Optoelectronic Oscillator Phase Noise Reduction via Fabry-Perot Etalon
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Solution Overview
Problem
Conventional optoelectronic oscillators require high-gain RF amplifiers and costly ultra-narrow bandwidth RF filters, leading to increased phase noise and temperature dependency, which affect RF frequency stability.
Innovation Solution
Replacing the RF filter with a high finesse Fabry-Perot etalon as the mode selector in the optoelectronic oscillator design, which provides higher Q and ultralow temperature dependency, resulting in reduced phase noise and improved RF frequency stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an ultra-narrow bandwidth RF filter is used in the OEO, then spectral purity is improved, but cost increases and phase noise increases
Solution Approach 1:
The patent replaces the RF filter (electronic system) with an optical filter based on a Fabry-Perot etalon (optical system). This substitution moves the filtering function from the RF domain to the optical domain, where the etalon's high finesse provides ultra-narrow bandwidth filtering without the phase noise and cost issues associated with conventional RF filters.
Solution Approach 2:
The patent changes the key parameter from RF filter bandwidth to etalon finesse. By using a high finesse etalon (e.g., finesse > 100), the system achieves ultra-narrow effective bandwidth equivalent to ultra-narrow RF filters, but with superior performance characteristics including lower phase noise and reduced temperature dependency.
2Stability of the object's composition
If the optical delay line is made longer to increase cavity Q, then spectral purity is improved, but the RF filter bandwidth must be ultra narrow which increases cost and phase noise
Solution Approach 1:
The patent substitutes the RF filter with an optical etalon, which provides the necessary narrow bandwidth filtering in the optical domain. This eliminates the need for costly and complex ultra-narrow bandwidth RF filters while maintaining high cavity Q through the combination of optical delay line and etalon.
3Ease of operation
If an RF filter is used in the OEO, then mode selection is achieved, but temperature dependency increases affecting frequency stability
Solution Approach 1:
The patent replaces the temperature-sensitive RF filter with a Fabry-Perot etalon that operates in the optical domain. The etalon provides mode selection functionality while exhibiting ultralow temperature dependency, thereby maintaining frequency stability across temperature variations.
Solution Approach 2:
The etalon acts as an intermediary between the optical delay line and the photodetector, performing mode selection in the optical domain before detection. This intermediary function eliminates the need for temperature-sensitive RF filtering while maintaining spectral purity and mode selection capability.
4Power
If a high gain RF amplifier is used to compensate RF loop losses, then signal level is maintained, but phase noise increases
Solution Approach 1:
The patent substitutes RF filtering with optical filtering using a high finesse etalon. This substitution reduces the required RF gain because the optical domain filtering is more efficient, thereby reducing the phase noise contribution from the RF amplifier while still maintaining adequate signal level.
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 use of a Fabry-Perot etalon in the optoelectronic oscillator design achieves lower phase noise and higher RF frequency stability compared to conventional designs, with a 100 dBc/Hz signal-to-noise ratio and 2.6 kHz frequency stability over one minute.
Implementation Method 1
a F-P interferometer, or etalon, is used in replacement of the RF Filter
Implementation Method 2
The inclusion of the Fabry-Perot etalon instead of the RF filter results in less phase noise, due to the higher Q
Implementation Method 3
the modulator is an electro-optic modulator that modulates an optical signal in response to RF input signals
Implementation Method 4
a photodetector converts the optical signal back to RF signals
Data Source
AI summary
An optoelectronic oscillator (OEO) is used to provide a continuous, high Q, modulated signal for a variety of purposes, including a carrier wave for communications, and radar emissions. The OEO of this invention replaces an RF filter in the conventional OEO with an interferometer, preferably a high finesse Fabry-Perot etalon as the mode selector, providing lower phase noise and higher RF frequency stability.