MZI Modulator Linearization via Carrier-AM Signal Cancellation
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Solution Overview
Problem
High-performance RF photonic links are limited by third-order intermodulation distortion components produced by Mach-Zehnder interferometer (MZI) modulators, which restrict the system's Spurious Free Dynamic Range (SFDR) and linearity.
Innovation Solution
A novel broadband MZI linearization scheme is introduced, utilizing the alternative output of the MZI modulator to create a linearizing optical signal that cancels or reduces third-order intermodulation distortion products by attenuating and combining it with the carrier signal, thereby improving the linearity and SFDR of the system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If MZI modulator is used for high-SFDR system, then linearity is improved, but third-order intermodulation distortion components are generated that limit system SFDR
Solution Approach 1:
The patent utilizes the alternative output of the MZI modulator, which contains third-order intermodulation distortion components, and converts this harmful signal into a beneficial linearizing signal. By attenuating and combining this alternative output with the carrier signal, the distortion components are transformed into a correction signal that when subtracted from the main output, eliminates the harmful third-order intermodulation distortion and improves system linearity and SFDR.
2Reliability
If alternative output of MZI modulator is utilized for linearization, then third-order intermodulation distortion is reduced, but device complexity increases
Solution Approach 1:
The MZI modulator serves dual purposes: it generates the main modulated output signal and simultaneously generates the linearizing signal through its alternative output. The system uses its own internally generated alternative output, which contains the distortion components, to create the correction signal needed for linearization. This self-service approach eliminates the need for external linearizing devices or additional complex circuitry, as the modulator itself provides both the problem signal and the solution signal.
Solution Approach 2:
The patent merges the carrier signal and the attenuated alternative output signal in a combiner device to create the linearizing signal. This combining operation integrates multiple signal paths (main output, alternative output, and carrier) into a unified linearized output, reducing the need for separate correction circuits and simplifying the overall system architecture while achieving SFDR improvement.
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 proposed solution significantly enhances the system's SFDR by eliminating or reducing third-order intermodulation distortion, leading to improved dynamic range and linearity, with potential applications in RF photonic links, I-Q modulators, and optical up-conversion/down-conversion systems.
Implementation Method 1
the optical phase difference between the two arms must be held constant over long time frames in order for coherent addition of the optical signals from the two arms to provide a useful output
Implementation Method 2
coherent addition of the optical signals from the two arms to provide a useful output
Implementation Method 3
utilizing the alternative output of the MZI modulator to create a linearizing optical signal that cancels or reduces third-order intermodulation distortion products by attenuating and combining it with the carrier signal
Data Source
AI summary
A novel transmitter is proposed that provides broadband all-optical linearization of a Mach-Zehnder interferometer (MZI) modulator for use in high linearity RF photonic links and optical up-converter and down-converter schemes. It is based on an amplitude modulated (AM) MZI modulator where part of the laser Carrier is passed around the MZI modulator and added back to the AM signal, creating a Controlled Carrier-AM (CC-AM) signal. In this new scheme, a dual output MZI modulator is utilized, and the alternative output (Carrier*) is used together with the Carrier from the laser to create a new signal, LO*, which when coherently combined with the AM signal can reduce or completely cancel its 3rd order intermodulation distortion.