Monolithic Optical Coupler for Circular-to-Rectangular Beam Conversion
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Solution Overview
Problem
Existing methods for optical coupling between circular-cross section and high aspect ratio cross section beams are bulky, require precise alignments, and are not suitable for integrated, all-glass designs, leading to increased manufacturing costs and inefficiencies, particularly when trying to transform a circular beam into an elliptical beam for semi-guiding high-aspect ratio core (SHARC) fibers.
Innovation Solution
A monolithic optical coupler with a high-aspect ratio cross section and a graded index profile in the slow-axis direction, functioning as a 1-D GRIN lens, allows the circular beam to maintain size and divergence in the fast-axis direction while expanding and collimating in the slow-axis direction, eliminating the need for free-space optics and precise alignments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If free-space optics methods (cylindrical lenses, telescopes) are used to reformat a circular beam into an elliptical beam, then beam re-formatting is achieved, but the device becomes bulky and requires precise alignments
Solution Approach 1:
The patent merges multiple optical functions (beam expansion, collimation, and reformatting) into a single monolithic optical coupler component. This eliminates the need for separate cylindrical lenses and telescopes, reducing the number of alignment interfaces and simplifying the overall optical system while achieving the same beam transformation from circular to high-aspect-ratio elliptical shape
Solution Approach 2:
The patent introduces a graded-index (GRIN) lens as an intermediary optical element that provides the necessary refractive index gradient to achieve beam reformatting. The GRIN lens acts as a mediator that transforms the circular beam profile into an elliptical one with the desired high aspect ratio, eliminating the need for complex free-space optical arrangements
2Shape
If free-space optics components are used, then beam re-formatting is possible, but manufacturing costs increase due to multiple components and alignments
Solution Approach 1:
The patent combines multiple discrete optical components (cylindrical lenses, telescopes) into a single monolithic optical coupler. This integration eliminates the need for separate manufacturing and assembly of multiple precision components, reducing manufacturing complexity and cost while achieving the same beam reformatting function
Solution Approach 2:
The monolithic optical coupler performs multiple optical functions simultaneously: beam expansion, collimation, and reformatting. This multi-functionality eliminates the need for separate specialized components, simplifying both manufacturing and system integration while achieving comprehensive beam transformation
3Length of moving object
If the coupler length is reduced to ~100 mm using lens pairs, then propagation distance is acceptable, but alignment sensitivity increases and manufacturing quality becomes difficult
Solution Approach 1:
The patent integrates multiple optical functions into a single monolithic component, eliminating the multiple alignment interfaces that would exist in a lens pair configuration. This integration maintains a compact length while removing the cumulative alignment sensitivity that arises from having multiple separate optical elements that must be precisely aligned
4Reliability
If butt coupling is used to match circular fiber to rectangular fiber, then coupling is achieved, but beam size and divergence cannot be varied, resulting in underfilling or overfilling
Solution Approach 1:
The patent employs a graded-index profile with variable refractive index to dynamically control beam parameters (size and divergence) within the optical coupler. This allows the beam to be transformed from the circular fiber mode to match the rectangular fiber mode with appropriate size and divergence characteristics, achieving reliable coupling while maintaining adaptability to different fiber configurations
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 beam re-formatting with a robust all-fiber amplifier architecture, maintaining single-mode operation and reducing manufacturing costs by eliminating the need for extra optical surfaces and precise alignments, while allowing for splicing of different optical fibers, thus providing a long operating lifetime.
Implementation Method 1
the optical core medium having a graded index profile, in the slow-axis direction to function as a 1-D GRIN lens
Implementation Method 2
functioning as a 1-D GRIN lens, allows the circular beam to maintain size and divergence in the fast-axis direction while expanding and collimating in the slow-axis direction
Implementation Method 3
propagating the signal beam through the optical core in a narrow, fast-axis direction while maintaining a size and a divergence of the signal beam by index-based waveguiding
Data Source
AI summary
A coupler and method of coupling a signal beam from a circular-core fiber (305) to a rectangular-core cross section fiber (313) includes providing an optical coupler (310) having an optical core (320) with a high-aspect ratio cross section at one end and a circular cross section at an opposite end to receive a signal beam having a circular cross section. The signal beam is propagated from the circular fiber to the rectangular-core cross section fiber in a narrow, fast-axis direction while maintaining the size and divergence of the signal beam as it propagates. The signal beam is expanded in size while producing a collimated beam from the circular cross section end to the rectangular-core cross section end in a wide, slow-axis direction. Curved claddings around core (320) provide a one dimensional GRIN lens function.