Flipped Waveguide Mirror With Underside Metal Coating
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Solution Overview
Problem
Conventional waveguide mirrors on silicon-on-insulator substrates face challenges such as high optical loss due to light traveling through the silicon-air interface and the need for complex fabrication techniques, which result in large footprints and increased fabrication timescales.
Innovation Solution
A method of fabricating a 'flipped' waveguide mirror by creating a cavity underneath the silicon device layer using an anisotropic etch, which forms a planar underside surface for light coupling, eliminating the need for light to travel through air and simplifying the fabrication process by avoiding the need for a filling step, and applying a metal coating to the underside surface for enhanced reflectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional waveguide mirrors are fabricated on silicon-on-insulator substrates, then the mirror structure can be formed, but light must travel through the silicon-air interface which causes high optical loss and scattering
Solution Approach 1:
The patent inverts the conventional mirror structure by forming the reflective surface on the underside of the silicon device layer rather than on the top surface. This is achieved by etching a cavity underneath the device layer and applying metal coating to the underside surface, allowing light to couple directly from the waveguide to the mirror without traversing a silicon-air interface, thereby eliminating scattering and optical loss associated with such interfaces
Solution Approach 2:
The invention transitions from a top-surface mirror configuration to an underside-surface mirror configuration by creating a three-dimensional cavity structure. The etch channel provides access to the underside of the device layer, enabling the formation of a planar reflective surface in a different spatial dimension that directly interfaces with the waveguide mode
2Productivity
If conventional fabrication techniques are used to create waveguide mirrors, then the mirror can be formed, but the process requires multiple steps including filling operations which increase fabrication timescales
Solution Approach 1:
The patent extracts and eliminates the filling step from the conventional fabrication process. By forming the cavity and applying metal coating to the underside surface without requiring subsequent filling operations, the process is simplified and fabrication time is reduced while maintaining the functional integrity of the mirror structure
Solution Approach 2:
The invention performs the critical mirror-forming actions earlier in the fabrication sequence by etching the cavity and applying the metal coating to the underside surface before any potential filling steps. This preliminary formation of the functional mirror structure eliminates the need for later filling operations and reduces overall fabrication complexity
3Area of stationary object
If conventional waveguide mirrors are designed, then the mirror function is achieved, but the structure occupies a large footprint area
Solution Approach 1:
The patent reduces the mirror footprint by transitioning from a planar top-surface configuration to a three-dimensional cavity structure with the reflective surface on the underside. This vertical integration allows the mirror to couple efficiently with the waveguide mode in a compact lateral footprint while maintaining reliable optical coupling through the direct interface between the waveguide and the planar underside surface
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 approach reduces optical loss by eliminating air exposure and simplifies the fabrication process, resulting in a more efficient and compact mirror structure with improved reflectivity and faster turnaround times.
Implementation Method 1
applying an anisotropic etch via the channel to regions of the silicon device layer and silicon support layer adjacent to the channel; the anisotropic etch following an orientation plane of the silicon device layer and silicon support layer to create a cavity underneath an overhanging portion of the silicon device layer
Implementation Method 2
a mirror structure for vertically coupling light into and out of a silicon device layer... applying a metal coating to the underside surface
Data Source
AI summary
A mirror and method of fabricating the mirror, the method comprising:providing a silicon-on-insulator substrate, the substrate comprising: a silicon support layer; a buried oxide (BOX) layer on top of the silicon support layer; and a silicon device layer on top of the BOX layer; creating a via in the silicon device layer, the via extending to the BOX layer; etching away a portion of the BOX layer starting at the via and extending laterally away from the via in a first direction to create a channel between the silicon device layer and silicon support layer; applying an anisotropic etch via the channel to regions of the silicon device layer and silicon support layer adjacent to the channel; the anisotropic etch following an orientation plane of the silicon device layer and silicon support layer to create a cavity underneath an overhanging portion of the silicon device layer; the overhanging portion defining a planar underside surface for vertically coupling light into and out of the silicon device layer; and applying a metal coating to the underside surface.