Optical Local Oscillator for Electronic Demodulation
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Solution Overview
Problem
Existing electronics-based analog-to-digital converters (ADCs) suffer from multiple noise sources such as thermal noise, sampling aperture jitter, and comparator ambiguity, which limit their performance, especially at high bandwidths.
Innovation Solution
The technology involves the electronic demodulation of optically phase demodulated signals by converting temporal optical modulation into the analog RF domain using an interferometric technique, which allows for the extraction of phase information without the need for optical hybrids.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If electronics-based ADCs are used for high bandwidth applications, then conversion speed is improved, but noise performance deteriorates due to thermal noise, sampling aperture jitter, and comparator ambiguity
Solution Approach 1:
The patent replaces the electronic ADC conversion process with an optical measurement process. Instead of using electronic components that suffer from thermal noise and jitter, the system uses optical interferometry to measure the phase of modulated signals, thereby substituting electronic mechanics with optical mechanics to achieve high bandwidth with low noise.
Solution Approach 2:
The patent introduces an optical intermediary (light) as a mediator between the input signal and the measurement process. By using optical phase modulation and interferometric detection, the system creates an intermediate optical representation of the signal that can be measured with high precision without the noise limitations of direct electronic conversion.
2Measurement precision
If optical hybrids are used to extract phase information, then measurement capability is improved, but device complexity increases
Solution Approach 1:
The patent extracts only the essential function needed for phase measurement - the interferometric mixing of signal and reference - while removing the complex optical hybrid component. By separating the reference arm and signal arm and performing interference detection without a hybrid, the system achieves phase information extraction with reduced device complexity.
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 approach enables high dynamic range, wideband, continuous time digitization, improving diagnostic sensitivity and reducing errors in applications like RF measurements, while avoiding the limitations of optical hybrids.
Implementation Method 1
modulate the optical pulse train with the analog RF input signal to produce a phase modulated optical pulse train
Implementation Method 2
converting temporal optical modulation into the analog RF domain using an interferometric technique
Implementation Method 3
with a photodetector and an RF filter
Data Source
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Figure 2B
AI summary
Device, methods and systems for the electronic demodulation of optically phase demodulated signals are described. An example optical local oscillator generator configured to generate a radio frequency (RF) tone at a desired RF frequency includes a first input configured to receive a broadband optical pulse train, a second input coupled to a delay line interferometer to receive a first control voltage for controlling a delay value of the interferometer and to produce an output optical pulse train, a dispersive element, coupled to the delay line interferometer, to map the output optical pulse train to a time-domain modulated optical pulse train, an optical-to-electrical converter, coupled to the dispersive element, to convert the time-domain modulated optical pulse train to an analog electrical signal, and an RF filter, coupled to the optical-to-electrical converter, to filter the analog electrical signal to generate the RF tone at the desired RF frequency.