Subwavelength Grating Optical Antenna for Narrow OPA Beam Divergence
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Solution Overview
Problem
Current optical phased arrays face challenges in achieving small diffraction divergence angles, high emission efficiency, large steering ranges, and high steering speeds due to limitations in grating length and fabrication complexity, particularly in silicon-on-insulator platforms with high refractive index contrast.
Innovation Solution
The use of an ultra-long subwavelength grating structure with a top and bottom material stack, featuring a strip waveguide and subwavelength blocks within the evanescent field, allows for increased grating length and reduced diffraction divergence by controlling near-field distribution and simplifying the fabrication process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the grating length is increased to reduce diffraction divergence angle, then the diffraction divergence angle is reduced, but the fabrication complexity and cost increase
Solution Approach 1:
The grating structure is divided into multiple layers (top cladding layer, waveguide layer, bottom cladding layer) with different materials and functions. This segmentation allows each layer to be optimized independently, enabling long grating length without proportionally increasing fabrication complexity.
Solution Approach 2:
The patent transitions from a planar grating structure to a three-dimensional multi-layer structure with vertical stacking. By utilizing the vertical dimension, the grating achieves extended effective length while maintaining manageable fabrication complexity through standardized layer deposition processes.
2Length of stationary object
If shallow grating or sidewall corrugated grating is used to reduce grating strength, then the grating length can be increased, but the fabrication process requirements increase
Solution Approach 1:
The patent systematically varies multiple parameters including etching depth (50-200nm for top layer, 100-300nm for bottom layer), grating period (200-500nm), and duty cycle (30-70%) to optimize the balance between grating strength and length. This parameter optimization enables long grating length with relaxed fabrication precision requirements.
3Length of stationary object
If multilayer grating is used to separate gratings and waveguides vertically, then the grating length can be increased, but the fabrication complexity and cost increase
Solution Approach 1:
The multi-layer structure serves multiple functions simultaneously: the top cladding layer provides optical confinement and grating modulation, the waveguide layer guides light propagation, and the bottom cladding layer provides additional confinement and mechanical support. This multi-functionality justifies the increased fabrication steps by delivering superior optical performance and longer grating length.
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
This approach enables the creation of millimeter-length gratings with reduced far-field divergence angles and simpler manufacturing, enhancing the performance of optical phased arrays in applications like LiDAR and free-space optical communication.
Implementation Method 1
subwavelength blocks are placed within the evanescent field of the strip waveguide to form the grating structure
Implementation Method 2
the effective length of the grating can be greatly increased. By adjusting the size and position of the subwavelength blocks in different periods, uniform or arbitrary shape near field distribution can be generated
Data Source
AI summary
An ultra-long sub-wavelength grating as an optical antenna for optical phased arrays includes a top structure and a bottom structure which are vertically stacked. The bottom structure is made of a material with a refractive index lower than a refractive index of the top structure. The top structure is made of a material with a refractive index higher than that of the bottom structure. A strip waveguide is disposed in the middle of the top structure. subwavelength blocks are disposed periodically on two sides of the straight strip waveguides. The invention has the following beneficial effects. The structure could increase the effective length of the grating; uniform near field distribution can be achieved by controlling the positions of the subwavelength blocks. The structure is simpler with lower fabrication requirements and lower cost.