Holographic Recording Material for Surface-Normal Optical Coupling
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Solution Overview
Problem
The disparity between on-chip and off-chip communication bandwidths in high-performance computing systems is exacerbated by limitations in high-speed serial transceivers and conductive electrical interconnections, leading to significant optical losses due to mode-size mismatch and alignment challenges in coupling light into and out of silicon optical waveguides.
Innovation Solution
An integrated circuit with a holographic recording material that diffracts optical signals out of the plane, using a surface-normal coupling technique to achieve low-loss coupling with optical fibers or waveguides, relaxing alignment requirements and enabling efficient mode matching and 90° bending.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional grating couplers are used to couple surface-normal light into sub-micron optical waveguides, then coupling is achieved, but significant optical losses occur due to mode-size mismatch and substrate scattering
Solution Approach 1:
The patent transitions from planar 2D grating structures to a 3D volumetric holographic grating structure embedded in an overclad layer. This dimensional change enables the grating to interact with both surface-normal incident light and the confined sub-micron waveguide mode simultaneously, achieving low-loss coupling without requiring sub-micron alignment precision between separate components.
Solution Approach 2:
The overclad layer containing the holographic grating acts as an intermediary between the optical fiber (or free-space light) and the sub-micron optical waveguide. This intermediary structure provides mode transformation and field confinement, enabling efficient power transfer while relaxing alignment tolerances compared to direct coupling approaches.
2Adaptability or versatility
If tapered optical waveguides are used for broadband light coupling, then a large range of wavelengths can be accommodated, but edge-coupling is required which prevents two-dimensional array definition on chip surface
Solution Approach 1:
The patent enables surface-normal (vertical) coupling geometry instead of edge-coupling, allowing light to enter through the top surface of the chip. This dimensional change in coupling geometry permits the definition of two-dimensional arrays of optical couplers on the chip surface and enables wafer-scale optical testing while maintaining broadband wavelength accommodation through the volumetric holographic grating design.
3Reliability
If silicon-on-insulator technology with thick buried-oxide layer is used to prevent mode leakage, then optical confinement is improved, but thermal performance is limited
Solution Approach 1:
The patent applies optical confinement locally at the waveguide region using the high-index-contrast silicon core and overclad layer with embedded holographic grating, rather than relying on a thick buried-oxide layer throughout the entire substrate. This localized confinement approach maintains optical integrity while improving thermal performance by reducing the thermal impedance introduced by thick oxide layers.
4Loss of energy
If precision edge polishing is performed to ensure inverse taper tips are close to chip edge, then coupling efficiency is improved, but fabrication difficulty increases
Solution Approach 1:
The patent extracts the critical coupling function from the chip edge region and relocates it to the chip surface through surface-normal coupling with volumetric holographic gratings. This extraction eliminates the need for precision edge polishing and inverse taper fabrication, significantly simplifying the manufacturing process while maintaining low coupling losses through the holographic mode-matching structure.
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 facilitates low-loss optical coupling with reduced misalignment issues, supporting high-density photonic devices and scalable integration, while maintaining thermal performance and allowing for wafer-scale testing.
Implementation Method 1
a holographic recording material substantially filling the cavity. The holographic recording material may diffract an optical signal propagating in a plane of the optical waveguide out of the plane through the cavity
Data Source
AI summary
An integrated circuit includes a holographic recording material substantially filling a cavity in a semiconductor layer. During operation of the integrated circuit, a holographic pattern in the holographic recording is reconstructed and used to diffract an optical signal propagating in a plane of an optical waveguide, which is defined in the semiconductor layer out of the plane through the cavity. In this way, the holographic recording material may be used to couple the optical signal to an optical fiber or another integrated circuit.