Optical Coupler Asymmetry for Robust TE-TM Polarization Control
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Solution Overview
Problem
Existing photonic integrated circuits (PICs) face challenges in controlling polarization due to uncontrolled conversion between transverse electric (TE) and transverse magnetic (TM) modes, leading to optical loss, interference, and reduced performance, particularly in harsh environments.
Innovation Solution
The implementation of a polarization changing spot size converter (PCSSC) that induces controlled asymmetry to fully transfer optical modes between TE and TM modes, reducing dependence on waveguide sidewall symmetry and enabling robust polarization control through evanescent coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional waveguides are used without controlled asymmetry, then manufacturing is simpler, but uncontrolled TE-TM mode conversion occurs causing optical loss and interference
Solution Approach 1:
The patent introduces controlled asymmetry in the waveguide structure by positioning auxiliary waveguide cores at specific offsets from the main waveguide core. This asymmetric configuration enables controlled evanescent coupling that transforms TE modes to TM modes and vice versa, providing reliable polarization control while maintaining manufacturing feasibility through standard fabrication processes.
2Reliability
If waveguide sidewall symmetry is required for controlled polarization, then polarization control is achieved, but manufacturing precision requirements increase
Solution Approach 1:
The patent uses auxiliary waveguide cores as intermediary structures that mediate the polarization transformation. These auxiliary cores provide the necessary coupling mechanism without requiring extremely precise sidewall symmetry in the main waveguide. The auxiliary structures act as intermediaries that compensate for fabrication variations and enable robust polarization control with relaxed manufacturing precision requirements.
3Reliability
If evanescent coupling is used for mode transformation, then polarization control is enhanced, but coupling region size increases
Solution Approach 1:
The patent applies local quality by concentrating the evanescent coupling interaction in specific localized regions where auxiliary waveguide cores are positioned close to the main waveguide core. This localized coupling approach enhances polarization control effectiveness while minimizing the overall coupling region size, as the asymmetric auxiliary structures provide strong coupling coefficients that reduce the required interaction length.
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 PCSSC enhances polarization control, reduces optical coupling losses, and improves PIC performance by increasing good die yield and reducing optical return loss, while relaxing fabrication requirements and lowering manufacturing costs.
Implementation Method 1
the optical signals can be transmitted by optical waveguides and can be confined within the silicon layer, for example, because there is an underlying buried oxide (BOX) layer made up of thermal silicon dioxide (i.e., silicon oxidized using a thermal process) and an overlying silicon dioxide cladding surrounding the silicon layers. In such examples, the index contrast between the high index of refraction of silicon and the low index of refraction of silicon dioxide can be responsible for the confinement.
Implementation Method 2
a portion of the first waveguide and a portion of the second waveguide are located in proximity to each other over a coupling region and are configured to (1) evanescently couple the first optical wave from the first mode to the third mode over the coupling region and (2) evanescently couple the second optical wave from the second mode to the fourth mode over the coupling region
Data Source
AI summary
A method comprises: receiving a first optical wave into a first waveguide that confines the first optical wave to a first mode over a first portion of a coupling region; evanescently coupling the first optical wave, over the coupling region, from the first mode to a second mode confined by a second waveguide; and over at least a portion of the coupling region, rotating a polarization of an electric field of the first optical wave by approximately 90 degrees independently from an initial direction of polarization of the electric field of the first optical wave when received into the first waveguide.