A new structure for storing a radio frequency (RF) signal utilising a fibre-optic delay line is presented. It is based on a frequency shifting recirculating delay line loop for the RF pulse storage, which prevents lasing and enables multiple recirculations and long storage time to be realised. The new photonic RF memory (PRFM) can realise a long reconfigurable storage time, wide instantaneous bandwidth and high dynamic range. Experimental demonstration of the frequency shifting loop based PRFM has been carried out for the first time, showing a long and reconfigurable storage time of more than 300 μs with high signal fidelity.
The integration of wideband electronic attack (EA) and electronic protection (EP) is a growing concern in electronic countermeasures (ECMs) as wireless technology advances. However, electronic hardware in conventional ECMs already approaches its bandwidth ceiling, making the solutions for high-performance, scalable, and reconfigurable optical signal processing extremely imperative, such as photonic RF memory (PRFM). This work demonstrates a phase–amplitude evolution mechanism in PRFM, where phase evolution enables radar range deception and amplitude evolution serves to scramble and diffuse the optical quantum noise for enhanced communication security. Founded on this, a novel microwave photonic front-end using orthogonal polarizations was developed and experimentally executed. In EA tasks, a 12-GHz optical frequency comb (OFC) signal was cyclically stored for$1000~\mu $s with high fidelity, creating 400 range false targets. Thanks to the Doppler frequency replication based on coherent OFC technology, the number of range–velocity compound 2-D false targets increased to 4400 (
400×11). In EP tasks, a 4-Gbaud QPSK signal was initially encrypted into a
216-QAM/quantum noise stream cipher (QNSC) signal and underwent 200 security adjustments in the loop at an 8% error vector magnitude (EVM) penalty, resulting in a nearly fourfold privacy improvement. Tuning of the number of circulations can compatibly reconstruct the jamming and security levels. Furthermore, an SNR monitoring probe was involved in the case of radar intrusion into communications, prompting communication tasks to adaptively respond to the threats. Therefore, our scheme pioneers the first integration of signal storage, 2-D radar jamming, private communication, security reconfiguration, and adaptive risk response in a wideband microwave photonic front-end, strongly addressing the reinforcement need of future ECMs.
Phase-stable radio frequency (RF) transfer attracts a growing research interest and attention in recent years, and transferring high stable RF signal to multiple places is greatly needed in many important applications such as frequency synchronization for very long base-line interferometry and connected-element interferometry in radio astronomy. [1]. For example, the Atacama Large Millimeter Array (ALMA) radio astronomy project is consist of an array of up to 64 antennas, and in order to achieve the unprecedented sensitivity and angular resolution, requires the local oscillator reference signal arriving at remote antennas with a maximum path length up to 18 kilometers must be stabilized under one picosecond [2]. The optical fiber link is a promising method for long-distance highly stable frequency distribution, however it suffers from the environment perturbations such as physical vibration and temperature fluctuations, which degrade the phase stability to be delivered [3].
We demonstrate a photonic radio-frequency transmission system via optical fiber. Optical radio-frequency signal is generated utilizing a Mach-Zehnder modulator based on double-side-band with carrier suppression modulation scheme. The phase error induced by optical fiber transmission is transferred to an intermediate frequency signal by the dual-heterodyne phase error transfer scheme, and then canceled by a phase locked loop. With precise phase compensation, a radio frequency with high-phase stability can be obtained at the remote end. We performed 20.07-GHz radio-frequency transfer over 100-km optical fiber, and achieved residual phase noise of -65 dBc/Hz at 1-Hz offset frequency, and the RMS timing jitter in the frequency range from 0.01 Hz to 1 MHz reaches 110 fs. The long-term frequency stability also achieves 8×10(-17) at 10,000 s averaging time.