Waveguide Structure for Low-Loss Optical Coupling
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Solution Overview
Problem
Conventional optical coupling schemes for silicon photonics face challenges in achieving low optical losses over a wide wavelength band while being compatible with CMOS processing, which is essential for efficient chip-to-chip coupling.
Innovation Solution
A waveguide structure comprising a first waveguide embedded in a lower refractive index cladding, a second waveguide of higher refractive index, and an intermediate waveguide formed by a filled trench in the cladding, allowing for adiabatic light transfer with low coupling losses, compatible with CMOS processing and suitable for flip-chip bonding or transfer printing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If grating couplers are used to transfer light between different chips, then optical coupling is achieved, but optical losses are excessive (in the range of 8 dB)
Solution Approach 1:
The patent introduces an intermediate waveguide layer formed by filling a trench in the cladding with high refractive index material. This intermediate waveguide acts as a mediator between the first embedded waveguide and the second surface waveguide, enabling adiabatic mode transformation and reducing optical coupling losses to below 1 dB while maintaining CMOS compatibility
Solution Approach 2:
The patent changes the refractive index parameter by introducing an intermediate waveguide layer with high refractive index material (such as silicon) into the low index cladding. This parameter change enables effective mode matching and adiabatic coupling between waveguides with different refractive indices, achieving low loss optical coupling
2Loss of energy
If mirrors are used to couple light between different chips, then optical coupling is achieved, but optical losses are still unacceptable (nearly 3 dB) and fabrication is not CMOS compatible
Solution Approach 1:
The patent changes the refractive index parameter by introducing an intermediate waveguide layer with high refractive index material (such as silicon) into the low index cladding. This parameter change enables effective mode matching and adiabatic coupling between waveguides with different refractive indices, achieving low loss optical coupling
Solution Approach 2:
The intermediate waveguide layer serves as a mediator that facilitates gradual mode transformation between the embedded and surface waveguides. This adiabatic coupling mechanism achieves low optical losses while being fully compatible with CMOS fabrication processes, unlike mirror-based approaches
3Loss of energy
If adiabatic coupling between waveguides is implemented, then optical losses are reduced to below 1 dB, but the fabrication process becomes complex due to the need for close proximity and removal of overclad material
Solution Approach 1:
The patent performs preliminary action by forming the intermediate waveguide layer in the cladding before finalizing the waveguide structures. This advance preparation creates the necessary refractive index profile that enables subsequent adiabatic coupling without requiring complex overclad removal or close proximity alignment, thus reducing fabrication complexity
Solution Approach 2:
The intermediate waveguide layer acts as a mediator that enables adiabatic coupling between embedded and surface waveguides without requiring their close proximity. This mediator layer provides the gradual mode transformation needed for low loss coupling while allowing standard CMOS fabrication processes to be used
4Reliability
If high quality silicon nitride waveguides are used instead of conventional silicon passive devices, then performance is dramatically improved, but active devices cannot be fabricated
Solution Approach 1:
The patent segments the photonic circuit into two parts: SiN waveguides for passive optical functions and silicon active devices. The intermediate waveguide layer enables optical coupling between these segmented components, allowing each to be optimized for its specific function while working together in an integrated system
Solution Approach 2:
The intermediate waveguide layer serves as an intermediary that enables optical coupling between SiN waveguides and silicon active devices. This mediator allows the system to combine the high performance of SiN passive devices with the functionality of silicon active devices without requiring monolithic integration
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 waveguide structure achieves optical coupling with losses below 1 dB, enabling efficient chip-to-chip coupling while maintaining compatibility with CMOS processing, allowing for planar surfaces and reduced material usage.
Implementation Method 1
The first and second waveguides each comprise a tapered end for adiabatically coupling light into and/or out of the intermediate waveguide
Data Source
Figure 1(a)~1(b)
Figure 2(a)~2(b)
Figure 3(a)~3(b)
AI summary
The present invention provides a waveguide structure 100 for optical coupling. The waveguide structure 100 includes a first waveguide 101 embedded in a cladding 102 of lower refractive index than the first waveguide 101, and a second waveguide 103 of higher refractive index than the cladding 102 and distanced from the first waveguide 101. The waveguide structure further includes an intermediate waveguide 104, of which at least a part is arranged between the first waveguide 101 and the second waveguide 103. The first waveguide 101 and the second waveguide 103 each comprise a tapered end 101e and 103e for coupling light into and/or out of the intermediate waveguide 104.