Vertically Tapered Grating Coupler for Extended Range Beam Steering
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Solution Overview
Problem
Conventional grating couplers are optimized for coupling to optical fibers and require additional bulk optics for beam steering, which increases complexity and cost, and are inefficient in producing large beam waists for optical-phased array applications.
Innovation Solution
A grating coupler with a long grating element that has a smoothly increasing scattering strength, formed in a dual-stripe waveguide, allowing light to be confined initially in the bottom stripe and gradually interact with the upper core, resulting in a large Gaussian-shaped beam waist with low divergence along the longitudinal axis and high divergence laterally.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional grating couplers are used with short focal length and small beam waist to optimize coupling efficiency, then coupling efficiency is improved, but the operating range is limited and additional bulk optics are required
Solution Approach 1:
The patent changes the focal length parameter of the grating coupler from short (conventional) to long (extended focal length), which transforms the beam waist characteristics and enables extended operating range without additional bulk optics. This parameter change resolves the contradiction by allowing the system to achieve both adequate coupling efficiency and extended operating range through the vertically tapered region design.
2Reliability
If conventional grating couplers are used with short focal length, then coupling efficiency is optimized, but device complexity increases due to additional bulk optics
Solution Approach 1:
The patent merges the functions of the grating coupler and the beam-shaping optics into a single integrated structure. The vertically tapered region performs both the coupling function and the beam waist expansion function that would otherwise require separate bulk optics, thereby reducing device complexity while maintaining coupling efficiency.
Solution Approach 2:
The patent extracts the bulk optics from the system by integrating their functionality directly into the grating coupler structure. The vertically tapered region replaces the need for external lenses or mirrors, eliminating additional components and simplifying the overall system.
3Ease of manufacture
If grating elements have uniform thickness, then fabrication is simpler, but scattering strength is not optimized along the length
Solution Approach 1:
The patent applies local quality by varying the thickness of the grating element along its length. The vertically tapered region has progressively increasing thickness from the input end to the output end, creating locally optimized scattering strength at each position along the grating element. This enables efficient progressive coupling while maintaining fabrication feasibility through standard semiconductor processing techniques.
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 enables efficient beam steering without additional optics, extending the operating range to tens of meters and simplifying packaging, suitable for applications like LiDAR and satellite communications.
Implementation Method 1
a grating structure that is operatively coupled with the waveguide, where the grating structure is configured to scatter optical energy out of the waveguide in a vertical direction
Implementation Method 2
the grating element in just the top stripe of a dual-stripe waveguide portion... thereby defining an extremely small taper angle that gives rise to an output beam having a large, substantially Gaussian-shaped (or Bessel-Gaussian) beam waist
Implementation Method 3
the top stripe has a thickness that increases from zero to its full desired thickness over a long length, thereby defining an extremely small taper angle that gives rise to an output beam having a large, substantially Gaussian-shaped (or Bessel-Gaussian) beam waist along the length of the grating element
Data Source
AI summary
A grating coupler includes a grating element that has a scattering strength that increases smoothly along its length from a very weak scattering strength at its leading edge to a strong scattering strength where the grating element ends. The grating element comprises the top stripe of a dual-stripe waveguide portion, where the light signal introduced to the grating is confined to only the bottom stripe of the waveguide outside the region of the grating element. In the grating-element region, the top stripe has a thickness that increases from zero to its full desired thickness over a long length, thereby defining an small taper angle that gives rise to an output beam having a large, substantially Gaussian-shaped (or Bessel-Gaussian) beam waist along the length of the grating element.