Silicon Optical Integrated Circuit Stray Light Management
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Solution Overview
Problem
In silicon optical integrated circuits using SOI substrates, end-surface coupling generates significant stray light that propagates and interferes with other optical elements, causing characteristic deterioration due to its confinement and reflection within the clad, especially when coupled to multimode optical waveguides.
Innovation Solution
The optical integrated circuit is designed with a specific positional relationship between the end-surface coupling part and the multimode optical waveguide element, utilizing a spot size converter and curved optical waveguides to manage stray light by determining optimal placement based on beam divergence angles and intensity distribution, thereby minimizing interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If end-surface coupling is used to couple external optical circuits to the silicon optical integrated circuit, then optical coupling efficiency is improved, but stray light is generated that propagates and interferes with other optical elements
Solution Approach 1:
The patent extracts the harmful stray light from the system by positioning multimode optical waveguide elements away from the end-surface coupling part, specifically placing them outside the region where stray light propagates (defined by beam divergence angle θ from the coupling point). This separates the useful optical coupling function from the harmful stray light effect.
Solution Approach 2:
The patent introduces a spatial dimension constraint by defining a specific placement region based on beam divergence angle θ. By considering the angular distribution of stray light and establishing exclusion zones in the plane of the optical integrated circuit, the solution transforms a one-dimensional coupling problem into a two-dimensional spatial arrangement problem.
2Area of stationary object
If multimode optical waveguide elements are placed close to the end-surface coupling part, then circuit area is reduced, but characteristic deterioration occurs due to stray light interference
Solution Approach 1:
The patent applies local quality by creating different spatial zones: a forbidden zone near the end-surface coupling part where multimode waveguide elements must not be placed (due to high stray light intensity), and permissible zones farther away where elements can be safely positioned. This local spatial differentiation optimizes both compactness and reliability.
Solution Approach 2:
The patent performs preliminary action by pre-defining the placement constraints for multimode optical waveguide elements before actual circuit design. By calculating the beam divergence angle θ and establishing exclusion zones in advance, designers can immediately determine valid placement regions without iterative optimization.
3Object-generated harmful factors
If additional measures are taken to suppress stray light, then stray light impact is reduced, but manufacturing cost increases
Solution Approach 1:
The patent employs self-service by utilizing the natural propagation characteristics of stray light (beam divergence at angle θ) to achieve suppression. Instead of adding active suppression components, the design allows stray light to naturally diverge and decay, and positions sensitive elements outside this natural propagation path, eliminating the need for additional costly suppression measures.
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 configuration effectively reduces the impact of stray light on the silicon optical integrated circuit, preventing characteristic deterioration while maintaining a compact circuit area without additional costly measures.
Implementation Method 1
by making it have a construction for coupling it with an end-surface of an external optical circuit and gradually reducing the width of the optical waveguide, it becomes possible to enhance integrity of an optical mode field with the external circuit
Implementation Method 2
By processing the silicon active layer to shape it to be a narrow line, and forming a top clad layer having an index of refraction lower than that of Si, an optical waveguide, that comprises the silicon as a core and the BOX layer and the top clad layer as clad parts, can be formed
Implementation Method 3
a position of an end-surface coupling part selected from arbitrary ones and a position of an arbitrary multimode optical waveguide element to which each optical waveguide is coupled via each curved part have a predetermined positional relationship based on a beam divergence angle θ of stray light that is repeatedly reflected by a bottom surface of the SiO 2 buried oxide film layer and a top surface of the top clad layer
Data Source
Figure 1
Figure 2
Figure 3(a)~3(b)
AI summary
An optical end coupling type silicon optical integrated circuit is provided using an SOI substrate. This optical integrated circuit is constituted so as to connect with an external optical circuit at an end coupling part and have signal light incident to an optical circuit that includes a curved part. In the plane of the optical integrated circuit, the position of one end coupling part selected from among any thereof and the position of any multimode optical waveguide element to which a respective optical waveguide is connected via a respective curved part satisfy a positional relationship defined on the basis of a beam divergence angle [theta] of stray light.