GRIN Expanded Beam Coupler for Passive PIC-FAU Alignment
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Solution Overview
Problem
The challenge of achieving low optical loss and precise alignment between photonic integrated circuits (PICs) and fiber array units (FAUs) in scalable and high-volume manufacturing is exacerbated by micron-scale misalignments and differing beam sizes, leading to increased coupling loss and complexity in optical co-packaging solutions.
Innovation Solution
A Gradient Index (GRIN) lens-based expanded beam coupler is introduced, which uses a GRIN lens with a radial gradient refractive index to achieve compact, low-loss optical coupling by expanding the mode field diameter (MFD) to match that of single-mode fibers, integrated with existing V-groove architecture for passive-active alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional optical coupling methods are used between PIC and FAU, then the coupling loss is high due to micron-scale misalignments and differing beam sizes, but using expanded beam coupling with GRIN lens increases device complexity
Solution Approach 1:
The patent changes the refractive index parameter of the lens material radially to create a GRIN lens. This radial gradient in refractive index enables the lens to expand the beam mode field diameter (MFD) to match single-mode fiber dimensions, thereby reducing optical coupling loss between PIC and FAU while maintaining a compact form factor.
Solution Approach 2:
The GRIN lens acts as an intermediary optical element between the PIC waveguide and the FAU fiber array. It mediates the mode field diameter mismatch by expanding the beam from the PIC to match the fiber MFD, reducing coupling loss without requiring complex active alignment mechanisms.
2Manufacturing precision
If active alignment methods are used to achieve precise alignment between PIC and FAU, then alignment precision improves, but manufacturing complexity and cost increase
Solution Approach 1:
The GRIN lens design enables passive alignment by utilizing the lens's inherent optical properties to automatically accommodate misalignments. The radial gradient refractive index profile allows the lens to focus and expand beams in a way that tolerates micron-scale positioning errors, eliminating the need for complex active alignment procedures while maintaining high coupling efficiency.
3Ease of operation
If the lens diameter is increased to expand the mode field diameter, then alignment tolerance improves, but the form factor becomes less compact
Solution Approach 1:
The patent achieves beam expansion and improved alignment tolerance by changing the refractive index parameter radially within a compact lens diameter. The GRIN lens profile creates the necessary beam expansion effect without requiring a proportionally large lens physical size, thus maintaining a compact form factor while improving alignment tolerance.
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 GRIN lens coupler enhances alignment tolerance, reduces sensitivity to contamination, improves yield and reliability, and maintains a compact form factor, minimizing optical coupling loss and facilitating high-volume manufacturing.
Implementation Method 1
A Gradient Index (GRIN) lens-based expanded beam coupler is introduced, which uses a GRIN lens with a radial gradient refractive index to achieve compact, low-loss optical coupling by expanding the mode field diameter (MFD) to match that of single-mode fibers
Data Source
AI summary
Architectures and methods for graded index (GRIN) lens expanded beam (EB) coupler for detachable fiber array unit (FAU) for use with a photonic integrated circuit (PIC). A system to optically couple a fiber optic array (FAU) to a PIC die includes a graded index (GRIN) lens to optically couple a single mode fiber (SMF) in the FAU to a waveguide in the PIC die. The GRIN lens has a first mode field diameter (MFD) that is a function of a spot size converter of the waveguide. The SMF is a conduit for optical light with a wavelength and a second MFD. The GRIN lens has a length that is a function of a predetermined whole number of periodic cycles of the wavelength.