Photonic Frequency Comb for Low Phase Noise RF Generation
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Solution Overview
Problem
Conventional methods for low noise frequency multiplication, division, and synchronization in microwave technology face challenges such as increased phase noise proportional to the square of the multiplication factor, limiting the use of frequency references at low radio-frequencies for high frequency RF or microwave generation.
Innovation Solution
The use of photonic oscillators and frequency combs to generate low phase noise RF signals through techniques like phase locking, error signal generation using beat signals, and frequency broadening in nonlinear waveguides, along with the integration of optical modulators and interferometers, allows for the reduction of phase noise in voltage-controlled oscillators (VCOs) and the generation of low noise microwave signals up to 1000 GHz.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional electronic frequency multiplication is used, then frequency generation capability is achieved, but phase noise increases proportionally to the square of the multiplication factor
Solution Approach 1:
The patent replaces conventional electronic frequency multiplication with photonic frequency multiplication using optical frequency combs. The optical domain system multiplies frequency by comparing optical comb lines with RF signals, achieving frequency multiplication without the phase noise penalty inherent in electronic multiplication. The optical comb acts as a photonic reference that enables clean frequency translation from RF to microwave bands.
Solution Approach 2:
The patent introduces an optical frequency comb as an intermediary between the RF frequency reference and the target microwave frequency. The optical comb provides a stable frequency reference that mediates the frequency multiplication process, allowing phase-coherent frequency translation while maintaining low phase noise through optical domain processing rather than direct electronic multiplication.
2Speed
If frequency references at low RF frequencies are used for high frequency generation, then frequency multiplication is enabled, but phase noise severely degrades the signal quality
Solution Approach 1:
The patent transitions the frequency reference system from the RF dimension to the optical dimension. By using optical frequency combs with frequencies in the hundreds of THz range, the system achieves high frequency generation with superior phase noise performance. The optical domain provides an additional frequency dimension that enables clean frequency multiplication without propagating low-frequency phase noise to the microwave output.
3Ease of operation
If conventional RF oscillators are used, then simple operation is maintained, but phase noise reduction capability is insufficient for high precision applications
Solution Approach 1:
The optical frequency comb system serves multiple functions simultaneously: it provides a stable frequency reference, enables frequency multiplication, and acts as a phase noise filter. This multi-functional approach allows the system to achieve ultra-low phase noise performance while maintaining operational simplicity through integrated photonic circuits and standardized optical components.
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 achieves significant reduction in phase noise, with single-side band phase noise densities as low as −140 dBc/Hz at 10 GHz and −172 dBc/Hz at 25 GHz, surpassing conventional RF oscillators, enabling reliable high-frequency RF signal generation.
Implementation Method 1
optical modulators driven by a VCO are used to generate optical side-bands to cw lasers
Implementation Method 2
The spectral extent of said side-bands can be increased via frequency broadening in highly nonlinear waveguides
Implementation Method 3
Free running mode locked low phase noise comb oscillators can then be used as reference oscillators
Implementation Method 4
Free running mode locked low phase noise comb oscillators can then be used as reference oscillators to generate beat signals between those side-bands and individual comb modes
Implementation Method 5
The beat signal generated from the RF modulated cw laser with individual comb frequencies can then be used for feedback to reduce the noise of the VCO in the RF domain
Data Source
AI summary
Low phase noise radio frequency (RF) sources generated by voltage controlled oscillators (VCOs) are described. Optical modulators driven by a VCO may be used to generate optical side-bands to cw lasers. The spectral extent of said side-bands can be increased via frequency broadening in highly nonlinear waveguides. Free running mode locked low phase noise comb oscillators can be used as reference oscillators to generate beat signals between those side-bands and individual comb modes at distal spectral regions, thereby creating an error signal used to reduce the phase noise of VCOs and the generation of low phase noise RF signals. VCO phase noise may be reduced by using free-running modelocked comb lasers phase locked to external frequency references, by omitting a reference comb and using a nonlinear interferometer for generating an error signal, or by locking a slave comb to the modulation frequency of an intra-cavity modulator driven by the VCO.