Photonic RF Link Jammer Suppression via Stimulated Brillouin Scattering
Solution Overview
Problem
Radio frequency (RF) links are limited by interference received by the link receiver, especially when located near high power transmitters like RADAR, as existing technologies struggle to effectively suppress narrow-bandwidth RF interference.
Innovation Solution
A photonic-enabled RF link that employs photonic time-delay encoding and seeded stimulated Brillouin scattering to selectively attenuate interference tones while minimizing the impact on the RF signal, using a combination of photonic encoders, decoders, and limiters to spread and compress signal and interference bandwidths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the link receiver is located near a high power transmitter such as RADAR, then the RF link can operate in challenging environments, but the link receiver experiences severe interference from the high power transmitter
Solution Approach 1:
The patent segments the RF signal processing into multiple photonic channels with different time delays. The encoder divides the RF signal into multiple optical channels, each experiencing a different time delay, and the decoder recombines them. This segmentation allows the system to process the desired signal while separately handling and suppressing interference through selective combining.
Solution Approach 2:
The patent introduces photonic intermediaries (optical modulators, optical delay lines, and photodetectors) between the RF transmitter and receiver. These photonic components act as mediators that transform the RF signal into the optical domain for processing, enabling interference suppression through photonic techniques while maintaining RF communication functionality.
2Reliability
If photonic time-delay encoding is used to spread the bandwidth of the RF signal, then the signal bandwidth is increased improving resistance to interference, but the device complexity increases due to multiple optical delay lines and modulators
Solution Approach 1:
The patent transitions the signal processing from the RF time domain to the optical time domain by modulating RF signals onto optical carriers. This dimensionality change allows the use of optical technologies (such as optical delay lines and optical modulators) to achieve time-diversity coding, providing interference resistance while leveraging the advantages of optical processing.
Solution Approach 2:
The patent applies preliminary encoding at the transmitter side using photonic time-delay modulation before transmission. The encoder pre-processes the RF signal by modulating it with a pseudorandom code and introducing controlled time delays in the optical domain. This preliminary action ensures that the signal is already in a form that is resistant to narrowband interference before it encounters the interference in the channel.
3Reliability
If photonic limiters are used to selectively attenuate interference tones, then the signal-to-interference ratio is improved, but the device complexity increases due to the need for precise frequency selectivity
Solution Approach 1:
The patent applies local quality by making different parts of the optical spectrum experience different attenuation. The photonic limiter is designed to selectively attenuate only the frequency components corresponding to the interference signal while leaving the desired signal components unaffected. This is achieved by tuning the photonic limiter to respond specifically to the interference frequency.
Solution Approach 2:
The patent changes the frequency parameter of the interference signal relative to the desired signal through the photonic encoding process. By modulating the RF signal with pseudorandom codes and introducing time delays, the desired signal's spectral components are spread and shifted. The photonic limiter then exploits this parameter change by being tuned to attenuate the interference frequency while the spread spectrum signal components pass through with minimal attenuation.
4Reliability
If multiple photonic channels with different time delays are used for encoding, then the processing gain is increased improving interference suppression, but the loss of time increases due to the need to process multiple delayed channels
Solution Approach 1:
The patent maintains continuous useful action by processing all photonic channels simultaneously rather than sequentially. The decoder receives multiple optical channels with different time delays and processes them in parallel using photodetectors and electronic combining circuits. This continuous parallel processing ensures that the full processing gain is achieved without introducing additional time delays from sequential processing operations.
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 significantly improves the signal-to-interference power ratio, allowing RF links to operate effectively near strong transmitters by reducing the visibility and impact of interference, thereby enhancing tolerance to strong, narrow-bandwidth interference.
Implementation Method 1
The SBS seed generator produces light at the Stokes frequency associated with only the interferer sidebands. This Stokes seed is injected into the primary SBS medium to effectively reduce the threshold for SBS of the interferer sidebands in that primary SBS medium. However, no Stokes seed is supplied at the frequencies of the optical carrier or the signal sidebands. Thus, the power-level of the interferer sidebands is attenuated by stimulated Brillouin scattering in the seeded primary SBS medium.
Data Source
AI summary
A radio frequency (RF) link includes a link transmitter that includes a data modulator for modulating a data waveform together with an RF carrier, a photonic encoder coupled to the data modulator, and a transmitter antenna for transmitting an RF signal, wherein the RF signal comprises an output of the photonic encoder, and a link receiver including a receiver antenna for receiving the RF signal, a first laser source, a photonic limiter coupled to the first laser source and to the receiving antenna, a photonic decoder coupled to the photonic limiter, a photo-receiver coupled to the photonic decoder, and a demodulator coupled to the photo-receiver for demodulating an output of the photo-receiver with the RF carrier to form a data output.