 1:
The patent introduces a grating coupler as an intermediary component between the two waveguides. This grating structure converts the direct coupling path into an indirect path through diffraction, enabling light to be coupled from one waveguide to another via the grating. This intermediary mechanism relaxes the alignment precision requirements while maintaining high coupling efficiency.
Solution Approach 2:
The patent modifies the coupling parameters by changing from direct end-to-end waveguide coupling to grating-mediated coupling. The grating structure with specific pitch, depth, and duty cycle parameters enables efficient coupling by transforming the light propagation mode and angle, thereby achieving high coupling efficiency with relaxed alignment tolerances.
2Stability of the object's composition
If narrow waveguides are used, then optical confinement is improved, but beam divergence increases and alignment tolerance decreases
Solution Approach 1:
The grating coupler acts as a mediator that accepts light from the narrow waveguide and redistributes it at different angles. This intermediary structure preserves the optical confinement benefits of narrow waveguides while providing angular diversity that increases alignment tolerance for coupling to the receiving waveguide.
Solution Approach 2:
The grating structure introduces angular diversity in the vertical dimension by diffracting light at multiple angles. This dimensional transformation allows the system to maintain narrow waveguide dimensions for good optical confinement while achieving tolerance in the lateral alignment dimension through the angular spread of diffracted beams.
3Manufacturing precision
If grating structure is added for coupling, then alignment tolerance is improved, but manufacturing complexity increases
Solution Approach 1:
The patent optimizes the grating parameters (pitch, depth, duty cycle) to achieve high coupling efficiency with simple fabrication processes. By carefully selecting these parameters, the grating structure can be manufactured using standard semiconductor fabrication techniques without requiring complex multi-step processes, thus balancing alignment tolerance improvement with manufacturing simplicity.
Solution Approach 2:
The grating structure is formed as an integrated part of the waveguide layer using the same material system, creating a composite structure that combines the waveguide and grating functions. This integrated approach reduces manufacturing complexity compared to adding separate grating components, as the grating is patterned directly into the existing waveguide layer during fabrication.
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
The proposed grating coupler system achieves high coupling efficiency with increased tolerance to misalignment, optimizing the refractive index configuration and sub-grating design to ensure efficient light transfer between optical chips, particularly in the wavelength range of 1530-1570 nm.
Implementation Method 1
a grating structure having grating lines arranged on the substrate... diffracts light at specific angles for efficient coupling between active and passive optical chips
Implementation Method 2
a cladding layer configured to cover the grating structure... arranged so as to reflect the light beam diffracted from the grating structure toward below the cladding layer
Implementation Method 3
the substrate having a first refractive index n1; a grating structure having a second refractive index n2, wherein the second refractive index n2 is greater than first refractive index n1
Data Source
AI summary
A grating coupler having first and second ends for coupling a light beam to a waveguide of a chip includes a substrate configured to receive the light beam from the first end and transmit the light beam through the second end, the substrate having a first refractive index n1, a grating structure having curved grating lines arranged on the substrate, the grating structure having a second refractive index n1, wherein the curved grating lines have line width w and height d and are arranged by a pitch Λ, wherein the second refractive index n2 is less than first refractive index n1, and a cladding layer configured to cover the grating structure, wherein the cladding layer has a third refractive index n3.