Rib Waveguide Core with Protruding Section for Low-Loss Modulation
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Solution Overview
Problem
The existing optical waveguide elements suffer from high optical loss due to rough sidewalls, limited refractive index modulation efficiency, complex production processes, and difficulties in integration with other optical circuits, particularly in polarization-division multiplexing applications.
Innovation Solution
The optical waveguide element incorporates a rib waveguide core with a protruding section and non-protruding sections forming a PN junction, where a depletion layer extends from the protruding section to the non-protruding sections, optimizing the electric field distribution and carrier density variations to reduce optical loss and driving voltage without increasing doping densities or element length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If light is confined using the difference in refractive index between sidewalls of silicon layers and cladding, then optical waveguide function is achieved, but optical loss increases due to scattering at rough sidewalls
Solution Approach 1:
The invention extracts the light confinement function from the sidewalls and relocates it to the top surface of the silicon layer. By forming a convex portion that protrudes from the top surface, the waveguide confines light through total internal reflection at the top interface rather than relying on sidewall reflection, thereby eliminating scattering losses from rough sidewalls while maintaining effective optical confinement
Solution Approach 2:
The invention transitions from two-dimensional sidewall confinement to three-dimensional top-surface confinement by creating a convex portion that extends upward from the silicon layer top surface. This dimensional change allows light to be confined in the vertical dimension through the convex structure while propagating horizontally, avoiding interaction with problematic sidewall surfaces
2Power
If doping density of silicon layers is increased to improve refractive index modulation efficiency, then driving voltage decreases, but optical loss increases due to carrier absorption
Solution Approach 1:
The invention applies local quality by creating a convex portion with distinct geometric properties from the surrounding silicon layer. The convex region serves as the primary light confinement zone with optimized curvature and dimensions, while the flat top surface areas provide electrical contact regions. This local differentiation allows optimized light-matter interaction in the convex region without requiring high doping densities throughout the entire structure
Solution Approach 2:
The invention changes geometric parameters by forming a convex portion with specific height, width, and curvature characteristics. By optimizing these geometric parameters, the waveguide achieves enhanced light confinement and mode confinement factors, improving refractive index modulation efficiency through geometric optimization rather than relying solely on doping density increases
3Power
If length of optical waveguide element is increased to improve refractive index modulation, then modulation efficiency increases, but device size increases
Solution Approach 1:
The convex portion creates a localized region of enhanced optical confinement and strong electric field interaction. This concentrated interaction region provides high modulation efficiency per unit length, allowing shorter overall device lengths while achieving the same or better modulation performance than longer conventional waveguides
Solution Approach 2:
The convex portion introduces curvature at the top surface of the silicon layer, creating a rounded or domed structure. This curvature enhances light confinement through geometric optics effects and increases the overlap between the optical mode and the region experiencing refractive index changes, improving modulation efficiency without increasing device length
4Reliability
If silicon layers are disposed on dielectric layer through special process steps, then optical waveguide structure is formed, but manufacturing complexity increases
Solution Approach 1:
The manufacturing process is segmented into standard steps: forming the silicon layer on substrate, patterning the convex portion using photolithography and etching, and forming metal electrodes. By breaking down the complex structure creation into these sequential, well-established fabrication steps, the invention achieves the desired waveguide geometry using conventional semiconductor manufacturing processes without requiring specialized or proprietary techniques
Data Source
AI summary
To reduce the optical loss, lower the driving voltage, produce a smaller product, and simplify the production process, an embodiment of the present invention includes a rib waveguide core (101) having a rib region (101r) and two slab regions (101s), where a depletion layer (113) is so formed as to extend from the rib region (101r) to the two slab regions (101s).