Tapered Surface Waveguide for Low-Loss Optical Coupling
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Solution Overview
Problem
High-contrast waveguides in planar lightwave circuits (PLCs) suffer from high propagation loss and poor optical coupling with conventional optical fibers, limiting their use in telecommunications and data communications due to their small mode-field profile mismatch and high production costs associated with precise tapering techniques.
Innovation Solution
A surface waveguide structure incorporating a high-contrast region, a low-contrast region, and a transition region acting as a spotsize converter, where the transition region adiabatically transitions the mode-field profile between the two, using silicon nitride layers with a thin silicon dioxide layer for optical coupling and precise tapering to maintain optical quality, reducing production costs and improving reproducibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If high-contrast waveguides are used to reduce chip real estate and enable tight bending radii, then waveguide density and routing flexibility improve, but propagation loss increases and optical coupling with conventional fibers deteriorates
Solution Approach 1:
The waveguide structure is segmented into high-contrast and low-contrast regions, allowing different sections to optimize for different functions: the high-contrast region provides tight confinement for dense routing, while the low-contrast region enables low-loss propagation and good fiber coupling
Solution Approach 2:
Different regions of the waveguide are assigned different refractive index contrasts tailored to their specific functional requirements, with the transition region providing a gradual change in mode-field profile to minimize losses
2Shape
If high-contrast waveguides are used to achieve tight bending radii, then routing flexibility improves, but optical coupling efficiency with conventional fibers deteriorates
Solution Approach 1:
The refractive index contrast parameter is varied along the waveguide length, transitioning from high contrast (enabling tight bends) to low contrast (enabling good fiber coupling), with the transition region providing a gradual parameter change to avoid mode-mismatch losses
3Loss of energy
If low-contrast waveguides are used to achieve low propagation loss and good optical coupling, then propagation efficiency improves, but waveguide density and routing flexibility deteriorate
Solution Approach 1:
The waveguide is divided into functional segments where the low-contrast region handles propagation and coupling functions, while the high-contrast region handles dense routing, allowing each segment to optimize for its specific purpose
4Ease of manufacture
If conventional photolithography and etching are used to form spotsize converters, then manufacturing simplicity improves, but coupling efficiency improvement is marginal
Solution Approach 1:
The spotsize converter utilizes vertical tapering in the thickness dimension rather than relying solely on lateral dimension changes, enabling more effective mode-field profile transformation and improved coupling efficiency
5Loss of energy
If shadow-mask etching is used to form two-dimensional tapered spotsize converters, then coupling efficiency improves, but manufacturing complexity and cost increase
Solution Approach 1:
The complex two-dimensional taper is segmented into a vertical taper component and a lateral waveguide component, allowing the vertical taper to be formed by simpler processes while maintaining the effectiveness of the spotsize converter
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 solution enables PLCs with high surface-waveguide density, tight bending radii, low optical propagation loss, and efficient optical coupling to external devices, suitable for telecommunications and data communications, while being more cost-effective and reproducible than prior art.
Implementation Method 1
the transition region operative as a spotsize converter between the high-contrast and low-contrast regions. The transition region enables adiabatic conversion of the mode-field profile of a light signal
Implementation Method 2
light propagating through the core of a surface waveguide is guided along the waveguide by the core due to internal reflection at the interface between the core and cladding materials
Implementation Method 3
The silicon dioxide layer is formed such that it is thin enough to enable optical coupling of the two silicon nitride layers such that they collectively support propagation of the light signal, while also mitigating perturbation of the optical mode as it propagates through the silicon nitride layers
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 3
AI summary
A method for forming a waveguide (200) having a thin-core region, a thick-core region, and a transition region of tapered thickness between them is disclosed. The method comprises forming a lower core layer (214) of a first material on a lower cladding (212), forming a thin central core layer (216) of a second material on the first core layer (214), forming an upper core layer (218) of the first material on the central core layer (216), and etching the upper core layer (218) in an etchant such that it is removed from the thin-core region and its thickness monotonically changes from its as-deposited thickness (t4) to extinction across the transition region, where the central core layer (216)protects the lower core layer (214) from exposure to the etchant.