Optical Single-Sideband Generation With Phase-Error Correction
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Solution Overview
Problem
Existing methods for producing optical single sidebands are limited by phase noise of RF references, particularly in microwave and millimeter wave bands, which affects system performance and coherence.
Innovation Solution
A system and method using a RF signal generator to generate a sawtooth drive voltage, modulating an optical carrier with phase modulators, and employing a phase detector and error correction feedforward path to suppress phase errors, resulting in a single sideband with improved coherence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If direct digital synthesis is used to generate sawtooth wave for precise frequency control and agile tuning, then frequency control precision and tuning agility are improved, but phase noise is elevated at higher offset frequencies
Solution Approach 1:
An all-pass filter is introduced as an intermediary component between the direct digital synthesis sawtooth wave generator and the electro-optical modulator. This filter acts as a mediator that reshapes the spectral characteristics of the sawtooth wave, suppressing harmonics above the Nyquist frequency while preserving the desired single sideband generation, thereby reducing phase noise without sacrificing frequency control precision or tuning agility
Solution Approach 2:
The system changes the spectral parameters of the sawtooth wave by applying an all-pass filter that selectively attenuates high-frequency harmonics. This parameter transformation converts the raw digital sawtooth waveform into a filtered waveform with reduced high-frequency content, achieving lower phase noise while maintaining the core functionality of precise frequency control and agile tuning
2Ease of manufacture
If RF reference frequency is used to determine offset frequency, then offset frequency generation is simplified, but coherence between original optical carrier and sideband is limited by phase noise
Solution Approach 1:
The all-pass filter serves as an intermediary that decouples the simplicity of RF reference-based offset generation from the problem of phase noise. By filtering the sawtooth wave generated from the RF reference, the system maintains the ease of offset frequency generation while significantly improving coherence between the original optical carrier and the generated sideband
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 system achieves reduced phase noise and improved coherence by suppressing phase errors through feedforward error correction, enabling precise frequency control and agile tuning across a wide range of frequencies.
Implementation Method 1
modulating an optical carrier with phase modulators, and employing a phase detector and error correction feedforward path
Implementation Method 2
converting the phase error signal to a baseband electrical signal
Data Source
AI summary
An optical single sideband generation system comprising a RF signal generator generates a sawtooth drive voltage with a first frequency. A laser source provides the initial optical carrier with a second frequency that is modulated by a first phase modulator. The modulation shifts the optical carrier by the amount of the first frequency, and with added phase errors due to the imperfections of the sawtooth drive. A directional coupler allows the optical carrier to be divided into the error measurement path and the error correction path. The modulated signal goes to a phase detector that measures the phase error and converts the phase error signal to a baseband electrical signal. The optical signal at the output of the second phase modulator is the desired single sideband shifted from the original carrier with the phase errors of the signal generator suppressed by the error correction feedforward path.