Optical Ring Modulator with Segmented Electrodes for Linear PAM-N
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Solution Overview
Problem
Existing silicon microring modulators used in advanced modulation formats like PAM-4 face challenges with nonlinearity, requiring complex and high-power consumption drivers, and scalability issues when transitioning from PAM-4 to PAM-N systems due to limited real estate.
Innovation Solution
The optical ring modulator design incorporates a first and second electrode region with pn junctions or metal oxide semiconductor capacitors, where the second phase shift is less than the first, allowing for efficient modulation by controlling the phase shifts through dopant concentrations and junction properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single drive electrode is used in the silicon microring modulator, then the device structure is simple, but the modulator becomes inherently nonlinear requiring complex high-power consumption drivers
Solution Approach 1:
The modulator is divided into multiple electrode regions (first and second electrode regions) with different phase shift characteristics. Each electrode region independently controls a portion of the phase modulation, allowing the system to achieve linear modulation by combining multiple segmented control signals rather than using a single complex drive electrode.
Solution Approach 2:
Different electrode regions are designed with different local properties - specifically different phase shift amounts (first phase shift vs second phase shift). This local differentiation in phase shift characteristics enables fine-grained control over the modulation process, allowing linear combination of phase shifts to achieve overall linear modulation without requiring complex drive electronics.
2Ease of operation
If dual drive versions with different electrode lengths are used, then linearity is improved, but the device complexity increases and scalability to PAM-N systems is limited due to real estate constraints
Solution Approach 1:
Instead of varying electrode lengths to achieve different phase shifts, this invention maintains uniform electrode geometry but varies the local phase shift through different electrode region designs (first electrode region with first phase shift, second electrode region with second phase shift). This approach achieves the same linearity improvement as dual-drive versions without the complexity of different electrode sizes, enabling better scalability to PAM-N systems.
Solution Approach 2:
The invention changes the phase shift parameter between different electrode regions rather than changing physical dimensions. By controlling the phase shift amount through electrical parameters (such as doping concentrations or material properties in the electrode regions) rather than geometric parameters (lengths), the system achieves linear modulation while maintaining a compact, scalable structure suitable for higher-order PAM-N modulation formats.
3Adaptability or versatility
If the ring resonator is scaled for PAM-N systems, then the modulation capability is enhanced, but the real estate requirements increase causing layout complications
Solution Approach 1:
The invention enables higher-order PAM-N modulation by changing the control parameters (phase shift amounts in different electrode regions) rather than scaling up the physical size of the ring resonator. This parameter-based approach allows the same physical footprint to support multiple modulation formats (PAM-4, PAM-8, and higher) by simply adjusting the phase shift values applied to different electrode regions, thus enhancing adaptability without increasing real estate requirements.
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 design enables efficient modulation with reduced power consumption and scalability to higher PAM-N systems by effectively controlling phase shifts, allowing the modulator to function as a PAM-4 or PAM-8 modulator depending on the configuration.
Implementation Method 1
a first pn junction configured to generate a first phase shift upon application of a given voltage across the pn junction
Implementation Method 2
a first metal oxide semiconductor capacitor (Moscap) configured to generate a first phase shift upon application of a given voltage across the Moscap
Data Source
AI summary
An optical ring modulator for use as a PAM-N modulator, the optical ring modulator comprising:a first optical waveguide which forms a bus waveguide;a ring waveguide optically coupled to the bus waveguide;wherein, the ring waveguide comprises:a first electrode region having a first pn junction or first Moscap, the first pn junction or first Moscap configured to generate a first phase shift upon application of a given voltage across the first pn junction or first Moscap; anda second electrode region having a second pn junction or second Moscap, the second pn junction or second Moscap configured to generate a second phase shift when the given voltage is applied across the second pn junction or second Moscap, wherein the second phase shift is less than the first phase shift.