Compact Optical Beam Spot Size Converter Using Segmented Waveguides
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Solution Overview
Problem
Existing optical beam spot size converters for photonic systems chips are too large and suffer from high coupling losses and misalignment tolerance issues, making them unsuitable for high integration scale applications and costly to produce.
Innovation Solution
A compact optical beam spot size converter design featuring a first optical waveguide coupled to multiple second optical waveguides with a reflective part, allowing for faster coupling and reduced length, utilizing silicon nitride and silicon materials compatible with CMOS production techniques, and incorporating tapers for efficient mode shape conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If existing SSC circuits (first type with inverse taper or second type with trident shape) are used, then optical beam spot size conversion is achieved, but the length becomes too large (hundreds of micrometres) for high integration scale PSoCs
Solution Approach 1:
The SSC circuit is divided into multiple sections: a first waveguide section, a second waveguide section with different refractive index material, and a third waveguide section. This segmentation allows the optical beam to undergo gradual mode transformation across different material regions, achieving spot size conversion in a shorter overall length while maintaining coupling efficiency through controlled refractive index transitions.
Solution Approach 2:
The patent uses composite waveguide structures where the first waveguide section has a core material with a first refractive index, the second waveguide section has a core material with a second refractive index (different from the first), and the third waveguide section has a core material with a third refractive index. This composite material approach enables precise control of optical mode transformation, achieving effective spot size conversion in a compact footprint with improved coupling characteristics.
2Area of stationary object
If the SSC circuit length is reduced for high integration, then device size decreases, but coupling loss increases and misalignment tolerance deteriorates
Solution Approach 1:
The waveguide dimensions are designed to vary dynamically along the propagation direction, with each waveguide section having different core widths and heights optimized for its specific function. The first section has dimensions matched to the input beam, the second section has intermediate dimensions for mode transformation, and the third section has dimensions matched to the output beam, enabling efficient coupling in a compact structure.
Solution Approach 2:
The patent systematically changes key parameters including refractive index (by using different materials in different sections), core width, and core height across the three waveguide sections. These parameter transitions are carefully designed to match impedance between waveguides of different spot sizes, minimizing reflection and coupling loss while maintaining a small overall device area.
3Ease of manufacture
If conventional SSC designs are used, then spot size conversion is achieved, but manufacturing cost increases due to complexity
Solution Approach 1:
The multi-section waveguide structure serves multiple functions simultaneously: it performs mode transformation, provides impedance matching, and acts as the complete spot size converter in a single integrated component. This eliminates the need for separate alignment-adjustment mechanisms and reduces the number of discrete components, thereby simplifying manufacturing while maintaining high precision through inherent design robustness.
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 design achieves a smaller size with similar or lower coupling loss and misalignment tolerance compared to existing converters, facilitating mass production at low cost and enabling increased photonic integrated circuit density in silicon photonic systems chips.
Implementation Method 1
a first optical waveguide having a first refractive index... arranged to receive an input optical beam
Implementation Method 2
a reflective part coupled to the plurality of second optical waveguides and to the output optical waveguide. The reflective part is arranged to focus optical beams received from the plurality of second optical waveguides into a single optical beam
Data Source
Figure 1
Figure 2
Figure 3a~3b
AI summary
An optical beam spot size convertor is provided having a body. The body comprises a first optical waveguide having a first refractive index and a plurality of second optical waveguides each having a second refractive index higher than the first refractive index. The first optical waveguide is arranged to receive an input optical beam. The first optical waveguide is further arranged such that light from the input optical beam is coupled from the first optical waveguide into the plurality of second optical waveguides. The body further comprises an output optical waveguide and a reflective part coupled to the plurality of second optical waveguides and to the output optical waveguide. The reflective part is arranged to focus optical beams received from the plurality of second optical waveguides into a single optical beam which is directed to the output optical waveguide.