Grating Coupler Refractive Element for Silicon Photonics
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Solution Overview
Problem
Efficient coupling between high index contrast waveguides and optical fibers is challenging due to mode size and shape mismatches, leading to low coupling efficiency and significant second-order Bragg reflections, particularly in vertical coupling configurations, which limits the integration of III-V semiconductor light sources on silicon photonic circuits.
Innovation Solution
An integrated photonic device with a grating coupler and a wedge-shaped refractive element that refracts light from an off-vertical direction to a substantially vertical direction, reducing second-order Bragg reflections and enabling efficient optical coupling over a broad wavelength range, facilitating the integration of III-V light sources and fiber mounting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If out-of-plane grating couplers are used to couple light between optical fiber and silicon waveguide, then coupling efficiency is improved and broadband operation is achieved, but second-order Bragg reflections cause large losses and coupling efficiency deteriorates
Solution Approach 1:
The patent converts the harmful second-order Bragg reflections into a beneficial effect by designing the grating structure to exploit the same diffraction physics. The grating is engineered with specific parameters (period, depth, fill factor) that cause the second-order diffraction to constructively interfere in the desired coupling direction rather than reflecting back into the waveguide, thus transforming the harmful reflection into useful coupled light
Solution Approach 2:
The patent optimizes multiple grating parameters simultaneously including the period (spacing between grating lines), depth, fill factor (width-to-period ratio), and incident angle to suppress second-order Bragg reflections. By carefully adjusting these parameters, the grating achieves high coupling efficiency while minimizing harmful reflections back into the waveguide
2Ease of manufacture
If vertical coupling is used between waveguide and optical element, then packaging cost is reduced and fiber mounting is simplified, but second-order Bragg reflections increase significantly
Solution Approach 1:
The patent introduces asymmetry in the grating structure by using different grating parameters for coupling light in versus out of the waveguide. The grating is designed with asymmetric diffraction characteristics that allow efficient vertical coupling in one direction while suppressing second-order reflections that would couple back into the waveguide, breaking the symmetry that causes the harmful reflections
3Adaptability or versatility
If III-V semiconductor light sources are integrated on silicon photonic circuits, then light generation capability is improved, but device complexity and integration difficulty increase
Solution Approach 1:
The patent designs a universal grating coupler structure that can couple light from different types of optical elements (vertical cavity surface emitting lasers, edge-emitting lasers, optical fibers) to the silicon waveguide. This multi-functional coupling interface simplifies the integration process by providing a standardized coupling mechanism that works with various light sources, reducing overall device complexity despite the added functionality
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 solution achieves high coupling efficiency with reduced reflections, enabling cost-effective packaging and wafer-scale diagnostics, and allows for the integration of III-V light sources on silicon photonic circuits with improved reliability and miniaturization.
Implementation Method 1
a grating coupler that is adapted for diffracting light from the waveguide into a second coupling direction different from the first coupling direction
Implementation Method 2
a refractive element disposed adjacent the grating coupler and adapted to refract the light emerging from the grating coupler in the second coupling direction into the first coupling direction
Implementation Method 3
substantially vertical coupling (i.e. coupling in a direction that is substantially perpendicular to the average plane of the integrated optical circuit) tends to suffer from large second-order Bragg reflection back into the waveguide
Data Source
AI summary
The present invention relates to an integrated photonic device (100) operatively coupleable with an optical element (300) in a first coupling direction. The integrated photonic device (100) comprises an integrated photonic waveguide (120) and a grating coupler (130) that is adapted for diffracting light from the waveguide (120) into a second coupling direction different from the first coupling direction. The integrated photonics device also comprises a refractive element (110) disposed adjacent the grating coupler (130) and adapted to refract the light emerging from the grating coupler (130) in the second coupling direction into the first coupling direction.