Hollow Waveguide Mode Conversion for Low-Loss Fiber Coupling
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Solution Overview
Problem
Existing optical devices face challenges in achieving low coupling loss and high reliability when coupling SiPh-PICs to optical fibers, due to mismatched mode diameters and polarized light dependence, which complicates the manufacturing process and increases costs.
Innovation Solution
The optical integrated device features a hollow structure optical waveguide with a dent portion near the dicing line, allowing for efficient mode diameter conversion and stable optical coupling without damaging the SiO2 waveguide during dicing, thereby reducing optical coupling loss and ensuring high reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a lens coupling technique is used to increase the mode diameter of the optical coupler, then the mode diameter can be increased to match the normal diameter of single mode fiber, but the device area increases and manufacturing complexity increases due to additional steps for adjusting the optical axis and needing special adjustment devices
Solution Approach 1:
The invention extracts and removes the lens component from the optical coupling system. Instead of using a lens to expand the mode diameter, the patent employs a mode diameter conversion structure (such as an inverse tapered waveguide or adiabatic taper) that is integrated directly into the optical coupler chip. This eliminates the need for separate lens adjustment steps and special adjustment devices, thereby reducing device complexity while maintaining the ability to match mode diameters between the optical coupler and single mode fiber.
Solution Approach 2:
The invention merges the mode diameter conversion function directly into the optical coupler waveguide structure. The inverse tapered waveguide or adiabatic taper is fabricated as an integral part of the optical coupler chip using standard CMOS or SiPh processes, combining the coupling function and mode conversion function into a single integrated structure. This eliminates the need for separate lens components and adjustment mechanisms, reducing both device area and manufacturing complexity.
2Manufacturing precision
If a lens coupling technique is used, then the mode diameter can be increased to match the normal diameter of single mode fiber, but the device area increases making small sized module implementation difficult
Solution Approach 1:
The invention extracts and removes the lens component from the optical coupling system. Instead of using a lens to expand the mode diameter, the patent employs a mode diameter conversion structure (such as an inverse tapered waveguide or adiabatic taper) that is integrated directly into the optical coupler chip. This eliminates the need for separate lens adjustment steps and special adjustment devices, thereby reducing device complexity while maintaining the ability to match mode diameters between the optical coupler and single mode fiber.
Solution Approach 2:
The invention uses an inverse tapered waveguide or adiabatic taper that expands the mode diameter gradually along the propagation direction (one dimension) rather than requiring a two-dimensional lens structure. This allows mode diameter conversion to occur within the waveguide itself as light propagates through the tapered section, achieving mode matching without increasing the lateral device area, thus enabling compact module implementation.
3Ease of manufacture
If an inverse tapered spot size converter structure is used, then the structure can be fabricated easily using only Si waveguide, but the mode diameter cannot be increased to nearly the mode diameter of single mode fiber and excessive loss occurs in fusion welding portion
Solution Approach 1:
The invention employs composite material structures for the mode diameter conversion section. Instead of using only Si waveguide, the patent utilizes combinations such as Si-SiO2 composite waveguides or SiN-SiO2 composite structures. These composite materials allow for better control of the refractive index profile and mode field distribution during the tapering process, enabling more efficient mode diameter conversion to match single mode fiber dimensions while maintaining fabrication compatibility with standard semiconductor processes.
4Device complexity
If the SiPh-PIC is directly connected to the optical fiber, then the structure is simple, but a large optical loss occurs due to mismatch with the mode diameter
Solution Approach 1:
The invention performs preliminary mode diameter conversion within the optical coupler chip before the light exits to the optical fiber. The inverse tapered waveguide or adiabatic taper pre-expands the mode diameter of the Si waveguide to match the larger mode diameter of the single mode fiber. This preliminary action ensures that when the light exits the chip and enters the fiber, the mode fields are already well-matched, minimizing coupling loss without requiring complex external coupling structures.
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 solution enables efficient optical coupling with minimal loss and high reliability, allowing for the connection of optical fibers with normal diameters, while also simplifying the manufacturing process and reducing costs.
Implementation Method 1
The optical waveguide converts a mode diameter to a mode diameter of an optical fiber in accordance with travelling of light from the first optical waveguide to the second optical waveguide
Implementation Method 2
The second optical waveguide is optically coupled to the first optical waveguide and has a relative refractive index difference that is smaller than a relative refractive index difference of the first optical waveguide
Data Source
AI summary
An optical integrated device includes a substrate and a waveguide that has a hollow structure. The waveguide includes a first waveguide and a second waveguide that is optically coupled to the first waveguide and that has a smaller relative refractive index difference than that of the first waveguide and converts a mode diameter to a mode diameter of an optical fiber in accordance with travelling of light. The optical integrated device includes a dent portion that is formed in the vicinity of the dicing line on the substrate such that the width of the output end surface is smaller than the core width of the optical fiber that is optically coupled to the output end surface in the state in which the dicing end surface of the substrate protrudes farther than the output end surface of the second waveguide in the axial direction of the optical waveguide.