Optical Link Linearization via Feedforward Distortion Cancellation
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Solution Overview
Problem
Current optical links are inadequate for radar system applications due to limited high, spur-free dynamic range, particularly at bandwidths above 1 GHz, as they struggle to minimize distortion products effectively.
Innovation Solution
The system employs a main transmission link and a feedforward optical link to modulate and translate radio frequency signals into optical frequency signals, with a receiver subtracting spurious components to achieve linearization over broad bandwidths, using two optical modulators operating in different regions to minimize distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If two Mach-Zehnder interferometric modulators are used to minimize distortion products, then spur-free dynamic range is improved, but bandwidth is limited to less than 1 GHz
Solution Approach 1:
The patent introduces a feedforward optical link as an intermediary system that generates a correction signal to cancel distortion products from the main transmission link. This mediator approach allows the system to achieve high spur-free dynamic range without being constrained by the bandwidth limitations of traditional Mach-Zehnder interferometric modulator configurations.
Solution Approach 2:
The optical link is segmented into two separate functional paths: a main transmission link for signal modulation and a feedforward optical link for distortion cancellation. This segmentation allows each path to be optimized independently, enabling the main link to operate at high bandwidth while the feedforward link handles distortion correction, thereby resolving the contradiction between bandwidth and spur-free dynamic range.
2Measurement precision
If electro-absorption modulators are biased for distortion reduction, then spur-free dynamic range is improved, but a compromise is required for bandwidth and distortion
Solution Approach 1:
The system employs a feedforward mechanism where distortion products are predicted and cancelled before they degrade the signal. By using a separate optical link to generate and subtract distortion components, the system achieves distortion reduction without requiring compromise in bandwidth or adaptability, as the main transmission link can operate optimally while distortion is handled independently.
3Adaptability or versatility
If optical links are designed for current state of the art applications, then general usability is improved, but radar system applications requiring very high spur-free dynamic range are inadequate
Solution Approach 1:
The patent creates a universal optical link architecture that can serve both general applications and specialized radar applications requiring very high spur-free dynamic range. The main transmission link provides general usability, while the integrated feedforward optical link enables the system to meet the stringent requirements of radar applications, making the system adaptable to multiple application domains without sacrificing performance in either.
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 provides a high, spur-free dynamic range over broad bandwidths, effectively addressing the limitations of existing optical links by significantly reducing distortion and maintaining low distortion across higher frequency ranges.
Implementation Method 1
a main transmission link for modulating an input radio frequency signal with a first optical frequency signal to produce a main signal comprising components of the input radio frequency signal translated in frequency by the first optical frequency
Implementation Method 2
The receiver re-translates the frequency of such optical frequency signal to a corresponding radio frequency signal
Data Source
AI summary
A system having a first optical modulator operates in a non-linear region thereof and fed by: an input radio frequency signal; and, a first optical frequency signal having a wavelength λ2. A second optical modulator operates in a linear region thereof and fed by: a fractional portion of the input radio frequency signal phase shifted relative to the input radio frequency signal by nπ radians where n is an odd integer; and a second different optical frequency signal wavelength λ1. A first photodiode is fed by an output of the first optical modulator. A second photodiode is fed by an output of the second optical modulator and a fractional portion of an output of the first optical modulator. An amplifier is fed by the second photodiode. A subtractor is fed by the amplifier and the first photodiode.