Conductive-Strap Electro-Optic Modulator for Photocurrent Extraction
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Solution Overview
Problem
Conventional semiconductor-based electro-optic modulators experience a reduction in electro-optic efficiency due to significant longitudinal sheet resistance in doped layers, leading to increased switching voltage and setup complexity, as photocurrent generated induces voltage drops that vary with optical power and pre-modulator SOA current levels.
Innovation Solution
Incorporating a conductive strap ohmically contacted with a doped layer below the optical waveguides to reduce longitudinal resistance, allowing photocurrent to be extracted and maintaining consistent bias conditions across the modulation region, thereby reducing switching voltage and its dependence on optical power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a doped layer is used in the optical waveguide structure, then electrical conductivity is improved, but longitudinal sheet resistance causes voltage drops that reduce electro-optic efficiency
Solution Approach 1:
A conductive strap is introduced as an intermediary element between the doped layer and the optical waveguide. The strap is ohmically contacted to the doped layer and positioned to collect photocurrent before it can cause voltage drops across the doped layer, thereby maintaining electro-optic efficiency while utilizing the doped layer's conductivity
Solution Approach 2:
The conductive strap extracts photocurrent directly from the doped layer by making ohmic contact with it. This extraction prevents the photocurrent from flowing through the high-resistance path across the doped layer, eliminating the voltage drop that would otherwise reduce electro-optic efficiency
2Reliability
If the doped layer resistance is reduced to maintain bias conditions, then electro-optic efficiency is improved, but device complexity increases
Solution Approach 1:
The conductive strap serves as a mediator that provides a low-resistance current collection path without requiring changes to the doped layer's doping concentration or thickness. This maintains bias stability while avoiding the complexity of modifying the doped layer structure
Solution Approach 2:
The conductive strap is positioned locally at specific points where photocurrent collection is most effective, rather than requiring a uniformly modified doped layer throughout the entire waveguide structure. This localized approach maintains simplicity while achieving the desired bias stability
3Reliability
If photocurrent is extracted through the doped layer, then bias conditions are maintained, but switching voltage increases due to voltage drops
Solution Approach 1:
The conductive strap acts as an intermediary current collection path that prevents photocurrent from flowing through the high-resistance doped layer. By collecting current locally at the strap contact points, voltage drops are minimized while bias conditions remain consistent, thereby reducing the switching voltage required
Solution Approach 2:
The conductive strap creates equipotential regions by collecting photocurrent at multiple points along the waveguide. This prevents potential differences from developing across the doped layer, maintaining consistent bias conditions and reducing the voltage required for switching
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 conductive strap reduces or eliminates the de-bias effect, improving electro-optic efficiency and simplifying setup complexity by maintaining consistent bias conditions across the modulation region, regardless of photocurrent levels, and reducing switching voltage at given pre-modulator SOA current levels.
Implementation Method 1
the conductive strap being between the first optical waveguide and the second optical waveguide and being ohmically contacted with the doped layer
Data Source
AI summary
An electro-optic modulator may include a radio frequency (RF) modulation region including a first optical waveguide, a second optical waveguide, a first set of electrode segments, a second set of electrode segments, and a conductive strap. The first optical waveguide may propagate a first optical signal. The second optical waveguide may propagate a second optical signal. The first set of electrode segments may apply a first RF signal to the first optical waveguide. The second set of electrode segments may apply a second RF signal to the second optical waveguide. The conductive strap may enable photocurrent generated in the first optical waveguide and the second optical waveguide and flowing through a doped layer below the first optical waveguide and the second optical waveguide to be extracted from the electro-optic modulator. The conductive strap may be ohmically contacted with the doped layer.