Grating Coupler Substrate Reflection 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 a shallow angle and reflects it towards the substrate, allowing for coupling between active and passive optical chips with improved alignment tolerance and efficiency.
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 diffracts light at shallow angles and redirects it through the substrate to couple with the receiving waveguide, thereby mediating the optical connection and relaxing alignment requirements while maintaining coupling efficiency.
Solution Approach 2:
The invention utilizes the substrate dimension as an additional optical path. By diffracting light into the substrate and having it propagate through the substrate thickness before coupling to the receiving waveguide, the system adds a dimensional degree of freedom that relaxes lateral alignment constraints.
2Productivity
If narrow waveguides are used to achieve tight bending and high density, then PIC density increases, but beam divergence increases making alignment more difficult
Solution Approach 1:
The grating coupler acts as a mediator that accepts divergent beams from narrow waveguides and redirects them through the substrate. This intermediary structure accommodates the divergent nature of narrow waveguide beams while still achieving efficient coupling, thus enabling the use of narrow waveguides for high density without sacrificing alignment tolerance.
3Manufacturing precision
If shallow angle emission is used to increase tolerance, then alignment tolerance improves, but coupling efficiency decreases without proper reflection
Solution Approach 1:
The patent converts the potentially harmful effect of shallow angle emission (which would normally result in light loss) into a benefit by using the substrate-facet interface as a reflective surface. The shallow angle diffracted light reflects off the substrate facet and is redirected into the receiving waveguide, transforming what would be wasted light into useful coupled power.
Solution Approach 2:
The invention replaces the need for precise mechanical alignment with an optical mechanism based on diffraction and reflection. Instead of relying on mechanical precision to align waveguides directly, the system uses the grating's diffraction pattern and substrate reflection to achieve coupling, substituting mechanical precision requirements with optical path design.
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 a tolerance to misalignment, enabling efficient optical connection between active and passive optical chips, particularly in the wavelength range of 1530-1570 nm, with simulated coupling coefficients exceeding 49% and optimized structural parameters.
Implementation Method 1
long period grating on a passive waveguide from an optical chip creates shallow angle emission towards the substrate side, diffracted at the chip facet (second end) at a steeper angle
Implementation Method 2
a cladding layer configured to cover the grating structure, wherein the cladding layer has a third refractive index n3, wherein the third refractive index n3 is less than the second refractive index n2, wherein the cladding layer is arranged so as to reflect the light beam diffracted from the grating structure toward below the cladding layer
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.