Chirped Grating Surface Emitter for Uniform Power Beam Steering
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Solution Overview
Problem
Optical phased array systems face challenges in achieving uniform power emission and practical fabrication of surface emission gratings with long effective coupling length and sharp instantaneous field of view, due to high refractive index contrast between silicon core and SiO2 cladding, making it difficult to fabricate gratings with ultra-shallow etching processes.
Innovation Solution
A chirped grating design with an optical waveguide core made of silicon and an overlay layer of silicon nitride, featuring continuously varying longitudinal duty cycles and lateral widths, integrated with a silicon dioxide cladding, which maintains a uniform propagation constant and increases emission rate, facilitating beam-steering capabilities in optical phased array systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If shallow etch depths are employed on silicon to reduce the surface emission rate, then the emission rate is reduced, but the fabrication difficulty increases significantly
Solution Approach 1:
The patent applies local quality by varying the duty cycle and lateral width of the overlay layer along the longitudinal direction of the waveguide. This creates a chirped grating structure where different sections have different emission characteristics, allowing the effective coupling length to be extended without requiring ultra-shallow etching throughout the entire structure. The local variation in grating parameters enables precise control of emission rate at different positions.
Solution Approach 2:
The patent changes physical parameters of the grating structure, specifically the duty cycle and lateral width of the overlay layer, which vary continuously along the longitudinal direction. This parameter variation transforms the grating from a uniform structure to a chirped structure, enabling extended effective coupling length and reduced emission rate without compromising manufacturability through standard fabrication processes.
2Measurement precision
If a long effective coupling length is provided in the surface emission grating, then the beam-steering resolution is improved, but the emission uniformity becomes difficult to maintain
Solution Approach 1:
The chirped grating structure implements local quality by having different duty cycles and lateral widths at different longitudinal positions. This local variation compensates for the natural decay of emission along the waveguide, maintaining uniform emission intensity across the entire long coupling length while achieving high beam-steering resolution through the extended interaction length.
Solution Approach 2:
The patent introduces dynamic variation in the grating parameters (duty cycle and lateral width) along the longitudinal direction. This dynamic structure, where parameters change continuously rather than remaining static, enables the system to maintain uniform emission properties over an extended length, resolving the contradiction between long coupling length and emission uniformity.
3Measurement precision
If a uniform emission angle is provided in the surface emission grating, then the far-field pattern sharpness is improved, but the effective coupling length is reduced
Solution Approach 1:
The patent employs parameter changes in the overlay layer dimensions (duty cycle and lateral width) along the longitudinal direction to create a chirped grating. This parameter variation enables the grating to maintain a uniform emission angle across different sections while accumulating a long effective coupling length, as each section contributes to the overall interaction length without compromising angular uniformity.
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 custom grating design achieves uniform emission intensity and longer effective coupling length, forming a clear far-field pattern with narrow beam width, while filtering undesired polarization rotations and enabling efficient beam steering in applications like lidar systems.
Implementation Method 1
an optical waveguide comprising a first material having a uniform lateral width, wherein the first material confines the optical waveguide as the optical waveguide core
Implementation Method 2
an overlay layer comprising a sequence of overlays made of a second material spaced across a top surface of the optical waveguide, wherein successive overlays in the sequence have continuously varying longitudinal duty cycles and continuously varying lateral widths
Data Source
AI summary
The disclosed embodiments relate to the design of an optical phased array grating. This optical phased array grating includes an optical waveguide comprising a first material having a uniform lateral width, wherein the first material confines the optical waveguide as the optical waveguide core. It also includes an overlay layer comprising a sequence of overlays made of a second material spaced across a top surface of the optical waveguide, wherein successive overlays in the sequence have continuously varying longitudinal duty cycles and continuously varying lateral widths between an input end and an output end of the overlay layer, and wherein the second material has a lower optical index than the first material. The optical phased array grating also includes a cladding layer comprised of a third material deposited over the overlay layer and the optical waveguide.