Rib Ring Waveguide Modulators for Large FSR and Low Loss
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Solution Overview
Problem
Conventional silicon-on-insulator (SOI) platform-based ring modulators face challenges in achieving low-loss and large free spectral range (FSR) due to increased propagation losses from optical mode leakage at small radii, limiting FSR to 1.2-2.4 THz and complicating bandwidth and inter-channel crosstalk in dense wavelength division multiplexing (DWDM) systems.
Innovation Solution
The development of micro ring modulators (MRMs) with rib ring waveguides having center radii less than 5 micrometers, featuring asymmetrical slab widths, dissimilar rib ring and bus waveguide widths, notched implantation masks, undercuts to reduce heat dissipation, and on-chip inductive components to enhance modulation efficiency and bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the rib ring waveguide radius is reduced to increase FSR, then the free spectral range increases, but propagation losses increase due to optical mode leakage
Solution Approach 1:
The patent applies local quality by making the inner slab width different from the outer slab width in the rib ring waveguide structure. This asymmetric slab configuration creates localized field confinement at critical regions of the small-radius ring, reducing optical mode leakage into the substrate while maintaining the small radius needed for large FSR. The different slab widths provide different confinement strengths at inner and outer edges of the ring waveguide.
2Length of stationary object
If the rib ring waveguide radius is reduced to increase FSR, then the free spectral range increases, but device complexity increases due to design constraints
Solution Approach 1:
The patent employs asymmetry by designing the rib ring waveguide with dissimilar inner and outer slab widths. This asymmetric structure simplifies the design process for achieving large FSR with low loss by providing clear design guidelines for slab width ratios, rather than requiring complex iterative optimization. The asymmetric configuration naturally provides mode confinement without needing additional complex structural elements.
3Ease of manufacture
If conventional ring modulator designs are used, then manufacturing is simpler, but bandwidth is limited and inter-channel crosstalk increases
Solution Approach 1:
The patent applies parameter changes by modifying the slab width parameters of the rib ring waveguide to achieve optimal performance. By carefully selecting the ratio between inner and outer slab widths, the design achieves both low propagation loss and high modulation bandwidth simultaneously. This parameter optimization enables the ring modulator to support wider bandwidth applications while maintaining compatibility with standard silicon-on-insulator manufacturing processes.
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 approach enables MRMs to achieve a large FSR of 3.2 THz with low loss, supporting 200 GHz channel spacing and high bandwidth, while simplifying the physical design and facilitating integration with electronic integrated circuits, thus addressing the limitations of existing solutions.
Implementation Method 1
increases propagation losses due to optical mode leakage in slabs of the MRM waveguide
Implementation Method 2
forming an optical modulation system in the silicon layer, including a bus waveguide that propagates an optical carrier, and a ring modulator that modulates the optical carrier... and a heater element that controls a temperature of the ring modulator
Data Source
AI summary
A silicon-on-insulator (SOI) dense-wavelength-division-multiplexing (DWDM) device includes micro-ring modulators (MRMs) having radii under 5 micrometers. A 16-channel embodiment may provide a free spectral range of 3.2 THz, 200 GHz channel spacing, 41 GHz bandwidth, and a Q factor of 4500. PN junctions of rib ring waveguides (RWRs) may be perpendicular or parallel with a plane of the RWRs. On-chip inductive components may be used to match reactances of the PN junctions. The RWRs may be relatively wide and a rib bus waveguide may be relatively narrow (e.g., narrower than the RWRs). MRM outer slaps may be wider than inner slabs. Regions inside and outside of the RWRs, including slabs at optical coupling gaps may be doped to improve modulation efficiency. Regions of the rib bus waveguide distant from the optical coupling gaps may be undoped. Cavities may be provided below the MRMs and associated heater elements.