Photonic RF Beat Generation for Low-Noise Frequency Multiplication
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Solution Overview
Problem
Current RF signal generation technologies face challenges in generating high-frequency RF signals with reduced phase noise, as phase noise increases with frequency multiplication, leading to issues like Common Phase Error and Inter-carrier Interference, and existing solutions either increase phase noise or limit bandwidth.
Innovation Solution
A photonic RF signal generation apparatus using a coherent optical source, optical splitter, modulation apparatus, and optical filters to generate optical harmonic signals, which are combined to produce a photonic RF signal with reduced phase noise by canceling optical and electrical phase noise through a delay mechanism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If frequency multiplication is used to generate high-frequency RF signals, then the RF carrier frequency can be increased, but phase noise is significantly increased
Solution Approach 1:
The patent replaces electrical frequency multiplication (PLL-based) with optical frequency multiplication. An optical modulator modulates an optical carrier with an electrical signal at frequency fe, generating optical sidebands at frequencies f0 ± fe. By selecting and combining specific sidebands, the system achieves frequency multiplication without the phase noise multiplication inherent in electrical PLL systems. This substitution of electrical processing with optical processing resolves the contradiction by eliminating the harmful phase noise effect while maintaining the desired frequency increase.
Solution Approach 2:
The patent introduces an optical carrier and optical modulator as intermediaries between the low-frequency electrical reference signal and the high-frequency output signal. The optical carrier at frequency f0 serves as a mediator that allows frequency multiplication without direct electrical multiplication. The optical modulator acts as an intermediary device that transfers the electrical signal characteristics to the optical domain, enabling frequency scaling without phase noise penalty. This intermediary approach resolves the technical contradiction by providing a pathway that decouples frequency multiplication from phase noise multiplication.
2Speed
If multiple PLL multiplication stages are used to achieve high frequency, then the RF frequency can be increased, but phase noise is multiplied and noise sources are added
Solution Approach 1:
The patent replaces multiple electrical PLL multiplication stages with a single optical modulation process. Instead of cascading electrical multipliers that each add noise, the system uses one optical modulator to generate all required frequency components in a single step. The optical domain processing eliminates the cumulative noise effect of multiple electrical stages, resolving the contradiction by substituting a single clean optical process for multiple noisy electrical processes.
Solution Approach 2:
The patent segments the frequency multiplication process into discrete optical sideband generation rather than continuous electrical multiplication. By creating distinct optical carriers at specific frequencies (f0 + fe, f0 - fe) through controlled modulation, the system can selectively combine only the necessary components. This segmentation approach allows precise frequency control without the noise accumulation inherent in continuous electrical multiplication chains.
3Object-generated harmful factors
If subcarrier spacing is increased to handle phase noise at high carrier frequencies, then phase noise effects are reduced, but bandwidth utilization is limited
Solution Approach 1:
The patent substitutes optical frequency multiplication for electrical frequency multiplication, which fundamentally changes how phase noise is handled. In the optical domain, phase noise from the reference signal is not multiplied by the same factor as in electrical systems. This allows the system to maintain smaller subcarrier spacings while operating at high carrier frequencies, thereby resolving the contradiction by eliminating the root cause of phase noise multiplication rather than compensating through larger spacing.
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 apparatus generates high-frequency RF signals with significantly reduced phase noise, allowing for increased spectral efficiency and stable RF signals suitable for 5G New Radio applications without additional optical noise.
Implementation Method 1
The optical modulation apparatus is driven by the at least one RF signal and is operable to modulate the first optical carrier signal and the second optical carrier signal at the initial frequency to generate a plurality of optical harmonic signals
Implementation Method 2
The photodetector is configured to detect the optical beat signal and output a corresponding electrical signal at a multiplied RF frequency
Data Source
AI summary
A photonic radio frequency, RF, signal generation apparatus has a source to output a coherent optical signal at a carrier frequency; an optical splitter to split the signal into a first and a second optical carrier signal; an RF signal generation apparatus generating an RF signal at an initial frequency; an optical modulation apparatus modulating the first and second signals at the initial frequency to generate optical harmonic signals around each signal; a first optical filter to select an nth order optical harmonic signal of a first sign, +n, of the optical harmonics around the first signal; a second optical filter to select the nth order optical harmonic signal of an opposite sign, −n, of the optical harmonics around the second signal; and a combiner to combine the selected +n and −n signals to generate an optical beat signal forming an output photonic RF signal.