Single Mode Optical Coupler with 45-Degree Mirror
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Solution Overview
Problem
Existing optical couplers for silicon photonics face challenges in achieving efficient coupling to single mode fibers with low back reflection and minimal emission angle variation, particularly due to limitations in multi-mode output characteristics and high back-reflection issues, which affect coupling loss and fabrication sensitivity.
Innovation Solution
The implementation of a multi-stage taper and a 45-degree mirror design, combined with programmable grayscale design for mirror angle control and multi-layer anti-reflection coatings, enables efficient vertical/near-vertical single mode coupling with reduced back reflection and improved fabrication control, optimizing the refractive index and waveguide structure for low-loss coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional optical couplers are used for silicon photonics, then fabrication is simplified, but coupling loss increases and back reflection remains high
Solution Approach 1:
The optical coupler is divided into multiple functional sections: an inverse taper waveguide section for mode field expansion, a rib waveguide section for mode transformation, and a 45-degree mirror section for vertical light redirection. Each section performs a specific function to progressively transform the light mode from the silicon waveguide to match the single mode fiber characteristics, thereby reducing coupling loss while maintaining manageable fabrication complexity through modular design
Solution Approach 2:
The coupler transitions light from horizontal propagation in the silicon waveguide to vertical emission toward the single mode fiber by incorporating a 45-degree mirror. This dimensional change in light propagation direction enables efficient coupling to vertically oriented fibers while managing the complex mode field transformation through staged geometric transitions in the waveguide structure
2Loss of energy
If multi-mode output characteristics are used, then coupling efficiency may be improved, but back reflection increases
Solution Approach 1:
The waveguide structure employs local quality variations through different sections: the inverse taper section creates a gradual mode expansion with specific refractive index profiling, while the rib waveguide section provides localized mode confinement and transformation. Each section's geometric and material properties are locally optimized to progressively transform the mode field while suppressing back reflection through adiabatic transitions and impedance matching
Solution Approach 2:
The optical coupler utilizes composite waveguide structures combining silicon core regions with silicon oxide cladding layers, and incorporates metal reflective coatings on the 45-degree mirror surface. These composite material systems enable precise control of light propagation, mode transformation, and reflection characteristics to simultaneously achieve low back reflection and high coupling efficiency
3Reliability
If emission angle variation is reduced, then coupling stability improves, but fabrication precision requirements increase
Solution Approach 1:
The coupler design incorporates a specific 45-degree mirror angle parameter that optimizes the transformation from horizontal to vertical light propagation. The waveguide dimensions, taper angles, and section lengths are carefully parameterized to control the mode field evolution and minimize emission angle variation. These parameter optimizations stabilize the coupling characteristics while accounting for fabrication tolerances through robust design
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 approach achieves low-loss optical coupling with minimal back reflection and stable emission angle, enhancing the efficiency and reliability of coupling light from silicon photonic transmitter chips to single mode fibers, thereby improving the performance and yield of silicon photonic devices.
Implementation Method 1
a multi-stage optical taper to transform light from a first mode field diameter to a second mode field diameter
Implementation Method 2
a 45-degree mirror to reflect light vertically
Implementation Method 3
multi-layer anti-reflection coatings, enables efficient vertical/near-vertical single mode coupling with reduced back reflection
Data Source
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AI summary
Embodiments of the present disclosure are directed toward techniques and configurations for a single mode optical coupler device. In some embodiments, the device may include a multi-stage optical taper to convert light from a first mode field diameter to a second mode field diameter larger than the first mode field diameter, and a mirror formed in a dielectric layer under an approximately 45 degree angle with respect to a plane of the dielectric layer to reflect light from the multi-stage optical taper substantially perpendicularly to propagate the light in a single mode fashion. Other embodiments may be described and/or claimed.