Rib Waveguide with Corrugated PN Junction for Low Voltage Modulation
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Solution Overview
Problem
Existing optical waveguide devices face challenges in achieving high-speed refractive index modulation with low optical loss and low driving voltage, particularly in small-footprint optical integrated circuits used for optical-fiber communication devices, due to issues like increased optical absorption, parasitic capacitance, and instability in laser light sources.
Innovation Solution
The optical waveguide device incorporates a rib waveguide with a corrugated PN junction and intrinsic regions to reduce optical loss and parasitic capacitance, featuring a P-type and N-type doped region configuration that extends the effective length of the PN junction, thereby reducing driving voltage and minimizing fabrication errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the effective length of the PN junction is increased to reduce driving voltage, then the driving voltage is reduced, but optical loss increases due to increased optical absorption by carriers
Solution Approach 1:
The patent applies local quality by creating distinct regions with different doping concentrations within the waveguide structure. Specifically, it uses a first doped region with higher carrier density adjacent to the PN junction boundary and a second doped region with lower carrier density extending along the waveguide. This localized variation in doping quality allows the junction region to provide strong refractive index modulation while the lower-density region minimizes optical absorption losses.
Solution Approach 2:
The patent employs composite material structure by combining multiple doped silicon regions with different electrical and optical properties. The composite structure consists of the PN junction interface region with high carrier density for effective index modulation, coupled with extended low-density doped regions for low optical loss propagation, creating a functionally optimized composite waveguide material system.
2Power
If the effective length of the PN junction is increased to reduce driving voltage, then the driving voltage is reduced, but parasitic capacitance increases due to fringe electric fields from slab regions
Solution Approach 1:
The patent extracts and removes the harmful fringe electric field effects by carefully designing the doped region geometry. The second doped region with lower carrier density is positioned to extend along the waveguide away from the junction boundary, effectively extracting the problematic capacitance-generating slab regions from the high-field zone while maintaining the beneficial low-loss propagation characteristics.
3Stability of the object's composition
If a rib waveguide with corrugated distribution profile in high refractive index contrast is used, then refractive index modulation is enhanced, but return loss decreases due to Bragg reflection and optical feedback causes mode hopping
Solution Approach 1:
The patent applies parameter changes by carefully controlling the doping concentration parameters and the geometric parameters of the corrugated profile. By optimizing the carrier density distribution and the corrugation dimensions, the design achieves sufficient refractive index modulation for effective operation while keeping the Bragg reflection conditions outside the operating wavelength range, thus preventing mode hopping and maintaining laser stability.
4Power
If the driving voltage is reduced in the optical modulator, then power consumption is reduced, but refractive index modulation degrades
Solution Approach 1:
The patent uses local quality enhancement at the PN junction boundary by concentrating high carrier density in the first doped region immediately adjacent to the junction interface. This localized high-quality doped region provides strong electric field confinement and enhanced refractive index modulation efficiency, enabling effective modulation at lower driving voltages while the second low-density region maintains low optical loss.
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 configuration enables high-speed refractive index modulation with low optical loss and low driving voltage, stabilizing optical modulation signals and reducing quality variations, making it suitable for long-haul or metro-area wavelength-division multiplexing optical-fiber communication and data center applications.
Implementation Method 1
refractive index is controlled by changing carrier density in PN junction formed in the transverse direction
Implementation Method 2
Bragg reflection caused by the periodic profile of the refractive index
Implementation Method 3
Silicon waveguide modulator based on carrier depletion in periodically interleaved PN junctions
Data Source
AI summary
An optical waveguide device includes a substrate; a lower cladding disposed on the substrate; a rib waveguide including a slab disposed on the lower cladding and a single rib disposed on the slab contiguous to the slab; and an upper cladding disposed on the rib waveguide. The rib waveguide includes a first doped region having a first electric conductivity exhibiting a P-type electric conductivity across the rib and the slab and a second doped region being contiguous to the first doped region and having a second electric conductivity exhibiting an N-type electric conductivity across the rib and the slab.