Compact DQPSK Modulator Using Electro-Absorption in InP
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Solution Overview
Problem
Existing DQPSK modulators are too large for pluggable transceivers due to the weak electro-optic effect in materials like GaAs and LiNbO3, requiring long phase modulators and complex designs, which are challenging to fabricate and result in low spectral efficiency and significant chip real-estate consumption.
Innovation Solution
A compact DQPSK modulator design utilizing the electro-absorption effect in InP with a three-arm interferometer, incorporating electro-absorption modulators (EAMs) instead of phase modulators, allowing for a shorter device length and simplified fabrication, and potentially integrating with a laser and optical gain element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If traditional phase modulators based on GaAs or LiNbO3 are used, then DQPSK modulation can be achieved, but the modulator becomes too large (52 mm or 43 mm long) for pluggable transceivers
Solution Approach 1:
The patent changes the material parameter from GaAs/LiNbO3 to InP, which has a stronger electro-optic effect in the C-band. This parameter change enables the same modulation function to be achieved in a much shorter length, reducing the modulator from 52mm to a compact size suitable for pluggable transceivers.
Solution Approach 2:
The patent replaces the traditional electro-refraction effect with the electro-absorption effect. This substitution of physical mechanism allows for a more compact design while maintaining the DQPSK modulation capability, as the electro-absorption effect provides a stronger interaction strength.
2Power
If a traveling-wave structure is used in InP to achieve reasonable Vπ, then phase modulation can be achieved, but the fabrication becomes highly demanding
Solution Approach 1:
The patent replaces the traveling-wave phase modulator structure with an electro-absorption modulator structure. This substitution eliminates the need for complex traveling-wave fabrication while achieving the desired Vπ performance through the strong electro-absorption effect in InP.
Solution Approach 2:
The patent divides the modulation function into separate electro-absorption modulator sections within the interferometer arms. This segmentation allows for simpler fabrication of individual EAM sections while achieving the overall modulation function, avoiding the need for complex traveling-wave structures.
3Reliability
If existing DQPSK modulator design with nested Mach-Zehnder modulators is used, then modulation function is achieved, but the device consumes significant chip real-estate
Solution Approach 1:
The patent changes the fundamental operating parameter from phase modulation to electro-absorption modulation. This parameter change enables a more compact interferometer design that achieves the same DQPSK modulation function with significantly reduced chip area, as EAMs are much shorter than traditional phase modulators.
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 compact design achieves high spectral efficiency and reduced size, enabling 100-Gb/s data transmission with improved fabrication simplicity and potential integration with other optical components, while maintaining high-speed operation and low insertion loss.
Implementation Method 1
The design is so compact because it uses the electro-absorption (EA) effect rather than the electro-refraction effect
Data Source
AI summary
A novel design for an optical differential quadrature phase shift keying (DQPSK) modulator comprises two intensity modulators in a three-arm interferometer.