GRIN-Lensed Tuned Wedge Waveguide Termination for Back Reflection
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Solution Overview
Problem
Existing optical waveguide terminations, particularly those using GRIN lenses, face significant challenges in reducing back reflections to levels below -50 dB while minimizing insertion loss, due to Fresnel reflections at air interfaces and the limitations of antireflection coatings which are often unreliable at extreme temperatures or prone to abrasion.
Innovation Solution
A GRIN-lensed, tuned wedge waveguide termination is introduced, featuring a GRIN lens with a pitch greater than a quarter pitch to form a waist, a tuned wedge subassembly with a bevel angle and thickness to capture more beam energy and reduce back reflections, and an offset between the GRIN lens and wedge subassembly to align the beam with the optical axis, along with a method to adjust the waveguide's connection to minimize back reflections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If antireflection coating is applied to reduce back reflections, then back reflection is reduced to -24 dB to -45 dB, but the coating cannot withstand extreme temperatures, chemicals or abrasion
Solution Approach 1:
The patent removes the vulnerable AR coating layer entirely and replaces it with a mechanical solution using a wedge-shaped termination with controlled back reflections that are directed away from the fiber core. This extracts the problematic coating function and substitutes it with a more robust geometric approach.
Solution Approach 2:
The patent introduces an intermediary wedge-shaped structure with controlled reflectivity that mediates between the fiber and air interface. This wedge acts as a mediator to control and redirect back reflections through its geometric shape rather than relying on coating materials.
2Object-generated harmful factors
If bevels are added to GRIN lens and fiber to redirect back reflections, then back reflections are rerouted, but insertion loss increases due to the nonzero exit angle of the beam
Solution Approach 1:
The patent changes the key parameter from bevel angle to wedge angle optimization. Instead of using bevels that create fixed nonzero exit angles, the wedge shape allows optimization of the angle parameter to balance back reflection reduction with minimal beam deviation, thereby reducing insertion loss.
Solution Approach 2:
The patent transitions from static bevel geometry to a dynamic optimization approach where the wedge angle and position are可调 (adjustable) to optimize performance. This allows the system to adapt the geometry to minimize both back reflection and beam deviation simultaneously.
3Volume of moving object
If quarter-pitch GRIN lens is used to expand beam, then beam expansion is achieved, but Fresnel back reflections occur at air interfaces with levels of -48 dB and -12 dB
Solution Approach 1:
The patent segments the beam path into distinct zones: the GRIN lens for expansion, the wedge-shaped termination for reflection control, and the bonding interface for mechanical support. This segmentation allows each component to be optimized for its specific function without compromising the others.
Solution Approach 2:
The patent converts the harmful Fresnel back reflections into a controlled phenomenon by using the wedge geometry to redirect them at specific angles. The reflections that would otherwise enter the fiber are transformed into useful directional information that can be managed through proper wedge angle selection.
4Strength
If epoxy is used to affix fiber to GRIN lens, then mechanical bonding is achieved, but the epoxy interface increases Fresnel back reflection to -25 dB
Solution Approach 1:
The patent extracts the bonding function from the optical path by using the wedge-shaped termination as both the mechanical support structure and the optical reflection control element. This eliminates the need for separate epoxy bonding that creates reflective interfaces.
Solution Approach 2:
The patent merges the mechanical bonding function with the optical reflection control function into a single integrated wedge-shaped structure. This consolidation eliminates the epoxy interface and its associated back reflections by combining structural support and optical management in one component.
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 achieves back reflections of less than -50 dB and potentially -60 dB, while maintaining low insertion loss by optimizing the GRIN lens pitch, wedge geometry, and alignment, effectively addressing the limitations of conventional GRIN-lensed collimators.
Implementation Method 1
a GRIN lens having a pitch greater than a quarter pitch such that a primary beam propagating through the GRIN lens subassembly forms a waist
Implementation Method 2
the tuned wedge subassembly further having a bevel angle selected to reduce a back reflection into the waveguide
Data Source
AI summary
A GRIN-lensed, tuned wedge waveguide termination, a method of reducing back reflection to a waveguide caused by the GRIN-lensed, tuned wedge waveguide termination and a terminated optical fiber. In one embodiment, the GRIN-lensed, tuned wedge waveguide termination includes: (1) a GRIN lens subassembly including a GRIN lens having a pitch greater than a quarter pitch such that a primary beam propagating through the GRIN lens subassembly forms a waist and (2) a tuned wedge subassembly bonded to the GRIN lens subassembly and having a length selected such that the tuned wedge subassembly ends at least proximate the waist, the tuned wedge subassembly further having a bevel angle selected to reduce a back reflection into the waveguide.