Silicon Nitride Polarization Rotator Splitter for Low-Loss Mode Hybridization
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Solution Overview
Problem
Existing on-chip polarization management solutions, particularly in FMCW LiDAR scanning devices, face limitations in optical power capacity and are adversely affected by tight fabrication tolerances, leading to high insertion loss and incomplete mode hybridization between TM0 and TE1 modes.
Innovation Solution
An integrated on-chip polarization rotator splitter (PRS) design using silicon nitride rib waveguides with a three-section tapered structure, featuring a first layer with varying width and a second layer with continuous width increase, combined with an asymmetric evanescent direction coupler, to facilitate full mode hybridization and reduce insertion loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If silicon photonic waveguides are used for polarization management, then device integration is achieved, but optical power capacity is limited and fabrication tolerances are tight leading to high insertion loss
Solution Approach 1:
The patent changes the material parameter from silicon to silicon nitride, which has different optical properties including lower propagation loss and lower refractive index. This material substitution resolves the contradiction by maintaining integration capability while reducing insertion loss and increasing optical power capacity
Solution Approach 2:
The patent employs a composite structure with silicon nitride rib waveguides on a silicon substrate, combining the advantages of both materials. The silicon nitride provides low loss and high power capacity, while the silicon substrate enables standard CMOS fabrication integration
2Power
If silicon nitride rib waveguides are used to overcome silicon limitations, then optical power capacity increases, but insertion loss increases and mode hybridization is incomplete
Solution Approach 1:
The patent applies local quality by creating a tapered rib structure where the rib width varies along the propagation direction. This gradual geometric transformation locally modifies the mode confinement, enabling adiabatic mode conversion that reduces insertion loss while maintaining the high power capacity of silicon nitride
Solution Approach 2:
The patent introduces dynamic geometric parameters through the tapered rib structure, where the waveguide dimensions change continuously along the propagation path. This dynamic structure enables progressive mode hybridization between TM0 and TE1 modes, achieving complete conversion while minimizing reflection losses
3Manufacturing precision
If tight fabrication tolerances are applied to silicon photonic components, then manufacturing precision is maintained, but device performance is adversely affected
Solution Approach 1:
The patent changes the characteristic dimensions and material properties of the waveguide structure. Silicon nitride's lower refractive index and different propagation characteristics allow for more relaxed tolerance specifications compared to silicon, improving robustness against fabrication variations while maintaining device performance
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 PRS achieves low insertion loss and complete mode hybridization, enhancing the efficiency of polarization management in FMCW LiDAR systems by ensuring high coupling efficiency for both TE and TM polarized light.
Implementation Method 1
an asymmetric evanescent direction coupler
Implementation Method 2
enabling a full mode hybridization between TM0 and the TE1 modes
Data Source
Figure 1~4
Figure 5~7
AI summary
An integrated on-chip polarization rotator splitter (26) comprises a waveguide polarization rotator (54) having a first and a second layer (62) that form a rib waveguide (66) together and are both made of silicon nitride. The first layer (62) has a first, a second and a third section. The first layer (64) has a first width (w1) that increases in the first section (S1), is constant in the second section (S1) and decreases in the third section (S3). The second layer (64) has a second width (w2) that continuously increases. The polarization rotator splitter (26) further includes a waveguide polarization splitter (61) comprising a first strip waveguide (71) and a second strip waveguide (72) that are separated by a gap (74). The first and second strip waveguides (71, 72) are also made of silicon nitride. The first and second strip waveguide (71, 72) form an asymmetric evanescent direction coupler.