Angled Waveguide End Facet Back Reflection Reduction
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Solution Overview
Problem
Back reflections in optical waveguides can cause destabilization of source lasers and resonance splitting in optical ring resonators due to light being reflected back from the interface between the waveguide and another medium, such as air.
Innovation Solution
A back-reflection reduction device is implemented using an angled waveguide end facet and a mode converter to convert reflected light into different spatial modes, which are then coupled out using a grating coupler, reducing back reflections by converting light into modes not supported by the original waveguide.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a waveguide end facet is used to terminate light propagation, then light coupling out of the waveguide is achieved, but back reflections occur that destabilize laser sources and cause resonance splitting
Solution Approach 1:
The waveguide end facet is angled relative to the waveguide axis, creating an asymmetric geometry that causes reflected light to diverge from the original propagation path. This asymmetric angle prevents reflected light from returning to the laser source, eliminating back reflections while maintaining simple manufacturing through standard angled cutting techniques.
Solution Approach 2:
The solution introduces a spatial dimension by angling the end facet, which redirects reflected light into a different spatial direction. By changing the angular dimension of the end facet, reflected light is directed away from the waveguide core and laser source, effectively separating the reflection path from the propagation path.
2Reliability
If an angled waveguide end facet is used to reduce back reflections, then laser destabilization is prevented, but the reflected light must be redirected into unsupported modes
Solution Approach 1:
The solution converts the potentially harmful reflected light into a beneficial outcome by directing it into cladding modes that carry the light away from the system. The reflected light, which would normally cause instability, is instead transformed into a useful mechanism for eliminating back reflections by coupling into higher-order or cladding modes that do not feed back to the laser.
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
Effectively minimizes back reflections, preventing destabilization of laser sources and resonance splitting by redirecting reflected light into unsupported modes where it dissipates, thereby maintaining system stability.
Implementation Method 1
A back reflection may occur when light from an optical source propagates along a waveguide and is reflected back toward the optical source at the interface of the end of the waveguide and another medium, such as air.
Implementation Method 2
a mode converter to convert light in a first set of spatial modes propagating in a first waveguide to a second set of spatial modes for propagating in a second waveguide
Implementation Method 3
a grating coupler to couple the light in the second set of spatial modes out of the second waveguide
Data Source
AI summary
In the examples provided herein, an apparatus has a mode converter coupled to a first waveguide to convert light propagating in a first set of spatial modes along the first waveguide to a second set of spatial modes. The apparatus also has a second waveguide coupled to the mode converter, where the second set of spatial modes propagate along the second waveguide in a first direction away from the mode converter. Further, the apparatus includes a coupler to couple a portion of the light propagating in the second set of spatial modes out of the second waveguide. Additionally, the second waveguide has an end facet away from the mode converter to reduce back reflection of the light not coupled out of the second waveguide to the first waveguide.