Multi-tip waveguide spot size converter for fiber coupling
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Solution Overview
Problem
The mismatch in spot sizes and effective refractive indexes between standard single-mode optical fibers and nanophotonic silicon strip waveguides results in significant coupling loss, making efficient coupling between them difficult and costly due to the need for high-resolution lithography in manufacturing spot size converters.
Innovation Solution
A multi-tip waveguide spot size converter is fabricated using deep UV lithography, featuring tapered gap regions between waveguide portions, allowing for efficient coupling by expanding the mode field diameter to match that of single-mode fibers without requiring expensive high-resolution lithography.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional single-tip SSC waveguides are used to minimize coupling loss, then coupling efficiency is improved, but manufacturing complexity and cost increase due to sub-micrometer feature requirements and high-resolution lithography needs
Solution Approach 1:
The waveguide is divided into multiple tips (at least two tips) instead of a single tip, allowing the mode field diameter to be expanded more effectively to match single-mode fiber dimensions while using manufacturable feature sizes with standard lithography processes
Solution Approach 2:
The waveguide structure incorporates varying geometries at different locations - the multi-tip configuration at the output end and tapered gap regions - to locally optimize mode field expansion where needed while maintaining manufacturability
2Manufacturing precision
If e-beam lithography is used to create sub-micrometer features for SSC waveguides, then manufacturing precision is improved, but production speed decreases and cost increases due to serial writing process
Solution Approach 1:
The invention changes the geometric parameters of the waveguide to use larger, manufacturable feature sizes (tip widths of several microns or more) that can be produced with standard deep UV or visible light lithography, eliminating the need for high-resolution e-beam lithography while maintaining effective mode field expansion through the multi-tip configuration
3Loss of energy
If conventional SSC designs are used to achieve large mode field diameter expansion, then coupling efficiency to single-mode fiber is improved, but manufacturing cost increases due to expensive high-resolution lithography requirements
Solution Approach 1:
The multi-tip waveguide structure achieves superior mode field diameter expansion (7 microns or more) that matches single-mode fiber dimensions, enabling low coupling loss while using standard lithography processes that are cost-effective for volume production
Solution Approach 2:
The invention replaces expensive, low-volume manufacturing processes (e-beam lithography) with cheaper, high-volume manufacturing-capable processes (standard lithography), making SSC waveguides economically viable for mass production despite the complexity of achieving large mode field expansion
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 multi-tip waveguide design reduces coupling loss to less than 2 dB, achieving a mode field diameter of 7 microns or more, enabling efficient and cost-effective coupling between optical fibers and silicon strip waveguides with looser misalignment tolerances.
Implementation Method 1
exposing the coated resist material to a deep UV beam
Data Source
AI summary
A method of making a spot size converter comprising a multi-tip waveguide comprising a first and a second waveguide portions, the method comprising the steps of: coating a multilayer wafer comprising a waveguide material layer with a resist material; exposing the coated resist material to a deep UV beam or an electron beam; developing resist material to form an partial waveguide pattern within the resist material; transferring the partial waveguide pattern to the waveguide material layer, forming an initial waveguide; placing a second layer of resist material over the initial waveguide; patterning a tapered gap region shape in the second layer of resist material by exposing the second layer of resist material to a deep UV beam or an electron beam; and transferring the tapered gap region shape to the waveguide material layer of the initial waveguide to form a tapered gap region inside the initial waveguide.